Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session C34: The Physics of Confined Structured Fluids IFocus
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Sponsoring Units: DPOLY Chair: Jaroslaw Majewski, LANL Room: 337 |
Monday, March 14, 2016 2:30PM - 2:42PM |
C34.00001: Pattern Formation in Polymer Blend Thin Films Nigel Clarke, Sam Coveney We introduce a model for thin films of multicomponent fluids which includes lateral and vertical phase separation, preferential component attraction at both surfaces, and surface roughening. We apply our model to thin films of binary polymer blends, and use simulations of different surface-blend interaction regimes to investigate pattern formation. We demonstrate that surface roughening couples to phase separation. For films undergoing lateral phase separation via a transient wetting layer, this results in distinct stages of roughening as the film evolves between different phase equilibria. [Preview Abstract] |
Monday, March 14, 2016 2:42PM - 2:54PM |
C34.00002: Intricacies of Polymer Dewetting: Nanoscaled Architectures for the Tailored Control of Polystyrene Thin Film Stability Justin Cheung, Mani Sen, Zhizhao Chen, Naisheng Jiang, Maya Endoh, Tadanori Koga, Sushil Satija Recently, structural properties of polymer thin films have garnered attention for their relevance in the fields of organic photovoltaics and biosensors. The dewetting of polymer films poses an obstacle in the face of widespread implementation. For this study, we show that adsorbed polymer chains on a substrate surface play crucial roles in film stability. Polystyrene (PS) thin films (20 nm in thickness) with different molecular weights (Mw) on silicon (Si) substrates were used as a model. The PS films were annealed at high temperatures for several days, and Mw dependence on film stability was evidenced. At the same time, the annealed PS films were leached with a good solvent and the residue films (i.e., irreversibly adsorbed layers) were characterized by x-ray reflectivity (XR). We reveal strong correlation between film stability and two different interfacial structures of the adsorbed polymer chains: their opposing wettability against chemically identical free polymer chains results in a wetting-dewetting transition at the adsorbed polymer-free polymer interface. This is a unique aspect of polymer thin film stability and may be generalizable to other polymer systems regardless of the magnitude of solid-polymer attractive interactions. [Preview Abstract] |
Monday, March 14, 2016 2:54PM - 3:06PM |
C34.00003: Two-dimensional directed polymers anchored at curved edges Benjamin Loewe, Paul M. Goldbart It is well known that the equilibrium statistical mechanics of a liquid of mutually avoiding directed polymers in two dimensions can be analyzed by means of an analogy with the imaginary-time many-body quantum mechanics of a system of particles moving in one dimension \footnote{P. G. de Gennes, J. Chem. Phys. 48, 2257 (1968).}. In this approach, the polymers have commonly been considered to be anchored to a straight-edge boundary. It has recently been shown that topological obstacles that constrain the polymer configurations, such as point-like pins, can induce voids in which the polymer density profile is heavily suppressed \footnote{D. Z. Rocklin, S. Tan, and P. M. Goldbart, Phys. Rev. B 86, 165421 (2012)}. Here, we extend this approach to the study of the equilibrium statistical mechanics of liquids of mutually avoiding directed polymers that are anchored at boundaries that form closed curves, either circular or (low-eccentricity) elliptic. Specifically, we study how the curvature and eccentricity of these boundaries modifies the free energy of the system. For the case of elliptic boundaries, we show that the eccentricity alters the ground state of the quantum system, and thereby influences the structure of any constraint-induced voids in the density profile. [Preview Abstract] |
Monday, March 14, 2016 3:06PM - 3:42PM |
C34.00004: Role of Corners in Fracture of Polymeric Adhesives Invited Speaker: Mark Stevens Understanding the molecular mechanisms of deformation and failure in structural polymer adhesives is a challenging problem. About a decade ago, we performed MD simulations on coarse-grained models of epoxies or highly crosslinked polymer networks between solid adherends finding very large failure strains in contrast to experimental data. We now have performed similar tensile simulations except with open ends between two solid adherends. The open boundary and the presence of corners dramatically alters the fracture behavior. In contrast to systems with periodic boundaries, the failure strain decreases with increasing system size. This decrease greatly reduces the difference between simulation and experiment. In the open geometry, the sides of the polymer network contract inward forming wedge shaped corners where the crack initiation occurs. The deformation of the open ends is constrained by the minimal paths in the network connecting the two adherends, but the initiation of frature is not related to the minimal paths. The crack initiation in the corners is consistent with a diverging stress in the corners according to fracture mechanics. The local stress in the corners becomes large well before failure, but in the direction parallel to the interface due to the deformation of the corners into the wedge shape. [Preview Abstract] |
Monday, March 14, 2016 3:42PM - 3:54PM |
C34.00005: Confinement Effects on Polymer Morphology and Properties Spiros H. Anastasiadis, Kiriaki Chrissopoulou, Elena Perivolari, Hellen Papananou The behavior of polymers restricted in space or to surfaces/interfaces can be very different from that in the bulk. In this work, we investigate the morphology and thermal properties of poly(ethylene oxide), PEO, in nanohybrids containing two kinds of silica nanoparticles of largely different sizes in an attempt to bridge the case of severely confined polymers within the galleries of layered silicates with that of polymer-single nanoparticle nanocomposites. Hybrids with different ratio between the two silica nanoparticles were prepared in order to increase the level of confinement. The good dispersion of the nanoparticles was verified by transmission electron microscopy whereas the morphology and crystallization behavior were investigated with X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and polarised optical microscopy. The polymer behavior in the three component systems is found indeed intermediate between that of PEO/montmorillonite and that of PEO/silica with a single-size particles. Moreover, the behavior can be tuned by varying the ratio of the large to the small nanoparticles. [Preview Abstract] |
Monday, March 14, 2016 3:54PM - 4:06PM |
C34.00006: Conjugated polymelectrolyte assembly at water-oil interfaces. FENG LIU, Caili Huang, Russell Thomas Conjugated polyelectrolytes featured with conjugated backbone and functional side chains are interesting optoelectronic materials and widely used to modify electrodes in electronic devices such as light emitting diodes and solar cells to enhance device performance. Conjugated polyelectrolyte can be designed to have alternating hydrophilic and hydrophobic side chains, and thus inducing interesting surface and interface properties. In this work, we using polyfluorene based material, to study its behavior at water-toluene interface. The aliphatic side-chains will favorably interact with toluene, and amine side-chains will interact with water, making this material a good surfactant. At interface the polymer chain is stretched to a Janus type of geometry. Flattened molecules will assemble into ultra thin films via pi-pi intermolecular stacking, and thus creating barriers between liquids. When liquid volume is reduced, jamming at interface will show up. These properties are strongly affected by the environment of the liquids, such as temperature and PH values, and polyelectrolyte diffusion to interfaces. This study leads to new methods to structure liquids using single component, which can be extended to applications such as electro-spinning or fabricate flow devices. [Preview Abstract] |
Monday, March 14, 2016 4:06PM - 4:18PM |
C34.00007: Neutron reflectivity as a tool to study the interdigitation of grafted polymer chains and its dynamics. Liliane Leger, Frédéric Restagno, Fabrice Cousin, François Boue, Alexis Chenneviere Three series of experiments aimed at characterizing the interdigitation between a brush and a melt, and based on neutron reflectivity, are presented and discussed. The density profile of brush chains has been analysed for series of annealing times, on h-PS brushes in contact with d-PS melts, as a function of molecular weights and grafting densities. We show that the relaxation dynamics of the brush chains can be modelled taking into account the long relaxation time of end tethered chains along with the reptation of the melt chains which accelerates the arm retraction process. Using a non-grafted layer with a thickness smaller than the equilibrium size of the brush when immersed into a thick melt allows one to apply chosen degrees of confinement to the brush. We show that the interdigitation dynamics is affected by such confinements, in a way reminiscent of the change of the glass transition temperature in nanometric PS films. Finally, when the upper d-PS layer is sheared above $T_{\mathrm{g}}$, flow with large slip at the wall has been observed and interpreted in terms of stretching and expulsion of the grafted chains from the melt. We show how neutron reflectivity directly evidence this expulsion. [Preview Abstract] |
Monday, March 14, 2016 4:18PM - 4:30PM |
C34.00008: Controlling Valence of DNA-Coated Emulsion Droplets with Multiple Flavors of DNA Angus McMullen, Dylan Bargteil, David Pine, Jasna Brujic We explore the control of valence of DNA-coated emulsion droplets as a first step in developing DNA-directed self-assembly of emulsions. Emulsion droplets differ from solid colloids in that they are deformable and the DNA strands attached to them are free to move along the emulsion surface. The balance of binding energy and droplet deformation provides control over a droplet's valence via its ligand density. After binding, some DNA often remains unbound due to the entropic cost of DNA recruitment. In practice, therefore, the assembly kinetics yield a distribution in valence. Our goal is to control valence by altering the binding kinetics with multiple flavors of DNA. We coat one set of droplets with two DNA types, $A$ and $B$, and two other sets with one complementary strand, $A^\prime$ or $B^\prime$. When an $AB$ droplet binds to an $A^\prime$ droplet, the adhesion patch depletes $A$ strands, leaving the rest of the droplet coated with more $B$ than $A$ strands. This increases the chance that the next droplet to bind will be a $B^\prime$ rather than an $A^\prime$. Controlling valence will allow us to build a wide array of soft structures, such as emulsion polymers or networks with a determined coordination number. This work was supported by the NSF MRSEC Program (DMR-0820341). [Preview Abstract] |
Monday, March 14, 2016 4:30PM - 4:42PM |
C34.00009: Unraveling the dynamics of aminopolymer/silica composites Jan-Michael Carrillo, Miles Sakwa-Novak, Adam Holewinski, Matthew Potter, Gernot Rother, Christopher Jones, Bobby Sumpter The structure and dynamics of a model branched polymer, representing poly(ethylenimine), was investigated through coarse-grained molecular dynamics simulations and neutron scattering experiments. The monomer concentration and solvent quality were varied in the simulations and detailed comparisons between the calculated structural and dynamical properties of the unconfined polymer and those confined within an adsorbing and non-adsorbing cylindrical pore, representing the silica based structural support of the composite, were made. The simulations show a direct relationship in the structure of the polymer and the non-monotonic dynamics of the polymers as a function of monomer concentration within an adsorbing cylindrical pore. However, the non-monotonic behavior disappears for the case of the branched polymer within a non-adsorbing cylindrical pore. Overall the simulation results are in good agreement with quasi-elastic neutron scattering (QENS) studies of branched poly(ethylenimine) in mesoporous silica (SBA-15) of comparable size, suggesting an approach that can be a useful guide for understanding how to tune porous polymer composites for enhancing desired dynamical and structural behavior targeting carbon dioxide adsorption. [Preview Abstract] |
Monday, March 14, 2016 4:42PM - 4:54PM |
C34.00010: A new, non-destructive, real-time measurement technique of the surface area of aerogel during synthesis Yang Shen, Jeongseop A. Lee, W. P. Halperin We have developed a new method of measuring surface area of silica aerogel during the synthesis stage using a standard pulsed NMR setup. The applicability of this method can be extended to a much broader type of chemical reactions yielding a rigid porous condensate whose surface relaxation rate differs substantially from its surrounding liquids. The number of various chemical species involved in the reaction poses little to no limitation to its applicability owing to the physics in the fast exchange limit. This is the main distinguishing feature from a conventional NMR or infrared spectroscopy method in which individual chemical bondings from various reaction intermediaries are tracked in time which is often difficult if not impossible due to complex reactions. The result from this technique yields a surface area that is analogous to the result from a well-established BET (Brunauer-Emmett-Teller) technique, but without the need for extraction or supercritical extraction of the porous medium. This work was supported by the DOE BES under grants No. DE-FG02-05ER46248. \\ [1] J. Lee, {\it et al.}, Phys Rev B., {\bf 90}, 174501 (2014).\\ [2] E. Collin, {\it et al.}, Phys Rev B., {\bf 80}, 094422 (2009). [Preview Abstract] |
Monday, March 14, 2016 4:54PM - 5:06PM |
C34.00011: PEE-PEO block copolymer exchange rate between micelles is detergent and temperature activated Allen Schantz, Patrick Saboe, Hee-Young Lee, Ian Sines, Paul Butler, Kyle Bishop, Janna Maranas, Manish Kumar We examine the kinetics of polymer chain exchange between polymer/detergent micelles, a system relevant to the synthesis of protein-containing biomimetic membranes. Although chain exchange between polymer aggregates in water is too slow to observe, adding detergent allows us to determine chain exchange rates using time-resolved small-angle neutron scattering (TR-SANS). We examine a membrane-protein-relevant, vesicle-forming ultra-short polymer, Poly(ethyl ethylene)20-Poly(ethylene oxide)18 (PEE20-PEO18). PEE20-PEO18 is solubilized in mixed micelles with the membrane-protein-compatible non-ionic detergent octyl-$\beta $ -D-glucoside (OG). We show that OG activates block copolymer exchange, and obtain rate constants at two detergent concentrations above the CMC (critical micellar concentration) of OG. We find that chain exchange increases two orders of magnitude when temperature increases from 308 to 338 K, and that even a 1 mg/mL increase in OG concentration leads to a noticeable increase in exchange rate. We also calculate the activation energy for chain exchange and find that it is much higher than for lipid exchange. These findings explain the need for high detergent concentration and/or temperature to synthesize densely packed polymer/protein membranes. [Preview Abstract] |
Monday, March 14, 2016 5:06PM - 5:18PM |
C34.00012: Electrically Responsive Soft Photonic BCP Films Atsushi Noro, Maho Ohno, Yushu Matsushita We report electro-responsive soft photonic films composed of lamellar-forming block copolymer/nonvolatile protic solvent/metal salt. Thin films of polystyrene-b-poly(2-vinylpyridine) (SP, $M$n$=$153k, $\varphi $S$=$0.57, PDI$=$1.18) were prepared by spin-coating of the solutions on ITO glass substrates, then mixture of glycol-based solvent and lithium bis(trifluoro methanesulfonyl)imidide (LiTFSI) was added to the thin films, producing soft photonic films. If needed, the spin-coated SP thin films were ionized by iodomethane before addition of the mixture of glycol-based solvent and LiTFSI. TEM observations and U-SAXS measurements revealed that these photonic films kept lamellar structures after addition of the solvent, that is, the P phase was swollen selectively with the solvent. Systematic electro-responsiveness of photonic properties of the films was also confirmed by applying voltages to the films. [Preview Abstract] |
Monday, March 14, 2016 5:18PM - 5:30PM |
C34.00013: Face-on and Edge-on Orientation Transition and Self-epitaxial Crystallization of All-conjugated Diblock Copolymer Hua Yang, Yanchun Han The orientation transition and self-epitaxial crystallization of all-conjugated diblock copolymers poly(p-phenylene)-block-(3-hexylthiophene) (PPP-$b$-P3HT, BmTn) were systematically investigated by in-situ temperature-resolved two-dimensional grazing incidence X-ray diffraction (2D GIXD) in step-by-step heating and cooling process. B39T18 was selected, the results of 2D GIXD showed that the PPP block crystal adopted a face-on orientation while the crystallization of P3HT block was hindered in as-casted films. Three different molecular orientations transition were obtained in self-epitaxial crystallization circles. First, P3HT crystallize with edge-on during the heating process and induced the PPP blocks crystallized with edge-on during the cooling process. Then, the as-casted film was heated in the melting temperature region of PPP blocks and isothermally crystallized. The partial melting of PPP blocks promoted the P3HT blocks crystallize in a face-on due to the steric limitation effect, PPP blocks crystallized with a face-on via the self-epitaxy during cooling. Furthermore, the face-on transformed to thermodynamically stable edge-on in the melt annealing process. [Preview Abstract] |
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