Mirau interferometry of fluid interfaces deformed by colloids under the influence of external fields

There exists a challenge in measuring how changes to the interfacial deformation around particles and three-phase contact angle modify particle pinning properties in situ as external curvature and electromagnetic fields are applied. Here we describe a modified technique based on phase-shifted Mirau interferometry to determine the relative height of the fluid interface surrounding interfacially pinned colloids while applying external fields.  The resolution of this technique is ±44 nm laterally in the plane of the interface and ±4 nm along the height axis, and corrections for in-plane motion of the particle and remnant far-field interfacial curvature are implemented.   The measured topography of the surface is used in conjunction with the particle geometry to identify the contact line where the two fluids meet the particle.  We apply this technique to quantify the contact angle (θ_c) and maximal interfacial deformation (∆u_max) of pinned ellipsoids in order to understand how changing particle characteristics and external field conditions modify interparticle capillary interactions. We find that electric fields increase θ_c but do not alter ∆u_max, indicating that the height of the particle at the interface changes upon application. Ongoing work is applying this technique to  additional interfacial systems, including biphasic ellipsoidal particles, and external field characteristics.