Simultaneous measurement of a droplet’s curvature and contact angle using asymmetric deformation of its reflected laser beam

Abstract

The asymmetric deformation of a laser beam reflected from the surface of a droplet on a slide was observed. The degree of deformation of the beam profile in the incident plane is related to the droplet contact angle, and the degree of deformation perpendicular to the incident plane is related to the droplet curvature. A simple, non-contact, real-time technique to measure droplet wetting parameters was established. The contact angle and radius of curvature for different liquid droplets were measured, and measurement errors were in the sub-degree and sub-millimeter orders of magnitude, respectively. The values obtained for the contact angle using the reported measurement technique compared with those obtained using a traditional measurement technique with an imaging contact angle meter showed the reported technique to be reliable. The contact angle and radius of curvature for four blood samples were measured and compared with those obtained from blood samples using a routine test. For samples with white blood cells, hemoglobin, and hematocrit exceeding the standard, their wetting parameters regularly deviated from those of normal samples.