Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B45: Polymer Melts & Solutions I |
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Sponsoring Units: DPOLY Chair: Debra Audus, National Institute of Standards and Technology Room: 216AB |
Monday, March 2, 2015 11:15AM - 11:27AM |
B45.00001: Domain Growth Kinetics in Stratifying Foam Films Yiran Zhang, Vivek Sharma Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Typical foam films consist of two surfactant-laden surfaces that are $\mu$ 5 nm -- 10 micron apart. Sandwiched between these interfacial layers is a fluid that drains primarily under the influence of viscous and interfacial forces, including disjoining pressure. Interestingly, for certain low molecular weight surfactants, a layered ordering of micelles inside the foam films (thickness \textless 100 nm) leads to a stepwise thinning phenomena called stratification. We experimentally elucidate the influence of these different driving forces, and confinement on drainage kinetics of horizontal stratifying foam films. Thinner, darker domains spontaneously grow within foam films. Quantitative characterization of domain growth visualized in a using Scheludko-type thin film cell and a theoretical model based on lubrication analysis, provide critical insights into hydrodynamics of thin foam films, and the strength and nature of surface forces, including supramolecular oscillatory structural forces. [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B45.00002: Atomistic Simulations of Poly(N-isopropylacrylamide) Surfactants in Water Lauren J. Abbott, Mark J. Stevens The amphiphilic polymer poly(N-isopropylacrylamide) (PNIPAM) displays a sharp phase transition at its LCST around 32 $^{\circ}$C, which results from competing interactions of the hydrophobic and hydrophilic groups with water. This thermoresponsive behavior can be exploited in more complex architectures, such as block copolymers or surfactants, to provide responsive PNIPAM head groups. In these systems, however, changes to the hydrophobic/hydrophilic balance can alter the transition behavior. In this work, we perform atomistic simulations of PNIPAM-alkyl surfactants to study the temperature dependence of their structures. A single chain of the surfactant does not show temperature-responsive behavior. Instead, below and above the LCST of PNIPAM, the surfactant folds to bring the hydrophobic alkyl tail in contact with the PNIPAM backbone, shielding it from water. In addition to single chains, we explore the self-assembly of multiple surfactants into micelles and how the temperature-dependent behavior is changed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B45.00003: Self-assembly of Giant Molecular Shape Amphiphiles in Solution Rong Wang, Shiying Ma The self-assembly of giant molecular shape amphiphiles consisting of a hydrophilic head and one or more hydrophobic tails is investigated by dissipative particle dynamics. The morphology can transform from vesicles to worm-like cylinders and further to spheres by increasing the interaction parameter between the hydrophilic heads. The results are in agreement with the experimental observations. Through changing the interaction parameter between hydrophilic head and solvents, the length of hydrophobic tail and the size of hydrophilic head, the self-assembled aggregates exhibit a rich variety of morphological structures, such as, spheres, vesicles, worm-like cylinders, disk-like micelles and layered-rod-like micelles. Vesicles form for short hydrophobic tail, while disk-like micelles are taken shape for longer hydrophobic tail. As further increasing the diameter of hydrophilic head, large compound micelles are obtained for short hydrophobic tail, however layered-rod-like micelles form for longer tail. The simulation findings might be valuable for guiding the experimental studies and fascinating new possibility and applications in material science. This work was financially supported by NNSFC (21474051 and 21074053), NBRPC (2010CB923303) and PCSIRT. [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B45.00004: Transition to Area-Dependent Dissipation in Droplet Spreading Kari Dalnoki-Veress, Mark Ilton, Oliver B\"aumchen We have studied the spreading dynamics of a liquid diblock copolymer in the pseudo-partial wetting regime, in which disordered droplets coexist with a wetting layer of the same liquid. Using optical microscopy, the relaxation time of the droplets is measured as they evolve towards an equilibrium contact angle. The relaxation is investigated as a function of the contact angle, droplet volume, and viscosity. In this unique system all three parameters can be systematically varied on the same sample and for both advancing and receding motion. The relaxation time of the droplets does not scale with the length of the contact line as is typically the case. Instead, the relaxation time depends on the contact area. We are able to describe the experiments with a model that assumes area-dependent dissipation with only two adjustable parameters. [Preview Abstract] |
Monday, March 2, 2015 12:03PM - 12:15PM |
B45.00005: Patterning Polymer Films with Bidirectional Control of Marangoni Flow by Photochemically Manipulating Surface Tension Chae Bin Kim, Dustin Janes, Sunshine Zhou, Austin Dulaney, Christopher Ellison Small variations in temperature or composition at a fluid interface, often spontaneously generated, can cause local changes in surface tension and promote dramatic movement of fluids through convective motion. This phenomenon, often referred as Marangoni convection, is typically experienced in everyday life as a macroscopic and seemingly stochastic phenomenon. One might imagine attempting to direct this process for reproducibly forming microscale and nanoscale patterns. While this might initially seem impractical, here we will report a photochemical strategy to harness the Marangoni convection as a versatile patterning method. Two photo-exposures with different irradiating wavelengths were applied to a solid, glassy styrene-acrylic copolymer thin film. Each photo-exposure imposes either a higher or lower surface energy in the light exposed regions without inducing topography on the flat film surface. Once this solid film is heated to a liquid state, however, bidirectional Marangoni-flows occur spontaneously from low-to-high surface tension regions. [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B45.00006: Coffee Stains from Drops with Receding Contact Lines Julian Freed-Brown We present a framework for calculating the surface density profile of a coffee stain deposited by a drying drop with a receding contact line. For standard coffee stains, the fluid pins to the substrate, forces flow towards the exterior of the drop and deposits a thin, concentrated ring of particles. Unlike a pinned drop, a receding drop pushes fluid towards its interior and continuously deposits mass across its substrate as it evaporates. This gives rise to a new class of mountain-like morphologies that are not seen in the standard coffee ring effect but are reminiscent of recent experimental results. For a thin, circular drop with uniform evaporation, we calculate the surface density profile analytically and find that it diverges towards the center of the drop as $\eta \propto r^{-1/2}$, where $r$ is the distance from the center. We estimate how this divergence is softened due to solute interactions at the final stage of drying. Our framework can easily be extended numerically or analytically to investigate novel stain morphologies left by drying drops of different shapes and evaporation profiles. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B45.00007: Supramolecular Structural Forces and Hydrodynamics of Stratifying Foam Films Vivek Sharma, Yiran Zhang, Subinuer Yilixiati Liquid foams are complex fluids, mostly formed by gas bubbles dispersed within a surfactant solution. The lifetime of foams depends critically on stability and drainage of thin liquid films that separate gas bubbles. It is well-established that the monotonic decrease in film thickness observed experimentally can be qualitatively described using lubrication approximation, where pressure is contributed by capillary and DLVO forces (electrostatic plus dispersion). However, foam films containing micelles, colloidal particles or polyelectrolyte-surfactant mixtures exhibit step-wise thinning or stratification. In this study, we use experiments and theory to investigate the influence of non-DLVO forces, including supramolecular oscillatory structural forces, on drainage and stratification of thin foam films (\textless 100 nm). We discuss how the supramolecular oscillatory structural forces provide a series of metastable states, that affect the kinetics and mechanisms of drainage and rupture. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B45.00008: Concentration Dependent Structure of Block Copolymer Solutions SooHyung Choi, Frank S. Bates, Timothy P. Lodge Addition of solvent molecules into block copolymer can induce additional interactions between the solvent and both blocks, and therefore expands the range of accessible self-assembled morphologies. In particular, the distribution of solvent molecules plays a key role in determining the microstructure and its characteristic domain spacing. In this study, concentration dependent structures formed by poly(styrene-b-ethylene-alt-propylene) (PS-PEP) solution in squalane are investigated using small-angle X-ray scattering. This reveals that squalane is essentially completely segregated into the PEP domains. In addition, the conformation of the PS block changes from stretched to nearly fully relaxed (i.e., Gaussian conformation) as amounts of squalane increases. [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B45.00009: Structure and flow properties of block copolyelectrolyte hydrogels Samanvaya Srivastava, Matthew Tirrell Polyelectrolyte complexes (PEC) are dense, polymer-rich phases that form when oppositely charged polyelectrolyte chains spontaneously associate and phase separate in aqueous mediums. Bulk phase separation of the PECs can be evaded by combining one or both of the polyelectrolytes with a neutral polymer, thus engineering pathways for self-assembly of PEC based micelles and hydrogels with large-scale ordering of the nanoscale PEC domains. The PEC domains in these assemblies can encapsulate both hydrophobic and hydrophilic therapeutics and thus have tremendous potential in drug delivery, diagnostic and tissue engineering applications. This study will present insights on the equilibrium structure and self-assembly kinetics of PEC hybrid hydrogels through detailed rheology studies of self-assembled materials comprising of functionalized polyallyl glycidyl ethers (PAGE) connected to either single poly(ethylene glycol) (PEG) chain to form diblock copolymers or as functionalized end-groups on a triblock copolymer with a PEG midblock. The effect of key parameters such as polymer concentration, polymer block lengths, salt, ionic strength, and degree of charge mismatch on the equilibrium materials properties will be discussed, with a special emphasis on the temporal evolution of flow properties, and will lead to comparisons with the rheology models for associating polymers. Complementary studies with extensive static and dynamic light, X-ray and neutron scattering investigations will also be presented, thus providing a comprehensive structural description of these materials. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B45.00010: Network structures of triblock copolymer by two-step phase separation Mikihito Takenaka, Ayano Inoue, Hirokazu Hasegawa We investigated network structures of polystyrene-b-polyisoprene-polydimethylsiloxiane (PS-PI-PDMS) triblock copolymer formed solvent cast processes. The obtained morphologies were observed by 3D-TEM and SAXS. Two-step phase transition occurs during the self-assembling processes of PS-PI-PDMS in solvent cast processes, resulting in the morphologies such as OBDD and P-surface, which is not formed in the equilibrium state of triblock copolymer. [Preview Abstract] |
(Author Not Attending)
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B45.00011: The Amphiphilic Character of Cellulose Molecules in True Solution in Solvent Mixtures Containing Ionic Liquid and its Utilization in Emulsification Sofia Napso, Yachin Cohen, Dmitry Rein, Rafail Khalfin, Noemi Szekely Cellulose is the most abundant renewable material in nature that is utilized as a raw material for fabrication of synthetic products. Although it is not soluble in common solvents, there is significant interest in the use of solvent mixtures containing ionic liquids (IL) and polar organic solvents for cellulose dissolution. We present evidence for true molecular dissolution of cellulose in binary mixtures of common polar organic solvents with an ionic liquid, using cryogenic transmission electron microscopy, small-angle neutron-, x-ray- and static light scattering. In particular, the measured low values of the molecular, gyration radius and persistence length indicate the absence of significant aggregation of the dissolved chains. We conjecture that the dissolved cellulose chains are amphiphilic. This can be inferred from the facile fabrication of cellulose-encapsulated colloidal oil-in-water or water-in-oil dispersions. This may be done by mixing water, oil and cellulose solution in an ionic liquid. A more practical alternative is to form first a hydrogel from the cellulose/ionic liquid solution by coagulation with water and applying it to sonicated water/oil or oil/water mixtures. Apparently the dissolution/ regeneration process affords higher mobility to the cellulose molecules so an encapsulation coating can be formed at the water-oil interface. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B45.00012: The Effect of Illumination on the Gelation Process of Optoelectronic Materials Brian Morgan, Mark Dadmun A tremendous amount of insight into the functionality of conjugated polymers in optoelectronic devices can be gained by the study of these materials as they progress through the gelation process. The nature of the percolated network structures formed directly affects exciton transport and device efficiency, thus precise knowledge of the evolution of structures provides crucial information towards improving device efficiency via processing techniques. Additionally, select optoelectronic polymers have exhibited reversibly altered physical properties such as viscosity upon exposure to white light, potentially indicative of temporary conformation changes. We have conducted a series of small angle neutron scattering experiments to probe the temperature-driven gelation process of the conjugated photoactive polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) in both the presence and complete absence of white light. Fitting the resultant data indicates the creation and steady growth of cylindrical aggregates formed by the agglomeration of free chain P3HT as the growth process. Furthermore, clear differences between illuminated and non-illuminated gels are observed across multiple length scales, pointing towards an optically-induced variation in the gelation process. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B45.00013: Effect of Water Concentration on the Molecular Structure of Polyacrylate Gels Sriramvignesh Mani, Fardin Khabaz, Rajesh Khare Recent studies have suggested pervaporation to be a promising alternative method for separation of aqueous solution of alcohol compared to distillation based separation processes. The ability to tune the hydrophobic/hydrophilic character makes polyacrylate gels attractive candidate materials for separating water-alcohol mixture by pervaporation. Experimentally, it is observed that the amount of water absorbed in the gel i.e. the degree of swelling of the gel shows a large variation with polymer chemistry. Relatively few studies exist highlighting the effects of water concentration on the membrane separation efficiency which in turn is directly related to the internal molecular structure of the water rich membranes. In this regard, an all-atom molecular dynamics (MD) simulation is employed to study water structure in polyacrylate gels. As a first step, polyacrylate copolymer systems with varying degree of hydrophobicity are prepared using the simulated annealing polymerization technique. Atomistic structures of gels containing different amounts of water are also prepared. Effect of water content on the acrylate-water system microstructure is determined by characterizing the packing of water molecules as well as the hydrogen bonding in these systems. In addition, the change in dynamics of water molecules due to the interactions with polymer is captured by monitoring the auto-correlation function of their dipole vector. [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B45.00014: Polymer-Carbon Nanotube Composite Films at the Oil/Water Interface: Assembly and Properties David Hoagland, Tao Feng, Thomas P. Russell Efficient carbon nanotube assembly at the oil/water interface was achieved by dissolving cationic polymers in the oil phase and oxidized nanotubes in the water phase, the two components spontaneously forming salt bridges to produce a composite interfacial film of nanoscopic thickness. As seen by pendant drop tensiometry, parameters such as carbon nanotube and polymer concentration, pH, polymer molecular weight, and degree of nanotube oxidation all affect assembly strongly, with measured trends to be described and explained. The frequency-dependent elastic and viscous moduli of films in dilation were characterized by interfacial pendant drop rheology. Structural (fast, minutes) and adsorption/desorption (slow, tens of minutes) relaxations were both noted, and at frequencies intermediate to the two, almost insensitive to assembly parameters, the films displayed expected behaviors for 2D critical gels, i.e., at the crossover between fluid and solid. Tan(delta) was frequency-independent over one to two decades of frequency, and the modulus of linear stress relaxation was a power law in time. Films wrinkled by larger (nonlinear) strains recovered over the structural relaxation time. [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B45.00015: The Generality of Parallel Offsets of Rheological Response of Filled Elastomers Shoubo Li, Guochun Zhan, Yongli Mi, Xiaorong Wang We investigated the frequency and strain responses of oscillatory shear-induced nonlinearity for 14 filled rubber compounds. The elastomers used were poly(styrene-co-butadiene) or SBR rubber, poly(dimethylsiloxane) or silicone rubber, 1,4-cis polyisoprene or natural rubber, and poly(acrylonitrile-co-butadiene) or nitrile rubber. The fillers used were nano-sized carbon black, silica, clay, and calcium carbonate. Despite the wide differences in the polymer structure, chemical composition and the type of the filler as well as the shape, average size and the distribution of the particles, all systems display a universal feature that in both linear and nonlinear regimes the relationship between moduli and strain in response to the frequency change shows striking parallelism. This remarkable feature directly proclaims the existence of a new shear-rate frequency superposition for rubber materials. This superposition can be appropriately accomplished by first normalizing G$'$ by G$'$0 and G$''$ by G$''$0, where G$'$0 and G$''$0 are the zero-strain limited value of G$'$ and G$''$, then by horizontally shifting the curves of G$'$/G$'$0 and G$''$/G$''$0 along the frequency axis for each fixed shear-rate amplitude. This superposition principle involves neither model assumption nor parametric adjustment. [Preview Abstract] |
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