Effects of oxyethylene chain length and temperature on partitioning of homogeneous polyoxyethylene nonionic surfactants between water and isooctane

Partition coefficients of homogeneous poly(oxyethylene glycol n-dodecyl ether) C12H25(OCH2CH2)(i)OH (i = 2-9) between water and isooctane were determined from experimental measurements in the temperature range 20-40 degreesC. All surfactants were found to have partition coefficients lower than unity, which indicates that their hydrophobic character is more important than their hydrophilic one. An increase in ethylene oxide number from 2 to 9 induces an exponential increase of the partition coefficient of 3 orders of magnitude, while an increase of 20 degreesC in the temperature decreases its magnitude only 0.5 of an order of magnitude. The hydroxyl. group contribution to the free energy of transfer of the surfactant molecules from water to isooctane was found to be more important than that of an ethylene oxide group. An increase in temperature leads to an important decrease in its contribution, while the ethylene oxide contribution remains practically constant. Contributions of the functional groups of the surfactant molecules to the free energy of partitioning are evaluated in order to build up a database to predict the partitioning of nonhomogeneous nonionic surfactants of the same family within the temperature range investigated.