Conformational features of poly(1,1-dihydroperfluorooctyl acrylate) and poly(vinyl acetate) diblock oligomers in supercritical carbon dioxide

Official URL: http://dx.doi.org/10.1063/1.1350640

We report detailed molecular dynamics calculations of single chain diblocks of poly(1,1-dihydroperfluorooctyl acrylate) (PFOA) and poly(vinyl acetate) (PVAc) in supercritical carbon dioxide, SCCO2. At the critical micelle concentration, this system exhibits self-assembly into micellar structures due to the solvent specific selectivity of the blocks. Although the intermolecular factors determining micelle formation are well studied for this system, the intramolecular single chain conformational features of the molecules have not yet been investigated in the literature. The specific aim of the present work is to study the conformational properties of the single diblock chains in supercritical carbon dioxide at 65 degreesC, and at four different pressures by molecular dynamics simulations. Fluctuations in the shapes of the PVAc and PFOA blocks are observed to be strongly dependent on pressure. The rate of approach of an initially rodlike chain to its equilibrium conformational space is likewise found to depend strongly on pressure. Calculations of the radial distribution function for the solvent molecules around the chain show that a solvation shell is formed around the polymer. Important correlations between the results of single chain calculations and micelle behavior are observed and discussed.