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

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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.