Molecular Dynamics Simulation Of Porous Carriers Prepared By ScCO₂ Induced Phase Separation

Supercritical carbon dioxide?ScCO₂?induced phase separation technology induces the phase separation of homogeneous polymer system by using the strong dissolving ability,diffusing ability and mass transfer ability of ScCO₂,which integrates phase separation and drying into a continuous process,avoids effectively the collapse of pore structure in the drying process of porous carrier and realizes the recycling of organic solvent.The dissolution and diffusion behavior of ScCO₂ in polymer molecules has an important influence on the porous carriers prepared by ScCO₂ induced phase separation.In this paper,the molecular dynamics simulation of different systems are made,such as the system of Polymethyl methacrylate?PMMA?and ScCO₂ in the range of310K-340K and 8-11MPa,the system of different kinds of polymer and ScCO₂,the system of Polylactic acid?PLA?modified by different functional groups and ScCO₂,the system of Poly lactide-co-glycolide?PLGA?with different monomer proportions and ScCO₂.The intermolecular radial distribution functions of the systems containing ScCO₂and polymer molecules is derived.The free volume fraction and the interaction energy of the systems containing ScCO₂ and polymer molecules are calculated.The influence of temperature,pressure,polymer molecule species,end group of molecule chain,and composition of molecule chain on free volume fraction,intermolecular interaction energy and movement ability of ScCO₂ molecules are investigated.The main factors of compatibility between ScCO₂ molecules and polymer molecules are analyzed.The results show that the interaction between ScCO₂ and PMMA decreases with the increase of temperature and increases with the increase of pressure.The diffusion coefficient of ScCO₂ in PMMA and the free volume fraction of the system containing ScCO₂ and PMMA are both positively correlated with temperature and negatively correlated with pressure.PLA has the strongest interaction with ScCO₂.PMMA and Polyvinyl alcohol?PVA?is slightly weaker than PLA.While Polyethylene glycol?PEG?is the worst.Compared with the unmodified PLA molecules,the interaction between PLA molecules modified by siloxy group and ScCO₂ is enhanced most significantly,followed by the interaction between PLA molecules modified by aldehyde group and ScCO₂.While the interaction between PLA modified by amido group and ScCO₂ has no obvious changes.hydroxyl group does not enhance the interaction between PLA molecules and ScCO₂.It is similar that interaction between PLGA with different molecule chain structures and ScCO₂,and the Van Der Waals force is main interaction style between PLGA and ScCO₂.With the increase of the proportion of lactate monomer,the interaction between PLGA molecules and ScCO₂ molecules is enhanced.The selection of raw materials and optimization of the process of the polymer porous carriers prepared by ScCO₂ induced phase separation technology are directed by the results.