Contact
    Start Publications Rheological and calorimetric study of alkyltrimethylammonium ...
    ←  Publication Finder
    Attension

    Rheological and calorimetric study of alkyltrimethylammonium bromide-sodium salicylate wormlike micelles in aqueous binary systems

    Year: 2018

    Journal: J. Colloid Interface Sci., Volume 515, APR 1, page 198–207

    Authors: Clinckspoor, Karl Jan; Jorge, Laila Lorenzetti; Hoffmann, Heinz; Sabadini, Edvaldo

    Organizations: FAPESP [2015/25406-5]; Cenpes-Petrobras; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq-Brazil) [140369/2015-5, 301016/2015-1]

    Keywords: Wormlike micelles; Rheology; Calorimetry; Intermicellar attraction; Gordon parameter

    Hypothesis: It is known that additives like glycerol and sucrose lead to the swelling of aqueous bilayer La phases. The swelling of the La phases can be explained by the increase of the refractive index of the mixed solvent, which lowers the van der Waals attraction between the bilayers. Afterwards, the undulation forces between the bilayers can push them apart. This hypothesis was previously extended to wormlike micelles (WLM) of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal). These types of self-assembly structures have vis-coelastic properties, and the zero shear viscosity of these solutions is dependent on the molar ratio NaSal/CTAB, R. At R = 0.6, R = 1.0 and R 2.6 the viscosity goes, respectively, through a maximum, a minimum and another maximum. These viscosities can be explained by differences in relaxation mechanisms predominant in each region. Similarly to what is observed to bilayer La phases, the additives would change the interaction between the WLM, affecting the relaxation processes of each region, altering the profile from two maxima and one minimum to a single maximum in viscosity. In the present manuscript, it is investigated whether it is only the refractive index, other solvent properties, or a combination of several factors that induce these changes in WLM. For this, several additives, forming binary mixtures with water, were studied, through rheology of CTAB/NaSal and calorimetry of tetradecyltrimethylammonium bromide (TTAB)/NaSal. Experiments: Herein, we present the zero-shear viscosity diagrams of NaSal and CTAB with glycerol, sucrose, dimethyl sulfoxide, 1,3-butanediol and urea combined with water. Additionally, isothermal titration calorimetry was used to obtain the variations of enthalpy for formation of WLM of TTAB and NaSal in mixtures of water and such additives. Findings: Based on our data, only the refractive index match is not enough to explain the rheological and calorimetric behaviors of the WLM. For instance, sucrose has little effect on the micelles, even at the same refractive index match conditions. Additional characteristics, such as dielectric constant, the cohesivity of the solvent (here symbolized by the Gordon parameter), and the interactions of the additive with the micelles, have to be considered to better describe the results. (C) 2018 Elsevier Inc. All rights reserved.
    View publication