Influence of polyethylene oxide on the rheological properties of semidilute, wormlike micellar solutions of hexadecyltrimethylammonium chloride and sodium salicylate

Abstract

The influence of polyethylene oxide (PEO) on the rheological properties of equimolar wormlike micellar solutions of hexadecyltrimethylammonium chloride (HTAC) and sodium salicylate (NaSal) is investigated, above the concentration where a micellar entanglement network is formed. PEO is known to have a temperature-dependent binding affinity for HTAC micelles. The influence of temperature, PEO concentration, and HTAC concentration is explored. Within the concentration and temperature range examined (25–100 mM HTAC and 25–50 °C), HTAC/NaSal solutions exhibit rheological characteristics of an entanglement network. Application of transient network theory provides information in the form of the plateau modulus, G ∞ ′ , the terminal viscoelastic relaxation time, τ R , the reptation time, τ rep , the micellar breaking time, τ br , the mean micellar length, L ¯ , and the entanglement length, l e . Consistent with literature data, increase of HTAC concentration results in an evolution from slow-breaking to fast-breaking behavior, accompanied by an increase in G ∞ ′ and τ rep , and decreases in τ R , and τ br , l e and L ¯ . Addition of PEO results in a substantial decrease in G ∞ ′ (increase in l e ), and corresponding increases in τ R and L ¯ . These observations are consistent with the idea that binding of HTAC micelles to PEO in aqueous solution decreases the number of surfactant molecules available to contribute to the entanglement network of wormlike micelles.