Abstract
The swelling of a poly (methyl methacrylate) in supercritical carbon dioxide was studied by means of full atomistic classical molecular dynamics simulation. In order to characterize the polymer swelling, we calculated various properties related to the density, structure, and dynamics of polymer chains as a function of the simulation time, temperature, and pressure. In addition, we compared the properties of the macromolecular chains in supercritical CO2 with the properties of the corresponding bulk system at the same temperature and atmospheric pressure. It was shown that diffusion of CO2 molecules into the polymer led to a significant increase in the chain mobility and distances between them. Analysis of diffusion coefficients of CO2 molecules inside and outside the poly(methyl methacrylate) sample has shown that carbon dioxide actively interacts with the functional groups of poly (methyl methacrylate). Joint analysis of the radial distribution functions obtained from classical molecular dynamics and of the averaging interatomic distances from Car-Parrinello molecular dynamics allows us to make a conclusion about the possibility of formation of weak hydrogen bonds between the carbon dioxide oxygen atom and the hydrogen atoms of the polymer methyl groups.
Highlights
In recent years, much attention has been paid to the study of polymer-supercritical fluid systems.This is eloquently echoed by a large number of reviews devoted to the use of supercritical carbon dioxide as a solvent for the physical processing of polymeric materials [1,2], as well as in polymer modification, formation of polymer composites, polymer blending, microcellular foaming, polymerization [3], particle formation [4], and applications of sc-CO2 in the fabrication of polymer systems for drug delivery [5]
The simulations performed on bulk PMMA at atmospheric pressure have been used to validate model and the force field employed in the classical molecular dynamics simulations
An equilibrated PMMA sample was placed in a sc-CO2 medium in different thermodynamic states
Summary
Much attention has been paid to the study of polymer-supercritical fluid systems. The authors of reference [25] have experimentally investigated the behavior of PMMA–based systems in pure sc-CO2 , and in sc-CO2 modified by acetone, ethanol, and methylene chloride They have found that processing PMMA-based polymers with pure sc-CO2 leads to polymer swelling, and addition of a liquid cosolvent to CO2 enhances polymer dissolution. Combining experimental and computational techniques, Zhang et al [30] studied CO2 -induced plasticization in a polyimide membrane They discussed the effect of the CO2 interactions with the ether groups on the mobility of polyimide chains, calculated the glass transition temperature of the polyimide at different CO2 content values in the polymer matrix.
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