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

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 con centration, this system exhibits self-assembly into micellar structures due to the solvent specific selectivity of the blocks. Although the intermolec ular 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 p resent work is to study the conformational properties of the single diblock chains in supercritical carbon dioxide at 65 degreesC, and at four differe nt pressures by molecular dynamics simulations. Fluctuations in the shapes of the PVAc and PFOA blocks are observed to be strongly dependent on pressu re. The rate of approach of an initially rodlike chain to its equilibrium c onformational space is likewise found to depend strongly on pressure. Calcu lations of the radial distribution function for the solvent molecules aroun d the chain show that a solvation shell is formed around the polymer. Impor tant correlations between the results of single chain calculations and mice lle behavior are observed and discussed. (C) 2001 American Institute of Phy sics.