Electron microscopy studies on the coil-to-globule transition of a polyelectrolyte in a water-acetone mixture

A high molar mass polycation poly(methacryloylethyl trimethylammonium methy lsulphate), PMETMMS, dissolved in mixtures of water and acetone, was studie d using light scattering during the reversible coil-to-globule transition. When the mass fraction of acetone in the solvent mixture, gamma, is higher than 0.80, PMETMMS adopts a globular state but does not aggregate. The coll apse of PMETMMS can also be induced by the dilution of the polymer solution , if 0.70 less than or equal to gamma < 0.80, and the solvent composition i s kept constant. The results obtained by light scattering have been confirm ed using a transmission electron microscope with which the collapse of PMET MMS has been observed. At high polymer concentration and 0.70 less than or equal to gamma < 0.80, a transient network is formed: coils strongly intera ct with each other via dipole-dipole interactions in a thermodynamically po or solvent. At low concentration regime when 0.70 less than or equal to gam ma < 0.80, or in solutions with the mass fraction of acetone higher than 0. 80, all the PMETMMS molecules are collapsed. In the intermediate region, th e collapse of PMETMMS is gradual and coils, globules, as well as fragments of the network coexist in the solution. (C) 1999 John Wiley & Sons, Inc.