Polynomial method

Method for determining the contact angle in drop shape analysis. In the polynomial method, the parameters of a polynomial function are fitted to the drop contour.

Background

Unlike all other methods of determining the contact angle (for example the circle method or conic section method), no assumptions are made regarding the shape of the drop contour. In each case, only part of the contour above the two points of intersection with the baseline (three-phase points) is analysed. Almost any contour shapes can be fitted by modifying a polynomial function.

The advantage is a highly flexible matching to the contour, even in the case of asymmetrical drops, for example when carrying out measurements with a tilting table or when measuring the dynamic contact angle with the needle still in the drop. A disadvantage is that irregularities in the contact region, for example due to contamination, or a baseline which is too deep can lead to severe adulteration of the measurement.