The aim of this work was to determine the cloud points of new oxyethylated methyl dodecanoates of various hydrophilicity (OMD-n, where n refers to the average degree of oxyethylation) and to correlate them with surfactant hydrophilicity and, for a given electrolyte, with water activity. Thus, it is shown that the cloud point in the absence of electrolyte (CP0) can be simulated by the following equation: CP0 = 165.5 log n - 112.0 (with R-2 = 0.987). The effects of NaCl, NaHCO3, and KSCN on the cloud point are also reported and discussed. The salting-out effect arising from the presence of NaCl or NaHCO3 is explained by the existence of a hydration shell with enhanced water structure as well as a zone with decreased salt concentration around the -(OCH2CH2)(n)- chain, as compared with the bulk. On the other hand, the salting-in effect is explained by depletion of water around the -(OCH2CH2) - chain. Thus, it is estimated that the number b of water molecules forced back into the bulk solution from the salt-deficient regions when the hydration shells of two -O-CH2-CH2- monomer units overlap ranges between 2 and 3 and 3 and 4 for NaCl and NaHCO3, respectively, depending on the average degree of oxyethylation it of OMD-n. It is also shown that the water activity is a useful parameter to simulate the variation of cloud point in the presence of an electrolyte (CP) at low and moderate concentration (e.g., < 1 M NaCl), CP0/CP approximate to 1 - (bR/alpha) lna(w), where R is the gas constant and a approximate to 15 JK(-1) mol(-1). At high electrolyte concentration, the relationship between CP0/CP and lna(w) significantly deviates from linearity. In the particular case of KSCN, an inversion of the salt effect can be observed. The salting-in effect of KSCN increases up to about 2 M, but decreases at higher KSCN concentrations, so that KSCN can even act as a salting-out salt at high concentration (typically above 3.3 M for OMD-14). (C) 2003 Elsevier Inc. All rights reserved.