Effect of polymers on worm-like micelles of cetyltrimethylammonium tosylate

Abstract

Abstract Aqueous solution behaviour of worm-like micelles of cetyltrimethylammonium tosylate (CTAT) was examined in the presence of some water soluble nonionic polymers viz. poly(ethylene oxide) 4000 (PEO 4K), poly(propylene oxide) 1000 (PPO 1K), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) and poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) type linear triblock copolymers and nonlinear octablock copolymers by an array of techniques. CTAT forms worm-like micelles at very low concentrations. Very hydrophilic PEO 4K molecules surround micelle surface leading to viscosity increase while PPO 1K and linear triblock copolymers demonstrates distinct interaction with worm-like CTAT micelles. They form smaller mixed micelles strongly depending on their structure and hydrophobicity. Structurally different PEO-PPO-PEO type nonlinear block copolymer display dissimilar effect on morphology of CTAT micelles. Small angle neutron scattering (SANS) measurements provide clear idea about structural transitions from worm-like to spherical/ellipsoidal micelles with different dimensions. The different behaviour shown by the polymers is explained on the basis of their interaction with different interiors of CTAT micelles. 1 H NMR and nuclear overhauser enhancement spectroscopy (NOESY) experiments provide idea about location of these additives and site of interaction. The present study validates how the size of worm-like micelles can easily be tuned up by different polymers.