On the solubility of long n-alkanes in water at room temperature

Ferguson et al. [A.L. Ferguson, P.G. Debenedetti, A.Z. Panagiotopoulos, J. Phys. Chem. B 113 (2009) 6405] did not find any evidence of a water-induced chain collapse for n-alkanes smaller than n-docosane: extended conformations are thermodynamically preferred. Using a simple geometric description of the different conformations of n-eicosane, reliable values of the reversible work to create a suitable cavity in water and to switch on alkane–water van der Waals attractions have been calculated. There is no chain collapse because the gain of attractive alkane–water interactions overwhelms in magnitude the loss in configurational/translational entropy of water molecules associated with the increase in the solvent-excluded volume on passing from a spherical shape to an elongated spherocylindrical one.