Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R9: Focus Sesion: Architectural Design of Polymers IIFocus
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Sponsoring Units: DPOLY Chair: Bryan Beckingham, Auburn University Room: 268 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R9.00001: Domain bridging in melts of starblock copolymers Russell Spencer, Mark Matsen Block copolymers that form thermoplastic elastomers have some blocks that form glassy domains and other elastic blocks that bind the glassy domains together, leading to strong, and yet elastic materials. Binding glassy domains requires molecular bridges between domains, with the greatest number of molecules bridging between domains being the most desirable. Starblock copolymers have several glassy end blocks and therefore a high potential to enter multiple domains. We investigate bridging fractions and other statistical properties of starblock arms using self-consistent field theory. For 9-arm stars, the fraction of stars that bridge domains can exceed $99.9\%$ - far above bridging fractions found for triblocks or linear multiblocks. High bridging fractions, combined with the ability for a single molecule to bridge more than two domains makes starblock copolymers an excellent candidate for strong thermoplastic elastomers. [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R9.00002: Inverse design of bulk morphologies in block copolymers using particle swarm optimization Mihir Khadilkar, Kris Delaney, Glenn Fredrickson Multiblock polymers are a versatile platform for creating a large range of nanostructured materials with novel morphologies and properties. However, achieving desired structures or property combinations is difficult due to a vast design space comprised of parameters including monomer species, block sequence, block molecular weights and dispersity, copolymer architecture, and binary interaction parameters. Navigating through such vast design spaces to achieve an optimal formulation for a target structure or property set requires an efficient global optimization tool wrapped around a forward simulation technique such as self-consistent field theory (SCFT). We report on such an inverse design strategy utilizing particle swarm optimization (PSO) as the global optimizer and SCFT as the forward prediction engine. To avoid metastable states in forward prediction, we utilize pseudo-spectral variable cell SCFT initiated from a library of defect free seeds of known block copolymer morphologies. We demonstrate that our approach allows for robust identification of block copolymers and copolymer alloys that self-assemble into a targeted structure, optimizing parameters such as block fractions, blend fractions, and Flory chi parameters. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R9.00003: Adjustable bridge blocks make huge difference to the self-assembly of multiblock copolymers Weihua Li We present theoretical studies on two types of multiblock copolymers, whose self-assemblies lead to a lot of novel ordered nanostructures. The first example is BABCB multiblock terpolymer, where A- and C-blocks separately aggregate into isolated domains and the three B-blocks with adjustable lengths form the matrix. As a result, the middle B-block forms a natural bridge connecting A- and C-domains. In contrast to ABC, the BABCB can form many binary spherical and cylindrical phases with tunable coordination numbers. In addition, the ABCB solution can form a lot of planet-satellite micellar superstructures with tunable number of satellites that varies from 3 to 20. The another system is AB-type multiblock copolymers. In contrast to the above system, there is no natural bridge. Accordingly, we introduce multiple arms into the architecture which tend to partition themselves into different domains to maximize their configurational entropy, thus forming effective bridges. Furthermore, each arm is devised as BAB triblock to enable adjustable length of bridges. With this copolymer, we predict a few non-classical ordered phases, including a square array cylinder. Our study opens the possibilities of fabricating desired nanostructures using designed block copolymers. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 9:12AM |
R9.00004: Self-Consistent Field Theories for the Role of Large Length-Scale Architecture in Polymers Invited Speaker: David Wu At large length-scales, the architecture of polymers can be described by a coarse-grained specification of the distribution of branch points and monomer types within a molecule. This includes molecular topology (e.g., cyclic or branched) as well as distances between branch points or chain ends. Design of large length-scale molecular architecture is appealing because it offers a universal strategy, independent of monomer chemistry, to tune properties. Non-linear analogs of linear chains differ in molecular-scale properties, such as mobility, entanglements, and surface segregation in blends that are well-known to impact rheological, dynamical, thermodynamic and surface properties including adhesion and wetting. We have used Self-Consistent Field (SCF) theories to describe a number of phenomena associated with large length-scale polymer architecture. We have predicted the surface composition profiles of non-linear chains in blends with linear chains. These predictions are in good agreement with experimental results, including from neutron scattering, on a range of well-controlled branched (star, pom-pom and end-branched) and cyclic polymer architectures. Moreover, the theory allows explanation of the segregation and conformations of branched polymers in terms of effective surface potentials acting on the end and branch groups. However, for cyclic chains, which have no end or junction points, a qualitatively different topological mechanism based on conformational entropy drives cyclic chains to a surface, consistent with recent neutron reflectivity experiments. We have also used SCF theory to calculate intramolecular and intermolecular correlations for polymer chains in the bulk, dilute solution, and trapped at a liquid-liquid interface. Predictions of chain swelling in dilute star polymer solutions compare favorably with existing PRISM theory and swelling at an interface helps explain recent measurements of chain mobility at an oil-water interface.\\ \\In collaboration with: Renfeng Hu, Colorado School of Mines, and Mark Foster, University of Akron [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R9.00005: Effect of Molecular Weight on Competitive Self-Assembly of Poly(3-dodecylthiophene)-block-poly(methyl methacrylate) Copolymers Kyu Seong Lee, Jicheol Park, Chungryong Choi, Jongheon Kwak, Hong Chul Moon, Jin Kon Kim The fabrication of poly(3-alkylthiophene) (P3AT) nanopatterns with 10$\sim$20 nm scale using block copolymer self-assembly is one of key issues to achieve highly efficient organic optoelectronic devices. However, most P3HT-containing rod-coil block copolymers show only fibril structures due to their strong rod/rod interaction. P3DDT containing block copolymer shows well defined nanostructure, however, when P3DDT block chain is much longer than coil block, it also shows fibril structure. We suggest a simple but effective strategy to induce block copolymer microphase separation: increasing $\chi$N$_{total}$ with larger N$_{total}$ instead of reducing rod/rod interaction. We investigated, via small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), the microphase separation of P3DDT-b-PMMA at high weight fractions of P3DDT. A high molecular P3DDT-b-PMMA (w$_{P3DDT}$ = 0.76) formed cylindrical morphology, which is quite different from fibril morphology of a lower molecular weight P3DDT-b-PMMA having the same w$_{P3DDT}$. Furthermore, the crystallinity of the P3DDT block chains confined in self-assembled microdomains showed higher than that of P3DDT homopolymer, which is verified by differential scanning calorimetry (DSC). [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R9.00006: Examining the Self-Assembly of Rod-Coil Block Copolymers via Physics Based Polymer Models and Polarized X-Ray Scattering Adam Hannon, Daniel Sunday, Donald Windover, Christopher Liman, Alec Bowen, Gurdaman Khaira, Juan de Pablo, Dean DeLongchamp, R. Joseph Kline Photovoltaics, flexible electronics, and stimuli-responsive materials all require enhanced methodology to examine their nanoscale molecular orientation. The mechanical, electronic, optical, and transport properties of devices made from these materials are all a function of this orientation. The polymer chains in these materials are best modeled as semi-flexible to rigid rods. Characterizing the rigidity and molecular orientation of these polymers non-invasively is currently being pursued by using polarized resonant soft X-ray scattering (P-RSoXS). In this presentation, we show recent work on implementing such a characterization process using a rod-coil block copolymer system in the rigid-rod limit. We first demonstrate how we have used physics based models such as self-consistent field theory (SCFT) in non-polarized RSoXS work to fit scattering profiles for thin film coil-coil PS-$b$-PMMA block copolymer systems. We then show by using a wormlike chain partition function in the SCFT formulism to model the rigid-rod block, the methodology can be used there as well to extract the molecular orientation of the rod block from a simulated P-RSoXS experiment. The results from the work show the potential of the technique to extract thermodynamic and morphological sample information. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R9.00007: Regioregularity-Driven Phase Transition of Poly(3-hexylthiophene)-Based Block Copolymers Jin-Seong Kim, Yongjoo Kim, Hyun-Jeong Kim, Hyeong Jun Kim, Hyunseung Yang, Yeon Sik Jung, Gila E. Stein, Bumjoon J. Kim Conjugated polymer-based block copolymers (BCPs) offer great potential to provide beneficial nanostructures for efficient organic opto-electronics. However, their complicated self-assembly behavior, attributed to the strong crystallization of the conjugated blocks, is still not well understood due to the lack of a model BCP system. Herein, we develop a series of novel conjugated BCPs, poly(3-hexylthiophene)-\textit{block}-poly(2-vinylpyridine) (P3HT-$b$-P2VP), in which the regioregularity (RR) of the P3HT block was varied from 95 to 73{\%}. The tunable RR content allows for precise regulation of P3HT crystallization with minimal influence on the microphase-separation force between two blocks. When RR is high (95 or 85{\%}), the structure is characterized by P3HT nanofibrils in an amorphous matrix. In contrast, as RR decreases to 78 and 73{\%}, P3HT crystallization is suppressed, self-assembly is dominated by the enthalpic interaction, and thermal annealing drives the formation of well-ordered lamellar or cylindrical phases. This morphological behavior is consistent with a Monte Carlo simulation based on our coarse-grained model. Significantly, this novel class of RR-controlled BCPs provides a simple method to tune phase behavior for a variety of applications in nanostructured organic electronics. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R9.00008: Melt Miscibility in Block Copolymers Containing Polyethylene and Substituted Polynorbornenes. William Mulhearn, Richard Register Very few polymer species exist with a sufficiently weak repulsive interaction against polyethylene (PE), characterized by a low Flory parameter $\chi $ or interaction energy density X, to be useful for preparing PE-containing block copolymers with disordered melts at high molecular weights. Most suitably miscible polymers are chemically similar to PE, such as copolymers of ethylene with a minority content of an $\alpha $-olefin, and so are only marginally useful for property modification due to similar physical properties like the glass transition temperature (T$_{\mathrm{g}})$. However, the family of polymers consisting of substituted norbornenes prepared via ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation is unique in that many of its members exhibit very low X against PE (comparable with the interaction energy between poly(ethylene-\textit{alt}-propylene) and PE), and some of these also exhibit high T$_{\mathrm{g}}$. The miscibility between PE and a substituted, hydrogenated ROMP polynobornene, or between two dissimilar hydrogenated polynorbornenes, is a strong function of the substituent appended to the norbornene monomer. The mixing thermodynamics of this polymer series are irregular, in that the interaction energies do not follow X $=$ ($\delta _{\mathrm{1}}$ -- $\delta_{\mathrm{2}})^{\mathrm{2}}$ where $\delta $ is the solubility parameter. However, other systematic trends do apply and we develop a set of mixing rules to quantitatively describe the experimental miscibility behavior. We also investigate statistical copolymerization of two norbornene monomers as a means to continuously tune miscibility with a homopolymer of a third monomer. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R9.00009: Generation of Complex Morphologies in Diblock Copolymers via Blending Ronald Lewis, Morgan Schulze, Seamus Jones, Haley Beech, Robert Hickey, James Lettow, Frank Bates Low molar mass, highly segregated diblock copolymers have received recent attention due to their capacity to form new and complicated ordered morphologies, such as the Frank-Kasper sigma phase. However, the current materials in which these structures form are few and therefore non-ideal for investigating broader applications which require specific chemistries or length scales. Recent theoretical work suggests that increasing compositional and molar mass dispersity through blending relatively well-defined block polymers can induce these complicated structures in conformationally symmetric systems that do not typically exhibit complex phase behavior. Our experimental findings validate these predictions, with the discovery of the Frank-Kasper sigma phase and hexagonally close packed spheres in blends of poly(ethylene-alt-propylene-b-lactic acid) diblock copolymers. These results establish blending as a concrete method for the generation of complex morphologies in diblock copolymer systems where they are otherwise inaccessible. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R9.00010: Systematic and Simulation-Free Coarse Graining of Polymer Blends Qiang Wang Here we extend our recently proposed systematic and simulation-free strategy [\textit{D. Yang and Q. Wang}, J. Chem. Phys. \textbf{142}, 054905 (2015)] to the structure-based coarse graining of binary polymer blends. We use the well-developed polymer reference interaction site model theory, instead of many-chain molecular simulations, for both the original and coarse-grained (CG) systems, and examine how the CG potentials vary with the coarse-graining level and how well the CG models at different levels can reproduce the thermodynamic properties of the original system. Our strategy is at least several orders of magnitude faster than those using many-chain simulations (thus effectively solving the transferability problem in coarse graining), avoids the problems caused by finite-size effects and statistical uncertainties in many-chain simulations commonly used in coarse graining, and does not change the spinodal curve (thus also the critical point) of the polymer blends. The structure-based coarse graining, however, does not give thermodynamic consistency (i.e., the same interchain internal energy per chain or virial pressure) between the original and CG systems at any level of coarse graining. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R9.00011: Probing Kinetic and Thermodynamic Effects on Self-Stratified Polymer Blends Samantha Rinehart, Mark Dadmun Coatings are used on everyday surfaces for protection and to improve durability. An intriguing development of the coating industry is the self-stratification of multi-component systems. However, current use of self-stratification utilizes polymer blends specific for optimizing properties of the desired application and does not fully investigate the driving forces that control the process. Understanding the respective role kinetic and thermodynamic effects have on final film morphologies formed by self-stratification is fundamental in optimizing polymer structure and improving the properties of thin films. We probe these effects by combining three themes: understanding solution phase behavior, monitoring film formation in-situ, and determining the depth profiles of the final film. Primary studies include thin films consisting of Poly(3-hexylthiophene-2,5-diyl) (P3HT), and Poly(methyl methacrylate) (PMMA). This polymer blend has provided promise of improving organic field effect transistors (OFET). Although this groundwork surveys stratification for applications in OFET, this research has potential to develop a global understanding of self-stratification and to impact a wide range of technologies by developing a cost efficient method for multi-layer film deposition. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R9.00012: Novel Modelling Tool for Energetics Licia Dossi Polymer science combines an understanding of chemistry and material properties to design, develop, model and manufacture new materials with special properties for new applications. The \textit{Binders by Design} UK programme, funded through the Weapons Science and Technology Centre (WSTC) by the Defence Science and Technology Laboratory (Dstl), develop new polymeric materials for energetic applications that can survive over the increased operating temperature ranges of future weapon platforms and satisfy international and national regulations. A multidisciplinary team of UK chemists, physicists, modellers and end users (Cranfield University, Sheffield-Hallam University, QinetiQ, Fluid Gravity Engineering, BAE Systems UK Land and Roxel UK) research together on the synthesis, characterisation and modelling of novel macromolecules with very promising thermal properties. Group Interaction Modelling supported by molecular mechanics calculations is used for a rapid assessment and selection of candidate molecules. New model and simulation protocols suitable for investigating the glass transition behaviour of HTPB oligomers are developed. The continuum level models and a constitutive model for a binder/energetic system are developing, for application in safety assessments (e.g. low-velocity impact tests). [Preview Abstract] |
Thursday, March 16, 2017 10:48AM - 11:00AM |
R9.00013: Phase behavior of particle-forming polyisoprene-b-polylactide diblock copolymers Kyungtae Kim, Ronald Lewis, Morgan Schulze, Akash Arora, Kevin Dorfman, Frank Bates Low-symmetry phases including the dodecagonal quasicrystal and tetrahedral close-packed Frank-Kasper $\sigma$ phase recently have been identified in various forms of soft materials including dendrimers, surfactants, and block polymers. In block polymers these complex phases emerge from the supercooled fluctuating disordered state, comprised of well-formed micelles. Rapid cooling to sufficiently low temperatures below the order-disorder transition extinguishes molecular exchange resulting in non-ergodic “liquid-like packing”. Here we present fresh findings obtained as a function of temperature and time from polyisoprene-\textit{b}-polylactide (PI-\textit{b}-PLA) diblock copolymers containing 15 to 25 \% PLA based on time dependent synchrotron X-ray scattering and draw connections with the thermal processing of metal alloys. [Preview Abstract] |
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