Effect of Sodium Dodecyl Sulfate on the Rheological Behavior of Poly(vinyl alcohol) Aqueous Solution

Rheological behaviors of poly(vinyl alcohol) (PVA) aqueous solution are influenced remarkably by the intermolecular hydrogen bond interaction in the semi-dilute solution region. Owing to the hydrogen bond network, 10 wt% PVA aqueous solution exhibits a high viscosity which limits the development of its solution processing method to some extent. Sodium dodecyl sulfate (SDS), as a surfactant, can destroy the hydrogen bond interaction, thus playing a certain viscosity-reducing role. Based on measuring the critical aggregation concentration (CAC) and critical micelle concentration of SDS in 10 wt% PVA aqueous solution (CMCP), the steady and dynamic rheological behaviors of PVA-SDS aqueous solution were studied in detail. The concentrations of SDS (c(sur)) can influence the rheological behavior of PVA aqueous solution in different ways at various regions. c(sur) < CAC, the apparent viscosity (eta(a)) of the solution doesn't change a lot as the csur changes. CAC < c(sur) < CMCP, eta(a) decreases as the csur increases. Particularly, eta(a) reaches the minimum while c(sur) = CMCP and a wider second platform is displayed in this area. c(sur) > CMCP, SDS form micelles that act as physical cross-linking points, and the dynamic storage modulus (G') of the composite solution also increases significantly. The changes in the hydrogen bond network of the PVA solution was indirectly characterized by the changes of the hydration number measured by Differential Scanning Calorimeter. After introducing SDS, the number of bound water (n) decreases due to the interaction between SDS and PVA. However, n almost keeps constant when c(sur) > CMCP. The viscous activation energy also shows a similar change. When csur is much larger, the micelles formed by SDS in water are conducive to the formation of physical cross-linking network, which contribute more to the solution elasticity, leading to the increase of G' (greater than that of dynamic loss modulus). Compared with the dilute solution, SDS has a greater viscosity reduction effect on the PVA semi-dilute solution.