The Measurements of Contact Angles of Teflon Powder and the Consideration of the Dependency of Tablet Porosity for the Wetting

In this paper, the authors proposed a relatively simple method for the measurements of contact angles of teflon powder by adhesional and immersional wetting and also evaluated on the dependency of teflon tablet porosity for wetting. At first, the changes of advancing contact angles of drop with time for the systems composed of the teflon powder pressed into tablet, the sodium dodecyl sulphate solutions, and the air, were measured at regular time intervals. Furthermore, the similar measurements were carried out by the use of various porosities of tablets. These results showed that there were a linear relationship between the change of advancing contact angle by wetting and time. Thus, the authors evaluated the contact angle (θ0*) by extrapolating to time zero from the plot of advancing contact angle vs. time. The extrapolated contact angles (θ0*) obtained were regarded as the apparent contact angle on teflon plate having rough surface. As expected from the corrected equation, cosθ0*=cosθ- (1+cosθ) εfχ, it was confirmed that the extrapolated contact angles (θ0*) increased linearly by the increasing porosity of teflon tablet and true contact angle (θ) can be calculated.