Peng Yang Thesis Defense 09/16/14

Thesis Defense

Peng Yang

Tuesday, September 16, 2014
9:30AM (206 JFB)

Title: A Molecular Dynamics Simulation Study of Dynamics Process and Mesoscopic Structure in Liquid Mixture System

The focus of this thesis is the computer simulation study (in our case, Molecular Dynamics (MD) simulation) of two different systems. First, we study the dynamic process of graphene exfoliation: graphene dispersion using ionic surfactants. Second, we investigate the mesoscopic structure of binary solute/ionic liquid (IL) mixtures through the comparison between simulations and corresponding experiments.

In the graphene separation study, we consider two separation mechanisms: changing the interlayer distance and sliding away the relative distance of two single-layer graphene sheets. By calculating the energy barrier as a function of separation (interlayer or sliding-away) distance and performing sodium dodecyl sulfate (SDS) structure analysis around graphene surface at different surface-coverage concentration of SDS surfactant/water + bilayer graphene mixture systems, we find that the sliding-away mechanism is the dominant, feasible separation process, in which SDS-graphene interaction gradually replaces the graphene-graphene Van der Waals (VdW) interaction, decreases the energy barrier until almost zero at critical SDS concentration. In the work of solute/IL study, we investigate nonpolar solute (CS_2 )/IL and dipolar molecules (CH_3 CN)/IL mixture systems. MD simulation shows that at low concentrations, IL is nano segregated into an ionic network and nonpolar domain, CS_2 molecules tend to be localized into the nonpolar domain, while CH_3 CN interacts with nonpolar domain as well as with the charged head groups in the ionic network because of its amphiphilicity. At high concentrations, CH_3 CN molecules eventually disrupt the nanostructural organization.

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