Free Energy And Phase Equilibrium Calculations On Surfactant Self-assemblies

Surfactants are among the most versatile chemicals for academic,industrial and consumer applications.The function is usually characterized by the decrease of interfacial tension,alteration of surface activity,promotion of emulsification,etc.All the useful features are closely related to several key properties of surfactant,e.g.equilibrium surface concentration,critical micelle concentration,micelle size distribution.However,experimental methods are not effective enough to measure all these properties accurately,unable to gain microscopic insight of the mechanism.The thermodynamic properties can also be predicted from theoretical models.And as the rapid development of computational skills,molecular simulation has become another powerful tool to calculate thermodynamic properties and simulate complex systems.In this work,I applied molecular simulation techniques combined with thermodynamics theory to study a number of key problems in the field of surfactant self-assembly.1)Using the thermodynamic integration method combined with thermodynamics theory to calculate the chemical potentials of surfactant on surface and in bulk,I predicted the partition of surfactants between the two phases which is consists with experiments.2)I improved a thermodynamic relationship proposed previously in the literature by removing an empirical parameter,and used the new relationship to predict the CMCs and micelle size distributions of nonionic surfactants solely based on computed data,and the results agree well with the experimental data.3)I explored the feasibility of using Hamiltonian Replica Exchange Molecular Dynamics to simulate the micelle formation process of surfactants.The simulation shows that the efficiency of molecular dynamics simulation can be significantly improved using the enhanced sampling technique and the sampled results are in line with long-time regular molecular dynamics simulation.4)As a part of the 9^th Industrial Fluid Properties Simulation Collective,I applied molecular dynamics to calculate oil/water interfacial tensions at high temperatures and pressure using all-atomic force field and the results are in close agreement with the experimental data.The work summarized in this thesis is of practical and theoretical interests to the research field of self-assembly in soft matters.