Surfactant Interactions with HEUR Associating Polymers

Abstract

The interactions between a HEUR (hydrophobically-modified ethoxylated urethane) AP (associating polymer) and the anionic surfactant SDS (sodium dodecyl sulfate) or the cationic surfactant DTAB (dodecyltrimethylammonium bromide) were studied using a combination of rheology measurements plus PGSE (pulsed-gradient spin-echo) NMR self-diffusion and NMR relaxation time measurements. For comparison, parallel experiments were performed using poly(ethylene oxide) (PEO) plus surfactant mixtures. At low concentrations (4 SDS per HEUR AP hydrophobe) added surfactant enhanced HEUR AP network formation. At high concentrations (33 SDS per HEUR AP hydrophobe) added surfactant totally disrupted the HEUR AP network and the HEUR AP self-diffusion came to resemble that of PEO. Both SDS and DTAB bound with greater affinity to the HEUR AP than to PEO. SDS bound with greater affinity than DTAB to either the HEUR AP or PEO. Despite the association of SDS with the ethylene oxide backbone of the HEUR AP, the results support the hydrophobe-replacement model as a description of the effects of surfactant on network formation in solutions of HEUR APs.