AQUEOUS-SOLUTION PROPERTIES OF AMPHOLYTIC COPOLYMERS PREPARED IN MICROEMULSIONS

The aqueous solution properties of a series of polyampholytes of sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS) and (2-(methacryloyloxy)ethyl)trimethylammonium chloride (MADQUAT) were investigated by turbidimetry and viscometry experiments. The solution behavior in the absence and presence of salt is directly related to the copolymer composition. Neutral copolymers with balanced stoichiometry collapse into globules in pure water and adopt a Gaussian configuration at high sodium chloride contents (>1 M), due to a screening of the attractive interactions. Copolymers with a large net charge (congruent-to 60%) behave more like conventional polyelectrolytes, with a decrease in viscosity upon increasing the ionic strength. Between these two limiting cases, and depending on the salt content, the solution behavior is dominated by either the polyampholyte effect (attractions) or polyelectrolyte effect (repulsions). The results are in good qualitative agreement with a recent theory of Higgs and Joanny (J. Chem. Phys. 1991, 94, 1543). In particular, the minimum in the optical transmission observed at intermediate salt concentrations can be well accounted for by the minimum in the effective excluded volume predicted by theory.