Nanostructured hybrid fluids of amphiphilic diblock copolymers and surfactant worm-like micelles complexes

Abstract

This paper reports the synthesis and characterization of two poly(methyl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers and their synergistic interaction with cetyltrimethylammonium tosylate (CTAT) worm-like micelles (WLMs) in aqueous solutions. The rheological behavior of the mixtures of the copolymers and CTAT was compared with the water soluble homopolymer, poly(2-(dimethylamino)ethyl methacrylate). The polymers were synthesized via ATRP, and were characterized using GPC, FTIR and 1H NMR. The rheological behavior of CTAT WLMs was explored under continuous shear flow, varying the (co)polymer concentration, adding salt to the (co)polymer/CTAT systems and changing the pH and the temperature. The effect of the copolymer on CTAT pseudoplasticity reveals the synergy between both compounds, leading to mixed worm like micelles. Based on our rheological results, spherical mixed micelles are not formed for the systems studied since shear induced structures (SIS) were formed even at high (co)polymer concentration. These SIS are characteristic of CTAT worm-like micelles and demonstrate that the surfactant keeps its micellar configuration in water, albeit modified by the co-micellization with the (co)polymer molecules. We demonstrate that shear produces a more pronounced effect in the viscosity of CTAT/polymer mixed worm-like micelles for systems containing interacting diblock copolymers than those containing homopolymers. The novel copolymer/surfactant fluids prepared here exhibit viscosities that can be tuned from 10 to 10,000 times the viscosity of water by selecting molecular weights, solution concentrations, ionic environment, temperature and shear rates.