Neutron scattering studies of the structure of a polyelectrolyte globule in a water-acetone mixture

The polycationic polyelectrolyte poly(methacryloylethyltrimethylammonium methyl sulfate) (PMETMMS) of high molecular weight (ca. 26 x 10(6) g mol(-)1) in dilute solutions with acetone-water mixtures displays a coil-globule transition above a certain threshold of acetone. SANS observations of this system indicate that the collapsed state of this molecule consists of a sequence of dense spheres with smooth surfaces connected by regions of loose polymer. The radius of the spheres, 28 nm, is smaller than either the hydrodynamic radius (R-H = 39 nm) or the radius of gyration (R-G = 42 nm). The number of such collapsed regions is small (3-4), the volume fraction of polymer inside them being about 8%.