Contact angles and wetting velocity measured electrically

We describe two new measurement techniques for studying the wetting behavior of a liquid on a surface. First, we measure the contact angle of a droplet, by measuring the capacitance between a conducting droplet and a subsurface counter electrode. The estimated error in the measured contact angle is 2% for contact angles in the range between 60° and 120°. In the second measurement technique, we detect the current as a function of time, which provides information about the dynamics of a droplet wetting the substrate. The time-integrated current is related to the base area of the droplet. Consequently, we can derive the radial velocity of the three-phase line of the droplet. The time resolution of the measurement technique is limited by the charging time of the initial capacitance, in our case approximately 0.5 ms. ©1999 American Institute of Physics.