Comparison between the interfacial and bulk rheology of sodium carboxymethylcellulose in the presence of cationic and non-ionic surfactants

Abstract

The bulk and interfacial rheological behavior of concentrated solutions of Sodium carboxymethyl cellulose (NaCMC) has been investigated in presence of cationic surfactant Cetylpyridinium bromide (CPB) and nonionic surfactant Sorbitan monopalmitate (Span 40) having same hydrocarbon chain length with different head groups. At NaCMC concentrations between 1.5 wt% to 2.5 wt% the polymer solutions exhibit two regions, a dilatant (shear thickening) region at lower shear rates followed by a pseudoplastic (shear thinning) region at higher shear rates. Steady state bulk rheological experiments indicate that 1 wt% NaCMC as well as 1 wt% NaCMC with varying concentrations of Span 40 and CPB show non-Newtonian pseudoplastic behavior. Interfacial steady shear tests of 2D Langmuir monolayer of 1 wt% NaCMC at air-water interface show non-Newtonian pseudoplastic behavior, however the mixed films of the polymer in presence of CPB and Span 40 at the same interface exhibit two distinct shear thinning regions.