Effect of symmetrical tetraalkylammonium salts on cloud point on nonionic surfactants

The salting in and salting out of the nonionic surfactant octoxynol NF by halides of ammonium and the four lowest symmetrical tetraalkylammonium cations were investigated by measuring their effect on the cloud point at various salt concentrations. The chloride anion tended to salt the surfactant out, lowering its cloud point. The iodide anion tended to salt it in, raising the cloud point, while the bromide ion had no pronounced effect. The ammonium and tetramethylammonium cations tended to lower the cloud point, the latter more extensively than the former. The tetraethylammonium cation had no pronounced effect, while the tetra-n-propylammonium and tetra-n-butylammonium cations tended to raise the cloud point, the latter more extensively than the former. The salt effect on the cloud point generally increased with increasing salt concentration. Tetramethylammonium chloride was the most efficient salt in lowering the cloud point (by 4 degrees at the 0.10-molal level and by 20 degrees at the 1.00-molal level), while tetrabutylammonium halides were the most efficient salts in raising the cloud point (by 18-19 degrees at the 0.10-molal level for chloride and bromide). Cloud point increased were attributed to the formation of mixed micelles or to hydrotropy. The salting-out efficiency of tetramethylammonium chloride and bromide was ascribed to their ability to increase the structure of water.

Effect of inorganic additives on solutions of nonionic surfactants IV: Krafft points

Two polydisperse polyoxyethylated nonionic surfactants were found to possess Krafft points as well as cloud points. The significance of the Krafft point and the reason why it is rarely observed in nonionic surfactants are discussed. The values of the Krafft and cloud points of the two surfactants underwent only small changes as a function of surfactant concentration in the range of 0.5-7.5% (w/w). All electrolytes investigated, as well as urea, raised the Krafft points by between 1 and 4 degrees in the concentration range of 0.5-4 molal. Included were salting-in electrolytes, which raised the cloud points, as well as salting-out electrolytes, which lowered them. Electrolytes that salt out nonionic surfactants strongly may depress the cloud point to the Krafft point temperature, rendering a water-soluble surfactant insoluble in salt solutions at all temperatures.

Effect of inorganic additives on solutions of nonionic surfactants III: CMC's and surface properties

Continuing work on the interaction of inorganic additives with nonionic surfactants in aqueous solution dealt with their effect on the CMC and surface tension. The surfactants were octoxynol and polyoxyethylated oleyl alcohol, containing an average of 9.5 and 10 ethylene oxide units, respectively. Their CMC values were lowered by most electrolytes studied, representing salting out of the surfactants. The steepest reductions in the CMC were produced by the nitrates of sodium and potassium, which had been found to lower the cloud points of nonionic surfactants, salting them out because of the inability of their cations to form complexes with the ether oxygen linkages of the polyoxyethylene moieties. However, even electrolytes with cations such as hydrogen, lithium, calcium, nickel, lead, and aluminum capable of forming complexes with the ether oxygens, thereby increasing the cloud points of the surfactants, lowered their CMC values. In the presence of increasing concentrations of the latter electrolytes, the CMC values frequently went through minima and approached the CMC of the surfactant in the absence of additives. Increases in the CMC over the entire range of additive concentrations investigated were produced by cadmium nitrate for octoxynol, urea for polyoxyethylated oleyl alcohol, and magnesium nitrate for both. Net increases in the plateau or micellar surface tension of polyoxyethylated oleyl alcohol, i.e., in the constant surface tension of surfactant solutions above the CMC, were brought about by the nitrates of cadmium, aluminum, and magnesium at low concentrations only and by urea at all concentrations. This increase is interpreted as salting in. The area per surfactant molecule adsorbed at the air-water interface was reduced by all added electrolytes. Urea caused no such reduction.

Effect of inorganic additives on solutions of nonionic surfactants II

The effect of electrolytes and urea on the cloud points of the following three nonionic polyoxyethylated surfactants was studied: cetyl, stearyl, and oleyl alcohol adducts containing 10 ethylene oxide units. The results were similar to those obtained previously with polyethylene oxide and with a polyoxyethylated alkylphenol. Nitrates of cations capable of forming stable solid complexes with model ethers like dioxane raised the cloud points in proportion to their concentrations by up to 35 degrees. They salted the surfactants in through complexation with the ether oxygens. The order of effectiveness in raising the cloud points was lead nitrate greater than hydrochloric acid greater than cadmium nitrate greater than sulfuric acid approximately equal to to magnesium nitrate greater than aluminum nitrate greater than nickel nitrate greater than lithium nitrate greater than calcium nitrate. Only the nitrates of sodium, potassium, ammonium, and cesium lowered the cloud points, salting the surfactants out. These cations do not form complexes with ether oxygens. Urea, sodium perchlorate, and sodium iodide, which break the structure of water, raised the cloud points. This salting-in process is ascribed to increased hydration of the ether groups of the polyoxyethylated surfactants due to depolymerization of water by urea and the perchlorate and iodide anions. The bromide, chloride, and sulfate of sodium lowered the cloud points. The surfactant with the alkylaryl moiety was salted in more extensively but salted out only slightly more than the three surfactants with the linear hydrocarbon chain. The data indicate the need for revising the theories of the effects of salts on the solubility of nonelectrolytes in water. None of the theories takes into account the interaction between electrolytes and nonelectrolytes, even though many nonelectrolytes compete with water as ligands for the cations.