Automatic measurement of surface tension and wetting angle - using optical measurement of drop or bubble illuminated by parallel light

摘要

Drops or air bubbles of the fluid are illuminated by a parallel beam of light. The intensity of the light reflected back from a background mirror is measured at different positions and the results are processed electronically to compute the surface tension and wetting angle. The computation uses a binary intensity signal generated by passing the direct measurements through a comparator. The level of the comparator threshold is adapted for each set of measurements. Full information is obtained by using both suspended and resting drops or bubbles. The technique is superior to conventional capillary action in that it readily permits automation.