The partition coefficients (K-X) for poly(ethylene glycol) n-alkyl ethers (C-m(OE)(m)OH, m = 2, n = 1; m = 4, n = 0-4; m = 6, n = 1) between water and dipalmitoylphosphatidylcholine liposome membrane were determined at the gel to liquid crystalline phase transition temperature of the liposome membrane. For poly(ethylene glycol) n-butyl ethers (C-4(OE)(n)OH) the plot of log K-X against the number (n) of oxyethylene groups decreased linearly with increasing n in the range n = 1-4. The standard free energy change of transfer per oxyethylene group (Delta G degrees(OE) = 1.13 kJ mol(-1)) from water to the liposome membrane was determined from the slope of this straight line and compared with corresponding values for micelles and dodecane. The local polarity around the OE group located in these molecular assemblies (liposome and micelle) and dodecane was estimated from ESR spectra by using a spin probe. We found that Delta G degrees(OE) values for these systems decreased linearly from a positive value (indicating the hydrophilic nature of the OE group) to a negative value (hydrophobic nature) as the local polarity around the OE group increased.