Solution behavior of poly(sodium(sulfamate-carboxylate)isoprene), a pH sensitive and intrinsically hydrophobic...

The solution properties of a novel pH sensitive and intrinsically hydrophobic polyelectrolyte poly(sodium(sulfamate-carboxylate)isoprene) (SCPI) were investigated by means of dynamic, static, and electrophoretic light-scattering and fluorescence spectroscopy techniques. Because of the pH dependent charge density of the polyelectrolyte chain, the dynamics and structure of the solution were studied at both pH 7 (high charge density) and pH 3 (low charge density) and at low ionic strength conditions for two samples of different molecular weights. In all cases, a fast and a slow diffusive mode were observed. The fast mode is attributed to the diffusion of isolated polyelectrolyte chains, while the slow mode denotes the presence of multichain domains in solution, formed by electrostatic and/or hydrophobic interactions. The size and density of the multichain domains were reduced with decreasing charge density and molecular weight. Effective charge of the particles does not depend appreciably on solution pH, while fluorescence spectroscopy revealed the presence of hydrophobic domains in the studied systems. It was found that increasing temperature resulted in the compaction of both isolated chains and multichain domains due to the hydrophobic effect. Furthermore the increase of the ionic strength of the solution led to a partial dissociation of the multichain domains at short times and at pH 7, while it led to increased aggregation and precipitation at pH 3 and long times. The performed experiments allowed for a separation of the electrostatic and hydrophobic contributions to the self-assembly of the particular polyelectrolyte systems.