Mesoscopic Simulation Of The Phase Separation On Triblock Copolymer

The phase separation of Pluronic was studied by MesoDyn simulation in mesoscopic scale. And these studies are helpful to understand, explain, and forecast experimental results and phenomenon, and offer academic methods for further study the system.1. The micelles phase of the pluronic aqueous solution.The microphase separation dynamics of triblock copolymer surfactant Pluronic in aqueous solution was simulated by a dynamic variant of mean-field density functional theory for Gaussian chains. Different morphologies depending on the simulation concentration and time are shown in low concentration (less than 35 vol%). With increasing the concentration, the self-assemble aggregates change from spherical micelles, micellar clusters, to disk-like micelles. (1) In the spherical micellar region (5 vol%-10 vol%), the result of simulation is similar to that of the experiment that micelle is a dense core consisting mainly of PPO and a hydrated PEO swollen corona. (2) Due to the coalescence among spherical micelles, bigger micellar clusters are formed in a concentration from 11 vol% to 15 vol%. (3) Since the attractions between the PEO coronas of micellar clusters, series of disk-like micelles are found above the concentration 16 vol%. The order parameters show that the phase separation of spherical micelles is easily formed, while the micellar cluster or disk-like micelles need longer time to get steady equilibrium. When the temperature increases, the core sizes and aggregate numbers of spherical micelles also increase, the micellar clusters vanish in the solution, and the phase separation becomes more difficult.2. Phase behavior of pluronic P65 solution in the absence andpresence of shearThe microphase separation dynamics of the triblock polymer surfactant P65 inaqueous solution was simulated in the absence and presence of shear. With the increase of concentration, different mesoscale structures are found in the absence and presence of shear. (1) In the absence of shear, there are three morphologies formed. The first is micellar phase including spherical micelle which has hexagonal packing and a FCC (face centered cubic) structure in the solution, and wormlike micelle; the second is bicontinuous phase, which belongs to gyroid-type connectivity; and the third is lamellar phase. (2) In the presence of shear, only two morphologies are formed in all concentrations, they are hexagonal and lamellar phases that align in the flow direction. We notice that the weaker shear makes the order parameter of simulation system oscillate, while the stronger shear makes the order parameter get equilibrated in a short time.3. The interaction between Pluronic F127 and C₁₂E₆The phase separation of Pluronic F127 and C₁₂E₆ were performed by MesoDyn simulation, and the interaction between F127 and C₁₂E₆ can be found. In the low concentration, the structure of pearl necklace was found. And when the concentration of F127 is lower than 6 vol%, the structure of pearl necklace is not found; increasing the concentration of F127 to 7 vol%-9 vol%, the concentration of C₁₂E₆ required to form the structure of pearl necklace is decreased; while the concentration of F127 is higher than 9 vol%, the required concentration of C₁₂E₆ is increasing.The new founds in the thesis are as fellows:1. Pluronic were simulated by MesoDyn method. Micellar clusters and disk-like micelles were defined in mesoscopic, and the structure of spherical micelles was outline by the density distribution of the different blocks, and the fact that water is in core and corona of micelles, and it agree very well with the experimental results.2. According to the change of the order parameter, the time evolution of spherical micelle can be divided into three stages: homogeneous system, formation and equilibrium. While in the micellaer cluster region, we divided the curve of orderparameter into four stages: homogeneous system, formation of micelles, formation of micellar clusters and equilibrium. And the process of aggregation of spherical micelles and micellar clusters can be observed in mesoscopic.3. Under weak shear, the order parameter is shown in the oscillation style, the morphology in top of peak are different with those at bottom, so the conclusion that the morphology can be restored was obtained. While under strong shear, a new phase can form in a short time.4. The interaction between Pluronic F127 and nonionic surfactant C₁₂E₆ was investigated, and the pearl necklace structure was found.