Rheological Studies on Interactions between CTAB and PEG in Aqueous Solution Using RSM

In this work, the study of the rheological behavior of the aqueous solution of cationic surfactant, cetyltrimethylammonium bromide (CTAB) and nonionic polymer, polyethylene glycol (PEG 3000) has been carried out. Response surface methodology of design of experiment technique was adopted to identify the effect of different variables and their interactions on viscosity. A preliminary experimental investigation was carried out to evaluate the rheological behavior of aqueous PEG, aqueous CTAB, and also of the binary solution of them. It is found that they all show Newtonian behavior for a shear rate of up to 1000 s^-1 for the studied concentrations. For the shear rate above 1000 s^-1 aqueous PEG solution shows shear thickening behavior. Combinations of levels of variables i.e. [surfactant], [polymer], and temperature were determined using a face-centered central composite design (FCD) of response surface methodology. Through regression, a quadratic model was generated and found to be very accurate in describing the relation between response and parameters with R² =0.987, predicted R² =0.9412 and adjusted R² =0.9776. The effect of interaction between surfactant and polymer on dynamic viscosity is identified with the help of contour and response surface plots. A sudden increase in viscosity is observed at low CTAB concentrations which were the result of weak interactions between CTAB and PEG and the effect of these interactions is found to be more pronounced at high temperatures.