Contact angle measurement for dispersed microspheres using scanning confocal microscopy

Scanning confocal microscopy was used for contact angle measurement of individual microspheres. The measurements were carried out by using different laser-scanned layers of the particle floating on the air-water interface. The ratio of the diameter for the cross-section of the protruded area of the particle at the air-water interface to the actual diameter of the particle is used for contact angle measurements. Two systems, i.e., glass and polystyrene microspheres with diameters of 3 - 10 and 6 mum, respectively, with water were used for this investigation (this size range of particles are most relevant to inhalation applications). Using the developed methodology, contact angles of 27degrees and 41degrees were measured (with water) for glass and polystyrene particles, respectively. The theoretical error in contact angle measurement for the developed methodology is determined to be generally about 1degrees with a maximum of 3degrees for contact angle of particles ranging from 2 to 24 mum in size; the experimental error was 4-6degrees. The contact angles of glass and polystyrene particles were compared to those obtained from pendant drop method and confirmed.