Phase Transitions and Dynamics in Block Copolymers

技术概述该奖项支持对嵌段共聚材料的平衡行为和动力学的计算研究，旨在确定普遍行为。长期以来，对这些材料的平衡行为的理解一直基于各种形式的自洽场理论。自洽场近似在很长、很强重叠的聚合物的极限中是有效的，但忽略了对较短、更强相互作用的聚合物具有非常重要影响的强集体关联。超越自洽场近似的更复杂的粗粒度理论产生了对所有物理性质的预测，这些预测取决于重叠的程度，正如无量纲参数所量化的那样。对两嵌段共聚物无序相的模拟已经证实了预测的结构因子的系统的、普遍的行为的存在，现在可以用最近发展的理论来定量描述。该奖项支持的两个研究项目将以不同的方式建立在这一进展的基础上。第一个项目是对两嵌段共聚物熔体中相界面的参数相关性进行全面的计算研究，使用图形处理器单元加速模拟和自由能方法精确识别相界面。该项目旨在使用模拟来生成有限两嵌段共聚物的通用相图。这将以一种允许准确定量预测相边界的方式来概括相图，即使对于短的、强相互作用的两嵌段共聚物也是如此。这种方法的显著特点包括开发了更复杂的方法来分析模拟结果，以最大限度地减少由于对唯象Flory-Huggins相互作用参数的不完善了解而产生的模棱两可。第二个重点是使用模拟来研究两嵌段共聚物熔体中的集体动力学现象。具体地说，它将讨论有序-无序转变附近无序阶段的集体动力学，以及有序-无序和有序-有序转变的动力学和机制。该奖项支持的研究将为研究生提供在提供丰富的聚合物科学实验方面的接触的环境中培训尖端计算和理论方法的机会。该奖项还支持开发、记录和传播用于基于粒子的模拟和自洽场计算的开源计算软件，这有助于软材料研究界的网络基础设施。非技术概述该奖项支持旨在促进对长链状分子和聚合物材料的理解的计算研究。嵌段共聚物是由不同化学组成的线性嵌段或子链组成的聚合物。包含A和B单体的两个这样的嵌段，通过它们的末端结合在一起形成更大的链(AB)的线形聚合物链被称为两嵌段共聚物。在纯A链和纯B链组成的液体混合物仍为液体的温度下，两嵌段共聚物形成周期性有序结构。这些周期性结构的自发形成是由不同块体的相分离倾向以及宏观相分离被两个块体之间的共价键抑制的事实所驱动的。这些有序结构材料被用作净水膜，以及微电子和存储设备的模板材料。研究表明，如果以正确的方式解释，不同类型的两嵌段共聚物表现出几乎相同的行为。该奖项支持旨在促进对两嵌段共聚物材料的基本了解的研究，并将有助于为新的应用设计具有所需性能的新的两嵌段共聚物材料的能力。PI将通过量化计算机模拟中看到的行为如何依赖于链之间的相互作用，来研究是否有可能对真实系统进行更准确的预测。这项研究的一个主要目标是使用计算机模拟来生成与化学结构和链相互作用相关的结构转换图。该奖项还支持开放源码软件的开发、记录和传播，这些软件有助于软材料研究社区的网络基础设施。

Technical SummaryThis award supports computational studies of the equilibrium behavior and dynamics of block copolymer materials aimed to identify universal behavior. Understanding the equilibrium behavior of these materials has long been based on various forms of self-consistent-field theory. The self-consistent-field approximation is valid in the limit of very long, very strongly overlapping polymers, but neglects strong collective correlations that have very important effects for shorter, more strongly interacting polymers. More sophisticated coarse-grained theories beyond self-consistent-field approximations yield predictions for all physical properties that depend upon the degree of overlap, as quantified by a dimensionless parameter. Simulations of the disordered phase of diblock copolymers have confirmed the predicted existence of systematic, universal behavior of the structure factor that can now be quantitatively described by recently developed theories. Two research thrusts supported by this award will build upon this progress in different ways.The first thrust is a comprehensive computational study of the parameter dependence of phase boundaries in diblock copolymer melts, using graphics processor unit accelerated simulations and free energy methods to precisely identify phase boundaries. This project aims to use simulation to produce a universal phase map for finite diblock copolymers. This will generalize the phase map in a manner that should allow accurate quantitative predictions of phase boundaries even for short, strongly interacting diblock copolymers. Distinctive features of this approach include development of more sophisticated methods for analyzing simulation results in order to minimize ambiguities that arise from imperfect knowledge of the phenomenological Flory-Huggins interaction parameter.The second thrust focuses on the use of simulations to study collective dynamical phenomena in diblock copolymer melts. Specifically, it will address collective dynamics in the disordered phase near the order-disorder transition, and the dynamics and mechanisms of order-disorder and order-order transitions. The research supported by this award will provide opportunities for training graduate students in cutting edge computational and theoretical methods in an environment that provides rich exposure to experimental aspects of polymer science. This award also supports the development, documentation, and dissemination of open source computational software for both particle-based simulations and self-consistent field calculations, which contributes to the cyberinfrastructure of the soft-materials research community.Nontechnical Summary This award supports computational studies aimed to advance understanding of materials made from long chain-like molecules, polymers. Block copolymers are polymers comprised of linear blocks or subchains of different chemistry. A linear polymer chain, that contains two such blocks, of A and B monomers, bonded together by their ends forming a bigger chain (AB), is called a diblock copolymer. At temperatures at which mixtures of liquids composed of pure A and pure B chains would still be a liquid, diblock copolymers form periodically ordered structures. Spontaneous formation of these periodic structures is driven by the tendency of different blocks to phase separate, and by the fact that macroscopic phase separation is suppressed by the covalent linkage of the two blocks with each other. These ordered structural materials found applications as membranes for water purification, and as template materials for microelectronics and storage devices. Studies suggest that diverse kinds of diblock copolymers display nearly identical behavior when interpreted in the correct way. This award supports research aimed to advance fundamental understanding of diblock copolymer materials and would contribute to the ability to design new diblock copolymer materials with desired properties for new applications.The PI will investigate whether much more accurate predictions might be possible for real systems by quantifying how the behavior seen in computer simulations depends on interactions between chains. A primary goal of this research is to use computer simulations to generate a map of structural transformations as related to chemical structure and chain interactions. This award also supports the development, documentation, and dissemination of open source software that contributes to the cyberinfrastructure of the soft-materials research community.