Open issues in the linear and NonLinear rheology of wormlike micelles

Abstract

We review experimental evidence and theoretical/modeling approaches on Wormlike Micelles (WLMs) dynamics in linear and nonlinear regimes. We focus on recent works regarding the extraction of quantitative microscopic information from linear rheology data and the possibility of quantifying the fast relaxation processes. Models for WLMs undergoing reptation and chain sequence rearrangement are discussed. Strong shear and elongational flows that can cause interesting phenomena, e.g. chain scission, structure formation, and elastic instabilities in WLMs, are considered. More specifically, start-up shear flow in the nonlinear regime, LAOS experiments, and relative data treatment are discussed, together with shear-banding phenomena and their dynamics, inertio-elastic instabilities, and secondary flow. Different techniques for measuring WLMs in extensional flow are compared, referring in particular to the recent dripping-onto-substrate (DoS) extensional rheometry, which is able to address some shortcomings of the CaBER technique. We finally deal with the potential source of triggering flow profiles and secondary flows with fluid properties and external conditions.