Research Assistant , Lamar University
Young Dupre Gedanken Experiment
We establish a tool for direct measurements of the work needed to separate a liquid from a solid. This method mimics a pendant drop that is subjected to a gravitational force that is slowly increasing until the solid-liquid contact area starts to shrink spontaneously. The work of separation is then calculated in analogy to Tate's law. The values obtained for the work of separation are independent of drop size and are in agreement with Dupré's theory, showing that they are equal to the work of adhesion.
Abstract: Surface forces and shape changes were simultaneously measured during the approach and coalescence of two liquid-liquid and liquid-air interfaces. Large normal and lateral deformations were observed that are nevertheless consistent with a simple theoretical analysis of the long-range effects of short-range attractive van der Waals forces. The results imply that two fluidlike structures such as liquid droplets and soft biological cells can sense each other at much larger separations than previously assumed based on criteria taken from the interactions of hard particles.
Pub.: 03 Feb '04, Pinned: 17 Jun '17
Abstract: A novel instrument allows for the first time measurements of the lateral adhesion forces at a solid-liquid interface, f(parallel), in a way that is decoupled from the normal forces, f(perpendicular). We use it to measure how f(parallel) between a drop and a surface is influenced by different f(perpendicular) and different histories of drop resting periods on the surface prior to sliding, t(rest). The variation of f(parallel) with t(rest) is similar for different f(perpendicular) and always plateaus as t(rest)-->infinity. We show that the f(parallel) plateau value is higher when f(perpendicular) is lower. This seemingly counterintuitive result is in agreement with recent theories.
Pub.: 07 Apr '10, Pinned: 17 Jun '17
Abstract: In a recent paper ('t Mannetje, D.; Banpurkar, A.; Koppelman, H.; Duits, M. H. G.; van den Ende, D.; Mugele, F. Electrically Tunable Wetting Defects Characterized by a Simple Capillary Force Sensor. Langmuir 2013, 29, 9944-9949), there are a few misconceptions regarding the interpretations of theories emanating from Shanahan and de Gennes in describing centrifugal adhesion balance (CAB) experiments, making their results seemingly contradictory to the theory. These are clarified here. We show that their results, if interpreted correctly, do not contradict the theories mentioned above.
Pub.: 22 Nov '13, Pinned: 17 Jun '17
Abstract: A lotus leaf retains water repellency after repeated condensation in nature but becomes sticky to water drops after condensation on a fixed cold plate. Our experiments show that mechanical vibration can be used to overcome the energy barrier for transition from the sticky Wenzel state to the nonsticking Cassie state, and the threshold for the dewetting transition follows a scaling law comparing the kinetic energy imparted to the drop with the work of adhesion. The vibration-induced Wenzel to Cassie transition can be used to achieve antidew superhydrophobicity.
Pub.: 13 Nov '09, Pinned: 02 Jun '17
Abstract: We establish a tool for direct measurements of the solid-liquid work of separation. This method mimics a drop that is subjected to a gravitational force that is slowly increasing until the solid-liquid contact area starts to shrink spontaneously. The work of separation is then calculated based on Tate's law. The values obtained for the work of separation are independent of drop size and are in agreement with Dupré's theory suggesting that it may equal the work of adhesion.
Pub.: 26 Jan '17, Pinned: 02 Jun '17