SUMMARY

Numerous engineering applications have been proposed to exploit the load-carrying and ‘non-contact’ nature of noncoalescing and nonwetting systems. One such application is a ‘lab-on-a-chip’, or LOC, where liquid samples sliding over a film of air are delivered from point-to-point without the large driving forces required to pump liquid through a microchannel. Due to the axisymmetry of the flow fields in both the lubricating gas and droplet, a stationary nonwetting droplet has a vanishing coefficient of static friction. However, once motion is imparted the droplet deforms which requires that a force be applied to sustain such motion. Given the very small volumes of droplets of interest in LOC applications, very little inertia must be overcome to initiate droplet motion in this near-frictionless situation. In fact, a small amount of friction in the LOC is actually desirable to enhance maneuverability of the drops on the chip. The program of research proposed focuses on investigating the lubrication force between a drop of silicone oil and a moving unwetted substrate due to the presence of a gas lubricating film. An apparatus to experimentally quantify the resistance has been designed and built. The frictional (or lubrication) force will be measured as a function of: (1) linear velocity of the moving solid; (2) relative displacement of the drop toward the solid; and (3) viscosity. The compression of the drop against the solid will be used to compute its load-carrying capabilities. The desired outcome will aid the engineer in the implementation of nonwetting to practical systems and will provide valuable experimental data to validate numerical models.