High-frequency dielectric and conductometric properties of poly-L-lysine aqueous solutions at the crossover between semidilute and entangled regime

The dielectric and conductometric properties of poly-1-lysine aqueous solut ions have been investigated in the frequency range from 1 MHz to 1.8 GHz, w here micro-Brownian dynamics and internal motion of side-chain polar groups result in a well-defined relaxation process, intermediate between that cau sed by counterion polarization (characteristic of the polyelectrolyte natur e of the polyion investigated) and that associated with the orientational p olarization of the aqueous phase. The polymer concentration has been varied in a wide interval in order to investigate the influence of different chai n conformations on the dielectric parameters as a consequence of the differ ent concentration regimes occurring in these systems. With the help of poly mer scaling theories, scaling relations for the dielectric strength and the relaxation time are presented, predicting, as the polymer concentration is increased, a transition from semidilute-unentangled to semidilute-entangle d regimes. We compare these predictions with the experimental findings over the whole concentration range investigated, with a qualitative agreement. Deviations from the scaling behavior related to a crossover regime between unentangled and entangled regions are briefly discussed. (C) 1999 John Wile y & Sons, Inc.