Draft:Centrifugal Adhesion Balance

• Comment: AI usage not fixed, no references have links yet. ~/Bunnypranav:<ping> 11:28, 28 June 2025 (UTC)

• Comment: Please clean up the "Key Applications" and "Related Research" sections, which evidently involve AI use, and properly link the papers in the references. JavaHurricane 09:10, 25 June 2025 (UTC)

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A current Centrifugal Adhesion Balance model.

The Centrifugal Adhesion Balance (CAB). is a scientific instrument, which measures the work of adhesion and lateral retention forces between a liquid droplet and a solid surface. Unlike conventional methods, CAB allows measuring lateral retention forces at different normal forces which mimic different gravitational accelarations. The CAB combines geometrical measurements (contact angle, drop height, drop diameter) with force measurements allowing a comprehensive understanding of the physics of the problem.

Background and Motivation

A common way of measuring the lateral retention force uses a tilt plate where the drop is sliding on the surface at some critical tilt angle. The tilt plate method aims to vary the lateral force, but as the tilt increases the normal force changes as well. This results in a situation where two variables are varied at the same time, thereby violating a basic experimental principle (namely change one variable at a time). This would not be a problem if the dependence between the two variables is known, but this is not the case for the drops on surfaces. For example, it is known that the pendant and the sessile drops behave differently but the way the normal force affects the lateral force in these cases is not fully understood. With the tilt plate method, the drop is never truly sessile or truly pendant, and at the extreme tilt (90°), the two converge. Additionally, the range of forces that can be applied with the tilt stage is limited between zero and the drop's weight (corresponding to 0° and 90° tilt angles, respectively). These problems prompeted several attempts to use centrifugal force instead of gravity culminating in the CAB along with other devices ^,.

In addition, historically, estimating the work of adhesion between a liquid and solid surface has been indirect using the Young-Dupré equation. This method is compromised because the apparent contact angle is different from the true nanoscopic equilibrium one just resulting in significant errors which fail to follow qualitative predictions. The CAB on the other hand, allows direct work of adhesion measurements.

Operation

The CAB consists of a centrifugal arm with a rotating chamber that houses a goniometer that includes a light source, and a camera that rotates with the arm. A droplet is placed on a solid substrate inside the goniometer. By gradually increasing the centrifugal rotation along with adjusting the tilt angle of the rotating chamber, the instrument precisely manipulates the normal and lateral forces acting on the droplet.

The governing force equations are:

Lateral force: $f_{\parallel }=m(\omega ^{2}L\cos \alpha -g\sin \alpha )$

Normal force: $f_{\perp }=m(\omega ^{2}L\sin \alpha +g\cos \alpha )$

A schematic illustration of the Centrifugal Adhesion Balance (CAB) setup, showing the forces acting on a droplet placed on a tilted surface. In this configuration, the normal force (f_⊥) is reduced (approaching zero), while the lateral force (f_∥∥) increases progressively with centrifugal acceleration.

A schematic illustration of the Centrifugal Adhesion Balance (CAB) setup, showing the forces acting on a droplet placed on a tilted surface. In this configuration, the lateral force (f_∥∥) is reduced (approaching zero), while the normal force (f_⊥) increases progressively with centrifugal acceleration.

where m is the mass of the drop, g is the gravitational acceleration, L is the length of the rotating arm, ω is the angular velocity, and α is the tilt angle (see Figure 1 that shows schematics of a drop resting in the CAB for cases where only lateral forces act, see Figure 2 that shows schematics of a drop resting in the CAB for cases where only normal forces act).

Key Applications

• Surface Energy Measurement: CAB provides a direct measurement of the surface energy of solid surfaces by using their work of adhesion on different surfaces using multiple probe liquids in a reliable way. Through this, the researchers found out that this method results in a reasonable breakdown of the surface energy to polar and dispersive components with a higher polar component for more polar solids .
• Lateral Adhesion Force Studies: CAB allows an independent manipulation of the lateral and the normal forces acting on a liquid droplet. This enabled the researchers to measure the lateral retention forces between the liquid droplet and a solid surface on which the droplet rested under different normal forces .
• Work of adhesion measurements: CAB allows a direct measurement of the thermodynamics work of adhesion between a solid surface and a liquid droplet. In other cases, researchers estimated the value of the work of adhesion using the Young-Dupré equation, which differs from the actual thermodynamic work of adhesion by several percentages. This overestimation of work of adhesion while using contact angles has been reported by researchers namely: (please see the references) ^,,.

Related Research

CAB has been featured in several peer-reviewed studies:

• Physical Review Letters 2009: In this paper, the researchers introduced the CAB to measure the lateral retention force between a solid surface and a liquid droplet.
• Langmuir 2017: In this paper, the researchers introduced the CAB to measure the work of adhesion between a solid surface and a liquid droplet.
• Colloids and Surfaces A: Physicochemical and Engineering Aspects 2017: In this paper, the researchers introduced Kerbero (similar to CAB). Kerbero is a device which (a) allows simultaneous rotation and tilting of the droplet supporting plate, and (b) three Wi-Fi cameras (viewing the droplet from X–Y–Z directions) follow the rotation/tilting motion. The above features permit on one hand the independent control of normal and tangential forces applied to the droplet and, on the other, allow real time 3D impressions of the droplet shape.
• Langmuir 2022: In this paper, the researchers used CAB to study the stages involved when a droplet depins as it slides on a solid surface .
• ACS Applied Polymer Materials 2022: In this paper, the researchers used CAB to stufy the tribological behavior of mucus-like hydrogels on solid surfaces .
• Physical Review E 2024: In this paper, the researchers used CAB to measure the surface energy of solid surfaces.
• Nature Communications Physics 2024: In this paper, the researchers used CAB to measure the normal drop detachment force between different solid liquid systems