Design and Implementation of an Experimental Apparatus to Measure Grain-Scale Adhesion Forces Open Access
Parker, Ashton (Spring 2026)
Abstract
Granular materials commonly experience cycles of wetting and drying in both natural
and engineered environments. During drying, evaporation can generate adhesive
interactions between grains through capillary forces and the formation of solid bridges
at particle contacts. These microscopic interactions can significantly alter the macroscopic
mechanical behavior of granular assemblies, transforming materials that are
initially loose and free-flowing into cohesive structures. Despite the importance of
these processes in soils, sediments, and other particulate systems, direct experimental
measurements of adhesion at individual grain contacts during drying remain limited.
This thesis presents the design and implementation of an experimental apparatus
capable of measuring adhesive forces between a single ∼100 μm sand grain and a
glass substrate under controlled desiccation conditions. In the experiment, the grain
is attached to the end of a thin silica fiber that acts as a cantilever beam. As the
grain adheres to the substrate, the cantilever deflects elastically. When the adhesive
contact fails, the cantilever rapidly returns toward equilibrium and undergoes damped
oscillations that are recorded using high-speed imaging. The maximum deflection
immediately prior to detachment is determined from the tracked grain position and is
related to the adhesive force using Euler–Bernoulli beam theory.
Baseline measurements indicate a force resolution of approximately 0.4–0.6 μN.
Under typical drying conditions, adhesive forces between the sand grain and the glass
substrate are found to be on the order of 2–3 μN. Larger forces are observed when
the contact is allowed to dry for longer periods, reaching approximately 10 μN after
roughly one hour and approximately 38 μN after three hours of drying. In experiments
where contamination was present at the grain contact, adhesive forces as large as
60 μN were measured.
These results demonstrate that the cantilever-based apparatus provides a sensitive
method for directly measuring grain-scale adhesion forces. Such measurements provide
a foundation for understanding how drying, surface chemistry, and environmental
conditions influence cohesion in granular materials.
Table of Contents
Chapter 1: Introduction…………………………………………………….1
Chapter 2: Background………………………………………………………4
Chapter 3: Experimental Design and Approach………………….9
Chapter 4: Beam Theory and Force Calibration………………..17
Chapter 5: Experiments……………………………………………………23
Chapter 6: Analysis………………………………………………………….28
Chapter 7: Conclusion…………………………………………………..…37
Appendix A: Appendix……………………………………………….….…40
Bibliography………………………………………………………………….…45
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