Polysaccharide-surfactant interaction. 2. Binding of cationic surfactants to carboxymethyl cellulose and dextrin

By use of the equilibrium dialysis technique, the extent of binding (Γ21) of cationic surfactants cetyltrimethylammonium bromide (CTAB), myristyltrimethylammonium bromide (MTAB), and dodecyltrimethylammonium bromide (DTAB) with dextrin and carboxymethyl cellulose (CMC) respectively have been measured as a function of surfactant concentration (C2), pH, ionic strength, and temperature. Γ21 increases with increase of C2 until it reaches a maximum value, Γ2m. On further increase of C2, Γ21 in all cases sharply decreases linearly with C2 until its value becomes zero at the azeotropic state when surfactant concentration is considerably higher than the bulk critical micelle concentration (cmc). With further increase of C2, Γ21 becomes negative and its magnitude increases with further increase of C2 without reaching a limiting value. Using the concept of the Gibbs surface excess, it has been shown that binding of both surfactant and water to polysaccharide is responsible for the observed overall shape of the bind...