Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S41: New Directions in Polymer Physics |
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Sponsoring Units: DPOLY Chair: Julie Albert, Tulane University Room: 214A |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S41.00001: Selective-Assemblies of Frank-Kasper A15 and Other Superlattices via Precisely Controlled Positional Interactions in Nano-Sized Giant Tetrahedra Mingjun Huang, Chih-Hao Hsu, Jing Wang, Kan Yue, Stephen Z.D. Cheng Diverse self-assembled hierarchical structures in soft materials including small molecules, polymers, and biomacromolecules have been intensely studied. Herein, we report a class of precisely defined, rigid, nano-sized giant tetrahedra molecules, which are constructed by positioning polyhedral oligomeric silsesquioxane (POSS) molecular nanoparticles with different functional groups at the apexes of a tetrahedron framework. Designed symmetry breaking of these giant tetrahedra accurately controlled the positional interactions, leading to diverse selectively assembled, highly ordered superlattices. In particular, a Frank-Kasper A15 superlattice was obtained from a series of giant tetrahedra with three hydrophobic and one hydrophilic POSS cages, which resembled the essential structure of certain metal alloys, but with tunable feature sizes at much larger length scales. Formation of the A15 phase is due primarily to the deformability of the self-assembled spherical building blocks that allows size polydispersity from monodisperse giant tetrahedra. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S41.00002: Relaxation suppression in stretched block-copolymer matrix above $T_{g}$ Dmitriy Alhazov, Michael Burman, Arkadii Arinstein, Eyal Zussman As was shown in our recent paper [1], electrospun thermoplastic polyurethane (TPU) block-copolymer nanofiber mats start massively to contract upon heating up to $\sim$90 $^{\circ}$C, whereas cast TPU films expand as expected. Further studies have shown that such temperature threshold is an artifact caused by process kinetics. It also turned out that cast TPU films can also massively contract upon heating, but only after the following thermo-mechanical programming: stretching the films ($\sim$100{\%}) at high temperature ($\sim$90 $^{\circ}$C), cooling to room temperature under constant strain, and finally, unloading the stretched films. Such behavior in films demonstrates that the contraction in electrospun fibers cannot be attributed only to confinement. Rather, the phenomenon in question should be attributed to relaxation suppression in non-equilibrium (stretched) states of TPU polymer matrix. This conclusion is unpredicted since the temperatures of the tested samples (before heating) were much higher than the glass transition temperature of the soft phase, and the concentration of hard segments in TPU macromolecules is too low in order to form a percolated ``solid'' structure. In such a situation the relaxation of the non-equilibrium is expected. A possible physical explanation of the observed phenomenon, based on the blob concept, is proposed.\\[4pt] [1] D. Alhazov, et al., Euro. Polymer J. (2013). [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 8:36AM |
S41.00003: The Influence of Interfacial Block Copolymer on the buckling and drainage of an emulsion droplet approaching a flat surface Damith Rozairo, Andrew B. Croll When a liquid droplet surrounded by a homogeneous fluid approaches a flat wall it can buckle and trap a thin layer of the surrounding fluid. The thin layer of trapped fluid slowly drains out, driven by the capillary forces which will eventually flatten the buckled droplet. The dynamics of these interactions are a critical stage of many industrial and biomedical applications. There is now a body of research surrounding the process and the effects of small surfactant molecules on thin film drainage. Long chain surfactants (block copolymers) are seeing increased use in emulsion stabilization, however, the unique effects of long polymer surfactants on simple hydrodynamic processes are often ignored. In this work we experimentally study how a self-assembled diblock copolymer interface on an emulsion drop influences the entrapment and subsequently drainage of surrounding fluid. Specifically, we investigate several different polystyrene-b-poly(ethylene oxide) (PS-PEO) molecules on toluene droplets in water as they approach an atomically flat mica surface. The film drainage rate is found to vary with the molecular weight of the PS-PEO molecules. Remarkably, we observe slower drainage rate for longer PEO chains, which can be understood with a simple hydrodynamic model. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 8:48AM |
S41.00004: Electrostatically driven selective deposition of nanoparticles on chemically modified block copolymer patterns Tom Wagner, Larisa Tsarkova, Alexander Boeker Targeting applications in catalysis, circuitry, molecule-recognition and optoelectronics, we selectively assembled negatively charged gold nanoparticles (AuNPs) on microphase separated poly(styrene-\textit{block}-2-vinylpyridine) (PS-$b$-P2VP) thin films by electrostatic interactions. Chemical crosslinking of PS-$b$-P2VP films results in positively charged P2VP domains ($q$P2VP). Control of charge density of the P2VP blocks is governed by varying the degree of crosslinking. To quantify the contribution of coulombic interactions we performed combinatorial studies including micro contact printing of negatively charged AuNPs onto $q$P2VP-homopolymer films as well as selective AuNP deposition on PS-$b$-$q$P2VP films by immersion. During manufacture, the chemical composition of precursors and final composites has been monitored by ATR-IR- and XPS-measurements whereas AFM- and FESEM-measurements revealed topographical features. XRR- and GISAXS-measurements provided information on the inner structure of the film. AuNP adsorption kinetics was followed by in-situ electrochemical impedance spectroscopy (EIS). Finally, the complementary analyses allowed for better understanding the fundamentals of electrostatically driven NP-adsorption on soft polymer surfaces. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S41.00005: The effect of added block copolymer on oil in oil emulsions Itaru Asano, Timothy Lodge Oil-in-oil emulsions, formed by polymer A and polymer B in the presence of an organic solvent (A/solvent-in-B/solvent), are a unique class of emulsion, because both phases are composed of organic components. Here, the effects of PS-$b$-PEGs (PS: polystyrene and PEG: polyethylene glycol) on the stability of the oil-in-oil emulsions composed of PS/CHCl$_{3}$-in-PEG/CHCl$_{3}$ were studied by varying the molecular weight (20 \textless $M_{n}$ \textless 200 kg/mol) and the volume fraction (0.40 \textless $f_{PS}$ \textless 0.82) of the PS-$b$-PEG. We found that higher $M_{n}$ of PS-$b$-PEGs with low $f_{PS}$ were able to stabilize the emulsions with reduced droplet size. In particular, using a large PS-$b$-PEG (200 kg/mol, $f_{PS} \quad =$ 0.52), the emulsion was stable for more than 2 weeks, and the droplet size decreased to the nanoscale, around 300 nm in diameter, whereas the emulsion was unstable with large droplets (\textgreater 50 $\mu $m) without the PS-$b$-PEG. In order to reveal the mechanism of stabilization, dye-labeled PS-$b$-PEGs in the emulsions were directly monitored by fluorescence microscopy. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S41.00006: Assembly of polymeric nanoparticles: Molecular dynamics study Sabina Maskey, Dvora Perahia, Gary S. Grest The assembly of polymeric nanoparticles or polydots has been studied using molecular dynamics simulations. These polydots are highly fluorescent and have potential applications in intracellular imaging, bio-sensors and other optoelectronic devices. Therefore their assembly is the key to their utilization. Here we probe the assembly of polydots made by para dialkyl phenyleneethynylenes (PPEs) whose conformation determines their degree of conjugation and enhance their electro-optical response. As in our previous study, PPE polydots were prepared by collapsing polymer by the procedure developed. The polydots were brought together two ways. Allowing the particles to approach each other at a constant velocity of 50m/s resulted in the particles bouncing off each other which is consistent with the dense object which we have previously reported. Then polydots were brought together at constant force and interface between them has been followed. Our results show that polydots under high velocity and forces remain stable. Closer look at the interface reveals that backbones of the polymer do not inter-penetrate and side chains dominate the interface. This interfacial structure suggests that one could retain the structure of polydots upon assembly. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S41.00007: Assembly of Magnetite Nanoparticles Grafted with Ion-Containing Diblock Copolymers Yang Jiao, Pinar Akcora Polystyrene (PS)-grafted iron oxide nanoparticles are shown to organize into highly ordered anisotropic nanostructures in bulk forms as of microphase separated morphologies of block copolymers. Ordered strings that are of one particle in width are created in composite films. In this work, we design a novel system of ion-containing block copolymer-grafted magnetic nanoparticles and study the effect of phase separation in grafted block copolymer on the aggregation of magnetic nanoparticles in the presence of ionic liquid, [HMIM][TFSI]. Styrene sulfonates neutralized with trioctylammonium are clicked to the thiolated ends of grafted PS through a thiol-ene click reaction. We show that the phase separated copolymer brush lead to stacking of strings of nanoparticles into planar structures. Miscibility of copolymer-grafted nanoparticles is being enhanced by the solvation of sulfonated groups with ionic liquid. Further, we demonstrate that the copolymer-grafted particles can be easily directed under magnetic fields in ionic liquid compared to their uncharged forms. The conductivity results indicate that the good miscibility between sulfonated particles and ionic liquid significantly enhances conductivity. [Preview Abstract] |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S41.00008: Engineer concentration gradient drug particles using microfluidic systems Jianbin Wang, Pavithra Sundararajan, Adam Procopio, Larry Rosen, Jerry Klinzing, Patrick Marsac Particles designed with spatial composition gradients have attracted increasing attention in the pharmaceutical industry. The designed distributions of drug, polymer or surfactants in the concentration gradient drug particles could enable control of the drug release kinetics or targeted delivery of the drug to provide therapeutic benefits. Here, we present a technique for generating concentration gradient particles from concentration gradient droplets using a microfluidic device. The concentration gradients in the liquid stream and the droplets were monitored with fluorescence microscopy and the concentration gradients were largely maintained. X-ray computed tomography was used to characterize the internal structure and concentration gradient profile in the solid particles. We successfully generated the concentration gradient particles in the coupled evaporative diffusive system by keeping the non-dimensional relative time scale for evaporation to diffusion to be 0.1 or less. Our experiments were instrumental to gaining fundamental insights into the processes controlling the concentration gradients in the particle and the droplet. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S41.00009: Steered molecular dynamics of epoxy-amine reactions in EPON862-DETDA Yae Ji Kim, Samuel Reeve, Alejandro Strachan The combination of steered molecular dynamics (SMD) and Jarzynski's equality have made free energy calculations for simulations of non-equilibrium pulling processes possible. This has been widely studied in protein folding and is now applied for epoxy-amine reactions for the first time using the reactive interatomic potential ReaxFF. This reaction in epoxy EPON862 and curing agent DETDA, commonly used in aerospace composite materials, is investigated in both the gas and condensed phases. The potential of mean force (PMF) is calculated during the simultaneous breaking of the epoxy ring and approach of the amine nitrogen to the terminal carbon. Minimization of the PMF is carried out by varying the timing of the reaction (e.g. delayed approach of C-N), as well as a variation of adaptive SMD via a parallel replica method. This adaptive SMD breaks the reaction into a series of time stages, reducing the necessary number of independent simulations and resulting in more rapid convergence of the PMF. Reaction completion is predicted using various initial geometric and molecular features. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S41.00010: Phase Transition in a Model of Y-shaped Molecules Donovan Ruth, Raul Toral, Danielle Holz, Jeffrey Rickman, James Gunton Increasing attention in statistical mechanics is being given to non-spherical molecules, such as polypeptide chains and protein molecules. One example is provided by immunoglobulin, which has a ``Y'' shape. In this work, we determine the phase diagram of ``Y''-shaped molecules on a triangular lattice through Monte Carlo Grand Canonical ensemble simulation, using histogram reweighting,multicanonical sampling and finite size scaling. We show that (as expected) this model is a member of the Ising universality class. For low temperatures, we implemented multicanonical sampling to induce faster phase transitions in the simulation. By studying several system sizes, we use finite size scaling to determine the two phase coexistence curve, including the bulk critical temperature, critical chemical potential and critical density. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S41.00011: Chirality Transfer in Chiral Homopolymers and Chiral Block Copolymers Rong-Ming Ho Herein, we deals with the chirality transfer of chiral polymers on different length scales. Helical conformation could be formed due to the stereoregularity of chiral entities in the chiral polymers and the BCPs*. Helical superstructures and phases can be fabricated by self-assembling polymer chains with helical conformation through intramolecular and intermolecular interactions. The transfer of chiral information from molecules to macroscopic level and the control of the handedness of the helical architectures are discussed. The examples of chirality transfer in the self-assembled chiral polymers and BCPs* are introduced. As found, the molecular chirality of constituted chiral entities in the chiral polymers and the BCPs* and corresponding conformational chirality plays an important role in the formation of helical architectures with exclusive handedness. Also, we deal with the chirality transfer in specific model systems, chiral polylactides and polylactide-containing BCPs*, at which homochiral evolution from chiral entity to helical phase is demonstrated. A methodology for systematic studies of the chirality transfer from molecular level to phase scale is suggested. Through the design and synthesis of macromolecules and the operation of self-assembly, the mechanisms of chirality transfer on different length scales can be understood, giving supplementary information to disclose the mysteries of morphological evolution from the molecular level. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S41.00012: Polydot at the interface with DPPC membrane: A Molecular Dynamics Simulation Study Sidath Wijesinghe, Dvora Perahia, Gary Grest, Christoph Junghans Luminescent polymers confined into long lived polydots are of potential interest because of their tunable properties and biocompatibility. These desired properties of polydots make them potential candidates for target drug delivering agents and bio markers. The first and foremost step in such applications is introducing these polydots to biological membranes which consist of different lipids whose collective dynamics mediate the cell membrane functions. Experimental studies suggest that their ability to penetrate cells depend on the polydot morphology, charge and the environmental characteristics including the type of the cell membrane. Here we report the results of an all atom molecular dynamics simulation of a carboxylate substituted dinonyl poly para phenylene ethynylene (PPE) polydot in one-component bilayer composed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Introduction of a polydot into the DPPC membrane initially results in deformation of the membrane however after equilibrated, the membrane relaxes and the polydot is stable within the membrane. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S41.00013: Investigation of a new approach for high-yield molecular electronic junctions with direct metal transfer method Hyunhak Jeong, Heejun Jeong, Takhee Lee To investigate the charge transport characteristics through molecular junctions which utilize molecules as an active channel, several approaches to form molecular junctions have been demonstrated [1]. Specifically, solid state device structure-based methods have been considered, however, one of the major obstacles of this method is generation of filamentary path which results in low device yield. To overcome this, several other methods that utilize a protective interlayer have been reported [2,3]. But, it is still difficult to investigate the genuine transport characteristics through molecular junctions because of the adoption of the interlayers. Here, we propose a new approach for high-yield molecular junctions with a direct metal transfer method. With this method, we measured inelastic electron tunneling spectroscopy (IETS) characteristics of molecular junctions made with alkanethiolate. We also observed discrepancies and device-to-device variations in the IETS spectra, which are possibly originated from defects in the molecular junctions and insulating wall.\\[4pt] [1] Xiang et al. Adv. Mater. 25, 4845 (2013)\\[0pt] [2] Akkerman et al. Nature 441, 69 (2006)\\[0pt] [3] Wang et al. Adv. Mater. 23, 755 (2011) [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S41.00014: Photo-crosslinking and Post-Functionalization of Solution Assembled Conjugated Polymer Nanofibrils Hyeong Jun Kim, Matthew Skinner, Alejandro Briseno, Todd Emrick, Bumjoon Kim, Ryan Hayward Conjugated polymer nanofibrils produced by solution assembly represent efficiently charge transporting nanostructures with promise for improving the performance of organic electronics. Despite their advantages, they have inherent instability upon treatment with heat or solvents, limiting the types of processing steps that may readily be employed. We utilize an azide-functionalized P3HT copolymer (P3HT-azide) to produce robust photo-crosslinkable nanofibrils that can be post-functionalized without structural distortion or degradation of performance. The solution assembled P3HT-azide nanofibrils were successfully photo-crosslinked by exposure to UV light, as judged by their stability against high temperature and addition of a good solvent such as chlorobenzene. Furthermore, azide units remaining after photo-crosslinking were functionalized with polyethylene glycol (PEG) using the azide-alkyne click cycloaddition reaction, allowing for dispersion of nanofibrils in very polar solvents including methanol and water, while maintaining good charge transport properties. [Preview Abstract] |
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