Transport of Water by Surfactant Spreading in Unsaturated Porous Media

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Particulate material which is exposed to moisture typically has the surface of each particle coated with a thin film of water. It is often necessary to remove this water before the material can be used. The water may contain dissolved substances which are important to recover. Drying and recovery are tedious and expensive operations. A new technique shows that surfactants spreading at the air-water interface in such "unsaturated" porous media drag a significant amount of water with them. This water movement occurs with essentially no external energy input. The criteria for surfactant effectiveness in moving thin water films are different from bulk systems, and are not understood. The objectives of this research are to understand and optimize water transport by surfactant spreading. Definitive experiments will be conducted using classical surface chemistry techniques available in the laboratory. The work will shed new light on the character of water at interfaces, and on thin film properties in general. It has direct applications to room temperature drying or de-watering stabilization of building foundations without mechanical tamping of the earth, and underground mining and environmental cleanup without expensive excavation.