INTRINSIC-VISCOSITY OF SMALL SPHERICAL POLYELECTROLYTES - PROOF FOR THE INTERMOLECULAR ORIGIN OF THE POLYELECTROLYTE EFFECT

Spherical polystyrenesulfonate particles in the size range between 7 n m<R<50 nm are synthesized via crosslinking copolymerization in microem ulsion and subsequent sulfonation via polymer reactions. These model p olyelectrolytes, when carefully purified, show the qualitative aspects of the polyelectrolyte effect, i.e., large excess viscosities with a strong increase of the intrinsic viscosity with decreasing concentrati on. A quantitative evaluation of these data on the basis of a modified Hess-Klein relation reveals that the complete dependence on polymer a s well as on salt concentration can be fitted with one parameter only, the effective charge number per particle, Z(eff). The specific viscos ity increases with decreasing particle size and inverse particle densi ty, but no simple explanations for the found relations can be given. S ince conformational changes play only a minor role for spherical syste ms, the comparison of the concentration dependence of the reduced visc osities of linear chains with those of the spherical polyelectrolytes allows for a differentiation between intra- and intermolecular effects . It is qualitatively shown that a major contribution to the polyelect rolyte effect is caused by intermolecular interactions, i.e., the incr ease of the electrostatic screening length and interparticle-coupling with decreasing concentration. The quantitative description of the con centration and molecular weight dependence of the reduced viscosity of linear polyelectrolytes in salt-foe solution reveals that Z(eff) does apparently not depend on molecular weight, the found molecular weight dependence of the reduced viscosity is due to the increase of the hyd rodynamic radius, only. In addition, our modified Hess-Klein model als o describes some quantitative features of the viscosity curves, such a s the molecular weight dependent shape of the maxima. Deviations betwe en theoretical description and experimental data which become signific ant for smaller linear polyelectrolytes are attributed to a concentrat ion dependent coil expansion. (C) 1996 American Institute of Physics.