Abstracts


Oral Presentations

Bioengineering

A Quantitative Analysis of Integrin Activation on T Cell Homing

Nicholas R. Anderson, Dooyoung Lee and Daniel A. Hammer

T cell homing to sites of infection and inflammation is critical for the adaptive immune response and the maintained of immune homeostasis. In addition, these cells must endure significant shear forces to exit the blood stream through the leukocyte adhesion cascade. Previously, we have showed the importance of substrate composition and density in controlling the extent and type of leukocyte adhesion through the creation of state diagrams. Here, we present work extending a previously published model combining Adhesive Dynamics, which accounts for the biophysical motion of the cell, and an intracellular signaling cascade, which allows for the simulation of integrins upon leukocyte exposure to chemokine. Specifically, we highlight our results regarding the role of the integrin activator protein kindlin-3, which is the critical protein in the immune disorder Leukocyte Adhesion Deficiency Type 3. Our model makes several predictions regarding the effects of various levels of kindlin-3 deficiency, which are then tested through an experimental flow chamber to confirm or refute model predictions and further improve the model.

CD4+ T lymphocytes persist prior shear flow migratory pattern via VLA-4—VCAM-1 interaction

Sarah Hyun Ji Kim and Daniel A. Hammer

Leukocytes must be able to tether, adhere, and transmigrate on endothelial layers in order to perform immune functions at sites of infection and inflammation, as well as maintaining immune homeostasis. Near sites of inflammation, endothelial cells present Intracellular Adhesion Molecule-1 (ICAM-1) and Vascular Cell Adhesion Molecule-1 (VCAM-1) to recruit CD4+ T lymphocytes and mediate migration. CD4+ T Lymphocytes then bind to ICAM-1 and VCAM-1 with integrins Lymphocyte Function-associated Antigen-1 (LFA-1, αLβ2) and Very Late Antigen-4 (VLA-4, α4β1), respectively. Previous studies describe that CD4+ T lymphocytes exhibit a unique migratory pattern; CD4+ T lymphocytes on ICAM-1 surface migrate upstream mediated by LFA-1, whereas cells on VCAM-1 move downstream. Using a laminar flow chamber and microcontact printed ICAM-1 and VCAM-1 on PDMS surfaces, we demonstrate that while upstream migration is a robust phenomenon mediated by LFA-1—ICAM-1 engagement, VLA-4-VCAM-1 interaction is required to maintain persistent directionality post flow. This post-flow migrational memory is further supported by PI3K activity upon activation of VLA-4.

Adhesive dynamic simulations and microfluidic experiments of DNA-functionalized colloids adhering to surfaces under shear flow

Christopher L. Porter and John C. Crocker

Adhesive dynamics is a powerful stochastic simulation method originally developed to study the recruitment process of leukocytes to sites of inflammation. This method is particularly adept for characterizing dynamic systems that form discrete molecular bonds, and how they respond to externally applied forces. Since its development, adhesive dynamics has been applied to a variety of biological systems. DNA-functionalized colloids have emerged as a novel and growing class of materials used in variety of applications from building blocks of crystalline structures, to smart drug delivery devices. Here we present a new application of Brownian adhesive dynamics to model DNA-functionalized colloids exposed to a shear flow and a substrate which the particles can adhere to and relate these results to microfluidic experiments. The dynamics and rheology of these system and the model fidelity to the experiments will be discussed.

Redox sensitive protein droplets from recombinant oleosin

Ellen H. Reed and Daniel A. Hammer

Molecular biology enables the creation of new materials with designer functionality and tailored responsiveness. We created a protein that at forms nanometer-sized spherical micelles at low concentrations and forms micron-sized liquid droplets at high concentrations. This work is based upon a surfactant protein, oleosin. Oleosin contains N and C-terminal hydrophilic regions and a central hydrophobic region. At low protein concentrations, the hydrophobic region drives formation of spherical micelles. At high protein concentrations, however, oleosin phase separates to form liquid droplets akin to membrane-less organelles. In this work, we explore strategies to control phase separation by introducing a cysteine residue to oleosin, a protein that does not contain any cysteines. Adding a cysteine residue to the N-terminal hydrophilic region of oleosin results in phase separation at a lower protein concentration. Furthermore, adding a reducing agent to phase-separated, cysteine-containing oleosin rapidly dissolves the droplets. We also demonstrate two strategies to precisely control the phase transition temperature of cysteine-containing oleosin. First, the transition temperature is tuned by varying the location of the cysteine in the oleosin backbone. Second, the transition temperature is tuned by blending the parent, cysteine-less molecule with the cysteine-containing mutant. These methods provide novel ways to control protein droplet formation and dissolution. This work will have applications as a system for the release of molecules with sensitivity to reducing conditions and as an engineered mimic of membrane-less organelles in synthetic protocells.

Hemodynamic force triggers rapid NETosis within sterile thrombotic occlusions

Xinren Yu, Jifu Tan and Scott L. Diamond

Neutrophil extracellular traps (NETs) are released when neutrophils encounter infectious pathogens, especially during sepsis. Additionally, NETosis occurs during venous and arterial thrombosis, disseminated intravascular coagulation, and trauma. Using microfluidics, we tested if hemodynamic forces trigger NETosis during sterile thrombosis. For perfusions at initial inlet venous or arterial wall shear rates, rapid platelet deposition occluded microchannels with subsequent neutrophil infiltration at either flow condition, however NETosis was only detected at the arterial condition as shown. With or without thrombin, venous perfusion for 15 min generated no NETs, but an abrupt shift-up to arterial perfusion triggered NETosis within 2 min, eventually reaching levels 15 min later that were 60-fold greater than microchannels without perfusion shift-up. SINs contained Myeloperoxidase and citrullinated histone and responded to DNase treatment, but were not blocked by inhibitors of platelet-neutrophil adhesion, HMGB1-RAGE interaction, cyclooxygenase, ATP/ADP or PAD-4. For measured pressure gradients exceeding 70 mmHg/ mm-clot across NET-generating occlusions to drive interstitial flow, calculated stress hot spots on neutrophils exceeded 1000 dyne/cm2. In conclusion, high interstitial hemodynamic forces can drive physically entrapped neutrophils to rapidly release NETs during sterile occlusive thrombosis. SIN might share similar thrombotic or inflammatory properties to NETs triggered by other stimuli.

Energy

Manufacturing High-Performance infiltrated Solid Oxide Fuel Cell Cathodes via backbone engineering and surface Modification

Yuan Cheng, Liang Zhang, Aleksandra Vojvodic, John Vohs and Raymond J. Gorte

Solid Oxide Fuel Cells (SOFCs) are high-efficiency electricity generating systems. The major resistance of the device comes from its cathode, where oxygen reduction reaction happens. In this study, two approaches were taken to reduce the cathodic resistance. First, a conductive composite cathode backbone was developed and successfully improved the cathodic performance at low catalyst loading. Second, the outermost layer of the perovskite phase (ABO3) cathode catalyst, La0.8Sr0.2FeO3 (LSF), was modified with Atomic Layer Deposition (ALD) of metal oxides. It was discovered that the surface resistance decreased significantly with small numbers of ALD cycles of AO metal oxides before again increasing at higher coverages. This implicates that an AO-terminating surface is favorable for oxygen reduction with LSF catalyst.

Insights for Catalyst Design: Using Well-Defined Metal Oxide Nanocrystals to Elucidate Structure-Activity Relationships

Paul Pepin and John M. Vohs

TiO2 is a prototypical catalyst for selective oxidation and photo-oxidation of organic molecules, and surface science studies with macroscopic single crystals have greatly advanced our mechanistic understanding of the structural requirements for many of these reaction pathways. While single crystal surfaces have been instrumental in providing these mechanistic insights, these unique materials do not exist for many surfaces of interest. Additionally, there exists significant disparity between these model single crystal systems and real-world catalysts – particularly in the realm of photocatalysis, where considerations must also be made for bulk phenomena. Well-defined nanocrystals of metal oxides provide an intermediary between these single crystals and industrially-relevant high surface area polycrystalline materials. In this talk, I will present my research using methanol and acetaldehyde as probe reagents to elucidate how nanostructure influences thermal and photocatalytic reaction pathways on size- and shape-selected A-TiO2 nanocrystals. The nanocrystals used were either of a platelet morphology, exposing a high fraction of (001) facets, or a truncated bipyramidal morphology, exposing primarily (101) facets, and ranged in size from 10 nm up to 25 nm. The nanocrystals were cast into thin films and their catalytic properties evaluated using traditional surface science techniques in an ultra-high vacuum environment, such as x-ray photoelectron spectroscopy and temperature-programmed desorption. It was found that the reactivity of these probe molecules was highly dependent on both shape and size. Furthermore, it was found that photoactivity was dependent on the presence of noble metals such as Pt as well as co-adsorbates at the surface of the nanocrystals for trapping photo-generated charge carriers. These results provide insight into how the activity of a material may be tuned by controlling nanostructure.

Scalable Energy Storage Devices for Emerging MEMS Systems

Mike Synodis, Minsoo Kim, Mark Allen and Sue Ann Bidstrup Allen

As the number and complexity of today’s microelectronic systems increase, so does the demand for power at a range of size scales. Often a limiting factor for commercialization of sensors, actuators, and other microsystems is the energy storage required for operation and the volume of the device needed to provide that power for the lifetime of the system. In general, inverse relationships between power density and energy density in devices limit their application versatility. However, this research focuses on the development of fabrication schemes that enable the generation of both high power and energy density devices, while maintaining precise control of the device geometry such that the overall volume (and thus outputs) can be tuned. Deterministically engineered structures enable this scalability, and this combination of geometrical adaptability with electrodeposited nanostructured active materials yields excellent performance. High power lithium-ion batteries and high energy oxide and conductive polymer based supercapacitors have been built and tested to demonstrate the utility of these MEMS-based fabrication approaches for energy storage.

Materials

Robust Underwater Anti-Fouling Coatings from Spray Assemblies of Polymer Grafted Silica Nanochains

Zhiwei Liao, Gaoxiang Wu, Daeyeon Lee and Shu Yang

Surfaces that have superhydrophilic characteristics are known to exhibit extreme oil repellency under water. Scalable manufacturing of such coatings that can be applied onto various surfaces is attractive for many applications including water-oil separations and anti-fouling coatings. In this work, we create a robust superhydrophilic coating that repels oil under water by controlling surface chemistry and assembly morphology. The coating is obtained by spray coating poly(acrylic acid) (PAA)-grafted SiO2 nanochains onto substrates, leading to the formation of a porous membrane with nanoscale roughness and large porosity. By comparing the wetting properties of these PAA-grafted SiO2 nanochain assemblies to other types of structures, we show that both the morphology created by spray-coating of nanochains and the surface grafting of PAA are necessary to enable robust underwater superoleophocity. In addition to superhydrophilicity (water contact angle in air ≈ 0°) and underwater superoleophobicity (underwater oil contact angle ≥ 165°), the polymer-grafted nanochain assembly exhibits extremely low contact angle hysteresis (< 1°) and small adhesion hysteresis (≈ −0.05 mN/m), and thus oil can readily roll off from the surface. More interestingly, we show that even after the PAA grafted nanochain coating is purposely impregnated with oil, oil can be readily and spontaneously removed from the coating within about 10 seconds when placed under water. Our approach offers a facile yet effective method to create a robust superhydrophilic and anti-oil fouling coating via a scalable manufacturing method.

Exploring Dispersion Behavior in Polymer Nanocomposites using Polymer Field Theoretic Simulations

Ben Lindsay, Boris Rasin, Jason Koski, Russell J. Composto and Robert A. Riggleman

Polymer nanocomposites (PNCs) are a unique class of materials that can have improved thermal, electrical, or optical properties compared to neat polymers. Controlling the dispersion of the nanoparticles in the polymer matrix is critical to enabling these property improvements. Polymer field theory is a framework that enables efficient simulations of PNC materials. In this presentation, I present how I have used polymer field theoretic simulations to explore the particle-particle and particle-polymer interactions that influence bulk dispersion properties in PNCs. I will show how interactions between particles and interfaces between microphase-separated polymer domains influence equilibrium configuration and orientation. I will also show how attractive interactions between particles and polymers can lead to counter-intuitive phase behavior. These insights can help guide and interpret experimental work.

Pathways to scalable, high filler-fraction polymer nanocomposites via solvent-driven infiltration (SIP)

Neha Manohar, Kathleen J. Stebe and Daeyeon Lee

We have previously introduced a one-step, room temperature method for high filler-fraction (> 50vol%) polymer nanocomposite fabrication through solvent-driven infiltration of polymer (SIP) into nanoparticle (NP) packings from a bilayer film composed of a densely packed layer of NPs atop a polymer film. The bilayer film is exposed to solvent vapor, which leads to capillary condensation of solvent in the voids of the NP packing, and subsequent plasticization and infiltration of the underlying polymer. Herein, we probe two potential mechanisms of SIP, solvation-based vs. surface-mediated. From a theoretical standpoint, we consider how these pathways arise from the competition between confinement, adsorption and solvation on the free energy landscape of a polymer chain trapped inside the solvent-filled voids of the NP packing. This is accessed experimentally by tuning the polymer-NP interactions through the use of polystyrene and poly(2-vinylpyridine), which have different surface interactions with the silica NP surface, and by varying the quality of solvent in the systems. The resulting differences in infiltration behavior are characterized via neutron reflectivity measurements.

Nearly Precise Ionomers Designed for Ion Transport

Lu Yan, Lauren Hoang and Karen I. Winey

Controlling the sequence of ionic groups in ionomers produces better defined nanoscale morphologies and allows new insights into the ionic conductivity. In this study, a series of nearly precise polyester-based carboxylate ionomers with different ion contents were synthesized from polymerizing diol and dianhydride monomers followed by neutralizing the carboxylic acid groups with lithium or sodium cations. This new synthetic route provides possible access to scalable production. By X-ray scattering, the nearly precise ionomers exhibit well-defined microstructures in contrast to the fully random polymers. As the ion content increases in the ionomer, ionic aggregates slow the polymer chain dynamics leading to a higher Tg. The ionic conductivity of nearly precise ionomers, as measured by electrochemical impedance spectroscopy, increases with the ion contents in the ionomer, reaching a maximum of 10-6 S/cm at 400K. All materials exhibit VFT behavior in ion conduction, indicating that the ion transport in these nearly precise ionomers are still coupled with polymer chain segmental motion. Analysis on the ionic conductivity show that the ion mobility is limiting the overall ionic conductivity. Future study will be focused on enhancing ion mobility within nearly precise ionomers.

Poster Presentations

Bioengineering

A Quantitative Analysis of Integrin Activation on T Cell Homing

Nicholas R. Anderson, Dooyoung Lee and Daniel A. Hammer

T cell homing to sites of infection and inflammation is critical for the adaptive immune response and the maintained of immune homeostasis. In addition, these cells must endure significant shear forces to exit the blood stream through the leukocyte adhesion cascade. Previously, we have showed the importance of substrate composition and density in controlling the extent and type of leukocyte adhesion through the creation of state diagrams. Here, we present work extending a previously published model combining Adhesive Dynamics, which accounts for the biophysical motion of the cell, and an intracellular signaling cascade, which allows for the simulation of integrins upon leukocyte exposure to chemokine. Specifically, we highlight our results regarding the role of the integrin activator protein kindlin-3, which is the critical protein in the immune disorder Leukocyte Adhesion Deficiency Type 3. Our model makes several predictions regarding the effects of various levels of kindlin-3 deficiency, which are then tested through an experimental flow chamber to confirm or refute model predictions and further improve the model.

Establishing the Transient Mass Balance of Thrombosis:From Tissue Factor to Thrombin to Fibrin Under Venous Flow

Jason Chen and Scott L. Diamond

We investigated the co-regulation of thrombin and fibrin as blood flows over a procoagulant surface. Using microfluidic perfusion of Factor XIIa-inhibited human whole blood (200 s-1 wall shear rate) over a 250-micron long patch of collagen/tissue factor (~1 TF molecule/μm2) and immunoassays of the effluent for fragment 1.2 (F1.2), thrombin-antithrombin (TAT), and D-dimer (post-endpoint plasmin digest), we sought to establish the transient mass balance for clotting under venous flow. F1.2 (but almost no free thrombin detected via TAT assay) continually eluted from clots when fibrin was allowed to form. Low dose fluorescein-PPACK stained fibrin-bound thrombin, a staining ablated by anti-γ’-fibrinogen or the fibrin inhibitor gly-pro-arg-pro (GPRP) but highly resistant to 7-min buffer rinse, demonstrating tight binding of thrombin to γ’-fibrin. With fibrin polymerizing for 500 sec, 92000 thrombin molecules and 203000 clot-associated fibrin monomer equivalents were generated per TF molecule (or per μm2). Fibrin reached 15 mg/ml in the pore space (porosity~0.5) of a 15-micron thick thrombus core by 500 sec and 30 mg/mL by 800 sec. For a known rate of ~60 fibrinopeptide-A per thrombin per sec, each thrombin molecule generated only 3 fibrin monomer equivalents over 500 sec, indicating an intraclot thrombin half-life ~70 msec, much shorter than its diffusional escape time (~10 sec).  By 800 sec, GPRP allowed 4-fold more F1.2 generation, consistent with GPRP ablating fibrin’s antithrombin-I activity and facilitating thrombin-mediated FXIa activation. Under flow, fibrinogen continually penetrates the clot and γ’-fibrin regulates thrombin.

Dynamic gene control through modulation of single transcription factor binding site

Samuel Keller, Yuji Yamazaki, Siddhartha Jena and Bomyi Lim

Past studies have emphasized the importance of precise regulation of gene expression boundaries, since mis-regulation of a gene expression pattern often leads to developmental defects. However, the kinetics of gene expression is not as well characterized and hence its role in normal development is not well understood. We employ quantitative live imaging methods to visualize the transcriptional dynamics of a key component of the Rho signaling pathway in living Drosophila embryos, t48. t48 displays dorsoventral gradients of expression via differential timing of transcription activation. Transcription begins as a narrow stripe of two or three cells along the ventral midline, followed by progressive expansions into more lateral regions. Quantitative image analyses suggest that these temporal gradients produce differential spatial accumulations of t48 mRNA along the dorsoventral axis. Resulting spatial gradient of t48 is correlated with myosin activity, which mediates downstream morphogenetic processes. To find out how disruptions in normal gene expression dynamics affect development, we either deleted or optimized a transcription factor binding site within the t48 enhancer sequence. Changes in a single binding site lead to changes in both the spatial boundary of the gene as well as the transcription activation kinetics. Enhancement of a binding affinity results in a wider t48 domain with precocious activation, while deletion of a binding site results in a narrower and stochastic t48 expression with delayed transcriptional activation. Moreover, higher and lower cell-to-cell stochasticity is observed upon deletion and enhancement of a binding site, respectively. We suggest that this precise spatio-temporal control of a gene expression pattern is important for downstream patterning and morphogenetic processes during development.

CD4+ T lymphocytes persist prior shear flow migratory pattern via VLA-4—VCAM-1 interaction

Sarah Hyun Ji Kim and Daniel A. Hammer

Leukocytes must be able to tether, adhere, and transmigrate on endothelial layers in order to perform immune functions at sites of infection and inflammation, as well as maintaining immune homeostasis. Near sites of inflammation, endothelial cells present Intracellular Adhesion Molecule-1 (ICAM-1) and Vascular Cell Adhesion Molecule-1 (VCAM-1) to recruit CD4+ T lymphocytes and mediate migration. CD4+ T Lymphocytes then bind to ICAM-1 and VCAM-1 with integrins Lymphocyte Function-associated Antigen-1 (LFA-1, αLβ2) and Very Late Antigen-4 (VLA-4, α4β1), respectively. Previous studies describe that CD4+ T lymphocytes exhibit a unique migratory pattern; CD4+ T lymphocytes on ICAM-1 surface migrate upstream mediated by LFA-1, whereas cells on VCAM-1 move downstream. Using a laminar flow chamber and microcontact printed ICAM-1 and VCAM-1 on PDMS surfaces, we demonstrate that while upstream migration is a robust phenomenon mediated by LFA-1—ICAM-1 engagement, VLA-4-VCAM-1 interaction is required to maintain persistent directionality post flow. This post-flow migrational memory is further supported by PI3K activity upon activation of VLA-4.

Redox sensitive protein droplets from recombinant oleosin

Ellen H. Reed and Daniel A. Hammer

Molecular biology enables the creation of new materials with designer functionality and tailored responsiveness. We created a protein that at forms nanometer-sized spherical micelles at low concentrations and forms micron-sized liquid droplets at high concentrations. This work is based upon a surfactant protein, oleosin. Oleosin contains N and C-terminal hydrophilic regions and a central hydrophobic region. At low protein concentrations, the hydrophobic region drives formation of spherical micelles. At high protein concentrations, however, oleosin phase separates to form liquid droplets akin to membrane-less organelles. In this work, we explore strategies to control phase separation by introducing a cysteine residue to oleosin, a protein that does not contain any cysteines. Adding a cysteine residue to the N-terminal hydrophilic region of oleosin results in phase separation at a lower protein concentration. Furthermore, adding a reducing agent to phase-separated, cysteine-containing oleosin rapidly dissolves the droplets. We also demonstrate two strategies to precisely control the phase transition temperature of cysteine-containing oleosin. First, the transition temperature is tuned by varying the location of the cysteine in the oleosin backbone. Second, the transition temperature is tuned by blending the parent, cysteine-less molecule with the cysteine-containing mutant. These methods provide novel ways to control protein droplet formation and dissolution. This work will have applications as a system for the release of molecules with sensitivity to reducing conditions and as an engineered mimic of membrane-less organelles in synthetic protocells.

Feasibility of a single-use, storage-stable, point-of-care microfluidic test of platelet and coagulation function under flow

Jason Rossi and Scott L. Diamond

Current diagnostic techniques used for point-of-care coagulation, such as thromboelastography, are indirect and can be unreliable and difficult to interpret. Microfluidics has become a powerful tool for phenotyping platelet and coagulation function of human blood, but has thus far been restricted to laboratory settings, with convenient single-use chips for clinical use in the emergency room or surgical suite have remained as yet undemonstrated. For this work, a microfluidic chip was developed that allows dry storage stability, rapid priming, and easy 8-channel pipette loading for 3-color imaging of 8 clotting events. The chip has demonstrate parity in data quality with standard microfluidic chips in assessing platelet function, fibrin formation, and Aspirin dose-response behavior in whole blood.

A Multiscale Model of Traumatic Bleeding

Evan Tsiklidis, Chris Verni, Jason Chen, Talid R. Sinno and Scott L. Diamond 

A multiscale model for simulating the dynamic response of traumatic blood loss in a dehydrated, anticoagulated, patient is developed. The model couples a lumped, global hemodynamic model of the human cardiovascular system - for blood pressure, heart rate, and total blood volume predictions - with a branching vasculature network – for local shear rate, blood flow rate, and blood perfusion predictions. The branching vasculature network spans from the muscular artery scale (≈ 0.1 – 10 mm) to the arteriole scale (≈ 100 - 300μm). In injury, a random distribution of wounds over the vasculature network can occur with varying degrees of severity. To investigate the impact of various wound distributions, Monte Carlo Simulations with injuries sampled over a uniform distribution was performed. To properly account for the effects of depressurization near the bleeding, wound locations were chosen a minimum 7-generations downstream of the root vessel. Model was validated with experimental measurements of blood pressure, flowrates, and wall shear rates prior to bleeding. Wall shear rates predicted by the model (≈ 103sec-1) is consistent with measured values of Von Willebrand Factor (vWF) multimerization. A comparison between simulations of entire generations of blood vessels being severed quantify the effects of downstream resistance in maintaining hemostasis, an effect that has long been recognized as significant but has never been quantified. A sensitivity analysis on the length to diameter ratio and the branching exponent of the vasculature network show that the outcome of the patient is highly dependent upon these two parameters suggesting that the location of the injury is important in determining patient outcomes as both parameters are known to vary depending upon their location.

Understanding platelet dysfunction in trauma-induced coagulopathy: significant inhibitory effects of patient-derived plasma

Christopher Verni, Carrie Sims and Scott L. Diamond

Trauma-induced coagulopathy (TIC) is a complex clinical condition observed in about 25% of patients and accounting for about 10% of deaths worldwide. Upon severe injury, various changes in blood biochemistry occur, leading to observed clotting factor activity deficiency, hyperfibrinolysis, and significant platelet dysfunction. In this work, we focus on platelet inactivity in trauma patients, which has been documented extensively but is still poorly understood on a mechanistic basis. A cohort of 13 enrolled trauma patients and 10 healthy donors was studied for platelet function and effects of plasma on cellular responses to stimuli. Platelet function was monitored via intracellular calcium mobilization and flow cytometry measurements. Dilute platelet-rich plasma (PRP) was isolated from anticoagulated whole blood, loaded with a fluorescent calcium dye or antibodies against activated integrin αIIbβ3, P-selectin, and phosphatidylserine (PS), and stimulated with an array of agonists. To study the effect of platelet-poor plasma (PPP) on the system, washed platelets were prepared and reconstituted in the presence and absence of healthy- and patient-derived PPP prior to stimulation. Trauma patients exhibited a significantly impaired platelet response as compared to healthy subjects in both calcium mobilization and flow cytometry assays. When supplemented with PPP, healthy platelets showed a significant reduction in fluorescent signal in the presence of plasma (~25% in healthy plasma; ~50% in patient plasma). Increasing the final plasma concentration caused a monotonic decrease in platelet calcium response, though patient plasma had a more potent inhi bitory effect at all doses tested. Very low plasma concentrations (1-3%) actually imparted an increase in platelet function above baseline. Inherent platelet dysfunction in TIC patients was studied and observed using healthy subjects as a control group. Further, the observed potent effect of patient plasma on healthy platelet activity suggests support for a soluble plasma species causing inhibition of transfused platelets.

Hemodynamic force triggers rapid NETosis within sterile thrombotic occlusions

Xinren Yu, Jifu Tan, and Scott L. Diamond

Neutrophil extracellular traps (NETs) are released when neutrophils encounter infectious pathogens, especially during sepsis. Additionally, NETosis occurs during venous and arterial thrombosis, disseminated intravascular coagulation, and trauma. Using microfluidics, we tested if hemodynamic forces trigger NETosis during sterile thrombosis. For perfusions at initial inlet venous or arterial wall shear rates, rapid platelet deposition occluded microchannels with subsequent neutrophil infiltration at either flow condition, however NETosis was only detected at the arterial condition as shown. With or without thrombin, venous perfusion for 15 min generated no NETs, but an abrupt shift-up to arterial perfusion triggered NETosis within 2 min, eventually reaching levels 15 min later that were 60-fold greater than microchannels without perfusion shift-up. SINs contained Myeloperoxidase and citrullinated histone and responded to DNase treatment, but were not blocked by inhibitors of platelet-neutrophil adhesion, HMGB1-RAGE interaction, cyclooxygenase, ATP/ADP or PAD-4. For measured pressure gradients exceeding 70 mmHg/ mm-clot across NET-generating occlusions to drive interstitial flow, calculated stress hot spots on neutrophils exceeded 1000 dyne/cm2. In conclusion, high interstitial hemodynamic forces can drive physically entrapped neutrophils to rapidly release NETs during sterile occlusive thrombosis. SIN might share similar thrombotic or inflammatory properties to NETs triggered by other stimuli.

Energy

Manufacturing High-Performance infiltrated Solid Oxide Fuel Cell Cathodes via backbone engineering and surface Modification

Yuan Cheng, Liang Zhang, Aleksandra Vojvodic, John M. Vohs and Raymond J. Gorte

Solid Oxide Fuel Cells (SOFCs) are high-efficiency electricity generating systems. The major resistance of the device comes from its cathode, where oxygen reduction reaction happens. In this study, two approaches were taken to reduce the cathodic resistance. First, a conductive composite cathode backbone was developed and successfully improved the cathodic performance at low catalyst loading. Second, the outermost layer of the perovskite phase (ABO3) cathode catalyst, La0.8Sr0.2FeO3 (LSF), was modified with Atomic Layer Deposition (ALD) of metal oxides. It was discovered that the surface resistance decreased significantly with small numbers of ALD cycles of AO metal oxides before again increasing at higher coverages. This implicates that an AO-terminating surface is favorable for oxygen reduction with LSF catalyst.

Effects of Iron Doped Cobalt Oxide Nanoparticles on Water Adsorption and Splitting

Anthony Curto, Liang Zhang and Aleksandra Vojvodic

Earth abundant transition metal oxides and their mixed metal oxide counterparts have shown promise as viable catalysts for the oxygen evolution reaction (OER). OER is a valuable reaction for renewable alternate energy applications and necessity for these catalyst materials increases as the need for new clean energy grows. Understanding the chemistry of these complex multi-component oxide catalysts at the atomic scale is required to effectively design better catalysts. Previous work found that a ternary CoFeW oxides exhibits low overpotentials for OER due to favorable surface chemistry of the OER reaction intermediates and the oxide surface. However, the exact oxide structure as well as the active site are unresolved. Therefore, we build off previous work where pure CoOx nanoparticles supported on Au(111) were studied and investigate the role of Fe doping in these Co oxide nanostructures. Using density functional theory (DFT), Fe doping into CoO bilayers is studied to understand dopant cluster location, size and shape preferences. Integration of our computational studies with scanning tunneling microscopy (STM) studies by reveal the doping patterns of Fe in these CoO bilayers. The effects the discovered Fe doping provides valuable insight into the catalytic promotion affects seen from these binary oxides compared to their single metal oxides and aids towards our ultimate goal of identifying the active site for water adsorption, dissociation and OER.

Three-dimensional lithium ion batteries using porous structures

Chenpeng Huang, James Pikul, Mark Allen and Sue Ann Bidstrup Allen

In this study, two different approaches were used to fabricate 3D lithium ion micro-batteries using porous structures. In the first approach, a porous structure was fabricated by co-deposition of active material and current collector in a single step. In the second approach, porous copper scaffold was deposited, onto which subsequent components of a lithium ion battery, including current collector and active material, were sequentially deposited using electrodeposition. The first approach enabled a more facile fabrication and higher areal capacity, while a more uniform and mechanically rigid structure could be fabricated using the second approach. However, both 3D structure electrodes achieved much higher areal capacity compared to 2D thin film electrodes. In addition, both 3D structures could be discharged up to a fast rate of 10C without significant capacity loss. To assist with the optimization of the battery performance in terms of energy and power densities, an electrochemical model was developed to study of the effect of geometric design parameters, such as pore size and active material thickness, on battery performance.

Computational study of functionalized 2D MXene materials for electrochemical N2 reduction (NRR)

Luke Johnson and Aleksandra Vojvodic

Ammonia (NH3) is vital to the agricultural industry as an agent in manufacturing fertilizer, resulting in the dramatic population growth of the 20th century. There is an interest in discovering catalytic materials for the NRR under ambient conditions to overcome the current energy intensive Haber Bosch process. In this presentation, we use density functional theory calculations to study the mechanism of MXenes with chemical formula M2XT2, a new class of materials, for electrochemically producing NH3 (NRR) under ambient conditions. 2-D carbides and nitrides (M = Ti, Zr, V, Nb, Ta, Mo, W) and surface functionalization (T=Bare, H, O, and N) are varied to screen for their catalytic activity based on thermodynamic energy pathways. W2C, W2N, Mo2C, and Mo2N are selected candidate electrocatalysts, but are unstable under working conditions. The adsorption free energy of the intermediates defines a descriptor, ∆GN, which confirms that H-, O-, and N-terminated MXenes are unsuitable electrocatalysts due to their inability to stabilize the N2H* intermediate. A comparison of how H poisoning affects HER (Hydrogen Evolution Reaction) activity versus the limiting potential step shows that only unstable bare MXenes compete against the HER. Charge analysis is implemented to show that surface chemistry is related to charge transfer from the surface to adsorbate, dependent on the adsorption geometry and the termination on the basal planes. Finally, we investigate two routes closely to enhance and tune the basal plane chemistry for NRR, namely impact of functional groups including S, F, and Cl and role of the crystal structure of the MXene.

BaCeO3 and BaZrO3 thin films as supports for Pd catalysts.

Rohit N. Kavassery Ramesh, K. L. Abdul-Aziz, and Raymond J. Gorte

Perovskite-supported catalysts have been referred to as “intelligent” catalysts for automotive emissions control because it has been reported that catalytic metals can be redispersed by reversible exsolution from the perovskite lattice. The exsolution process involves the segregation of the transition metal dopant from the pervoskite support to the surface upon reduction and restoration back to its initial atomic state during oxidation. A major barrier to implementing this technology is the low surface areas of the perovksites. The present study examined the synthesis of thin films of Barium Zirconate (BaZrO3) and Barium Cerate (BaCeO3) over high surface area alumina using Atomic Layer Deposition. The individual growth rates of barium, zirconia and ceria as well as the growth rates of BaZrO3 and BaCeO3 films were examined and the ALD synthesized materials were tested for the CO oxidation. It was observed that the Pd could be exsolved from the lattice; however, the exsolution process appears to be irreversible in this system.

High-Surface-Area, Intelligent Ni catalysts Prepared by Atomic Layer Deposition

Chao Lin and Raymond J. Gorte

“Intelligent Catalysts” are ones in which metal cations can be reversibly incorporated into the lattice of a perovskite under oxidizing and then exsolved as metal particles under reducing conditions. It has previously been shown that Ni particles ex-solved from Titania-based perovskites (e.g. SrTiO3) exhibit a high tolerance against coking, apparently due to the fact that the particles are anchored to the support. However, because the perovskites have a low specific surface area, these catalysts are not practical. In the present work, we prepared CaTiO3 films on high-surface-area MgAl2O4 using Atomic Layer Deposition. We demonstrate that Ni supported on these composite supports also exhibits a high tolerance against coke formation and can therefore be used for dry reforming of methane and ethane oxidative dehydrogenation (ODH). Activities for these catalysts in steam reforming and dry reforming were found to be comparable to normal Ni catalyst but the samples with CaTiO3 were much more stable. In the ODH of ethane by CO2, the intelligent catalyst showed a very different selectivity.

Metal Oxide Supports prepared by Atomic Layer Deposition for CO Oxidation and Methane Oxidation

Xinyu Mao and Raymond J. Gorte

“It is possible to prepare metal oxide supports which have catalytic properties for certain reactions by performing ALD of corresponding organometallic precursors on high-surface-area γ-Al2O3. Comparing to traditional infiltration methods, ALD can generate conformal thin films which have more well-dispersed particles. Unlike for CO Oxidation the reaction rates are very correlated to the Pd dispersions, the Methane Oxidation rates on the catalysts did not depend strongly on the supports. The influence of water vapor on Methane Oxidation is more different for the catalysts than in dry condition, and Pd/CoOx/γ-Al2O3 exhibited the best water resistance among the Pd/CoOx/γ-Al2O3, Pd/CeO2/γ-Al2O3, Pd/NiO/γ-Al2O3, Pd/Fe2O3/γ-Al2O3, and Pd/ZrO2γ-Al2O3. The differential reaction rates of Methane oxidation also imply that the spinel structure of CoAl2O4 and NiAl2O4 do not promote the activity of catalysts on Methane Oxidation, and not provide any extra ability of water resistance.

Surface Modification of SOFC Cathodes via ALD of Co, Ni and Pd oxides

Julian Paige, Danyi Sun, Yuan Cheng, John M. Vohs and Raymond J. Gorte

The performance of solid oxide electrochemical cells (SOEC) is usually limited by the air electrode, and significant effort has gone into understanding the factors that control electrode kinetics. A major difficulty associated with this is the fact that electrode performance is a complex function of electrode composition and structure. Because Atomic Layer Deposition (ALD) allows modification of the surface composition without significantly changing the structure, it is an ideal method for determining the likely rate-limiting step in the electrode reaction. For example, previous studies of ZrO2 ALD on La0.8Sr0.2FeO3 (LSF)-YSZ electrodes has shown that the electrode impedance increases linearly with ZrO2 coverage, increasing by a factor of 5 at a coverage corresponding to one monolayer, suggesting that the rate-limiting step is the adsorption of O2. In the present study, we aim to determine whether the addition of submonolayer amounts of catalytic metals could be used to enhance O2 dissociation and decrease electrode impedances. Thin films of nickel, palladium, and cobalt oxides were deposited onto La0.8Sr0.2CoO3, La0.8Sr0.2MnO3, La0.8Sr0.2FeO3, and La0.6Sr0.4Co0.2Fe0.8O3 electrodes and the impedances were measured as a function of film thickness.

Insights for Catalyst Design: Using Well-Defined Metal Oxide Nanocrystals to Elucidate Structure-Activity Relationships

Paul Pepin and John M. Vohs

TiO2 is a prototypical catalyst for selective oxidation and photo-oxidation of organic molecules, and surface science studies with macroscopic single crystals have greatly advanced our mechanistic understanding of the structural requirements for many of these reaction pathways. While single crystal surfaces have been instrumental in providing these mechanistic insights, these unique materials do not exist for many surfaces of interest. Additionally, there exists significant disparity between these model single crystal systems and real-world catalysts – particularly in the realm of photocatalysis, where considerations must also be made for bulk phenomena. Well-defined nanocrystals of metal oxides provide an intermediary between these single crystals and industrially-relevant high surface area polycrystalline materials. In this talk, I will present my research using methanol and acetaldehyde as probe reagents to elucidate how nanostructure influences thermal and photocatalytic reaction pathways on size- and shape-selected A-TiO2 nanocrystals. The nanocrystals used were either of a platelet morphology, exposing a high fraction of (001) facets, or a truncated bipyramidal morphology, exposing primarily (101) facets, and ranged in size from 10 nm up to 25 nm. The nanocrystals were cast into thin films and their catalytic properties evaluated using traditional surface science techniques in an ultra-high vacuum environment, such as x-ray photoelectron spectroscopy and temperature-programmed desorption. It was found that the reactivity of these probe molecules was highly dependent on both shape and size. Furthermore, it was found that photoactivity was dependent on the presence of noble metals such as Pt as well as co-adsorbates at the surface of the nanocrystals for trapping photo-generated charge carriers. These results provide insight into how the activity of a material may be tuned by controlling nanostructure.

Facet-dependent segregation of Pt in ATiO3 (A=Ca, Sr, Ba) perovskites: Insights into the exsolution process

Abhinav S. Raman and Aleksandra Vojvodic

Although the current state of the art in most commercial catalysts, supported metal catalysts pose issues of degradation and coking over time. A promising alternative to this, has been the exsolution of transition metal cations from a host perovskite lattice followed by their subsequent condensation to form catalytically active nanoparticles on the surface of the host perovskite. In this study, we use first-principles methods coupled with high performance computing to delineate potential thermodynamic driving forces for the surface segregation of Pt in stoichiometric ATiO3 perovskite oxides (A= Ca, Sr, Ba). We considered the effects of the different crystal facets of the host perovskite, in-plane strain to the host lattice as a result of the lattice mismatch, different doping sites and doping ratio, as potential players in the segregation process. We observed trends indicating preferential segregation along specific crystal facets, as well as a strain dependence on the segregation process, while generally, surface segregation was independent of the host perovskite. Electronic structure based analysis was performed to provide a rationale to explain the observed trends. The observed segregation trends and electronic structure based descriptors provide important insights into the surface segregation of transition metal cations in a host perovskite, aiding in the development of novel synthesis methods such as exsolution.

Scalable Energy Storage Devices for Emerging MEMS Systems

Mike Synodis, Minsoo Kim, Mark Allen and Sue Ann Bidstrup Allen

As the number and complexity of today’s microelectronic systems increase, so does the demand for power at a range of size scales. Often a limiting factor for commercialization of sensors, actuators, and other microsystems is the energy storage required for operation and the volume of the device needed to provide that power for the lifetime of the system. In general, inverse relationships between power density and energy density in devices limit their application versatility. However, this research focuses on the development of fabrication schemes that enable the generation of both high power and energy density devices, while maintaining precise control of the device geometry such that the overall volume (and thus outputs) can be tuned. Deterministically engineered structures enable this scalability, and this combination of geometrical adaptability with electrodeposited nanostructured active materials yields excellent performance. High power lithium-ion batteries and high energy oxide and conductive polymer based supercapacitors have been built and tested to demonstrate the utility of these MEMS-based fabrication approaches for energy storage.

A Mechanistic Study of the Direct Hydrodeoxygenation of m-Cresol over WOx‑decorated Pt/C Catalysts

Cong Wang, Alexander V. Mironenko, Abhishek Raizada, Tianqi Chen, Xinyu Mao, Ashwin Padmanabhan, Dionisios G. Vlachos, Raymond J. Gorte and John M. Vohs

The hydrodeoxygenation (HDO) of m-cresol to produce toluene over carbon-supported Pt and Pt-WOx catalysts was studied. In stark contrast to Pt/C that exhibits only modest selectivity and low stability for this reaction, Pt-WOx/C was found to be unusually active and selective to toluene with over 94% selectivity to this product while exhibiting little to no deactivation under a wide range of reaction conditions. Reactivity studies in combination with density functional theory(DFT) calculations for the adsorption and reaction of m-cresol on structurally optimized, WOx-decorated Pt(111) structures indicate that the HDO reaction on Pt-WOx/C proceeds via a direct hydrogenolysis of the C-O bond in m-cresol adsorbed on oxygen vacancy (or redox) sites on WOx species. The DFT results also indicate that Pt helps stabilize the WOx film while facilitating oxygen vacancy formation.

Materials

Direct Identification and Quantification of Bound Polymer in Polymer Nanocomposites

Eric J. Bailey, Philip J. Griffin, Russell J. Composto and Karen I. Winey

The addition of nanoparticles (NPs) to a polymer matrix, forming a polymer nanocomposite (PNC), can significantly enhance the thermal, mechanical, and functional properties of the host material, making them relevant for a variety of fields. Due to the large surface area to volume ratio of NPs, PNC properties are often dominated by interfacial polymer near the NP surface. However, directly probing the static and dynamic properties of interfacial polymer remains an experimental challenge. Using ion scattering techniques, we directly observe and quantify the interfacial polymer in a model PNC system with strong NP-polymer attraction for a variety of annealing conditions. To do so, free polymer is permitted to diffuse from a PNC thin film into bulk polymer while the NPs are engineered to remain immobile, thus separating polymer chains that diffuses freely and those adsorbed to the NP surface. By correlating the measured amount of bound polymer and the known NP concentration, we extract the areal density of adsorbed chains and the thickness of the bound polymer layer, two parameters that are difficult to experimentally measure in the melt state. Furthermore, we find that polymer relaxation and desorption from the interface occurs as a function of annealing time and temperature, but bound polymer remains after more than 106 reptation times. These results provide fundamental insights to help understand static and dynamic properties of interfacial polymer in PNCs and reveals non-equilibrium properties that can be used to engineer equilibrium dispersion of bare NPs in various polymer melts.

Bicontinuous biphasic emulsion gels for catalysis and separation applications

Giuseppe Di Vitantonio, Tiancheng Wang, Daeyeon Lee and Kathleen J. Stebe

Simultaneous operation of catalysed reaction and separation had transformative impact increasing the efficiency of chemical processes; very successful particle-stabilized emulsion-based phase-transfer catalysis has been developed, however the traditional water in oil/oil in water emulsion cannot perform a steady and robust separation of the product. A bicontinuous particle-stabilized emulsion (bijel) can overcome this limitations, in our lab we developed the solvent-transfer induced phase separation (STRIPS) technique to produce such material in a simple, flexible and continuous fashion. We show how bijel chemistry can be tuned to improve its mechanical and chemical properties, as well as introducing catalytic nanoparticles in the bijel scaffold. We use this soft material to run simultaneous reaction and separation taking advantage of the different water affinity of reagent and products. We are able to perform a broad variety of chemical reactions in bijels: non catalytic, homogenous catalysis and heterogenous catalysis, accessing temperature ranges of about 100°C.

Parallel Alignment of Nanoplate Additives in Self-Assembled Polymer Nanocomposite Coatings

Nadia M. Krook, Russell J. Composto and Christopher B. Murray

Polymer nanocomposites (PNCs) leverage polymers as a flexible and processable platform in which to imbed a variety of nanoparticles (NPs). The properties of these hybrid materials not only depend on the independent materials, but also on the spatial distribution, organization, and orientation of the additives. However, precise orientational control of anisotropic NPs through self-assembly techniques remains challenging in synthetic composites. If complimentary geometries and favorable thermodynamic factors are achieved between the NPs and matrix, block copolymer (BCPs) have the potential to direct the alignment of anisotropic NPs. However, limited studies have explored the directed orientation of non-spherical NPs, especially plates, in BCPs since several challenges arise when considering incorporating common two-dimensional particles (e.g. clay and graphite) into BCPs. These factors include NP polydispersity, incompatible particle dimensions with BCP domains, and difficulties modifying the platelets’ surface chemistry. The presented study establishes a model nanoplate system to address these challenges and systematically study the alignment of nanoplates in BCPs. Monodisperse, surface modifiable gadolinium trifluoride rhombic nanoplates doped with ytterbium and erbium [GdF3:Yb/Er (20/2 mol%)] are synthesized through rapid thermal decomposition. Comparable with BCP dimensions and functionalized with Mn = 5 kg/mol phosphoric acid functionalized polyethylene glycol (PEG-PO3H2), the plates’ longest and shortest diagonals and thicknesses measure 35 nm, 22 nm, and 3 nm, respectively. A Mn = 38k-b-36.8k g/mol lamellar-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) with domains oriented parallel to the substrate serves as a template to align the PEG-PO3H2grafted nanoplates. At low loadings, the nanoplates not only segregate to the PMMA domains, but directed parallel alignment in an ordered lamellar structure is achieved. At approximately the calculated overlap volume fraction (φ* = 0.051), the lamellae become frustrated and the nanoplates disperse isotropically. The results of this study not only extend our thermodynamic understanding of PNCs, but also provide insight into variables that control NP orientation. PNCs designed for specific properties (such as barrier coatings) could be made accessible if preferential orientation of non- spherical NPs is improved.

Robust Underwater Anti-Fouling Coatings from Spray Assemblies of Polymer Grafted Silica Nanochains

Zhiwei Liao, Gaoxiang Wu, Daeyeon Lee and Shu Yang

Surfaces that have superhydrophilic characteristics are known to exhibit extreme oil repellency under water. Scalable manufacturing of such coatings that can be applied onto various surfaces is attractive for many applications including water-oil separations and anti-fouling coatings. In this work, we create a robust superhydrophilic coating that repels oil under water by controlling surface chemistry and assembly morphology. The coating is obtained by spray coating poly(acrylic acid) (PAA)-grafted SiO2 nanochains onto substrates, leading to the formation of a porous membrane with nanoscale roughness and large porosity. By comparing the wetting properties of these PAA-grafted SiO2 nanochain assemblies to other types of structures, we show that both the morphology created by spray-coating of nanochains and the surface grafting of PAA are necessary to enable robust underwater superoleophocity. In addition to superhydrophilicity (water contact angle in air ≈ 0°) and underwater superoleophobicity (underwater oil contact angle ≥ 165°), the polymer-grafted nanochain assembly exhibits extremely low contact angle hysteresis (< 1°) and small adhesion hysteresis (≈ −0.05 mN/m), and thus oil can readily roll off from the surface. More interestingly, we show that even after the PAA grafted nanochain coating is purposely impregnated with oil, oil can be readily and spontaneously removed from the coating within about 10 seconds when placed under water. Our approach offers a facile yet effective method to create a robust superhydrophilic and anti-oil fouling coating via a scalable manufacturing method.

Pathways to scalable, high filler-fraction polymer nanocomposites via solvent-driven infiltration (SIP)

Neha Manohar, Kathleen J. Stebe and Daeyeon Lee

We have previously introduced a one-step, room temperature method for high filler-fraction (> 50vol%) polymer nanocomposite fabrication through solvent-driven infiltration of polymer (SIP) into nanoparticle (NP) packings from a bilayer film composed of a densely packed layer of NPs atop a polymer film. The bilayer film is exposed to solvent vapor, which leads to capillary condensation of solvent in the voids of the NP packing, and subsequent plasticization and infiltration of the underlying polymer. Herein, we probe two potential mechanisms of SIP, solvation-based vs. surface-mediated. From a theoretical standpoint, we consider how these pathways arise from the competition between confinement, adsorption and solvation on the free energy landscape of a polymer chain trapped inside the solvent-filled voids of the NP packing. This is accessed experimentally by tuning the polymer-NP interactions through the use of polystyrene and poly(2-vinylpyridine), which have different surface interactions with the silica NP surface, and by varying the quality of solvent in the systems. The resulting differences in infiltration behavior are characterized via neutron reflectivity measurements.

Comparing Phase Separation Behavior of Polymer Blends and Nanocomposites

Shawn M. Maguire, Nadia M. Krook, Patrice Rannou, Manuel Maréchal, Koji Ohno and Russell J. Composto

In polymer nanocomposites (PNCs), the spatial orientation and distribution of nanoparticles (NPs) dictate material properties. Having precise control of the placement and alignment of NPs requires an understanding of the thermodynamics and dynamics of the PNCs. By studying the phase separation behavior of a model PNC system, the thermodynamics (enthalpic and entropic contributions) that dictate the dispersion of the NPs is hoped to be elucidated. Here, we utilize binary composites incorporating NPs grafted with Poly (methyl methacrylate) (PMMA NPs) and Poly (styrene-co-acrylonitrile) (SAN) and ternary composites consisting of PMMA NPs, SAN, and PMMA. Employing a combination of transmission electron microscopy, optical microscopy, and small angle x-ray scattering techniques, the phase behavior for these two system is tracked, revealing lower critical solution temperature type behavior, with a slight increase in miscibility for the ternary system.

Effects of Microstructure Formation on the Stability of Vapor Deposited Glasses

Alex Moore, Patrick Walsh, Zahra Fakhraai and Robert A. Riggleman

Glasses formed by physical vapor deposition (PVD) are an interesting new class of materials, exhibiting properties thought to be equivalent to those aged for thousands of years. Exerting control over the properties of PVD glasses formed with different types of glass forming molecules is now an emerging challenge. In this work, we study coarse grained models of organic glass formers containing fluorocarbon tails of increasing length, corresponding to an increased tendency to form microstructures. We use simulated PVD to examine how the presence of the microphase separated domains influences the ability to form stable glasses. This model suggests that increasing molecule tail length results in decreased thermodynamic and kinetic stability of the molecules in PVD films. We find that the relaxation time near the surface of ordinary glass films formed by these molecules remains essentially bulk-like, and the surface diffusion is markedly reduced. Based on these results, we propose a trapping mechanism where tails are unable to move between local phase separated domains on the relevant simulation time scales.

Ion transport and morphology in precise sulfophenylated ionomers

Benjamin A. Paren, Lionel Picard, Patrice Rannou, Manuel Marechal, William J. Neary, Aaron Kendrick, Justin G. Kennemur and Karen I. Winey

Solid polymer electrolytes (SPEs) are non-volatile, unlike liquid electrolytes, and are more mechanically stable than the liquid electrolytes commonly used in Li-ion batteries. SPEs also have the potential for improved mechanical stability and reduced degradation compared to polymer salt mixtures. The recent publication by Trigg et al. (Nature Materials, 2018) has illustrated the profound impact of the organization of acid groups in semi-crystalline precise polymers to facilitate proton transport, for use in fuel cell membranes. It may be possible for ionic aggregates to improve ion transport in SPEs in a similar fashion. This study focuses on a novel set of precise ionomers, p5PhSO3X , a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon, where X is the counterion (H+, Li+, Na+, or Cs+). The structures of these systems are characterized with X-ray scattering, and the ion transport properties are characterized with electrical impedance spectroscopy. These specific materials are mechanically robust above 100°C, demonstrate fast ion transport and highly ordered ionic aggregates, and may have the potential to serve as a fuel cell membrane (X=H+), or solid polymer electrolytes in batteries (Li+, Na+, Cs+).

Polymer Diffusion is Fastest at Intermediate Levels of 2D Confinement

James F. Pressly, Robert A. Riggleman and Karen I. Winey

Understanding the structure and dynamics of polymers under nanoconfinement is critical in a variety of applications and industries, including semiconductor manufacturing, natural gas extraction, and polymer nanocomposites. Despite its importance, the relationship between the effect of chain length and pore radius on polymer properties (entanglement density, chain conformation, diffusion coefficient, relaxation time) is not well understood, with several studies indicating conflicting results. Using molecular dynamics, we simulated several systems with polymer chain lengths of N = 25-500 confined to discrete cylindrical pores of radii r = 2.5-20σ and examined their properties in confinement. Most interestingly, our results indicate a non-monotonic change in diffusion coefficient, D, as the pore radius is decreased, with longer chains exhibiting larger changes in D. We believe this is caused by the competing effects of chain disentanglement (faster diffusion) and confinement induced chain segregation (slower diffusion).

Pair interaction and structure formation on a curved fluid interface

Alismari Read and Kathleen J. Stebe

A great deal of attention has been focused on colloidal particles at interfaces due to their wide range of applications in which the substantial desorption energy of particles is harnessed to stabilize the interface. When a particle attaches to a fluid interface it either adopts an equilibrium contact angle at the three phase contact line or it can be pinned with an undulated contact line due to chemical heterogeneities or surface roughness. In the early stages of this work our lab took advantage of the capillary energies or self-energies that arise from the distortions made by particles with such contact line pinning, which mainly is the product of surface tension and the distortion area. It has been shown that this energy field can be use to direct, rotate, and assemble anisotropic particles on planar interfaces. Fundamentally, this assembly occurs through capillary interactions where particles come together to minimize the free energy of the system to reduce the exposed interfacial area. The same physics of migration and assembly hold for curved interfaces, where microspheres have been shown to migrate along deterministic trajectories toward regions of maximum deviatoric curvature where the free energy is also minimized. With this fundamental understanding on how particles behave on different kinds of interfaces, our current focus is on comprehending the underlying physics behind pairs of particles on curved interfaces both experimentally and analytically. We are currently pursuing this by examining pair potentials through force and torque calculations, and investigating the ability of spherical particles to form well-defined structures around a cylindrical micropost.

Probing the evolution of polyacrylamide hydrogel structure using nanoprobes during UV photopolymerization using fluorescence recovery after photobleaching (FRAP)

Katie A. Rose, Catherine Picart, Daeyeon Lee and Russell J. Composto

Understanding the diffusion of probe molecules through biologically relevant matrices, such as hydrogels, is important to a variety of fields. However, there has been little work to correlate the diffusion at the nanoscale, which is especially important for heterogenous hydrogels that exhibit a large distribution of mesh sizes, and that associated with bulk diffusion. Furthermore, understanding the kinetics of gelation of these hydrogels could yield valuable information for kinetically trapping functional nanoparticles, imparting new mechanical, electrical and magnetic properties. Photopolymerization is a particularly interesting area of hydrogel gelation, given that the polymerization can be turned “on” and “off” with the addition or removal of the light source, and its rising popularity for not only the curing of polymer resins, but for stimuli-responsive hydrogel applications. In this work, we investigated the transport phenomena of FITC-dextran of various hydrodynamic radii and FITC-BSA in polyacrylamide gels using Fluorescence Recovery After Photobleaching (FRAP) at different time points of photopolymerization. Decreased diffusion was observed for increasing monomer weight percent and increased time of polymerization, as a decreased percentage of probes that were able to recovery as polymerization time increased. Interesting, similarly sized probes (20 kDa FITC-dextran, FITC-BSA) exhibited different diffusion profiles. Continuation of this work to look at the nanoscale will be done using single (nano)particle tracking using the same hydrogel system.

Dynamics of Solvent Driven Infiltration of Polymers (SIP) into nanoparticle packing

Bharath Venkatesh, Tianren Zhang, Neha Manohar, Robert A. Riggleman, Kathleen J. Stebe and Daeyeon Lee

Polymer Nanocomposites are invaluable due to the diversity of tunable material properties that can be accessed by varying the chemical nature of the nanoparticle and the polymer. Synthesis methods are usually focussed on dispersion of nanoparticles in the polymer matrix with the aid of a solvent which is later evaporated. This method suffers from the problems of phase separation and aggregation of the nanoparticles from the polymer matrix. Recently, the Lee lab has developed a solvent driven infiltration approach to create dense, stable nanocomposites by using solvents wetting the nanoparticle packing to drive the polymers into a nanoparticle packing. This process called SIP(Solvent induced Infiltration of Polymer) is along the same lines as the previous work done in our lab where thermal annealing was used to drive the polymer from a melt into the packing(CARI). Molecular dynamics simulations of the coarse grained model of the system are used to study the infiltration in the presence of a solvent. The mechanism of this infiltration and the influence of solvent quality, chain length of polymers, etc. on the dynamics of the process are determined from MD simulations. Specifically, we have been able to find two mechanistic regimes of infiltration: 1) surface-driven regime, whereby strong interactions of the nanoparticle with the polymer ensure that the polymer advances into the nanoparticle layer by adhesion to the particle surface, and 2) dissolution-driven regime, whereby solvent drives the polymer chains into the nanoparticle packing. The poster will illustrate the models and methods used in the simulations and discuss our findings.

Diverse Colloidal Crystals from DNA-grafted Spheres via Self-assembly

Yifan Wang, Ian Jenkins, James McGinley, Talid R. Sinno and John C. Crocker

DNA-grafted colloids are advantageous in making different structure colloidal crystals through self-assembly. In our lab, diverse crystal structures including CsCl, CuAu, NaCl, NiAs, Cu3Ti, NbP, α-IrV, intermedium between different crystal types and partially transformed crystals are prepared through a slowly quenching method, in which temperature goes down as 0.4 degree per hour. Specifically, we coat certain type DNA on to the polystyrene (PS) beads of various sizes through a swelling and deswelling method. At the same time, another type DNA is coated on to another batch of PS particles that the two type DNA on each particle species could be bond via linker. The DNA type on certain kind PS particles could be either pure or some combinations of the two. We mix two type particles at a certain volume ratio, heat them 5 degrees above the melting temperature of the DNA strands, and then slowly quench them. After the quench, we get nice crystals with good crystallinity which can be observed under optical microscope. By changing the stoichiometry of the two type particles, particle size ratios, as well as the composition of DNA strands on each type particles, we are able to explore new ways of making diverse structure colloidal crystal and get multiple types of crystals in the same sample. Furthermore, the transformation patterns and paths between some crystal types are discussed and mechanisms are well studied. To analyze the crystal structures and measure the exact lattice spacing and bond angles, crystallography can be studied via confocal microscopy.

Ion-Conductive Telechelic Polyethylenes Oligomers from Fatty Acids

Lu Yan, Manuel Häußler, Stefan Mecking and Karen I. Winey

Telechelic polyethylenes (PEs) containing carboxylic acid or metal cation (e.g. Na+, Cs+ or Zn2+) coordinated carboxylate end groups with 23 or 48 CH2 units (C23, or C48) in between have been synthesized by catalytic dimerization of erucic acid. After neutralizing the carboxylic acid groups with metal cations, the melting temperatures of the C23 and C48 telechelic PEs increase by 30-70 °C, accompanied with a reduction in crystallinity by ~20-40%. The linear and monodisperse telechelic PEs self-assemble into well-defined lamellar structure with acid or ion rich layers embedded in the orthorhombic or monoclinic crystallites due to the hydrogen bonding between the carboxylic acid groups or ionic interactions between the ionic carboxylate groups. Interestingly, C48Cs and C23Na exhibit a crystal phase transition from orthorhombic to hexagonal or monoclinic structure at ~ 135 °C or 156 °C, according to DSC and X-ray scattering. The crystal phase change in C48Cs and C23Na is mainly due to increased chain rotation at elevated temperature, but the strong ionic interaction in the layered structure prevent the crystal from direct melting. Finally, the ionic conductivity is invested among C48Na, C48Zn and C48Cs via Electrochemical Impedance Spectroscopy. All three materials show an Arrhenius-like ion conduction behavior suggesting the decoupling of ion transport from the PE segmental movements. This work offers important insights for designing telechelic molecules with well-defined morphology and tunable ion transport properties.