Measurement of Lateral Adhesion Forces at the Interface between a Liquid Drop and a Substrate

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.

Free-decay and resonant methods for investigating the fundamental limit of superhydrophobicity

“…However, the method suffers from the inability to control the normal and lateral forces independently. This is a major drawback because the relationship between these forces can be non-trivial 30,31 . A centrifugal adhesion balance can overcome the force coupling problem, but is more suitable for quasi-static measurements (for example, to study the lateral force required to unpin a droplet) than for dynamic measurements (for example, to investigate energy dissipation and the corresponding dissipative forces as a function of droplet speed).…”

Physics and applications of superhydrophobic and superhydrophilic surfaces and coatings

“…The centrifugal adhesion balance, introduced in 2009, uses centrifugal and gravitational forces to induce different normal and lateral force combinations for direct adhesion measurements between a liquid drop and a solid surface. 29 Then in 2011, Samuel et al 60 introduced a microbalance with a specially designed hydrophobic loop to hold a liquid drop capable of measuring the liquid-solid surface interactions on drop-surface approach (snap-in force) and pull-off force (adhesion) during liquid drop detachment. The authors found for a large number of samples having various surface characteristics that advancing contact angles correlate better with the snap-in force whereas receding contact angle with the pull-off force.…”

“…[24][25][26][27][28] This results in an increase in the force required to slide a drop on the solid surface as can be measured using the centrifugal adhesion balance. 3,4,26,29 Mutual saturation between phases or preferential adsorption at interfaces can be very fast, but sometimes, it occurs as a very slow process and thus exceeds the time of contact angle measurements, resulting in data measured under non-equilibrium conditions. 30 A good protocol requires contact angle measurements in liquidsaturated gas environment to at least secure equilibrium solid surface conditions.…”

Water tribology on graphene

“…Tribology teaches us that the frictional force is proportional to the contact area, whereas the Amonton law is a special case for very rough surfaces in which the load is roughly proportional to the contact area 2 . Recently, it was shown that for drops on surfaces, the frictional force can be inversely proportional to the load if, for example, we compare sessile and pendant drops 3,4 . This peculiar behaviour is a result of enhanced intermolecular interactions at the three-phase contact line which dominates the frictional force for this system 3,4 .…”

“…Recently, it was shown that for drops on surfaces, the frictional force can be inversely proportional to the load if, for example, we compare sessile and pendant drops 3,4 . This peculiar behaviour is a result of enhanced intermolecular interactions at the three-phase contact line which dominates the frictional force for this system 3,4 . The Shanahan-de Gennes surface deformation at the three-phase contact line 5,6 reorients the molecules resulting in a new distribution of functional groups between those on the surface and those buried deeper in the surface.…”