Pendant Drop Method

Pendant Drop Method

The pendant drop technique determines surface or interfacial tension by analyzing the shape of a drop suspended from a needle. The drop’s curvature results from the balance between gravity and surface/interfacial tension, governed by the Young–Laplace equation.

As gravity causes hydrostatic pressure within the drop, the drop elongates into a pear-like shape. This distortion depends on the drop’s weight and the density difference (Δρ) between the two phases. Accurate measurements require the actual drop size, which is obtained by calibrating the image scale.

The drop contour is extracted using greyscale video analysis. A shape factor (B) is varied numerically until the theoretical shape fits the observed profile. The interfacial tension is then calculated using Δρ and the optimized B value.