Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P42: Small Molecule Transport in Polymers and Polymer Nanocomposites I - Industry DayFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Praveen Agarwal, Dow Chemical Company Room: 345 |
Wednesday, March 16, 2016 2:30PM - 2:42PM |
P42.00001: Chemical and Temperature Effects on Diffusion in a Model Polymer/Nanoparticle Composite Dustin Janes, Christopher Durning Polymers and inks used in medical devices may be strengthened with nanoparticle fillers, so an understanding of how they may affect the release of residuals and additives via diffusion will help modernize biocompatibility testing. Transport of small molecules in polymers with increasing volume fraction of impermeable nanoparticles is often poorly predicted by the simple Maxwell model for heterogeneous media. In this presentation we will examine two diffusant classes, only one of which possesses hydrogen bonding interactions with the nanoparticle surface. Since similar reductions in mutual diffusion coefficients were observed in both cases we attribute the enhancement of the ''blocking effect'' in nanocomposites to a reduction in polymer mobility in the interfacial volume near the nanoparticle. The temperature and penetrant concentration dependence of the diffusion coefficients were examined in the context of a Vrentas-Duda free volume model that includes a thermally activated prefactor. While data obtained for rubbery poly(methyl acrylate) clearly obeys the expected Arrhenius scaling with E$_{\mathrm{A}}=$ 11 kJ/mol, results for films containing d $=$ 14 nm spherical silica nanoparticles do not, providing more evidence that polymer free volume is perturbed in unexpected ways even for conceptually simple systems. [Preview Abstract] |
Wednesday, March 16, 2016 2:42PM - 2:54PM |
P42.00002: Controlling Free Volume for Permeability enhancement in Polymer-Grafted Nanocomposites Connor Bilchak, Eileen Buenning, Sanat Kumar, Christopher Durning, Brian Benicewicz Significant advances in polymer membrane technology have been made by exploring glassy materials with intrinsically high `free volume', allowing for diffusion selectivity. However, the permeability of these materials is restricted by the Robeson Upper Bound and exhibits long-term aging. While nanofiller have been used to avoid the deleterious effect of aging, they further limit transport properties and can result in non-equilibrium structures that phase-separate. We here show that 14nm silica nanoparticles grafted with rubbery Poly(Methyl Acrylate) (PMA) chains form hexatic lattices, solving a common difficulty in this class of membrane constructs of controlled dispersion morphology. In addition, our results show that these materials have permeabilities elevated relative to the neat polymer matrix, offering surprising beneficial gas transport properties. We also show that the `free volume' available for diffusion can be adequately controlled by tuning polymer chain length and graft density. We propose the morphology of these grafted nanoparticle systems may be manipulated to optimize these composites for a wide variety of vital gas separations. [Preview Abstract] |
Wednesday, March 16, 2016 2:54PM - 3:06PM |
P42.00003: Gas Transport in Polymer-Grafted Nanoparticles Kai Zhang, Sanat Kumar The efficient separation of gases is crucial for clean energy technologies. With their intrinsic multiscale features and excellent self-assembly properties, polymer-grafted nanoparticles (PGNP) material makes a good candidate for effective gas separation, but the basic understanding of gas transport in PGNPs is still missing. While the nanoparticles cores are spherical, the corona of the PGNPs can be deformed into anisotropic space-filling polygons at high density that are commensurate with the crystal structures (Wigner-Seitz cells). Such deformation indicates that the polymer chains are extended or compressed along different directions and create cavities within the crystals that can help to improve the gas selectivity. We use coarse-grained computer simulations to study the solubility and diffusion of gas molecules inside the crystalline packing of the NP cores. By tuning the degree of polymerization, the surface density of grafting chains and the size of gas molecules, we systematically investigate the dependence of gas transport on these parameters. We find that the void formed by three contacting monomers imposes a critical lengthscale beyond which the transport becomes highly size selective. [Preview Abstract] |
Wednesday, March 16, 2016 3:06PM - 3:42PM |
P42.00004: Understanding transport in model water desalination membranes Invited Speaker: Edwin Chan Polyamide based thin film composites represent the the state-of-the-art nanofiltration and reverse osmosis membranes used in water desalination. The performance of these membranes is enabled by the ultrathin (\textasciitilde 100 nm) crosslinked polyamide film in facilitating the selective transport of water over salt ions. While these materials have been refined over the last several decades, understanding the relationships between polyamide structure and membrane performance remains a challenge because of the complex and heterogeneous nature of the polyamide film. In this contribution, we present our approach to addressing this challenge by studying the transport properties of model polyamide membranes synthesized via molecular layer-by-layer (mLbL) assembly. First, we demonstrate that mLbL can successfully construct polyamide membranes with well-defined nanoscale thickness and roughness using a variety of monomer formulations. Next, we present measurement tools for characterizing the network structure and transport of these model polyamide membranes. Specifically, we used X-ray and neutron scattering techniques to characterize their structure as well as a recently-developed indentation based poromechanics approach to extrapolate their water diffusion coefficient. Finally, we illustrate how these measurements can provide insight into the original problem by linking the key polyamide network properties, i.e. water-polyamide interaction parameter and characteristic network mesh size, to the membrane performance. [Preview Abstract] |
Wednesday, March 16, 2016 3:42PM - 3:54PM |
P42.00005: Salt transport properties of model reverse osmosis membranes using electrochemical impedance spectroscopy Kathleen Feldman, Edwin Chan, Gery Stafford, Christopher Stafford With the increasing shortage of clean water, efficient purification technologies including membrane separations are becoming critical. The main requirement of reverse osmosis in particular is to maximize water permeability while minimizing salt permeability. Such performance optimization has typically taken place through trial and error approaches. In this work, key salt transport metrics are instead measured in model reverse osmosis membranes using electrochemical impedance spectroscopy (EIS). As shown previously, EIS can provide both the membrane resistance R$_{m}$ and membrane capacitance C$_{m}$, with R$_{m}$ directly related to salt permeability. The membranes are fabricated in a molecular layer by layer approach, which allows for control over such parameters as thickness, surface and bulk chemistry, and network geometry/connectivity. R$_{m}$, and therefore salt permeability, follows the expected trends with thickness and membrane area but shows unusual behavior when the network geometry is systematically varied. By connecting intrinsic material properties such as the salt permeability with macroscopic performance measures we can begin to establish design rules for improving membrane efficiency and facilitate the creation of next-generation separation membranes. [Preview Abstract] |
Wednesday, March 16, 2016 3:54PM - 4:06PM |
P42.00006: Using Indentation to Characterize Water Transport and Structure in Nafion Thin Films Eric Davis, Nichole Nadermann, Kirt Page, Christopher Stafford, Edwin Chan Perfluorinated ionomers, specifically Nafion, are the state-of-the-art polymer used in fuel cells. For this application, Nafion is utilized in both a bulk (hundreds of microns) and confined (tens of nanometers) state. For Nafion thin films in a confined state, i.e., Nafion as thin film coatings on catalyst particles, in-plane transport may play a critical role in the movement of water and protons through this catalysis layer. In this study, water transport was measured for a series of Nafion thin film thicknesses using poroelastic relaxation indentation (PRI). Unlike traditional through-thickness diffusion measurement techniques for thin polymer films (e.g., quartz crystal microbalance), PRI can be used to probe the in-plane water transport behavior. Relative to bulk Nafion, reduced in-plane water diffusion was observed in thin film Nafion, and below approximately 1 micron, water diffusivity and Nafion film thickness exhibited a logarithmic relationship. Equilibrium swelling measurements of water saturated Nafion thin films were used in conjunction with pore network theory to develop a picture of how the molecular-scale structure of Nafion changes with confinement to nanoscale film thicknesses. [Preview Abstract] |
Wednesday, March 16, 2016 4:06PM - 4:18PM |
P42.00007: Water and polymer dynamics in highly crosslinked polyamide membranes Bradley Frieberg, Edwin Chan, Madhu Tyagi, Christopher Stafford, Christopher Soles Highly crosslinked polyamides for reverse osmosis are the state-of-the-art active material in membranes for desalination. The thin film composite membrane structure that is used commercially has been empirically designed to selectively allow the passage of water molecules and minimize the passage of solutes such as salt. However, due to the large roughness and variability of the polyamide layer, there is a limited understanding of the structure-property relationship for these materials as well as the transport mechanism. To better understand the water transport mechanism we measure the water and polymer dynamics of polyamide membranes using quasi-elastic neutron scattering (QENS). By hydrating the membrane with deuterated water, we are able to isolate the dynamics of the hydrogenated membrane on the pico- and nanosecond time scales. By subsequently hydrating the membranes with hydrogenated water, the QENS measurements on the same times scales reveal information about both the translational and rotational dynamics of water confined within the polyamide membrane. Further understanding of the water diffusion mechanism will establish design rules in which the performance of future membrane materials can be improved. [Preview Abstract] |
Wednesday, March 16, 2016 4:18PM - 4:30PM |
P42.00008: CO$_{2}$ adsorption in a hierarchically structured carbon by SANS Lilin He, Jitendra Bahadur, Yuri Melnichenko, Cristian Contescu, Nidia Gallego This contribution investigated the high pressure adsorption behavior of CO$_{2}$ at T~$=$~296~K in hierarchically structured carbon using small-angle neutron scattering (SANS) technique. We observed a strong densification of CO$_{2}$ in micropores accompanied by non-monotonic adsorption-induced pore deformation. Liquid-like density of CO$_{2}$ confined in the micropores was reached with increasing pressure to 20~bar, which corresponds to the relative pressure of P/P$_{sat}\sim $0.3. At P~\textgreater ~20~bar, density of confined CO$_{2}$ approached a plateau. The size of micropores first increases with pressure, reached a maximum at 20~bar, and then decreased with further increasing pressure. A complementary SANS experiment carried out on the same microporous carbon saturated with argon that is neutron-transparent and non-adsorbing inert shows no deformation of micropores at pressures up to $\sim $200~bars. This result proved that the observed deformation of micropores in CO$_{2}$ was an adsorption-induced phenomenon, caused by the solvation pressure - induced strain and strong densification of confined CO$_{2\, }$in the micropores$_{.}$ [Preview Abstract] |
Wednesday, March 16, 2016 4:30PM - 4:42PM |
P42.00009: Characterization of nanoscale spatial distribution of small molecules in amorphous polymer matrices Ralm Ricarte, Marc Hillmyer, Timothy Lodge Hydroxypropyl methylcellulose acetate succinate (HPMCAS) can significantly enhance the efficacy of active pharmaceutical ingredients (APIs). Yet, the interactions between species in HPMCAS-API blends are not understood. Elucidating these interactions is difficult because the spatial distributions of HPMCAS and API in the blends are ambiguous; the polymer and drug may be molecularly mixed or the species may form phase separated domains. As these phase separated domains may be less than 100 nm in size, traditional characterization techniques may not accurately evaluate the spatial distribution. To address this challenge, we explore the use of electron energy-loss spectroscopy (EELS) for detecting the model API phenytoin in an HPMCAS-phenytoin blend. Using EELS, we directly measured with high accuracy and precision the phenytoin concentrations in several blends. We present evidence that suggests phase separation occurs in blends that have a phenytoin loading of approximately 50 wt percent. Finally, we demonstrate that this technique achieves a sub-100 nm spatial resolution and can detect several other APIs. [Preview Abstract] |
Wednesday, March 16, 2016 4:42PM - 4:54PM |
P42.00010: Quantitative monitoring of membrane permeation via in-situ ATR FT-IR spectroscopy Bryan Beckingham, Daniel Miller Ion conducting membranes are of interest for various energy applications including fuel cells and artificial photosynthesis systems. Within the context of artificial photosynthesis, membranes are desired that facilitate the ion transport necessary to feed the electrochemical reactions while meeting various additional selectivity and permeability demands depending on the CO2 reduction products. Herein, we demonstrate the use of in-situ ATR FT-IR spectroscopy to quantitatively resolve the concentration of single and multicomponent mixtures of various CO2 reduction products including methanol, formate and acetate. We then apply this methodology to the in-situ monitoring of the permeation of single and multicomponent mixtures across commercially available membranes. Membrane permeabilities and selectivities calculated from the single component time-resolved concentration curves are compared to the multicomponent permeation experiments. [Preview Abstract] |
Wednesday, March 16, 2016 4:54PM - 5:06PM |
P42.00011: Transport of Water in Semicrystalline Block Copolymer Membranes Daniel Hallinan, Onyekachi Oparaji Poly(styrene)-block-poly(ethylene oxide) (PS-$b$-PEO) is a semicrystalline block copolymer (BCP) with interesting properties. It is mechanically tough, amphiphilic, and has a polar phase. The mechanical toughness is due to the crystallinity of PEO and the high glass transition temperature of PS, as well as the morphological structure of the BCP. The polymer has high CO$_{\mathrm{2}}$, water, and salt solubility that derive from the polar PEO component. Potential applications include CO$_{\mathrm{2\thinspace }}$separation, water purification, and lithium air batteries. In all of the aforementioned applications, water transport is an important parameter. The presence of water can also affect thermal and mechanical properties. Water transport and thermal and mechanical properties of a lamellar PS-$b$-PEO copolymer have been measured as a function of water activity. Water transport can be affected by the heterogeneous nature of a semicrystalline BCP. Therefore, Fourier transform infrared - attenuated total reflectance (FTIR-ATR) spectroscopy has been employed, because water transport and polymer swelling can be measured simultaneously. The effect of BCP structure on transport has been investigated by comparing water transport in PS-$b$-PEO to a PEO homopolymer. The crystalline content of the PEO and the presence of glassy PS lamellae will be used to explain the transport results. [Preview Abstract] |
Wednesday, March 16, 2016 5:06PM - 5:18PM |
P42.00012: Elasticity dominated surface segregation of small molecules in polymer mixtures Salvatore Croce, Jaroslaw Krawczyk, Tom McLeish, Buddhapriya Chakrabarti When a binary polymer mixture with mobile components is left to equilibrate, the low molecular weight component migrates to the free surface. A balance between loss of translational entropy and gain in surface energy dictates the equilibrium partitioning ratio and the migrant fraction. Despite its ubiquity and several theoretical and experimental investigations, the phenomenon is not fully understood. Further, methods by which migration can be controlled are in its nascent stage of development. We propose a new phenomenological free energy functional that incorporates the elasticity of bulk polymer mixtures (reticulated networks and gels) and show (using mean field and self-consistent field theories) that the migrant fraction decreases with increasing the bulk modulus of the system. Further, a wetting transition observed otherwise for large values of miscibility parameter and polymerization index can be avoided by increasing the elastic modulus of the system. Estimated values of moduli (for the effect to be observable) are akin to those of rubbery polymers. Our work paves the way for controlling surface migration in complex industrial formulations with polymeric ingredients where this effect leads to decreased product stability and performance. [Preview Abstract] |
Wednesday, March 16, 2016 5:18PM - 5:30PM |
P42.00013: Anomalous Diffusion of Water in Lamellar Membranes Formed by Pluronic Polymers Zhe Zhang, Michael Ohl, Youngkyu Han, Gregory Smith, Changwoo Do Water diffusion is playing an important role in polymer systems. We calculated the water diffusion coefficient at different layers along z-direction which is perpendicular to the lamellar membrane formed by Pluronic block copolymers (L62: (EO$_{\mathrm{6}}$-PO$_{\mathrm{34}}$-EO$_{\mathrm{6}}))$ with the molecular dynamics simulation trajectories. Water molecules at bulk layers are following the normal diffusion, while that at hydration layers formed by polyethylene oxide (PEO) and hydrophobic layers formed by polypropylene oxide (PPO) are following anomalous diffusion. We find that although the subdiffusive regimes at PEO layers and PPO layers are the same, which is the fractional Brownian motion, however, the dynamics are different, i.e. diffusion at the PEO layers is much faster than that at the PPO layers, and meanwhile it exhibits a normal diffusive approximation within a short time period which is governed by the localized free self-diffusion, but becomes subdiffusive after t \textgreater 8 ps, which is governed by the viscoelastic medium. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700