Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y9: Polymers for Biological and Energy Applications |
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Sponsoring Units: DPOLY Chair: Mithun Chowdhury,, Princeton University Room: 268 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y9.00001: Physics of the gut: How polymers dynamically structure the gut environment Asher Preska Steinberg, Sujit Datta, Said Bogatyrev, Rustem Ismagilov While the gut microbiome and biological regulation of the gut environment is being exhaustively studied by the microbiology community, little is known about the rich physics that governs the macro- and microstructure of the gut environment. The mammalian gut abounds in soft materials; ranging from soluble polymers (e.g. dietary fibers, therapeutic polymers and mucins) to colloidal matter (e.g. bacteria, viruses and nanoparticles carrying drugs). We have found experimentally that soluble polymers can dynamically re-structure the colonic mucus hydrogel by modulating its degree of swelling. We implemented a mean-field Flory-Huggins model to reveal that these polymer-mucus interactions can be captured using a simple, first principles thermodynamics model. In this model, the amount of deswelling increases with polymer concentration and size. We then used these physical principles to make predictions about how different polymer solutions affect the structure of mucus. Lastly, we explore applying this framework and similar physical principles to a variety of biological problems in the gut. [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y9.00002: A Physically Motivated and Improved Fitting Function to Analyze the Performance of Passive Drug Delivery Systems: Going Beyond the Weibull Empirical Fits Gary W. Slater, Mykyta V. Chubynsky, Maxime Ignacio We examine the diffusion-controlled release of molecules from passive drug delivery systems using both analytical solutions of the diffusion equation and numerically exact Monte Carlo data. Not surprisingly, the release process follows a sqrt(t) law for short times, as expected for diffusion processes, while the long-time asymptotic behavior is exponential. The cross-over time between these two limits is determined by the initial loading of the system if the latter is inhomogeneous. Although the widely used Weibull function provides a reasonable fit (at least visually), it has two major shortcomings: (i) its limiting behaviours are wrong and (ii) there is no connection between the system's properties and the value of the fitting parameters. We introduce a new, physically motivated interpolating fitting function that correctly includes both time regimes and clearly outperform the Weibull function. An analysis of the new function allows us to predict the values of the Weibull parameters. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y9.00003: Reaction-diffusion degradation model for delayed erosion of cross-linked polyanhydride biomaterials. Sergii Domanskyi, Katie Poetz, Devon Shipp, Vladimir Privman We develop a theoretical model to explain the long induction interval of water intake that precedes the onset of erosion due to degradation caused by hydrolysis in the recently synthesized and studied crosslinked polyanhydrides. Various kinetic mechanisms are incorporated in the model in an attempt to explain the experimental data for the mass loss profile. Our key finding is that the observed long induction interval is attributable to the nonlinear dependence of the degradation rate constants on the local water concentration, which essentially amounts to the breakdown of the standard rate-equation approach, potential causes for which are then discussed. Our theoretical results offer physical insights into which microscopic studies will be required to supplement the presently available macroscopic mass-loss data in order to fully understand the origin of the observed behavior. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y9.00004: Measuring the change in hydration of a polypeptide-based block polymer vesicle as a function of pH Ian Smith, Alban Charlier, Alexander Shishlov, Daniel Savin Amphiphilic AB2 star polymers undergo directed self-assembly into vesicles in aqueous solution. The overall structure of the assembly is responsive to a change in solution pH by incorporating an ionizable polypeptide as the A-block and two lipid-like tails for the B-blocks. Herein, we present some recent results in the solution characterization of polyglutamate-octadecanethiol2 (PE-DDT2) star polymers using static and dynamic light scattering, as well as transmission electron microscopy. An increase in pH will induce a transition in secondary structure of the PE block from an $\alpha $-helix to an extended coil, thereby perturbing the morphological structure and resulting in an expansion of the vesicle. The magnitude of this response is much larger than what is expected based on the conformational transition of the peptide. The mechanism of this process can be probed by measuring the change in hydration at the surface of the hydrophobic bilayer. Towards this end, we utilize 2,4,6-trichloro-1,3,5-triazine (TCT) as a modular linker to install spin labels into the assembly as a mechanism to directly interrogate local hydrophobicity using electron paramagnetic resonance (EPR). [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y9.00005: Micropipette Deflection Measurements of Agar-Glass Adhesion Richard Parg, Erin Shelton, John Dutcher Micropipette deflection experiments were used to study the adhesive strength at an agar-glass interface. Agar is a hydrogel commonly used in biological research; however, many of the mechanical properties of this hydrogel are not well characterized. By measuring the peak force required to slide an agar puck supported by a Teflon ring across a clean glass slide, we are able to compare the adhesive strength of 1 {\%} w/w and 1.5 {\%} w/w agar. On average, the force required to break the agar-glass interface was approximately a factor of 2 larger for 1.5 {\%} w/w agar than for 1 {\%} w/w agar. We discuss this result within the context of a simple model of agar adhesion. Additional experiments were performed to measure the kinetic friction between agar and glass to obtain insight into its dependence on agar concentration. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y9.00006: Spontaneous deswelling of pNIPAM microgels at high concentrations Urs Gasser, Andrea Scotti, Emily S. Herman, Miguel Pelaez-Fernandez, Jun Han, Andreas Menzel, L. Andrew Lyon, Alberto Fernandez-Nieves Polydisperse suspensions of pNIPAM microgel particles show a unique, spontaneous particle deswelling behavior. Beyond a critical concentration, the largest microgels deswell and thereby reduce the polydispersity of the suspension [1]. We have recently unraveled the mechanism of this spontaneous, selective deswelling. pNIPAM microgels carry charged sulfate groups originating from the ammonium persulfate starter used in particle synthesis. Most of the ammonium counterions are trapped close to the microgel surface, but a fraction of them escapes the electrostatic attraction and contributes to the osmotic pressure of the suspension. The counterion clouds of neighboring particles progressively overlap with increasing volume fraction, leading to an increase of free counterions and the osmotic pressure outside but not inside the microgel particles. We find particles to deswell when the resulting osmotic pressure difference between the inside and the outside becomes larger their bulk modulus [2]. For pNIPAM microgels synthesized with the same protocol, the largest particles are the softest and deswell first. (1) A. St. Iyer and L.A. Lyon, Angew. Chem. Int. Ed. 48, 4562-4566 (2009). (2) A. Scotti et al., PNAS 113, 5576 (2016). [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y9.00007: Generation of Electricity at Graphene Interface Governed by Underlying Surface Dipole Induced Ion Adsorption Shanshan Yang, Yudan Su, Qiong Wu, Yuanbo Zhang, Chuanshan Tian Aqueous droplet moving along graphene surface can produce electricity This interesting phenomenon provided environment-friendly means to harvest energy from graphene interface in contact with sea wave or rain droplets. However, microscopically, the nature of charge adsorption at the graphene interface is still unclear. Here, utilizing sum-frequency spectroscopy in combined with measurement of electrical power generation, the origin of charge adsorption on graphene was investigated. It was found that the direct ion-graphene interaction is negligibly small, contrary to the early speculation, but the ordered surface dipole from the supporting substrate, such as PET, is responsible for ion adsorption at the interface. Graphene serves as a conductive layer with mild screening of Coulomb interaction when aqueous droplet slips over the surface. These results pave the way for optimization of energy harvesting efficiency of graphene-based device. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y9.00008: Investigating polarized fluorescence emission of Napthalene Diimide polymer films via Stokes Spectroscopy Steven Ulrich, Thabita Sutch, Matthias Schweizer, Greg Szulczewski, Newton Barbosa Neto, Paulo Araujo Structural studies of materials, especially polymers, has been an area of growing interest in the past decades. This is due to the wide variety of physical, optical and chemical properties which can be tuned to obtain desired outcomes. Such polymers include P(NDI2OD-T2) an organic n-type, donor-acceptor polymer. Techniques to measure the structure, chemical and optical properties of these materials include XRD, time resolved spectroscopy and other timely and expensive methods. This work seeks to implement Stokes parameter analysis to create a new spectroscopic method, which can be implemented at a fraction of the cost and with relative ease. This technique, when used to probe P(NDI2OD-T2), has been able to discern information about polymer aggregate formation, energy transfer and out of plane stacking on the basis of solvent choice and sample thickness. Additionally, this technique gives information regarding the polarized emission from excited sources, which could provide insight for increased device performance. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y9.00009: Fracture: Genesis of Dielectric Breakdown Mayank Misra, Sanat K Kumar Despite abundant experimental study on dielectric properties of polymers, the origins of the high dielectric breakdown in polymers remains an open question. Although dielectric breakdown in a polymer is a non-trivial problem, there has been a significant increase in understanding the phenomena in polymeric materials. The classical models developed for understanding the failure have been deterministic in nature: that is the breakdown occurs as a direct effect of an earlier event or condition produced by crossing over a threshold electric field. Conventionally the prediction of dielectric strength has focused on ground state energy calculation, thus restricting the analysis of the breakdown process to purely electronic. While this provides reasonable predictions for very low-temperature systems, we believe that the mechanism for the breakdown in polymers is significantly different. Using molecular dynamics, we delineate dielectric breakdown in polymeric capacitors. Our simulation results suggest that fracture mechanics drives electromechanical breakdown, which dominates over electronic breakdown at relevant operating temperatures. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y9.00010: Breath figures of P3HT and of its photovoltaic blend with PC71BM Aurora Nogales, Jing Cui, Esther Rebollar, Adolfo del Campo, Mircea Cotlet, Juan Rodriguez Surface structured films of poly(3-hexyl thiophene) and of its photovoltaic blend with PC71BM are obtained by the breath fi gure technique, a micropatterning process that is based on the competition between solvent evaporation and water condensation. By this method, long range honey-comb like ordered structures of these functional organic blends are obtained. The characterization of these systems by several techniques including micron-resolved Raman Spectroscopy, microphotoluminiscence and Kelvin probe microscopy allow to probe that, due to the different hydrophobicity of both components of the blend, a hierarchical phase separation is obtained around the pores formed. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y9.00011: Theoretical insights into multiscale electronic processes in organic photovoltaics Sergei Tretiak Present day electronic devices are enabled by design and implementation of precise interfaces that control the flow of charge carriers. This requires robust and predictive multiscale approaches for theoretical description of underlining complex phenomena. Combined with thorough experimental studies such approaches provide a reliable estimate of physical properties of nanostructured materials and enable a rational design of devices. From this perspective I will discuss first principle modeling of small-molecule bulk-heterojunction organic solar cells and push-pull chromophores for tunable-color organic light emitters. The emphasis is on electronic processes involving intra- and intermolecular energy or charge transfer driven by strong electron-phonon coupling inherent to pi-conjugated systems. Finally I will describe how precise manipulation and control of organic-organic interfaces in a photovoltaic device can increase its power conversion efficiency by 2-5 times in a model bilayer system. Applications of these design principles to practical architectures like bulk heterojunction devices lead to an enhancement in power conversion efficiency from 4.0{\%} to 7.0{\%}. These interface manipulation strategies are universally applicable to any donor-acceptor interface, making them both fundamentally interesting and technologically important for achieving high efficiency organic electronic devices. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y9.00012: Photovoltaic Cells involving Iodine-doped Nonconjugated Conductive Polymers: Studies of Cell Stability over time Justin Van Cleave, Mrinal Thakur The stability of photovoltaic cells involving iodine-doped nonconjugated conductive polymers in Gratzel-type cells has been evaluated. These devices require a liquid electrolyte for cell functions. Typically a cell constructed using TiO$_{\mathrm{2}}$/iodine-doped polyisoprene/carbon on ITO structure has a photovoltage of about 0.73 volt and a current density of about 0.27 mA/cm$^{\mathrm{2}}$ for an incident light intensity of about 4 mW/cm$^{\mathrm{2}}$. As the liquid electrolyte introduced in the cell is lost its performance degrades until the device no longer functions. A sealing method has been developed in order to preserve the electrolyte within the cell and its effect on the lifetime of the cell has been determined. Optical microscopy along with electrical measurements were performed to evaluate the cell functions over time. Sealed cells were found to function for around 30 days, while the unsealed ones degraded within 3 days. Improvement of the sealing methods is presently under investigation. [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y9.00013: Charge-regularized swelling kinetics of polyelectrolyte gels Swati Sen, Arindam Kundagrami The swelling kinetics of polyelectrolyte gels with fixed[1] and variable degrees of ionization in salt-free solvent is studied by solving the constitutive equation of motion of the spatially and temporally varying displacement variable. Two methods for the swelling kinetics - the \textit{Bulk Modulus Method} (BMM), which uses a linear stress-strain relationship (and, hence a bulk modulus), and the \textit{Stress Relaxation Method} (SRM)[1], which uses a phenomenological expression of osmotic stress, are explored to provide the spatio-temporal profiles for polymer density, osmotic stress, and degree of ionization, along with the time evolution of the gel size. Further, we obtain an analytical expression for the elastic modulus for linearized stress in the limit of small deformations. We match our theoretical profiles with the experiments of swelling of PNIPAM (uncharged) and Imidazolium-based (charged) minigels available in the literature.\\(1) S. Sen and A. Kundagrami, J. Chem. Phys. \textbf{143}, 224904 (2015). [Preview Abstract] |
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