Molecular Dynamics Simulations of Micellization in Model Surfactant/CO2 Systems

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Title: Molecular Dynamics Simulations of Micellization in Model Surfactant/CO2 Systems
Author: Li, Zhengmin
Advisors: Carol K. Hall, Committee Chair
Peter K. Kilpatrik, Committee Member
John H. van Zanten, Committee Member
Abstract: Discontinuous molecular dynamics simulations are performed on surfactant (H[subscript n] T[subscript m])/solvent systems modeled as a mixture of single-sphere solvent molecules and freely-jointed surfactant chains composed of <i>n</i> slightly solvent-philic head spheres (H) and m solvent-philic tail spheres (T), all of the same size. We use a square-well potential to account for the head-head, head-solvent, tail-tail and tail-solvent interactions and a hard sphere potential for the head-tail and solvent-solvent interactions. We first simulate homopolymer/supercritical CO&#8322; (scCO&#8322;) systems to establish the appropriate interaction parameters for a surfactant/scCO&#8322; system. Next we simulate surfactant/scCO&#8322; systems and explore the effect of the surfactant mole fraction, packing fraction and temperature on the phase behavior of a surfactant/scCO&#8322; system. The transition from the two-phase region to the one-phase region is located by monitoring the contrast structure factor of the equilibrated surfactant/scCO&#8322; system and the micelle to unimer transition is located by monitoring the micelle size distribution of the equilibrated surfactant/scCO&#8322; system. The phase diagram for the surfactant/scCO&#8322; system and the density dependence of the critical micelle concentration are in qualitative agreement with experimental observations. The phase behavior of a surfactant/scCO&#8322; system can be directly related to the solubilities of the corresponding homopolymers that serve as the head and tail block for the surfactant. The location of the micelle-unimer transition is strongly affected by the head-solvent attraction but only weakly affected by the tail-tail and tail-solvent attractions. Both micellization and phase separation upon decreasing the temperature are found in our simulations.
Date: 2003-04-22
Degree: MS
Discipline: Chemical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/2274


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