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theses

Dissipative Particle Dynamics (DPD) is a mesoscale tool bridging the gap between microscopic atomistic simulation and macroscopic thermophysical modeling. After its interaction parameters are mapped to the Flory-Huggins parameters (Groot and Warren, Journal of Chemical Physics, 1997), DPD has become very popular in studying the selfassembly of polymer and surfactant solution. Although DPD has demonstrated the capability to qualitatively describe the equilibrium morphology of soft matter, quantitative prediction compared with experiments is rarely achieved. The reasons are, non-separately, the ambiguous physical unit interpretations and the case-dependent force field parameterizations. Here we present a scale-bridging method to extract both microscopic and macroscopic information for parameterization. The interaction parameters are calibrated by Monte Carlo simulation and mapped to infinite dilute coefficient of the reference compounds in the coarse grained particles. The robustness and consistency of the parameterization are examined against the experimental micellar properties of several surfactants, by varying coarse grained levels and reference compounds. Modeling dynamic properties in self-assembled materials using DPD is even tricky. A practical example is to model proton transfer of polyelectrolyte membrane (PEM) in the fuel cell, where proton dissociates from the acidic sites of hydrated PEM and transfer within the hydrophilic domain. Such detailed, reaction-like behavior can’t be quantified directly from the simulation due to the simplicity of current DPD model. One would need to either correlate the morphology to the proton diffusivity by empirical equations, or perform inverse mapping and continue with expensive atomistic simulations. Here we present an advanced approach which describes the proton dynamics in water as well as its dissociation equilibrium from the acid. Combined with the scale-bridging parameterization, the model predicts the morphology, water transfer, and proton conductivity of sulfonated polystyrene at several sulfonation and hydration levels, and has very good agreements with experimental measurement and atomistic simulation results.

ETD_6764

Ph.D.

Includes bibliographical references

by Ming-Tsung Lee

doi:10.7282/T34M96H5

ETD doctoral

The author owns the copyright to this work.