Observation of the dynamics of polyelectrolyte strong solutions by quasi-elastic neutron scattering

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Abstract
We report results of quasi-elastic neutron scattering experiments on concentrated polyelectrolyte solutions in water without added salt. The polyion is sulphonated polystyrene, associated successively with sodium and tetramethylammonium counterions. In this second case, all possible configurations of deuterated and non deuterated charged components are tested. The quantities first derived from the experiment are the static polyion and counterion structure factors. Next, the coherent and incoherent contributions to the time-dependent structure factors are separated. The counterion self diffusion coefficient is determined from the incoherent scattering. A wave-dependent diffusion coefficient is derived from the coherent scattering. This coefficient is associated with the slow collective relaxation mode. The mobility related to this mode is found to have a characteristic wavevector dependence, settling thereby a question raised earlier about the dynamic structure factor of polyelectrolytes made of flexible coils. The attempt to observe the fast relaxation mode using the different labelled combinations failed