Studies on Solubilization.

Abstract

In addition to their properties as wetting, suspending, emulsifying, and colloidstabilizing agents, dilute aqueous and non-aqueous solutions of soaps and other soap-like detergents-non-electrolytic as well as anionand cation-active materials-possess the remarkable property of being able actually to dissolve otherwise insoluble substances (4,15,16,19,25). Not only do such solutions form spontaneously, but the resulting colloidal solutions are thermodynamically stable, as shown by the fact that they enter into true reversible equilibria with non-aqueous solutions where the solute exists as simple molecules, such as a water-insoluble dye in toluene. They likewise form true equilibria with solid crystals (14).The formation of such solubilized systems is accompanied by a lowering of free energy. For example, the vapor pressure of a volatile insoluble liquid taken into colloidal solution by a solubilizer is far less than that of the volatile liquid alone (17). The vapor pressure of a solution of a soluble volatile hydrocarbon in water is reduced by adding a detergent, and the solubility is correspondingly increased. Clearly this phenomenon is quite distinct from peptization of preexisting particles or droplets, which do not exist in the cases just cited.The present communication includes experiments which help to clarify detergent processes, and provides systematic measurements of the "solubilization" of dyes. The formation of such thermodynamically stable colloidal solutions,-"solubilization,"-must be distinguished from other phenomena such as (a) emulsification, where the vapor pressure of the emulsified liquid is equal to that in bulk or even greater due to the curvature of the droplets; (b) change in solvent power due to the addition of a large proportion of a second liquid; (c) peptizing, protective, and suspending action of preexisting particles, or those formed by mechanical means or by condensation from a supersaturated solution; (d) "sequestration," for example, of calcium soaps in water by substances such as Calgon (sodium hexametaphosphate) for the action of which we may tentatively, in the absence of more definitive evidence, accept the explanation of Hall (5) as being due to the formation of complexes with the cation, especially since Reitemeier and Buehrer (22) found no colloidal particles visible in the ultramicroscope;and (e) "solutizing" of mercaptans (28), in part due to salt formation, by strongly alkaline concentrated solutions of substances which are not effective in dilute solution and where colloids are probably not involved.In general, the above actions are possessed in varying degrees by most commercial detergents and protective colloids. For example, some excellent proi Presented at the Eighteenth Colloid Symposium, which was held at

Solubilization of Water-Insoluble Dye in Aqueous Solutions of Commercial Detergents

“…), the data indicate that they form micelles in solution, are therefore colloidal, and thus tend to confirm a prediction made in 1920 (12) that the then new class of colloidal electrolytes would be more numerous than all acids and bases. The increase in solubilizing action with increasing chain length shown by the Aerosols, Tergitols, and Santomerses, together with the data on a series of 0.01 N pure long-chain sulfonates and sulfates presented in another paper (13) show that, in general, solubilizers containing a large proportion of hydrophobic material are best. Those which are anion-active such as the Aerosols, Tergitols, and bile salts, cation-active such as the pyridinium and other quaternary ammonium halides, and nonelectrolytes such as polymers of ethylene oxide, fatty acids, and alcohols, are all possibly of the same order of effectiveness as solubilizers if they are comparable in purity and hydrophobic character.…”

Solubilization of Hydrophobic Dyes in Surfactant Solutions

“…The use of surfactants for solubilization of dyes dates back to the 1940s [ 1 , 2 , 3 , 4 , 5 , 6 ]. For the majority of applications an aqueous medium is used and the choice of surfactant is decisive of the adsorption and fixation of the dye at the substrate (e.g., textile fiber/fabric) [ 7 ].…”

Dependence of ultraviolet absorbers' performance on ultraviolet wavelength

“…of a hydrogen bond [19]. The formation of inter-or intramolecular hydrogen bond shifts the signal to a lower magnetic field, although a general signal of a hydroxyl group is at about 5 ppm.…”