Interfacial Free Energies and Surface Areas of Cycloalkanols and alpha,omega-Alkanediols at the Air-Water Interface.
The surface area occupied at the air/water interface for cycloalkanols and alpha,omega-alkanediols has been estimated from surface tension measurements. From these data, standard free energies of transfer of the alkanols from the bulk of the solution to the interface were obtained. Cycloalkanols constitute a family whose surface excess diminishes when the size of the alkyl ring increases and whose free energies of transfer at zero surface pressure are similar to those of 1-alkanols of similar hydrophobicities. alpha,omega-Alkanediols occupy considerably larger surface areas than 1-alkanols, a result that can be interpreted in terms of a different geometrical arrangement of the molecules at the interface. In particular, for alkanediols with n > 7, the data suggest an important contribution of bent conformations to the average arrangement of the molecules in the monolayer. The need to adopt bent conformations to allow the interaction of both hydroxyl groups with the aqueous interface results in a less favorable change in free energy when they are transferred from the solution standard state to the interface at constant surface pressure. Copyright 1998 Academic Press.
Aspée
A
Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
Lissi
EA