Molecular Simulations On Proton Exchange Membrane And Surfactant Systems

In this thesis, we have studied the applications of polymer and surfactant with the force field as the core. The research topics involve the establishment of fragment rule in force field, water storage calculation of polymer, predictions of surface tension and foam stability. The employed computational methods include ab initio quantum chemistry theory and molecular dynamics method. The contents of this work are as follows:1. To establish a transferable force field, we studied different functional groups'effect to chemical environment with quantum chemistry calculation. Through comparisons of bond, bond order and charge, we established the fragment rule and provided the possibility to make transferable force field and build database of force field.2. STPES(Sulfonated polyarylenethioethersulfone) is one of proton exchange membranes which has been synthesized recently. It may replace Nafion and have big commercial value with good heat and mechanical stability, excellent property of proton transfer and small toxicity. First, we developed the force field of this polymer with ab initio quantum chemistry theory and carried out the molecular simulations. Many properties were prepared to the Nafion and water storage was also predicted. We found that STPES had the more water storage capability than Nafion though the analysis of density, radium distribution function and excess potential.3. Surfactant is one molecule which has both hydrophilic and hydrophobic group and it plays a key role in daily life and industry such as cleaning, food processing, cosmetics and petroleum abstraction. The surfactant behaviors at the air-water interface affects application. We used fragment rule to develop force field of alkyl benzene sulfonic acid. Then we compared the differences of these surfactant isomers which have different attachment to the carbon chain.4. Water hardness ions may affect applications of surfactant. As we know, there is not any theoretical research about how water hardness ions affect the behaviors of surfactant. We made simulation of 12phenylLAS to study the effect of water hardness ions with the guide of surface tension. Surface tension, density distribution, number density distribution, charge distribution, radium distribution function, diffusion and conformers of carbon chain have been analyzed to study the effect of Ca and Mg ions.5. Foam stability is also important in research. There are many experimental results while there is few theoretical work. Through building stretching model, we directly simulated the critical thickness of foam with surfactants. Density distribution, system potential and surface tension were analyzed to judge whether the foam broke. The behaviors of surfactant were also studied when the foam broke.