CAREER: Chemically specific polymer models with field-theoretic simulations

聚合物是一种长链状分子，是各种技术的基础，从表面活性剂和粘合剂到生物材料和电池。聚合物在柔性电子、有机太阳能电池和下一代过滤膜等新兴技术中也发挥着关键作用。在所有这些应用中，聚合物的化学细节是至关重要的：对聚合物进行微小的化学修饰可以导致材料具有完全不同的性能。不幸的是，很难预测聚合物化学的变化将如何影响最终的材料性能，因此新材料必须通过反复试验来艰苦地优化。该CAREER奖支持开发一种新的计算方法，该方法将利用模拟加速新型聚合物材料的设计。这种新方法的基础依赖于一种替代策略来模拟聚合物，这种策略比现有技术快得多，并且可以实现目前用现有方法难以实现的计算。该项目将扩展这种新方法，包括有关聚合物化学的特定信息，同时保持足够的效率来预测聚合物材料固有的大结构。通过在如此宽的长度范围内准确预测聚合物的结构，这种新的计算工具有可能显著加快现有和新兴应用中新聚合物的设计。该职业奖还支持教育和推广活动，这些活动将在现代计算的多个教育水平上培训学生。这些活动将：(1)发起一个新的编码俱乐部，为中学女生提供编码经验；(2)通过德雷塞尔大学的合作项目，让本科生接触到计算研究；(3)通过在线和免费的讲座和作业，培训研究生进行聚合物模拟。这个教育平台将技术项目的关键要素纳入适合年龄的活动，将发现过程与传播联系起来。技术概述聚合物材料的定义特征之一是长度尺度的层次结构，涉及单体（1nm）、分子（10nm）和介观（100nm）特征之间复杂的相互作用。这种长度尺度的层次结构使得设计新的聚合物材料具有挑战性，因为很难预测在最小长度尺度上的化学变化如何传播到材料的最大长度尺度。在这个项目中，将追求一种新的模拟方法，可以同时解决单体水平的化学和介观长度尺度内的聚合物材料。这种策略的基础是一种新的“多表示”方法，其中基于粒子和场论的模拟被连接到一个统一的框架中。初步结果表明，这种新方法可以使计算速度提高几个数量级，但与现有技术相比，没有近似或信息损失。因此，这个新的框架有可能使目前难以处理的聚合物模拟成为可能，并且可以为单体水平化学如何产生中尺度结构提供新的基本见解。该职业奖支持这种新的模拟方法的发展，将该方法扩展到化学特定的相互作用电位，并将其应用于内在无序多肽。更一般地说，该项目还探索了粒子和基于场的模拟之间的基本交叉点，以及如何将这些方法结合在一起，以方便地获取分子构型、介观结构和自由能。该项目还将推进场论模拟方法，并将导致新的工具和数值方法的发展，这将扩大这一强大而新兴的模拟技术的适用性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYPolymers are long chain-like molecules that underlie diverse technologies ranging from surfactants and adhesives to biomaterials and batteries. Polymers also play a critical role in emerging technologies such as flexible electronics, organic solar cells and next-generation filtration membranes. In all of these applications, the chemical details of the polymers are critical: small chemical modifications to polymers can result in materials with drastically different properties. Unfortunately, it is exceptionally difficult to predict how changes in polymer chemistry will affect the resulting material properties and so new materials must be laboriously optimized through trial-and-error experimentation. This CAREER award supports the development of a new computational method that will accelerate the design of new polymeric materials using simulation. The basis for this new approach relies on an alternative strategy for simulating polymers that is considerably faster than existing techniques and can enable calculations that are currently intractable with existing methods. This project will extend this new method to include specific information about a polymer's chemistry while remaining efficient enough to predict the large structures inherent to polymeric materials. By accurately predicting the structure of polymers across this wide range of length scales, this new computational tool has the potential to significantly accelerate the design of new polymers for both existing and emerging applications.This CAREER award also supports educational and outreach activities that will train students at multiple education levels in modern computation. These activities will: (1) initiate a new coding club to provide coding experiences for middle-school girls, (2) expose undergraduates to computational research through Drexel's co-op program, and (3) train graduate students in polymeric simulations with online and freely accessible lectures and assignments. This educational platform incorporates key elements from the technical project into age-appropriate activities that will link the discovery process with its dissemination. TECHNICAL SUMMARYOne of the defining features of polymeric materials is a hierarchy of length scales that involves a complex interplay between monomer (1 nm), molecular (10 nm) and mesoscopic (100 nm) features. This hierarchy of length scales makes it challenging to design new polymeric materials because it is difficult to anticipate how chemical changes at the smallest length scales will propagate up to the largest length scales in a material. In this project, a new simulation method will be pursued that can simultaneously resolve both monomer-level chemistry and mesoscopic length scales within a polymeric material. The basis for this strategy is a new "multi-representation" approach where particle-based and field-theoretic simulations are linked together into a unified framework. Preliminary results indicate that this new method can accelerate calculations by several orders of magnitude yet involves no approximation or information loss relative to existing techniques. As such, this new framework has the potential to enable polymer simulations that are currently intractable and could provide new fundamental insights into how mesoscale structures emerge from monomer-level chemistry. This CAREER award supports the development of this new simulation method, the extension of the method to chemically specific interaction potentials and its application to intrinsically disordered polypeptides. More generally, this project also explores the fundamental intersections between particle and field-based simulations and how these methods can be combined together to provide facile access to molecular configurations, mesoscopic structure and free energies. This project will also advance the field-theoretic simulation method and will lead to the development of new tools and numerical methods that will broaden the applicability of this powerful, yet nascent, simulation technique.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.