Molecular Dynamics Simulations of Micellization in Model Surfactant/CO2 Systems

micelle;supercritcal carbon dioxide;surfactant

Li, Zhengmin ; Carol K. Hall, Committee Chair,Peter K. Kilpatrik, Committee Member,John H. van Zanten, Committee Member,Li, Zhengmin ; Carol K. Hall ; Committee Chair ; Peter K. Kilpatrik ; Committee Member ; John H. van Zanten ; Committee Member

University:North Carolina State University

关键词: micelle;    supercritcal carbon dioxide;    surfactant;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/2274/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

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 n 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 CO₂ (scCO₂) systems to establish the appropriate interaction parameters for a surfactant/scCO₂ system.Next we simulate surfactant/scCO₂ systems and explore the effect of the surfactant mole fraction, packing fraction and temperature on the phase behavior of a surfactant/scCO₂ 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/scCO₂ system and the micelle to unimer transition is located by monitoring the micelle size distribution of the equilibrated surfactant/scCO₂ system.The phase diagram for the surfactant/scCO₂ system and the density dependence of the critical micelle concentration are in qualitative agreement with experimental observations.The phase behavior of a surfactant/scCO₂ 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.