Molecular Dynamics Simulation Of Solid Selective Adsorption And Surfactants And Self-assembles

Aggregation,adsorption and deposition are physical phenomena that widely present in nature.The site-selective deposition behavior of organic molecules onto self-assembled monolayers（SAMs）patterned substrate is a hot research topic.Surfactant molecules can form a variety of self-aggregates in aqueous solution due to their amphiphilic characteristics,so they have specific properties and they are widely used in many fields.Studying these physical phenomena by molecular dynamics simulation,allow us to comprehend the mechanism of the process of these phenomena,which is certainly guiding and helpful to the synthesis of the new functional materials.The main contents of this thesis are summarized as follows:（1）The site-selective deposition behavior of 3（5）-（9-anthryl）pyrazole（ANP）onto self-assembled monolayers（SAMs）patterned substrate was studied using the equilibrium and steered molecular dynamics methods.Two kinds of different densely packed SAMs were constructed on silicon oxide substrates as the patterned templates,which represent liquid expanded（LE）and liquid condensed（LC）phases.Equilibrium MD simulations showed that the packing density of alkyl chains on the substrate could influence the deposition behavior of the ANP molecules.On the LE covered SAM,the small molecule would submerge deeply into the alkyl chains film,while ANP molecule would deposit on the surface of LC film.Steered molecular dynamics showed that ANP molecule was hindered from the densely packed LC film.However,there was less hindrance for ANP to submerge into the LE film.Using umbrella sampling and the weighted histogram analysis method,the potential of mean force（PMF）of the deposition process of ANP onto the two patterned templates was calculated.From the PMF curves,the favorite deposition location of ANP onto the two SAMs was determined,which agreed well with that obtained from equilibrium MD simulations.The binding energies between ANP and the two SAMs can be estimated based on PMF,which could be used to explain the site-selective deposition of ANP on different densely packed SAMs.（2）The effect of sodium salicylate（NaSal）salts on the spherical-to-threadlike micelle shape transition in 3-hexadecyloxy-2-hydroxy-propyl trimethyl ammonium bromide(R₁₆HTAB)solution was studied using molecular dynamics simulation.Our simulations showed that the preassembled threadlike micelle in the absence of NaSal was unstable and assembled into a spherical micelle.While in the presence of NaSal,the threadlike micelle exhibited fluctuations but remained the threadlike shape during the long simulation run.The Sal-ions were found to penetrate inside the micelle,which promoted the junction between the surfactant cation and salicylate counterion.Our studies showed that the H-bonds and electrostatic interactions between the Sal-ions and the surfactants played an important role in micellar growth and stabilizing the threadlike micelle.（3）The effects of aromatic salts like sodium salicylate（NaSal）and sodium1-hydroxynaphthalene-2-carboxylate（1SHNC）,and sodium2-hydroxynaphthalene-3-carboxylate（2SHNC）on the spherical-to-threadlike micelle shape transition in 3-tetradecyloxy-2-hydroxy-propyl trimethyl ammonium bromide(R₁₄HTAB)solution were studied using molecular dynamics simulation.Our simulations showed that the micelle of R₁₄ HTAB in the presence of three kinds of aromatic salts remained stable.The average reduced density gradient（aRDG）method was used to study the weak interaction between the surfactant cation and aromatic salts counterion.The aromatic salts ions were solubilized in the different positions of micelle,we observed the H-bonds and electrostatic interactions and vdW force between the salts ions and the surfactants by the scatter diagram and isosurface graph of aRDG.Our studies also showed that the H-bonds and electrostatic interactions and vdW force between the salts ions and the surfactants increased shear viscosity of micelle and the stability of the micelle.