As an alternative, salt effects for NS are measured by The effect of salts on the nonionic surfactant octoxynol 9 was changes in CMC or in CP. Most NS have small CMC values. studied by the changes they produced in its cloud point (CP): CP Therefore, the increases in CMC through salting in and the increases indicate salting in. The temperatures by which the sodecreases through salting out have even smaller absolute dium salts of water structure-breaking (chaotropic) anions invalues (1-5). creased the CP of 2.0% octoxynol solutions were measured as a The cloud points or lower consolute temperatures of function of salt concentration. The curves representing changes in NS, on the other hand, while nearly independent of surfac-CP versus salt molality rose to a maximum in a parabolic fashion, tant concentration between Β£0.5 and Β§5% ( 6 ) , are followed by steep decreases. Their ascending branches, correstrongly dependent on additives, including electrolytes ( 1, sponding to salting in, were caused by a disruption of the water structure due to the chaotropic effect of the anions combined with 7 -11 ) . Electrolytes that raise the CP extend the temperathe effect of elevated CP temperatures. The descending branches ture range in which NS form undersaturated isotropic soluwere due to salting out by Na / . The net CP increases due to the tions. This represents salting in. Reductions in CP reprechaotropic effect of the anions were calculated at each concentrasent salting out ( 6 ) .
tion by subtracting the CP decrease due to Na / from the observed The changes in CP produced by individual ions are addi-CP increase of the respective Na / salts. With the exception of tive algebraically. Characteristic CP shift values of various ClO 0 4 , the plots of CP changes produced by the chaotropic anions anions and cations for several NS have been published (10, rose in a nearly linear fashion to a maximum and then levelled 11). All cations examined except Na / , K / , NH / 4 , Rb / , off. The levelling off occurred at the salt concentration and CP and Cs / salt NS in through complexation with the multiple temperature leading to the maximum disruption of the water ether groups (8, 9, 12). The effects of anions in salting NS structure of which each anion was capable. The chaotropic anions in or out, raising or lowering their CP, are considerably were ranked in the following order according to their capacity for increasing the CP: SCN 0 ΓΊ I 0 ΓΊ [Fe(CN) 5 NO] 20 ΓΊ ClO 0 4 ΓΊ greater than those of the cations (1, 11). The present study BF 0 4 . Even though the thiosulfate anion is a very soft Lewis base, focusses on anions and employs only sodium salts.