Ultrasound-induced formation of high and low viscoelastic nanostructures of micelles

Abstract

We report on the unprecedented ultrasound-driven engineering of typical wormlike micelles to well-aligned, much higher viscoelastic threadlike micelles and lower viscoelastic tubular micelles that have potential practical applications in medicine and oilfield industries. The sonication of the CTAB/salicylate micelle system at 211 kHz in aqueous solutions generated two nanostructures with specific but contradicting properties: stably aligned threadlike micelles of ∼2 nm in diameter and several μm in length with a high viscoelasticity and low viscoelastic tubular micelles of ∼30 nm in diameter and a few hundred nanometres in length. The tubular micelles are relatively unstable structures formed by the coalescence of vesicular intermediates generated during sonication. Acoustic cavitation-generated physical effects are primarily responsible for the generation of these novel nanostructures. This study also provides the first ever experimental evidence in support of a well-known theoretical model that was proposed in the 1990s on the structural transformation of micelles.