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高的界面体积比而引起人们的广泛关注。然而，他们往往只是亚稳态的，和传统的策略，旨在通过减轻包装挫折通过多分散性或blending.We建议制造PNM可重复地引导结构形成的动力学向所需的亚稳态形态和稳定它通过随后的交联增加其热力学稳定性。我们的策略依赖于（i）热力学状态的快速变化（淬火），（ii）淬火后从高度不稳定形态到亚稳网络结构的热驱动结构形成，以及（iii）通过热激活成核从亚稳状态逃逸到平衡之间的时间尺度分离。粗粒度模型和数值自洽场（SCF）计算我们将研究快速淬火后的自由能景观（例如，分子结构的转变或压力跃变）并探索可接近的亚稳态形态。我们的研究将采用两个最近开发的计算技术：（i）场论伞采样将使我们能够构建基于粒子的模拟模型的自由能作为片段物种密度（序参数）的函数。 (ii)使用改进的弦方法，我们将获得从不稳定的初始状态，通过亚稳态PNM平衡的最小自由能路径和设计的过程，以优化在所需的中间体的捕获。SCF理论的预测将与基于粒子的结构形成模拟进行比较，以评估热波动的作用和链构象与瞬时密度分布平衡的假设。将设计用于通过交联稳定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.