Computationally-Driven Rational Control of Glass Formation in Block Copolymers

该奖项支持采用粗粒度分子动力学模拟来建立控制嵌段共聚物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，嵌段共聚物中的玻璃化转变受到纳米尺度的相分离结构域的影响。正如在聚合物薄膜中一样，预计这些效应会伴随着机械和输运性质的变化。因此，对纳米限制对嵌段共聚物动力学和玻璃形成行为的影响的基本理解可以为合理调整这些材料在从药物释放到膜分离等应用中的性能的新变革方法奠定基础。目前，由于缺乏对决定其大小和方向的分子机制的坚定理解，利用纳米约束效应来设计嵌段共聚物玻璃形成受到阻碍。这项工作将探讨纳米约束对玻璃化转变的影响来自两部分机制的假设：首先，界面上的迁移率因接近或多或少受限的环境而改变；其次，这些迁移率的变化通过合作的片段重排传播到材料中，这是许多玻璃形成材料的动力学特征。通过对珠-弹簧嵌段共聚物的模拟，本研究将实现三个目标：1)通过将玻璃化过渡限制效应与一系列嵌段共聚物的协同运动的程度和性质相关联，确定玻璃化过渡限制效应的明确机制；2)量化玻璃化过渡纳米约束效应对相对块体Tg、块体混相和每个块体玻璃形成脆性的依赖；3)建立合理控制嵌段共聚物玻璃形成行为的新方法：插入调节Tg约束效应的短中间嵌段。由于玻璃化过渡纳米约束效应在广泛的系统中被观察到，通过这项工作获得的对这些效应机理起源的新见解将为纳米结构聚合物系统的设计提供信息，并对从膜到屏障膜到微电子中使用的聚合物纳米结构的应用产生影响。这项研究将与一项新的暑期实习计划相结合，该计划将贫困高中学生与来自类似挑战背景的优秀本科生配对。通过让低收入家庭的学生参加PI小组的带薪实习，该项目将克服贫困青年进入stem职业的障碍，因为他们无力负担无薪实习。通过选择来自同样贫困背景的成功本科生，该项目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研究领导方面的关键经验，并加强对STEM教育过程的参与。该奖项支持计算研究和教育，重点是建立指导“纳米结构嵌段共聚物”合理设计的原则，具有目标的机械，运输和玻璃形成特性。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它们的内部结构是由纳米到几十纳米大小的独立结构域组成的事实。虽然这些结构域各自在化学上与简单的均聚物（如聚苯乙烯）相似，但它们在纳米尺度上的相互接触极大地改变了这些结构域的工程性质。由于嵌段共聚物是下一代水和空气净化技术的关键先进材料，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尺度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，该计划将贫困高中学生与来自类似挑战背景的优秀本科生配对。通过让低收入家庭的学生参加PI小组的带薪实习，该项目将克服贫困青年进入stem职业的障碍，因为他们无力负担无薪实习。通过选择来自同样贫困背景的成功本科生，该项目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研究领导方面的关键经验，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.