Developing Local Order Parameters for Order-Disorder Transitions From Particles to Block Copolymers: Application to Macromolecular Systems

AJ Mukhtyar and FA Escobedo, MACROMOLECULES, 51, 9781-9788 (2018).

DOI: 10.1021/acs.macromol.8b01683

In part 1 of this two-paper series, a local order parameter framework was put forth that could track the changes occurring when block copolymer-like mesophases formed from a disordered state. The framework was developed using a two-particle model and involved identifying the local symmetries and geometric motifs that were unique to a given mesophase. In this paper, this framework is suitably modified to track the mesophase formation of standard coarse-grained bead-spring simulation models of polymers and oligomers. In particular, a mesoscale chain model typically employed with dissipative-particle dynamics is used to study the ordering transition of a linear symmetric diblock copolymer into a lamellar phase, and a more detailed bead-spring model of branched bolaamphiphile molecules is used to track the formation of a single diamond phase. These applications illustrate the robustness of the method in handling molecules with intramolecular degrees of freedom (including multiple chemical blocks and branched architectures), varying levels of coarse graining, and rare mesophases with complex 3D order (like the single diamond phase). These features are suggestive of the potential suitability of the proposed framework as a tool to map transition pathways leading to complex macromolecular morphologies.

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