Structure and dynamics in aqueous solutions of amphiphilic sodium maleate-containing alternating copolymers

The structure of aqueous solutions of sodium maleate copolymers with comonomers of variable hydrophobicity are examined using a combination of small-angle neutron scattering, small-angle X-ray scattering, and rheometry. Semidilute solutions of the copolymers made with mildly hydrophobic comonomers exhibit scattering and rheology that are typical of flexible polyelectrolytes, with a correlation length scaling with polymer concentration as c(-alpha) with alpha = 1/2 and specific viscosity scaling as c(1/2)/c(3/2) when unentangled/entangled. In contrast, copolymers with more than eight carbons in their hydrocarbon comonomer form micelles (globules) at low concentrations and molecular weights. For these more hydrophobic copolymers, the correlation length scales as c(-alpha) with alpha < 1/3 and the viscosity remains small until a relatively high concentration at which the globules start to overlap. Once these more hydrophobic copolymers overlap, the micelles open up and allow intermolecular associations that cause the viscosity to increase rapidly with concentration, typical of associating polymer solutions.