Phase Transitions and Dynamics in Block Copolymers

该奖项支持嵌段共聚物材料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是基于各种形式的自洽场理论。自洽场近似在非常长、非常强重叠的聚合物的极限下是有效的，但忽略了对更短、更强相互作用的聚合物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可以预测所有依赖于重叠程度的物理性质，这些物理性质由无量纲参数量化。对二嵌段共聚物的无序相的模拟已经证实了结构因子的系统的、普遍的行为的预测存在，这种行为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重点将以不同的方式建立在这一进展的基础上。第一个重点是对二嵌段共聚物熔体中相界参数依赖性的综合计算研究，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。本项目旨在利用模拟来生成有限二嵌段共聚物的通用相图。这将以一种方式推广相图，即使对于短的，强相互作用的二嵌段共聚物，也应该允许对相边界进行准确的定量预测。这种方法的显著特点包括开发更复杂的方法来分析模拟结果，以最大限度地减少由于对象象学弗洛里-哈金斯相互作用参数的不完全了解而产生的歧义。第二个重点是利用模拟来研究双嵌段共聚物熔体中的集体动力学现象。具体来说，它将讨论在有序-无序过渡附近的无序阶段的集体动力学，以及有序-无序和有序-有序过渡的动力学和机制。该奖项支持的研究将为培养研究生在尖端计算和理论方法方面提供机会，在一个提供丰富的聚合物科学实验方面的环境中。该奖项还支持开发、记录和传播开源计算软件，用于基于粒子的模拟和自洽场计算，这有助于软材料研究社区的网络基础设施。该奖项支持旨在促进对长链状分子、聚合物制成的材料的理解的计算研究。嵌段共聚物是由不同化学性质的线性嵌段或亚链组成的聚合物。一个线性聚合物链，包含两个这样的A和B单体，通过它们的末端连接在一起形成一个更大的链（AB），被称为双嵌段共聚物。在由纯A链和纯B链组成的液体混合物仍然是液体的温度下，二嵌段共聚物形成周期性有序的结构。这些周期性结构的自发形成是由不同的嵌段相分离的趋势驱动的，并且两个嵌段相互之间的共价键抑制了宏观相分离。这些有序的结构材料被用作水净化的膜，以及微电子和存储设备的模板材料。研究表明，当以正确的方式解释时，不同种类的二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二嵌段共聚物材料的基本理解的研究，并有助于设计具有新应用所需性能的新型二嵌段共聚物材料的能力。PI将通过量化计算机模拟中观察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做出更准确的预测。本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。该奖项还支持开源软件的开发、文档和传播，为软材料研究社区的网络基础设施做出贡献。

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.