Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y42: Theory and Modeling of Diblock Copolymers and Blends |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Charles Sing, University of Illinois at Urbana-Champaign Room: 214B |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y42.00001: Ordering in Mixed Polymer Brushes Amalie L. Frischknecht, Chester K. Simocko, Dale L. Huber Mixed polymer brushes, consisting of two different homopolymers grafted to a substrate, microphase separate into phases reminiscent of those of diblock copolymer thin films. However, mixed polymer brushes typically display less long range order than diblock copolymers. One reason for the lack of long-range order is variations in the grafting densities of the two polymers, which result in quenched disorder in the system. Here we use self-consistent field theory (SCFT) to explore whether mixed brushes consisting of AB and AC diblock copolymers grafted to the surface can order better than homopolymer mixed brushes. In particular, we consider the case when A is a random copolymer of B and C, and thus has equivalent interaction strengths with both B and C blocks. Large cell SCFT calculations are performed for systems with Gaussian-correlated grafting density distributions. The theory predicts that mixed diblock brushes with a random copolymer block grafted to the surface are more ordered than the equivalent mixed homopolymer brush. The dependence of these results on polymer volume fractions and interaction parameters, as well as preliminary comparison with experiments, will be discussed. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y42.00002: Transferable potentials for coarse-grained simulations of block copolymer biomimetic membranes Malgorzata Kowalik, Ian Sines, Janna K. Maranas, Manish Kumar We present a framework of minimal model transferable coarse-grained potentials for use in molecular dynamics simulations of amphiphilic block copolymer biomimetic membranes. Testing two, three, and five-bead models of polyethylene oxide polyethylethylene (PEO-PEE) polymer membranes, we show that values for membrane thickness and area per polymer chain obtained using the two-bead model are consistent with our experimental and previously published data. The calculated variation in membrane thickness ($d$) with hydrophobic molecular weight ($M_h$) conforms to a known scaling law ($d \sim M_{h}^{a}$). The same scaling exponent describes the area per polymer chain. We demonstrate that cross interactions can be represented using combining rules with the use of a scaling factor which is correlated with the difference in hydrophobicities of the interacting hydrophobic/hydrophilic monomers. In this way it becomes possible to rapidly simulate and screen new combinations of block copolymers with minimal potential development effort. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y42.00003: Molecular Dynamics Simulations of Microphase Separating Tapered Diblock Copolymers Youngmi Seo, Jonathan R. Brown, Lisa M. Hall Tapered AB copolymers consist of pure A and B blocks separated by a middle block whose composition is a statistical linear gradient from pure A to pure B (or from B to A for an inverse taper). These systems microphase separate into ordered structures similar to typical AB diblock copolymers. Prior experiments and theory suggest that one can use taper length as an adjustable parameter (beyond those available in the diblock system) to control interfacial and phase behavior, and that tapers potentially make the bicontinuous double gyroid phase more accessible at high molecular weight. Using a simple coarse-grained model, we perform molecular dynamics (MD) simulations to determine the interfacial profiles and other features of the structure and dynamics as a function of taper length. We reproduce the results from self-consistent field theory (SCFT); specifically, tapering increases miscibility, widens the interfacial region, shortens domain spacing, and makes network phases more preferable. The significantly smaller lamellar spacing for inverse tapers is explained in terms of polymer chain folding or snaking across the interface The dynamic analysis shows the diffusion and relaxation behavior are closely related to the chain conformations and interfacial behavior. The effect of tapering on penetrant diffusion through one of the microphases will also be discussed. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 8:48AM |
Y42.00004: Dynamic and Topological Properties of Lamellar Phases Vaidyanathan Sethuraman, Venkat Ganesan We investigate the local dynamical and global topological properties of a diblock copolymer system in its lamellar phase. Explicitly, we investigate the heterogeneity in the dynamics and non-Gaussian parameter ($\alpha$) of different segments in the ordered phase as a function of its distance from the interface for a chain length of $N = 100$. At short time scales, weak heterogeneities are observed for low degree of compositional segregation and the heterogeneities increased for increased interactions between unlike monomers. Monomers near the interface also showed higher $\alpha$ values compared to those away from the interface. We also investigate the entanglements of ordered lamellar phases using molecular dynamics simulations which reveal a reduction in the average entanglement length for increasing $\chi N$. We use self consistent field theory calculations to probe the number of topological constraints near the interface. Such calculations showed an increase in the number of constraints near the interface, thus corroborating the results obtained from molecular dynamics simulations. [Preview Abstract] |
Friday, March 6, 2015 8:48AM - 9:00AM |
Y42.00005: Field-theoretic Monte Carlo simulations of a diblock copolymer melt Bart Vorselaars, Pawel Stasiak, Mark Matsen Using field-theoretic Monte Carlo simulations (MC-FTS) we report on a melt of diblock copolymers. Our focus is on the region near the transition between the disordered and lamellar phase. The MC-FTS method in use [1] makes it possible to study systems with a vast number of chains beyond that what is attainable by classical molecular dynamics simulations, and without compromising on neglecting compositional fluctuations, as is the case with self-consistent mean field theory. The assumption that the fluctuations in the incompressibility field are of a Gaussian nature allows one to use standard MC techniques. We compare the simulation results with predictions from theories that include fluctuations, such as a theory developed by Fredrickson and Helfand (FH) and the recently published renormalized one-loop calculations. Once the incorporation of the ultra-violet divergence is taken care of in an accurate way, the simulation results can be nicely mapped onto the theoretical predictions near the transition region, even for moderate simulation resolutions. [1]: Stasiak and Matsen, \emph{Macromolecules} \textbf{46}, 8037 (2013) [Preview Abstract] |
Friday, March 6, 2015 9:00AM - 9:12AM |
Y42.00006: Accurate fluctuation-corrected phase diagrams of high-molecular-weight block-copolymer melts Kris Delaney, Glenn Fredrickson We describe a theoretical framework for accurately computing fluctuation-corrected phase diagrams of block polymer melts. The method is based on complex Langevin sampling of a UV regularized field-theoretic model, with Helmholtz free energies computed using thermodynamic integration. UV regularization ensures that the free energies thus computed do not have an arbirary reference; they can be compared between incommensurate phases, permitting for the first time the explicit computational determination of order-order transitions with fluctuation corrections included. We further demonstrate that free energies are accurate in the disordered phase by comparing to perturbation theory on the one-loop level. We note that our method uses no uncontrolled approximations beyond the initial definition of a coarse-grained molecular model for the polymer melt. The method can be applied straightforwardly to melts and solutions containing multiple species with diverse polymer architectures. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y42.00007: Morphology of Tapered and Ion-containing Diblock Copolymers from Fluids Functional Density Theory Jonathan R. Brown, Lisa M. Hall We use classical, fluids density functional theory (fDFT) to study microphase separation in block copolymer systems. We focus on systems where local monomer scale ordering may be more important than for typical diblock copolymers, so fDFT allows us to generate more accurate density profiles and free energies at constant pressure. Specifically, we study the effect of tapering, or adding a gradient region (taper) between the pure A and B blocks of an AB diblock; the taper changes in composition smoothly from A to B. This additional control parameter allows one to increase the miscibility of the two blocks and change the effective segregation strength $\chi N$ of the system. In contrast to our prior SCFT study, we capture the effect of the depletion of monomer density near the A-B interface, which changes as a function of taper length and interfacial width. Further, these methods can also be applied to ion containing systems, in which case monomer scale packing around ions is also important; we will show the fDFT predicted microphase morphology of block ionomers. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y42.00008: Survey of experimental data from diblock copolymer melts: Do experiments and simulations agree? Pavani Medapuram, David Morse Recent simulations by our group have established that a variety of different simplified simulation models of symmetric diblock copolymers exhibit universal behavior that is now well characterized. In this talk, we report our progress in analyzing published experimental data for a variety of nearly symmetric diblock copolymers using methods closely analogous to those used to analyze simulation results. We will discuss the extent to which experiments on a wide variety of systems are consistent with the results of simulations, and with one another.~ [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y42.00009: Finite Size Effects and Commensurability in Lattice Simulations of Symmetric Diblock Copolymers Akash Arora, Frank S. Bates, Kevin D. Dorfman Monte Carlo (MC) simulations have been used widely to study the fluctuation driven weakly first-order transition in symmetric diblock copolymers. However, the predicted value of the order-disorder transition ($\chi_{\textrm{ODT}}N$) often differs from the true value (thermodynamic limit) because of the finite size of the simulation box. In order to locate the true ODT, we have studied finite size effects in lattice MC simulations of lamella forming symmetric diblock copolymers. The straightforward application of finite size scaling (FSS) is questionable due to incommensurability between the ordered structure domain spacing and the periodicity of the lattice. To address this issue, we estimate the preferred domain spacing by simulating multiple system sizes to find nearly commensurate systems. Furthermore, we apply FSS to these nearly commensurate systems to predict the ODT in the thermodynamic limit. [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y42.00010: Dynamical self-consistent field theory of the evolution of instabilities in polymer blends and diblock copolymer melts Douglas Grzetic, Robert Wickham We demonstrate our recently-developed dynamical self-consistent mean-field theory [\emph{J. Chem. Phys.} \textbf{140}, 244907 (2014)] in a polymeric context, by studying the early-time spinodal decomposition of a symmetric binary polymer blend and the dynamics of the order-order transition between the LAM and HEX phases in an asymmetric diblock copolymer melt. A Brownian dynamics description of a dense system of Rouse chains interacting pair-wise via a modified, species-dependent Lennard-Jones potential is reformulated, through a novel dynamical mean-field approximation, as that of a single chain interacting with a self-consistently determined dynamical mean force-field. A large ensemble of single chain Brownian dynamics simulations, run in parallel, efficiently determines the space- and time-dependent density that is used to weight the Lennard-Jones interaction in the mean force-field calculation. Our theory gives access to chain conformation statistics, maintains a connection to microscopic time-scales and scales favorably with chain-length via a fast Rouse transform. We examine the performance of our method, and discuss our results for the growth of unstable modes in the blend and in the diblock copolymer melt. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y42.00011: Free energies and commensurability effects in simulations of three-dimensional ordered phases of diblock copolymers Taher Ghasimakbari, David Morse We present an approach to the calculation of precise phase boundaries in simulations of diblock copolymer melts that is based on the calculation of free energies by thermodynamic integration. Results of simulations of three dimensionally periodic structures are extremely sensitive to commensurability effects, i.e., to the relationship between the dimensions of the (generally small) periodic simulation cell and the (generally unknown) preferred dimensions of a particular ordered phase. We avoid this by measuring the free energy for each ordered phase of interest using several different simulation sizes to estimate free energies as functions of unit cell size and thereby estimate the optimal cell size and corresponding free energy. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y42.00012: Estimation of $\chi $ parameter from molecular simulations Ashwin Ravichandran, Chau-Chyun Chen, Rajesh Khare The $\chi $ parameter introduced in Flory-Huggins theory is widely used to determine polymer miscibility and its value is generally obtained by fitting to experimental data. In spite of its wide usage, techniques for predicting $\chi $ parameter from the knowledge of molecular structure are not yet well established. In this work, we apply molecular simulations to estimate the value of the $\chi $ parameter for a polymer blend system. In particular, we propose to use the approach suggested by Schweizer {\&} Curro [\textit{Journal of Chemical Physics}, \textbf{91}, 5059 (1989)] which estimates $\chi $ parameter in terms of the direct correlation functions. The $\chi $ parameter thus obtained is related to the molecular structure factor, thereby making comparisons with experiment possible. Molecular dynamics simulations with atomistically detailed models are performed to estimate the value of the $\chi $ parameter. Results will be presented for the application of this formalism to the binary blend of polyisobutylene (PIB) and polybutadiene (PBD) for which experimental data are available [\textit{Industrial {\&} Engineering Chemistry Research}, \textbf{47}, 3551 (2008)]. Finally, important structural features of the condensed phase which influence the value of the $\chi $ parameter will be discussed. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y42.00013: Effects of dipole reorientations on ion solvation in polymer blends and block copolymer melts Issei Nakamura We study the thermodynamic property of ion solvation in polymer blends and block copolymer melts and develop a dipolar self-consistent field theory for polymer mixtures. Our theory accounts for the chain connectivity of polymerized monomers, the compressibility of the liquid mixtures under electrostriction, the permanent and induced dipole moments of monomers, and the resultant dielectric contrast among species. We show nonmonotonic changes in the volume fraction profile and the dielectric function of the polymers with respect to those of simple liquid mixtures. Importantly, the spatial variations near an ion can be at nanometer scales, producing significant differences in the solvation energy among simple liquid mixtures, polymer blends, and block copolymers. Furthermore, we illustrate the oscillatory behavior of the dielectric function near an ion pair and the disparity of the dielectric functions between like and unlike charges. These results depend significantly on the chain length and Kuhn length of the diblock copolymers. [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y42.00014: Interfaces between immiscible large and small block copolymers Russell Spencer, Mark Matsen Experiments and theory have shown that mixtures of short and long symmetric AB diblock copolymers macrophase separate if their sizes differ by more than a factor of about five. Here we examine the interface between the two coexisting phases using self-consistent field theory (SCFT). The presence of periodic order in this phase-separated system confers novelty to this problem, in both potential applications and the challenges involved. This investigation is confined to the simple case of parallel lamellae, as may be found in thin films. Our focus is on the structure and tension of interfaces between coexisting phases, in terms of the relative size of the long and short copolymers. As the blend approaches the critical point, which marks the disappearance of phase separation, the interfacial tension vanishes and the width diverges. When the short polymers are too small for periodic order to be stable in bulk, coexistence exists between long lamellae and disorder; and lamellar order is induced in the disordered phase, close to the interface. [Preview Abstract] |
Friday, March 6, 2015 10:48AM - 11:00AM |
Y42.00015: Tailoring the morphology of polymer blend particles: 3D simulations and linear stability analysis B.S. Sarath Pokuri, Baskar Ganapathysubramanian Polymer blend micro-/nano- particles find a variety of uses in novel applications including electronics, luminescent devices, and drug delivery. Solvent evaporation driven phase separation is one of the easiest way to fabricate these particles. However, tailoring morphology of these particles is still challenging. This has resulted in complex methods to tailor morphology. Understanding how morphology evolves and in particular how phase separation is initiated will provide valuable insight to tune morphologies. We characterize the evolution of morphology during evaporation based phase separation into a finite set of fundamental modes. We approach the problem at two levels of complexity. A full 3D modeling framework describing evaporation induced phase separation is used to model the emulsification process as a function of processing parameters: droplet radius, blend ratio, and evaporation rate. Subsequently, high throughput analysis is enabled by using ideas from linear stability analysis to classify the parameter space by morphology. These complementary analysis allows us to identify a fundamental set of morphology evolution modes and map the set of processing conditions to a unique mode. Ergo, one can gain control over the morphology by regulating the processing conditions. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700