Computational Studies of Polymeric Materials: Dynamics, Structure and Aggregation

Computational studies provide insights into understanding the dynamics, structure, and aggregation of materials, especially if one or all the stages of design, synthesis, testing, and analysis of the system in experiments are energy and cost-inefficient. In this thesis, molecular dynamics simulations were employed to investigate the underlying origins of the complex behavior of two classes of polymeric materials: Pluronic amphiphilic copolymers and cellulose nanocrystals. The amphiphilic nature of triblock ethylene oxide - propylene oxide copolymers, known as Pluronics, confers them a thermo-responsive characteristic that can be harnessed in various industries such as wastewater treatment, drug delivery, and so forth. However, the dependence of the thermo-responsive behaviors, such as critical micelle temperature (CMT), on the copolymers’ composition or size remains unknown. The laborious and costly design-synthesis-test-analysis cycle for optimizing the suitable copolymer for a certain application and wide arrays of degrees of freedom in controlling the Pluronic behavior necessitates the establishment of computational approaches to bridge this knowledge gap. In this thesis, a molecular dynamics model was used to calculate the variation of the propylene oxide trimer partitioning free energy between polar and nonpolar solvents with temperature. The obtained partitioning free energy versus temperature profile was used as the foundation for the development of a coarse-grained model that reproduces this profile. Unlike other coarse-grained models with universal temperaturetransferability limitations, the model developed here accurately captures the thermo-responsive behaviors of Pluronics, such as CMT, and spherical-to-globular micelle shape transition. Although various industries, such as electronics and membrane technologies, leverage the remarkable properties of CNCs, their low dispersibility in nonaqueous media poses significant challenges for their use in organic solvent-based processes, such as graphene ink formulations for printing electronic devices. In this thesis, an MD model was proposed which outperforms many of the previous models in capturing the structural properties of CNCs, such as primary alcohol conformation, hydrogen bond occupancy, crystalline properties, and so forth. Thereafter, the established model was adopted to investigate the origins of the low dispersibility of CNCs in a nonaqueous medium and the impacts of surface functionalizations with the alkyl groups on their aggregation tendency. The model predicted enhanced stability in nonaqueous media by lengthening the size of the alkyl groups, which was corroborated by the experimental findings. Finally, a multiphysics model is proposed for studying the filtration of stabilized 2D materials using cellulose nanocrystals, accurately reproducing experimental data.