On the effect of acids and bases on water-amphiphile interactions

In supplying more experimental material on the Hofmeister (or lyotropic) se ries on the effect of inorganic anions on the solubility of proteins and no nionic micelles in water, we studied the effect of inorganic and organic ac ids and bases on the phase diagrams of binary water-nonionic amphiphile mix tures, as well as on those of ternary water-oil-amphiphile mixtures (microe mulsions). We found that acids make nonionic amphiphiles effectively more h ydrophilic. With inorganic acids, the effect increases with increasing acid ity; with weak organic acids, however, it increases with decreasing acidity . A strong inorganic base such as NaOH, on the other hand, makes nonionic a mphiphiles effectively less hydrophilic, whereas a weak organic base such a s formamide has an opposite effect. The application of dicarboxylic acids, in particular, for lowering the mean temperature of the three-phase bodies in ionic sodium bis(2-ethylhexylsulfosuccinate) (AOT)-microemulsions is bri efly discussed.