A Reversible Polyelectrolyte Involving a β-Cyclodextrin Polymer and a Cationic Surfactant

A new model of polyelectrolyte has been elaborated by mixing in water a neutral polymer of β-cyclodextrin (poly(β-CD)) and a cationic dodecyltrimethylammonium chloride surfactant (DTAC). The driving forces for the poly(β-CD)/DTAC association in aqueous solution are reversible inclusion interactions between the CD cavities of the polymer and the alkyl group of DTAC. Viscometry, surface tension, and conductance measurements have first been used to prove the formation of such complexes. From these studies, it follows that both components form exclusively 1:1 inclusion complexes. Afterward, the association constant between poly(β-CD) and DTAC has been determined by considering 1:1 association from fluorescence, surface tension, and conductance data. It has been shown that both the architecture of poly(β-CD) and the electrostatic repulsions induced between the DTAC molecules are unfavorable to the association. The association constant is significantly stronger in the presence of salt, when the electrostatic repulsions are screened. Finally, the structural properties of the poly(β-CD)/DTAC complex have been studied by viscosimetry. A polyelectrolyte behavior has been observed when the stoichiometry of the poly(β-CD)/DTAC mixture in pure water reaches a critical value.