The time dependence of chitosan nonionic surfactant solution viscosity

Abstract

The measurement of the viscosity of semiconcentrated chitosan (0.08-0.14%) solutions in the system with octaethyleneglycol mono n-dodecylether (C(12)E(8)) was carried out using Cannon-Fenske capillary viscometer. The interaction was - as expected - very weak, but when the time dependent hydrodynamic behaviour of the system was considered, the interaction has been established at particular surfactant concentrations. The most significant time dependence is shown in a form of sudden viscosity drop in a region close to and above CMC value of the surfactant, which implied existence of the interaction between chitosan and surfactant. At low surfactant concentrations viscosity values vere constant with increasing surfactant concentration, but solution also showed time dependent decrease in the viscosity which has been connected with well known time dependent viscosity of pure chitosan solution. The viscometry enabled monitoring of the extent of chitosan/surfactant association by establishing the viscosity decrease rate constant. The rate constant was derived from the first order constant of the quadratic polynomial curves used for the approximation of experimental values when these are presented in the form of viscosity-time profiles. This method showed the existence of critical surfactant concentration values (C-1, C-2, and C-3) These values are closely connected with the proposed interaction model which is based on the assumption that spherical surfactant micelles are bound by chitosan molecule.