Drop Retention Forces and Interfacial Modulu

We established a device--Centrifugal Adhesion Balance (CAB) for measuring the combination of centrifugal and gravitational forces that apply on liquid droplets. By using CAB, we can manipulate the lateral retention force f|| and normal force f⊥? respectively. It can be used for direct measurements of the solid-liquid work of separation1, the value of which is independent of drop size and in agreement with Dupre's theory.2 This device can also be used for investigating the motion of the drop on the solid surface. Here, experiments for identifying the pattern of motion of liquid drops under different microgravity are performed. A liquid drop that partially wets a solid surface will slide along the plane when a force beyond a critical value is applied to it. This critical value is defined as onset of motion. The required lateral retention force is dependent on the surface heterogeneities and other factors. Based on the investigation, we classify the drop motion into different zones, which includes no motion zone, transition of motion, slow motion and fast motion zones. It is the subject matter of our discussion. We also find out that the drop length stretches to its first maxima at the onset of motion before it shrinks back, when 1 mg as the normal force is applied to the drop.;The correlating equations3-6 for lateral retention force are discussed as well. Based on Tadmor's equation, G modulus values for different solid-liquid systems are calculated5.