(635f) Direct Measurement of Lateral Capillary Force with a Cantilevered Capillary Force Apparatus

This presentation will include experimental results from efforts to utilize a cantilevered capillary force apparatus (CCFA) to directly measure the lateral (i.e. in-plane) capillary forces that exists between two objects immersed in a planar fluid-fluid interface. Capillary forces between objects pinned at fluid-fluid interfaces drive self-assembly of such objects into film structures that can be utilized for various materials science applications including the production of Pickering emulsions, or large-scale thin-films with controlled optical properties. One challenge to using this information to engineer such systems is that measuring or estimating such forces can be difficult. Theoretical models of lateral capillary force that consider object size, shape, contact angle, and other properties do exist, but complexities such as object surface roughness and contact-angle hysteresis are often challenging to capture with such models. In addition, lateral capillary forces are typically estimated from indirect measurements, where observations of object displacement over time are related to capillary forces via estimates of the local drag force, object size, and contact angle for a given system. In some experimental systems it is unclear how to estimate drag force and contact angle, one example being two-dimensional particles pinned to fluid-fluid interfaces, which make indirect measurements of lateral capillary forces difficult. To directly measure forces between objects pinned to a fluid-fluid interface a CCFA was modified to hold particles at the interface and measure the lateral forces between them as a function of distance and time. The presentation will include details of the CCFA, the modifications that were necessary to enable the measurements, results from preliminary measurements, and a perspective on where this device may be most valuable in future investigations of this kind.