Hysteresis of contact angle of water on paraffin. Effect of surface roughness and of purity of paraffin

Abstract

The experimental results show that when very thin films of purified paraffin were formed in vacuum by volatilization on smooth glass surfaces and water drops were placed upon them, the advancing and the receding contact angles were sensibly the same, 112[deg]; that is, hysteresis effects did not exist on these very thin and very smooth surfaces.Measurable hysteresis effects from 5[deg] to 35[deg] were found for less smooth films, and coatings of appreciable thickness formed in vacuum, in nitrogen, or in air, whether from a melt or by volatilization.The magnitude of the hysteresis effects appeared to be closely associated with the microscopic roughness of the surfaces, the roughness adding to the magnitude of the advancing angle but subtracting from the receding angle to the same degree, so that the average angle remained the same for paraffin films of different roughnesses but of the same degree of purification. The average contact angle for purified paraffin was slightly larger than the average angle for unpurified paraffin.