Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K43: Architectural Design of Polymers II: Sequences, Branching and NetworksFocus
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Sponsoring Units: DPOLY Chair: Gila Stein, Univ of Tennessee, Knoxville Room: LACC 503 |
Wednesday, March 7, 2018 8:00AM - 8:12AM |
K43.00001: Adsorption of random copolymers onto heterogeneous nanostructures Trung Nguyen, Ting Xu, Monica Olvera De La Cruz Previous studies on polymer adsorption onto flat surfaces showed that the monomer density profile in the adsorbed layers is dependent upon the attraction strength between the wall and the polymers, polymer bulk concentration and solvent selectivity. For a solution of polymers with regularly distributed sticky monomers near a flat surface it was predicted that the morphologies of the adsorbed layers result from the competition between the average nearest distance between the sticky sites on the polymer chain and that between the substrate sticky sites. In this talk we analyze the adsorption of random copolymers with hydrophobic and hydrophilic groups onto nanoparticles with a heterogeneous surface. We show that the optimal composition of the random copolymers to encapsulate the nanoparticles is determined by the interplay between adsorption energy, polymer composition and solvent selectivity. There is a strong correlation between the sequences of the adsorbed polymer chains, indicating that the surface is able to pick certain subsets out of the randomly shuffled sequences. Our study shows that copolymers with similar compositions encapsulate numerous types of surface patterns fairly effectively. |
Wednesday, March 7, 2018 8:12AM - 8:24AM |
K43.00002: Understanding Linear and Cyclic Polymer Chain Conformations and Thermodynamics in Solution Thomas Gartner, Arthi Jayaraman Comparing the chain conformations and thermodynamics in solutions of linear and cyclic polymers has been a topic of interest for many years. Despite this large body of work, due to challenges related to sample purity, dispersity, end-group/linker chemistry, and others, there is little consensus in the literature about the value of key properties such as the ratio of the radius of gyration between cyclic and linear polymers in solution. In recent work, small-angle neutron scattering (Hore lab, Case Western) on high-purity and low-dispersity cyclic and linear polystyrene (synthesized in Grayson lab, Tulane) has elucidated key differences in the temperature dependence of the Flory exponent in cyclic and linear polymers of identical molecular weight in deuterated cyclohexane. However, the effects of sample purity and the linker chemistry used to cyclize the ring polymers remain unclear. In this work, we apply explicit-solvent coarse-grained molecular dynamics (MD) simulations to provide the chain conformations as a function of solvent quality and linker chemistry. These MD results are then used within the framework of Polymer Reference Interaction Site Model (PRISM) theory to understand the thermodynamics of the system in terms of an effective polymer-solvent χ parameter. |
Wednesday, March 7, 2018 8:24AM - 8:36AM |
K43.00003: Coherent States Field Theory for Supramolecular Polymer Physics Kris Delaney, Glenn Fredrickson Supramolecular polymers contain reversibly bonding functional groups that can combine to generate supramolecular species. Telechelics, for example, are di-end-functional polymers that link to form species of arbitrary lengths, while polymers containing three or more bonding groups can combine to generate networks of complex and varied topologies. Polymer field theory provides a formally exact platform for efficient simulation of dense melts of high molecular weight polymers. However, the traditional formulation based on auxiliary chemical potential fields is challenging to apply to supramolecular polymers: explicit identification and correct weighting of contributions from each molecular species present in the reaction-product ensemble is required. Here we demonstrate that an alternative field-theoretic framework resembling the coherent-states (CS) formulation of quantum field theory provides a more natural and efficient method for building supramolecular polymer models: all reaction products, including loops, are automatically enumerated and correctly weighted. In addition to providing analytic analyses, we demonstrate the ability to simulate the resulting CS field theory with approximation-free complex Langevin sampling techniques. |
Wednesday, March 7, 2018 8:36AM - 9:12AM |
K43.00004: Does co-monomer sequence in random copolymers matter? Invited Speaker: Jan Genzer “Random” copolymers are synthesized by either direct copolymerization of the individual monomers or by post-polymerization modification (PPM) of a homopolymer with a reactive chemical species. It is a great challenge to characterize properly the “degree of randomness” using existing experimental tools. In our presentation we will provide evidence that Kerr effect (not the conventionally-employed NMR) is the method of choice for this daunting task. In our work, we prepare “random” copolymers by PPM of polystyrene with bromine that leads to the formation of poly(styrene-co-4-bromostyrene) (PBrxS), where x is the mole fraction of 4-bromostyrene units (4-BrS) . We will document that the distribution of the distribution of the 4-BrS units depends intimately on the solvent quality during the bromination reaction. We will also discuss that in some cases (i.e., RAFT) direct copolymerization of styrene and 4-BrS leads to PBrxS with a gradual variation of chemical composition and tacticity. We will provide overview of previous work in our group that aimed at determining the effect of co-monomer sequences on adsorption of “random” copolymers on surfaces form melts and from solutions. We will also review computational methods to monitor the formation and behavior of such “random” copolymers in solution and in bulk. Specifically, using turbidity measurements and small angle-neutron scattering experiments we will establish that while phase separation of PBrxS comprising “truly random” distribution of styrene and 4-BrS segments resembles closely that of homopolymers, PBrxS that possess “random-blocky” co-monomer distribution exhibits “pretransitional clouding” at temperatures above the phase separation. The temperature at which this “pretransitional clouding” occurs varies with cooling rate. We attribute this behavior to the formation of micro-aggregated domains of PBrxS in solution due to limited solubility of the 4-BrS in cyclohexane. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K43.00005: Dynamics of bottlebrush polymers in flowing solutions Sarit Dutta, Charles Sing Over the past decade, bottlebrush polymers have emerged as an attractive |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K43.00006: Functional Surfaces Using Bottlebrush Copolymer Additives Adeline Mah, Travis Laws, Hao Mei, Rafael Verduzco, Gila Stein Bottlebrush polymers are macromolecules with polymeric side chains grafted onto a linear backbone. The highly branched architecture leads to unusual physics in polymer blends, such as limited miscibility with long linear polymers and a strong entropic attraction to surfaces and interfaces. The tendency for bottlebrush accumulation at the interfaces can be used to design functional coatings. We examine the thin film phase behavior of bottlebrush poly(styrene-r-deuterated styrene) (PS-r-dPS) in linear PS. The bottlebrush side chain length (Nsc) and linear PS length (Nm) were varied to examine their impacts on film structure. Thin films were prepared by flow coating, and the through-film structure was measured with time-of-flight secondary ion mass spectrometry (TOF-SIMS). The as-cast films exhibited a strong surface and weak substrate excess for nearly all bottlebrush architectures. After thermal annealing, the equilibrated film structures strongly depend on bottlebrush architecture: At fixed Nsc, the segregation of bottlebrush polymers at the surface and substrate interfaces increases with increasing Nm. At fixed Nm, the enrichment of bottlebrush polymers at the free surface increases with decreasing Nsc. These studies provide guidelines for the design of surface-active additives. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K43.00007: Effect of Grafting Density on the Crystallization of Bottlebrush Polymers with Poly(ethylene oxide) Side Chains Adam Burns, Christopher Soles The rate and extent of crystallization in branched macromolecules are sensitive functions of the branch length and spacing. This work investigates the extreme case of bottlebrush polymers, which comprise crystallizable polymeric branches (side chains) densely grafted to a linear polymer backbone. In particular, the effect of the grafting density (expressed as the percentage of backbone units bearing a side chain, z) on the crystallization behavior is investigated using a series of bottlebrushes with crystallizable poly(ethylene oxide) side chains and z = 40, 60, 80, and 100% (denoted PEOBB-z). Isothermal crystallization experiments, by differential scanning calorimetry, reveal that the crystallization rate is a non-monotonic function of z. The crystallization rate of PEOBB-80 is nearly equal to that of the analogous linear PEO, whereas for the other three bottlebrushes the crystallization rate is depressed and decreases with decreasing z. The crystallization exotherm for a given crystallization temperature and time, and the resulting peak melting point, follow the same trend. These results reflect the competition between increased chain stretching, decreased intermolecular overlap, and a lower fraction of non-crystallizable backbone units in the melt with increasing z. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K43.00008: Solution Properties of Fluorinated Bottlebrush Polymers Revealed by Neutron and X-Ray Scatterings Kunlun Hong, Yingdong Luo, Shuo Qian Bottlebrush polymers are densely grafted polymers with long side-chains attached to a linear polymeric backbone. Their unusual structures endow them with a number of unique properties. Despite many studies of bottlebrushes that have been reported so far, their structure–property relationships are still far from understood. In this contribution, we present the solution properties of fluorinated bottlebrush polymers in different solovents (including tetrahydrofuran, toluene) by small angle neutron and X-ray scatterings, dilute solution viscosity. The results indicate that the conformations of these bottlebrush polymers depend on the size of the side chain, the concentrations of the solutions. These findings provide key information towards the design of architecturally tailored fluorinated polymers with desirable properties. |
Wednesday, March 7, 2018 10:00AM - 10:12AM |
K43.00009: Architecture of Telechelic Star Polymer Networks Ioana-Cristina Garlea, Christos Likos The study of star polymers is not only motivated by their industrial applications but also by the theoretical interest they present, as they constitute a bridge between colloids and polymeric chains. Structurally star polymers are composed of a number of polymeric chains (called arms) which all have one end attached to a single central point. If in addition the outer ends of each arm are functionalized so that they can attach to each other, the star is called telechelic. Provided that their density is high enough, telechelic star polymers self-assemble to form networks where the connecting points are aggregates of functionalized ends. Here, we investigate the formation of such networks using Molecular Dynamics simulation. We find that, depending on the strength of the interaction between the attractive ends, we can distinguish three different types of networks architecture exhibiting very distinctive properties. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K43.00010: Impact of Molecular Architecture on Dynamics of Miktoarm Star Polymers Joshua Sangoro, Thomas Kinsey, Emmanuel Mapesa, Weiyu Wang, Jimmy Mays Broadband dielectric spectroscopy is employed to investigate the impact of morphology and architecture on dynamics of a systematic series of poly (styrene-b-cis 1,4-isoprene) miktoarm star copolymers. While no change in the spectral shapes and mean rates of segmental relaxation is observed with variation of the number of arms and chain composition for all the samples probed, systematic broadening of the distribution of microscopic chain relaxation times is found for architecturally complex polymers. These results will be discussed within the framework of some recent theories and models of polymer dynamics in architecturally complex systems. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K43.00011: Stress-induced Orientation of Bicontinuous Nanostructures within Randomly End-linked Copolymer Networks Di Zeng, Ryan Hayward Bicontinuous morphologies with preferred orientation are of interest in a variety of contexts, ranging from membranes to energy dissipating materials. Previously, we have studied the microphase separation of randomly end-linked copolymer networks (RECNs), as a robust method to generate bicontinuous structures. Here, we study the ability to introduce controlled orientation in bicontinuous polystyrene/poly(D, L-lactide) RECNs through uniaxial stretching above the glass transition temperatures, followed by quenching to room temperature. Small angle X-ray scattering (SAXS) shows a progressive increase in orientation along the stretching direction with applied strain, while the primary domain spacing remains unchanged. The evolution of SAXS patterns as a function of strain reveals that the domains initially undergo non-affine stretching, followed by domain rotation accompanied by the rearrangement of interfaces during deformation. A comparison of real-space morphologies obtained from transmission electron microscopy (TEM) tomography indicates an increase in interfacial area and Euler characteristic upon stretching, revealing a change in topology. Orientation of domains by stretching at high temperature is found to yield dramatically improved mechanical toughness. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K43.00012: Computational Studies of Poly[n]catenanes Phillip Rauscher, Stuart Rowan, Juan De Pablo The rheological and dynamical behaviors of polymeric systems depend on the molecular architecture and the density of entanglements. Recently, a new polymer architecture has been realized synthetically in “poly[n]catenanes” - linear chains of mechanically interlocking ring molecules. This new architecture is dominated by topological bonds along the polymer backbone and can therefore possess entanglements not only between chains, but also between neighboring repeat units. Accordingly, these poly[n]catenanes offer an opportunity to access and exploit new dynamical and rheological regimes. Inspired by this recent advance, we present computational studies on the structure and dynamics of model poly[n]catenane systems in solution, the melt, and the solid state. In particular, we focus on the rheological properties as well as characteristic motions that are unique to interlocking molecules. |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K43.00013: Designing Multivalent Polymers to be Broad Spectrum Inhibitors, A Computational Study Emiko Zumbro, Katharina Ribbeck, Alfredo Alexander-Katz Mucins, glycoprotein polymers found in mucus, play a key role in protecting us from pathogens by using multiple sugar binding sites simultaneously to create strong multivalent binding interactions. Synthetic glycopolymers have had similar success inhibiting specific toxins, but single polymers have not been able to inhibit two species at once to approach the broad-spectrum protection of native mucins. It remains unclear how the inhibitor structure and binding site arrangement influences its overall binding affinity for substrates. To explore the effect of multivalent polymer structure, we use a Brownian dynamics bead-spring model coupled with a reactive polymer-pathogen binding model to investigate how variables such as degree of polymerization, binding site affinity, and binding site patterns influence a polymeric inhibitor’s affinity for a model substrate. We found that increasing inhibitor length has limited benefit, while increasing individual binding site variety can improve total polymer binding affinities over uniform binding site analogs. Our results suggest design rules for creating broad-spectrum polymeric inhibitors. |
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