Computationally-Driven Rational Control of Glass Formation in Block Copolymers

技术概述该奖项支持使用粗粒度分子动力学模拟来建立能够控制嵌段共聚玻璃形成行为的基本设计原则的研究。几十年来的研究结果强调，嵌段共聚物的玻璃化转变受纳米尺度的相分离区域的特征存在的巨大纳米限制效应的影响。正如在聚合物薄膜中一样，预计这些效应会伴随着机械和传输特性的变化。因此，对嵌段共聚物的动力学和玻璃形成行为的纳米限制效应的基本了解可以形成一种新的变革性方法，以合理地调节这些材料在从药物释放到膜分离的应用中的性能。目前，由于缺乏对决定其大小和方向的分子机制的确切了解，利用纳米限制效应来设计嵌段共聚玻璃的形成受到了阻碍。这项工作将探索这样一个假设，即纳米限制对玻璃转变的影响来自两个部分的机制：第一，界面上的迁移率因接近或多或少受限的环境而改变；第二，这些迁移率的变化通过合作的分段重排传播到材料中，这在许多玻璃形成材料中是动力学的特征。通过对微珠-弹簧嵌段共聚物的模拟，本研究将实现三个目标：1)通过将玻璃化转变限制效应与一系列嵌段共聚物中的协同运动的程度和性质相关联来确定玻璃转变限制效应的明确机制；2)量化玻璃化转变纳米限制效应与相对嵌段Tg、嵌段的可混性以及各嵌段玻璃形成的脆性的依赖关系；3)建立了一种合理控制嵌段共聚物玻璃形成行为的新方法：插入一个调节玻璃化温度限制效应的短中间块。由于玻璃化转变纳米限制效应在广泛的体系中都可以观察到，通过这项工作获得的对这些效应的机制起源的新见解将普遍地指导纳米结构聚合物系统的设计，其应用范围从膜到阻挡膜到微电子学中的聚合物纳米结构。这项研究将与一项新的暑期实习计划相结合，该计划将贫困高中生与来自类似挑战背景的优秀本科生配对。通过面向低收入学生提供PI小组的带薪实习机会，该计划将克服贫困青年因无力支付无薪实习费用而进入STEM职业生涯的障碍。通过挑选来自类似贫困背景的成功本科生，该计划将为面临相当大挑战的高中生提供STEM职业生涯的关键榜样，同时为来自代表性不足背景的优秀本科生提供关键的研究领导经验，并加强对STEM教育过程的参与。非技术概述该奖项支持计算研究和教育，重点是建立指导合理设计具有针对性的机械、运输和玻璃形成特性的“纳米结构嵌段共聚物”的原则。与更简单的“均质”材料不同，嵌段共聚物的性质本质上反映了这样一个事实，即它们的内部结构由单独的结构域组成，这些结构域的大小通常是纳米到几十纳米。虽然这些结构域本身在化学上类似于简单的均聚物(如聚苯乙烯)，但它们在纳米尺度上的相互接触强烈地改变了这些结构域的工程性质。由于嵌段共聚物是解决水和空气净化等应用的下一代技术的关键先进材料类别，因此了解和控制这些变化至关重要。通过对模型嵌段共聚物进行分子动力学计算机模拟，这项工作将清楚地建立在分子水平上控制这些效应的基本机制。这项研究将与一项新的暑期实习计划相结合，该计划将贫困高中生与来自类似挑战背景的优秀本科生配对。通过面向低收入学生提供PI小组的带薪实习机会，该计划将克服贫困青年因无力支付无薪实习费用而进入STEM职业生涯的障碍。通过挑选来自类似贫困背景的成功本科生，该计划将为面临相当大挑战的高中生提供STEM职业生涯的关键榜样，同时为来自代表性不足背景的优秀本科生提供关键的研究领导经验，并加强对STEM教育过程的参与。

Technical summaryThis award supports research employing coarse-grained molecular dynamics simulations to establish fundamental design principles enabling control of block copolymer glass formation behavior. Results over several decades emphasize that the glass transition in block copolymers is subject to large nanoconfinement effects due to the characteristic presence of phase-separated domains with nanometer size-scales. As in polymer thin films, it is expected that these effects are accompanied by changes in mechanical and transport properties. A fundamental understanding of nanoconfinement effects on the dynamics and glass formation behavior of block copolymers could thus form the basis for a new transformative approach to rationally tuning the performance of these materials in applications ranging from drug release to membrane separations. Presently, the use of nanoconfinement effects to engineer block copolymer glass formation is hampered by the lack of a firm understanding of the molecular mechanisms determining their magnitude and direction. This work will explore the hypothesis that nanoconfinement effects on the glass transition emerge from a two part mechanism: first, mobility at the interface is altered by close proximity to a more or less restrictive environment; second, these mobility changes propagate into the material via cooperative segmental rearrangements that are characteristic of dynamics in many glass-forming materials. By employing simulations of bead-spring block copolymers, this research will accomplish three goals: 1)Determine a clear mechanism for glass transition confinement effects by correlating them with the extent and nature of cooperative motion in a range of block copolymers;2)Quantify the dependence of glass transition nanoconfinement effects on relative block Tg, block miscibility, and fragility of glass formation of each block;3)Establish a new method for rational control of block copolymer glass formation behavior: the insertion of a short intermediate block that tunes Tg confinement effects.Since glass transition nanoconfinement effects are observed in a broad range of systems, the new insights into the mechanistic origin of these effects obtained through this work will inform the design of nanostructured polymeric systems generally, with an impact on applications ranging from membranes to barrier films to polymeric nanostructures employed in microelectronics. This research will be integrated with a new summer internship program pairing underprivileged high-school students with outstanding undergraduate students from similarly challenged backgrounds. By targeting low-income students for paid internships in the PI's group, this program will overcome the barrier to entry of underprivileged youth into stem careers presented by their inability to afford unpaid internships. By selecting successful undergraduate students from similarly underprivileged backgrounds, this program will provide a high school student facing considerable challenges with a key role model towards a STEM career, while providing outstanding undergraduates from underrepresented backgrounds with key experience in research leadership and enhanced engagement in the STEM educational process. Non-technical summaryThis award supports computational research and education focused on establishing principles guiding the rational design of "nanostructured block copolymers" with targeted mechanical, transport, and glass formation properties. Unlike simpler, "homogenous" materials, block copolymers' properties intrinsically reflect the fact that their internal structure is comprised of separate domains that are often nanometers to tens of nanometers in size. While each of these domains, on its own, is chemically similar to a simple homopolymer (such as polystyrene), the domains' engineering properties are strongly altered by their mutual contact at the nanoscale. Because block copolymers are a key class of advanced materials for next-generation technologies addressing applications such as water and air purification, understanding and controlling these changes is essential. By performing molecular dynamics computer simulations of model block copolymers, this work will clearly establish the fundamental mechanisms controlling these effects at a molecular scale. This research will be integrated with a new summer internship program pairing underprivileged high-school students with outstanding undergraduate students from similarly challenged backgrounds. By targeting low-income students for paid internships in the PI's group, this program will overcome the barrier to entry of underprivileged youth into stem careers presented by their inability to afford unpaid internships. By selecting successful undergraduate students from similarly underprivileged backgrounds, this program will provide a high school student facing considerable challenges with a key role model towards a STEM career, while providing outstanding undergraduates from underrepresented backgrounds with key experience in research leadership and enhanced engagement in the STEM educational process.