Journal of Colloid and Interface Science, Vol.547, 275-290, 2019
Worm-like micelles and vesicles formed by alkyl-oligo(ethylene glycol)-glycoside carbohydrate surfactants: The effect of precisely tuned amphiphilicity on aggregate packing
Carbohydrates are appealing non-ionic surfactant head-groups as they are naturally abundant, generally biocompatible and biodegradable, and readily functionalized. Recent work has produced a promising molecular candidate for the formation of viscoelastic worm-like micellar solutions: a tri(ethylene glycol)-linked oleyl-beta-D-glucoside surfactant (GIcC18:1) exhibited near ideal Maxwell behavior at low concentrations (2.9 wt%) without additives at room temperature. Here, fourteen surfactants have been synthesized with structural variations based around GIcC18:1. Each contain an oligo(ethylene glycol) linker of varying length (2, 3, 4, 6 EO units) between a carbohydrate head-group (glucose, galactose, man nose, maltose, lactose, cellobiose) and a cis-unsaturated alkyl tail-group (oleyl, linoleyl, erucyl). The aqueous adsorption kinetics and self-assembly of these surfactants was explored using tensiometry and small-angle neutron scattering (SANS), respectively. With SANS we observed the formation of worm-like micelles for four surfactants, and vesicles for two surfactants which exhibited behavior similar to insoluble lipids. We also observed temperature-induced micellar elongation due to dehydration of the oligo(ethylene glycol) linker, resulting in a further three surfactants forming worm-like micelles at 50 degrees C. Worm-like micellar fluids were further characterized using rheology to reveal two surfactants with vastly superior viscoelastic properties compared to GIcC18:1, with >2 orders of magnitude increase in viscosity and >3 orders of magnitude increase in stress relaxation time. These results provide insight into structure-function relationships for non-ionic surfactants and demonstrate a class of designed amphiphiles with a special propensity for forming viscoelastic worm-like micellar solutions at low concentrations. Crown Copyright (C) 2019 Published by Elsevier Inc. All rights reserved.
Keywords:Carbohydrate surfactants;Alkyl-glycosides;Worm-like micelles;Vesicles;Small-angle neutron scattering;Rheology