Unveiling the microstructures of micelles from polyoxyethylene alkyl ether-based multi-responsive nonionic amphiphile

Abstract

The present study was undertaken to unveil the self-assembly of a polyoxyethylene alkyl ether carboxylic acids based nonionic amphiphile known as Akypo® RO90 VG (hereafter written as Akypo) in aqueous medium using cloud point (CP), solution viscosity, dynamic light scattering (DLS), small-angle neutron scattering (SANS) measurements. Surfactants belonging to Akypo family have an average formula C x EO y CH 2 COOH (i = 8–18, j = 2.5–10) [1] . The surfactant micellizes in aqueous media analogous to conventional surfactants but with some dissimilarity. The influence of external stimuli viz. temperature, pH and electrolyte has been examined to assess the response on the microstructural changes in micelles. SANS experiments provided the exact size and shape of micelles; the micellar growth proposed by high solution viscosity and hydrodynamic diameter (D h ) of micelles from DLS and further reinforced by SANS data. This further divulges that increase of temperature and addition of electrolyte persuade the ellipsoidal to worm-like micellar transition. Change of pH towards an alkaline medium favors the transformation of ellipsoidal micelles into spherical ones which can be correlated with deprotonation of carboxylic acid groups that results in increased solubility of Akypo. The current study authorizes how the size of Akypo micelles can effortlessly be amended in the presence of external stimuli to the desired extent. • Akypo self-assemble to form micelles in analogy to conventional surfactants. • Thermo-responsive Akypo exhibit micellar transition at elevated temperature. • Increase of solution pH facilitate ellipsoidal to spherical micellar transition.