The clouding behavior of aqueous polypropylene glycol 725 (PPG725) solutions in the absence and presence of various anionic surfactants and amino acids were studied. It was found that, all of the investigated amino acids reduce the water-solubility of PPG725 and so induce a reduction in the cloud point temperatures (salting-out effect). However, anionic surfactants with long alkyl chain length induce the salting-in effect on the aqueous PPG725 solutions and increase the cloud point temperatures. The thermodynamic parameters of clouding process in the investigated systems were computed and it was found that entropy is the main motive force for clouding process in aqueous PPG solutions.
