Behaviour of non-stoichiometric polyelectrolyte complexes in aqueous salt solutions

Abstract

A study was made of the behaviour of dilute solutions of non-stoichiometric polyelectrolyte complexes in the presence of low molecular weight electrolytes in a wide range of concentration variation of these electrolytes. Using a number of systems it was shown that with an increase in the ionic strength of the solution a reduction was observed in the dimensions of polycomplex particles and second virial coefficients of their solutions. The molecular weight of polycomplex particles remained unchanged. On reaching a given salt concentration in the solution of the non-stoichiometric polycomplex, phase separation took place with a stoichiometric complex in the concentrated phase. It was shown that the ionic strength of the solution where particles of the polycomplex become insoluble is determined by a number of factors, first of all the chemical structure of individual polyelectrolytes forming the polycomplex and its composition. A study was made of the effect of the type of low molecular weight anion and cation on phase separation in solutions of polycomplexes. The behaviour of these solutions was examined using ionic strength I > 0·4 and it was shown that the complex breaks down to individual polyelectrolytes under these conditions; the system becomes single phase in the meantime. A system is proposed and described for physical and chemical conversions of particles of the polyelectrolyte complex in dilute solutions of low molecular weight salts.