Hydrophobic Interactions and the Origin of Hydrophobic Force
by
Roe-Hoan Yoon, Director
Center for Advanced Separation Technologies
Virginia Tech
Blacksburg, VA24061
Abstract
Biological membranes, proteins and other structures are formed by hydrophobic interactions.
Also, all of the fossil fuels including coal, oil, natural gas, bitumen, and kerogen are hydrophobic.
Further, most of the gases such oxygen, nitrogen, hydrogen, CO2, methane, etc. are hydrophobic, and
their solubilities in water are controlled by hydrophobic interactions. Yet, the basic mechanisms
associated with the behavior of the various hydrophobic species and materials of different length scales in
water are not fully understood.
In 1982, Israelachvili and Pashley reported the first measurement of the hydrophobic forces
acting between macroscopic surfaces. It has been shown also that the kinetics of coagulation of
hydrophobic particles is controlled by the hydrophobic force (Xu and Yoon, 1990). In addition, air
bubbles are hydrophobic, and the hydrophobic force is the major force destabilizing foams at low
surfactant concentrations (Wang and Yoon, 2008). However, the origin of hydrophobic force is not yet
known, and some investigators have suggested that the macroscopic hydrophobic forces are due to the
artifacts of nano-bubbles nucleating on hydrophobic surfaces. In this seminar, evidences for the
hydrophobic force originating from the structural changes of water in the confined spaces between
hydrophobic surfaces will be presented.