Techniques for measuring the wetting of leaf surfaces

摘要

AbstractDifferent types of plant leaves exhibit a broad spectrum of wetting behaviour because of their different pubescence, wax layer, scales, veins, etc. The wetting tension is used to express the wetting of a leaf with βsf= σf. cos θ (σf = the surface tension of a liquid and θ= the contact angle of a liquid to the surface of a leaf). Three different methods are used for measuring contact angles: the contact angle goniometer method, the meniscus rise method and the Wilhelmy plate method. All three methods are based on completely independent theories and produce absolutely uniform contact angles on smooth paraffin surfaces. Closed cup systems which could be thermostatted were used for making the measurements. Substantial differences in the contact angles become apparent when contact angle measurements on roughened and smooth firm surfaces are compared, as for example contact angles on smooth and roughened paraffin surfaces. If the figures for the contact angles on a smooth surface are 90° or>90°, they will be bigger on a roughened surface; if they are<90° on a smooth surface, they will be smaller on a roughened surface. These results obtained with paraffin were confirmed by contact angle measurements made on plant leaves. The contact angles, measured on plant leaves with the help of the three different measuring methods, show a high degree of uni