Rapid Quench Structure Formation: Fabrication of periodic network morphologies and their stabilization via crosslinking in diblock copolymers

嵌段共聚物的周期性网络形态(PNM)因其良好的力学性能和较高的界面体积比而引起了人们的广泛关注。然而，它们通常只是亚稳态的，传统的策略旨在通过多分散或共混来减少堆积受挫，从而提高它们的热力学稳定性。我们建议通过重复地将结构形成的动力学指向所需的亚稳态形态并通过后续的交联来稳定它来制备PNM。我们的策略依赖于(I)热力学状态的快速变化(猝灭)，(Ii)热力学驱动的结构从失稳后的高度不稳定的形态形成为亚稳态网络结构，以及(Iii)通过热激活的形核从亚稳态逃逸到平衡之间的时间尺度分离。利用基于粒子的软模型的计算机模拟和数值自洽场(SCF)计算，我们将研究快速猝灭(例如，分子结构的变化或压力跳跃)后的自由能格局，并探索可获得的亚稳态形态。我们的研究将采用两种最近发展的计算技术：(I)场论伞形采样将允许我们将基于粒子的模拟模型的自由能构造为片段物种密度(序参数)的泛函。(Ii)使用改进的弦方法，我们将得到从不稳定的初始态通过亚稳态的PNM到平衡的最小自由能路径，并设计过程来优化所需中间体中的捕获。将SCF理论的预测与基于粒子的结构形成模拟进行比较，以评估热涨落的作用以及链构象与瞬时密度分布平衡的假设。将设计出通过交联剂稳定PNM的有效策略。

Periodic network morphologies (PNM) of block copolymers have attracted abiding interest because of their beneficial mechanical properties and high interface-to-volume ratio. However, they are often only metastable, and traditional strategies aim at increasing their thermodynamic stability by mitigating packing frustration via polydispersity or blending.We propose to fabricate PNM by reproducibly directing the kinetics of structure formation towards the desired metastable morphology and stabilizing it by subsequent crosslinking. Our strategy relies on the time scale separation between (i) the rapid change of thermodynamic state (quench), (ii) the thermodynamically driven structure formation from the highly unstable morphology after the quench to the metastable network structure, and (iii) the escape from the metastable state to equilibrium via thermally activated nucleation.Using computer simulation of a soft, particle-based, coarse-grained model and numerical self-consistent field (SCF) calculations we will study the free-energy landscape after a rapid quench (e.g., transformation of molecular architecture or pressure jump) and explore the accessible metastable morphologies. Our study will employ two recently developed computational techniques: (i) Field-theoretic umbrella sampling will allow us to construct the free energy of a particle-based simulation model as a functional of the densities of the segment species (order parameter). (ii) Using the improved string method we will obtain the minimum free-energy path from the unstable initial state via the metastable PNM to equilibrium and design the process to optimize the trapping in the desired intermediate. The predictions of SCF theory will be compared with particle-based simulations of structure formation in order to assess the role of thermal fluctuations and the assumption that the chain conformations be in equilibrium with the instantaneous density distribution. Efficient strategies for stabilizing the PNM via crosslinking will be devised.