Research On Surfactant Self-Assembly Using Molecular Dynamics And Construction Of Web Force Field Repository

With the rapid advancement of computer technology and molecular simulation theory,the force field simulation method is widely applied on many large scale simulation systems such as protein folding,molecule self-assembly and etc.In this thesis,we have studied the surfactant properties both on surface and in bulk,and the impact of additives on surfactant self-assembly using molecular dynamics simulation method.Meanwhile,we have explored the importance of construction of a web-based force field repository for applications.The significance of this thesis is to probe the process of self-assembly at molecular level,enhance the force field capacity,and enable force field distribution and re-usability.The research topics involve predicting surface concentration and surface tension of surfactants and research on the distribution of micelle during self-assembly,impact on dynamics of surfactant self-assembly with additives and research on morphology and size effect of micelle,and on development of a force field repository.Three ionic surfactants(SHS,SNS and SDS)with different carbonic chain length were studied.The bilayer model was constructed using reasonable partition derived from chemical potentials for simulating surface and bulk properties simultaneously.The results show that after saturation on the surface,the surface concentration and surface tension can be predicted well.Continuing to add surfactants,aggregations in bulk and the distributions of micelle size agree well with the experiment.At last,by counting the free surfactants,the critical micelle concentration(CMC)was calculated.The longer carbonic chain is,the larger deviation with experiment will be.Eight fragrance molecules with wide range of Log P were chosen as additives.Based on the all-atom simulation result and thermodynamic experimental data,the coarse-grained force field for fragrances was developed,and then it was applied on selfassembly to investigate the effect of fragrances.From the simulations,we found fragrance could speed up the initial aggregation process,and after equilibrium,the partition between surfactants and fragrances in micelle was obtained.The size of micelle was predicted with/without fragrances using free energy calculations.The results demonstrate that hydrophilic fragrance has negative effect and hydrophobic fragrance has positive effect on the size of micelle.Finally,the distribution of fragrances in micelle was analyzed and the results agree with that obtained using SAXS measurement.The morphology of micelle was also calculated and it showed that with the added fragrance,the micelle became more ellipsoidal.For enable reuse and distribution of force fields developed,we constructed a webbased force field repository.In this framework,force field searching and parameter assigning for given molecule is done automatically,adding or updating force field parameters are supported.The repository provides a platform for sharing and communicating among molecular modelers.Examples of using the repository are presented.