Georgia Institute of TechnologypicoForce Laboratory
Zinc Oxide nanobeltProfile: Elisa RiedoNanofriction plot

Long and Short Range Hydrophobic Forces

    The interaction of water with solid surfaces at the micro and nano-scale is a topic relevant to processes in tribology, geophysics and atmospheric science. Amid the interesting phenomena which occur when water is confined between two surfaces in nano-scale gaps, one of the most important and obscure is the attractive force between hydrophobic surfaces across aqueous solutions. This force is of central importance for protein folding, lipid aggregation and chemical self assembly of macroscopic objects. A better understanding of the interaction between hydrophobic surfaces in aqueous solutions in confined geometries  can lead to important improvements in the oil and gas industry in terms of pollution control and oil extraction.  In spite of this key role in life and technology, the nature and the origin of hydrophobic forces remain not well understood.

    Several studies have pointed out the presence of attractive forces between hydrophobic surfaces whose range and magnitude could not be explained with the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (a double layer ions repulsion and van der Waals attraction). Some theories have been developed in order to explain these new forces but none could account for the diversity of behaviors observed. It appears now evident that two hydrophobic forces can be found in nature: short range and long range forces. The presence of one or the other one seems to depend on surface properties. However, the nature and the origin of these forces is still matter of hot debate  and it remains unclear what are the properties which determine the appearance of short or long range forces, i.e. if the degree of hydrophobicity, the mobility of chemical groups or the topography.

    The goal of our research is to gain an atomistic insight in the origin and nature of short and long range attractive forces between hydrophobic surfaces in aqueous solution. To achieve this goal, we propose to measure hydrophobic forces with nano-scale spatial resolution on different kinds of hydrophobic surfaces and to characterize them at the atomic scale before, during and after each interaction.

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