Micellar crowding and branching in a versatile catanionic system

TL;DR

This study investigates the structure, dynamics, and rheological behavior of a versatile catanionic micellar system composed of DDAB and STDC, revealing branching, crowding effects, and unique flow instabilities.

Contribution

It provides new insights into micellar branching, crowding, and the dynamic properties of a specific catanionic system using advanced NMR and rheological techniques.

Findings

Presence of branched, interconnected micelles at higher DDAB/STD ratios

Extended L1 region indicating micellar crowding

Unique rheological oscillations due to elasticity and slippage

Abstract

The catanionic system didodecyldimethylammonium bromide (DDAB)- sodium taurodeoxycholate (STDC)-D2O is characterized by an exceptionally extended L1 region. The comparison of self-diffusion coefficient of the solvent and the DDAB embedded in the micelles provided information about hydration of the aggregates. Moreover, correlating self-diffusion and 14N NMR relaxation measurements new insight could be obtained regarding the translational and rotational micellar motions in the crowded solutions of systems with 0.2 DDABSTDC molar ratio. 1H 2D NMR spectra gave some hints about the mutual arrangement of DDAB and STDC within the aggregates. For samples with 1.8 and 2.6 DDAB/STD molar ratios the 14N data were in agreement with the presence of somewhat branched, interconnected micelles. 23Na and 81Br dynamic parameters resulted particularly sensitive to the surrounding environment. The peculiar rheological behaviour of the, highly concentrated, branched micelles samples, namely the steady oscillations in the step tests, was found to be an example of instability originated by the combined effect of material elasticity and slippage at the fixed wall.