Computationally-Driven Rational Control of Glass Formation in Block Copolymers

点击翻译按钮获取中文摘要

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.