Shear-induced nanostructural changes in micelles formed by sugar-based surfactants with varied anomeric configuration

Hypothesis: The self-assembly of long tail sugar-based surfactants into worm-like micelles has recently been demonstrated, and the rheological properties of such systems have been shown to be tuneable through subtle modifications of the molecular characteristics of the surfactant monomer. In particular, the anomeric configuration of the hexadecylmaltoside headgroup was shown to induce profound changes in the nanostructure and rheology of the system. The origin of such changes is hypothesised to arise from differences in the structure and relaxation of the micellar networks in the semi-dilute regime. Experiments: Here we explore the molecular background to the flow properties of the two anomers of hexadecylmaltoside (alpha- and beta-C(16)G(2)) by directly connecting their rheological behaviour to the micelle morphology. For this purpose, 1-3 plane rheo-small-angle neutron scattering measurements, using a Couette cell geometry, probed the structural changes in the micellar phase under shear. The effect of surfactant anomeric configuration, surfactant concentration, temperature and mixing ratio of the two anomers were investigated. The static micelle structure in the semi-dilute regime was determined using the polymer reference interaction site model. Findings: The segmental alignment of the micellar phase was studied under several flow conditions, showing that the shear-thinning behaviour relates to the re-arrangement of beta-C(16)G(2) worm-like micelles, whilst shorter alpha-C(16)G(2) micelles are considerably less affected by the flow. The results are rationalised in terms of micelle alignment and disruption of the entangled network, providing a detailed mechanism by which sugar-based surfactants control the rheology of the fluid. To further enable future studies, we provide the complete code for modelling micelle structure in the semi-dilute regime using the polymer reference interaction site model. (C) 2021 The Authors. Published by Elsevier Inc.

Automated summary

Recent studies have demonstrated that the rheological properties of systems formed by the self-assembly of long tail sugar-based surfactants into worm-like micelles can be tuned by subtle modifications of the surfactant monomer's molecular characteristics. The anomeric configuration of the surfactant was found to induce significant changes in nanostructure and rheology, with shear-thinning behavior relating to the re-arrangement of worm-like micelles. These findings provide a detailed mechanism by which sugar-based surfactants control the rheology of the fluid, offering potential for future studies in this area.