The main goal of this proposal is to develop a new Centrifugal Adhesion Balance (CAB) model that includes temperature and humidity controls in one compact unit to enable evaluating their effect on drop retention force, and allow a systematic study of surface robustness from CAB measurements. This will make the CAB applicable to new systems, and significantly enhance its use by other researchers.
The problem of drops on surfaces has wide industrial implications related to contact lenses, eye drops, inhalation drugs, and cosmetic industry as well as implication in phenomena like deformable particles and nanotechnology. Roughness plays a crucial role in wetting properties of many surfaces in nature, and can be used to control the wettability of a surface. In some applications, it is useful to retain the drops on the surfaces, for example in the case of water-based herbicides, or in heat exchanger surface, or when trying to retain a spill. In other applications, it is desired that the drops slide off the surfaces as in oil extraction from porous rock and self-cleaning surfaces. The interest in self-cleaning surfaces is being driven by the desire to fabricate such surfaces for satellite dishes, solar energy panels, photovoltaics, exterior architectural glass, and green houses.
Theories initiated by Shanahan and de-Gennes and confirmed experimentally using the CAB show that a central parameter in relating normal to lateral forces is a shear modulus that corresponds just to the outmost layer of the solid surface, termed here interfacial modulus, . This property describes the surface resilience to conform its outmost layer to a liquid drop in contact with it, and is expected to be a strong function of the temperature and relative humidity. The new CAB will enable temperature and humidity controls and thereby allow measurements that lead to understanding of the influence of these parameters on for different systems. Science is also lacking in understanding of the physics related to nano-structured surfaces, and its relation to the ability of such solid structures to conform to the liquid above them. These systems are particularly sensitive to humidity and temperature. Biological surfaces are also extremely sensitive to temperature and humidity. The proposed instrument will enable systematic study of these systems.