Unified Concept of Solubilization in Water by Hydrotropes and Cosolvents

Abstract

In the present work hydrophobic dyes, i.e. disperse red 13 (DR-13; (2-[4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino]ethanol) and Jaune au gras W1201 (1H-indene-1,3(2H)-dione,2-(2-quinolinyl)), are solubilized in water with the help of different additives: acetone and 1-propanol as typical cosolvents, sodium xylene sulfonate (SXS) as a representative of a classical hydrotrope, sodium dodecyl sulfate (SDS) as a typical surfactant, and finally some "solvosurfactants" [ propylene glycol monoalkyl ether derivatives (CiPOj: i = 1, j = 1 and 3; i = 3, j = 1 and 2; i = 4 and tertio-butyl, j = 1) and 1-propoxy-2-ethanol (C3EO1)]. These solvosurfactants are short amphiphiles that do not form well-defined structures in water such as micelles. For all additives an exponential increase in the solubilizations of the two studied hydrophobic dyes was observed when their concentrations in water were increased. Except for the SDS solution, no difference in the overall shapes of the solubilization curves (dye solubility against additive concentration) was found. All the studied molecules were classified according to their hydrotropic efficiencies, i.e., their abilities to solubilize a hydrophobic, sparingly soluble compound in water. The volume of the hydrophobic parts of the studied additives, roughly evaluated by simple calculations, was found to influence strongly the hydrotropic efficiency; i.e. the larger the hydrophobic part of the additive, the better the hydrotropic efficiency. By contrast, the hydrophilic part carrying a charge or not is of minor importance. Taking the hydrophobic part of the molecules as the key parameter, the water solubilization efficiency of cosolvents, hydrotropes, and solvosurfactants can be described in a coherent way.

Surfactant behaviour of metallacarboranes. A study based on the electrolysis of water

“…The latter belongs to a class of molecules generally called hydrotropes, that are defined as small amphiphilic molecules that do not form well defined micelles in water. 13 The least efficient electrolytes are the metallacarboranes and DBSA, which appear at the same region in the I/V plot through the whole range of applied voltages. Although the molecular structure of [1] -does not display the conventional structure of a surfactant, in this work we provide the results of a macroscopic experiment proving the surfactant behaviour in aqueous solutions of [1] -and that this is due to the formation of aggregates.…”

Poly(vinylalcohol)-borate hydrogels with improved features for the cleaning of cultural heritage surfaces

“…PVA/borax hydrogels, on the other hand, show mechanical features suitable for easy removal by peeling from surfaces, without need of strong mechanical or chemical actions, and have been therefore proposed for cleaning purposes [14,[18][19][20]. Water/ cosolvent mixtures can be embedded into these high viscosity polymeric dispersions, making them able to soften and swell water-insoluble materials, in a way similar to that proposed in a study concerning the solubilization of hydrophobic substances by hydrotropes in water [21].…”

Eco-solvents – cluster-formation, surfactantless microemulsions and facilitated hydrotropy

“…The compositions used for these experiments are Bauduin et al showed a way to characterize the hydrophobic efficiency a. 36 It is linked to the evaluation of the slopes of the linear part in the log-linear plots of the solubility of the hydrophobic dye, which is defined using the following equation:…”