Dissertations, Theses, and Capstone Projects

Date of Degree

6-2024

Document Type

Dissertation

Degree Name

Ph.D.

Program

Physics

Advisor

Jeffrey Morris

Advisor

Mark Shattuck

Committee Members

Nicolas Giovambattista

Joel Koplik

Charles Maldarelli

Subject Categories

Physics

Abstract

Capillary bridges are ubiquitous in nature and have important implications in processes like inkjet printing. They are an important area of study not only because of their industrial applications but because many of the questions in capillary bridge research are applicable to other systems. For example, they exhibit pinning and unpinning patterns that are similar to those in sliding droplets. The rules underlying this pinning are essential to predicting liquid shapes and understanding how contact lines move across surfaces. Many previous studies have focused on axisymmetric capillary bridges and neglected to model the tangential forces that arise due to asymmetry. This thesis uses both experiments and simulations to measure tangential forces and connect them to the shape of the contact line. The first part of this thesis focuses on capillary bridges with changing height that are pinned between parallel flat plates. We created an experimental protocol that measures the bridge shape and the normal force simultaneously to create a full picture of the bridge evolution. We found that the contact line pinning was not always total as has been seen in previous works. We formulated a model that relates the degree of contact line pinning with the change in the contact angle. This model was successfully incorporated into Matlab simulations to recreate experimental results. We also studied the effects of non parallel flat plates on capillary bridges. We connected the asymmetric contact line movement with the pinning and unpinning of the contact line. The second part of this thesis looks at sheared capillary bridges between spheres. We took direct measurements of the normal and tangential forces exerted on the spheres and imaged the bridge shape. We also performed Surface Evolver simulations to study the effects of pinned and unpinned contact lines during shearing. We found that the tangential force was related to bridge asymmetry. Symmetric bridges had no tangential forces while asymmetric bridges exerted tangential forces that were comparable in scale to the normal force. We developed an equation that successfully predicted the tangential force based on the shape of the bridge. We also found that the forces and energy of sheared bridges with unpinned contact lines were identical to those of capillary bridges with changing height if there was equivalent distance between spheres.

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