Simulation of bicontinuous phase formation in additive-filled and shape-asymmetric diblock copolymers

本项目的目标是使用分子模拟来(1)量化聚合物和纳米颗粒添加剂对线性两嵌段共聚物(DBC)中双连续相的起始和结构的影响，以及(2)阐明DBC链段之间的熵差异对双连续相行为的影响。第一个目标是了解对给定块具有选择性亲和力的添加剂将如何分布和改变复杂DBC双连续相的结构(如回转体、双钻石和少数组分块形成两个交织的3D网络的管道噩梦相)；可以预见，适当选择添加剂类型、大小、亲和力和浓度可以抑制或稳定特定的双连续相。因此，一个具体的目的是阐明最优添加剂的设计(例如，在尺寸和拓扑结构上)，以最大化目标双连续相的稳定性的组成范围。还将调查竞争共连续阶段(其少数块形成单个3D网络的阶段)的存在。我们的第二个目标是系统地量化块厚度和主干灵活性的差异对双连续相行为的影响。非热分子在厚度(形状)和硬度方面存在固有差异，可能导致不对称堆积相互作用，即粒子两端之间的有效“排斥”，这可能导致类似于传统DBCS(具有能量块间差异)的相行为。将有一项关于如何设计系统的调查，在该系统中，熵而不是能量将成为不同双连续相组装的主要驱动力。从通过晶格上蒙特卡罗模拟和连续空间蒙特卡罗模拟以及分子动力学模拟对纯DBCS的双连续相进行分析开始，开展了以下工作：(I)确定不同尺寸和结构的选择性添加剂(聚合物和纳米颗粒)对这种双连续相的影响，特别是在颗粒集中区域，(Ii)模拟具有不同嵌段亲和力、灵活性和厚度的DBC类分子的非晶格粗晶模型，以确定这种变化如何影响相行为，以及如何利用它们来稳定不同的双连续相。为了绘制可靠的相图和改进遍历采样，使用并进一步发展了几种蒙特卡罗方法；特别是优化的展开和用于测量自由能和化学势平衡的密集技术。广泛的影响这项研究提供了相图，这些相图将作为“路线图”，不仅可以用来将模拟与实验数据相关联，还可以指导未来的实验工作，走向更有技术针对性的系统。鉴于当今合成具有精确结构和组成的共聚物以及有机-无机杂化材料和纳米颗粒的前所未有的能力，更好地从微观上了解包含这些构建块的流体的结构和相行为，可以为未来应用的新材料的合理设计提供更合理的基础，包括燃料电池等储能设备。PI与康奈尔大学的一个实验小组的密切合作提供了模拟和实验努力之间的协同作用，我们的发现也将在实验聚合物化学家社区中传播。通过康奈尔大学每年一度的聚合物推广计划研讨会，向业界传播研究成果。主要的教育结果将是培训一名博士生，该博士生也将成为康奈尔大学一个实验小组的纽带。此外，预计至少有一名来自不同大学的本科生研究人员将在一个夏天通过CCMR(康奈尔材料研究中心)的REU计划参与这个项目，另一名康奈尔大学的本科生将在两个常规学期内从事这一项目。这项研究的结果将至少用于两节课：分子模拟新课程和高级热力学核心课程。

CBET-0756248EscobedoIntellectual MeritThe goal of this project is to use molecular simulation to (1) quantify the impact of polymeric and nanoparticle additives on the onset and structure of bicontinuous phases in linear diblock copolymers (DBC), and (2) elucidate the effect of entropic disparities between blocks of DBC chains on the behavior of bicontinuous phases. The first goal is focused on understanding how additives with selective affinity for a given block will distribute and modify the structure of complex DBC bicontinuous phases (like the gyroid, double diamond, and plumbers nightmare phases where the minority component block forms two interweaving 3D networks); it is envisioned that a suitable choice of additive type, size, affinity, and concentration may suppress or stabilize a particular bicontinuous phase. A specific aim is thus to elucidate the design of optimal additives (e.g., in size and topology) that maximize the composition range of stability of a target bicontinuous phase. The existence of competing co-continuous phases (those whose minority block forms a single 3D network) will also be investigated. Our second goal is to systematically quantify the effect of disparities in block thickness and backbone flexibility on bicontinuous phase behavior. Athermal molecules having intrinsic disparities in thickness (shape) and stiffness can lead to asymmetricalpacking interactions, i.e., an effective "repulsion" between opposite ends of the particles which could give rise to a phase behavior akin to that of conventional DBCs (that have an energetic inter-block disparity). There will be an investigation as to how to design systems where entropy, as opposed to energy, would be the main driving force underlying the assembly of different bicontinuous phases. Starting from the analysis of bicontinuous phases of pure DBCs via both on-lattice Monte Carlo simulations and continuum space Monte Carlo and molecular dynamics simulations, the following tasks are carried out: (i) determining the effect of selective additives (polymers and nanoparticles) of different sizes and structure on such bicontinuous phases, particularly in the particle-concentrated regime, (ii) simulating off-lattice coarse-grained models of DBC-like molecules with varying disparities in block affinity, flexibility, and thickness (pure and with additives) to determine how such changes affect the phase behavior and how they could be exploited to stabilize different bicontinuous phases. To map out reliable phase diagrams and improve ergodic sampling, several Monte Carlo methods are used and further developed; in particular, optimized expandedensemble techniques for measuring free-energies and for chemical potential equilibration.Broader ImpactsThis investigation provides phase diagrams that will serve as "road maps" which could not only be used to correlate simulations with experimental data but also to guide future experimental efforts toward more technologically targeted systems. Given Today's unprecedented ability to synthesize copolymers of precise architecture and composition as well as hybrid organic-inorganic materials and nanoparticles, a better microscopic understanding of the structure and phase behavior of fluids containing these building blocks could provide a sounder basis for rational design of new materials for future applications, including energy-storing devices like fuel cells. The close collaboration of the PI with an experimental group at Cornell provides the synergy between simulation andexperimental efforts and that our findings will also be disseminated within the community ofexperimental polymer-chemists. Dissemination of results to industry is made through Cornell's annual Polymer Outreach Program symposium. The main educational outcome will be the training of a Ph.D. student who will also serve as a link with an experimental group at Cornell. In addition, it is expected that al least one undergraduate researcher from a different university will work on this project during a Summer via the REU program of CCMR (Cornell Center for Materials Research) and another Cornell undergraduate during two regular Semesters. Results of this investigation will be used in at least two classes: a new course on molecular simulations, and the advanced thermodynamics core course.