Determination of the contact angles and pseudo-line tensions on heterogeneous surfaces with different size of bubbles

The wettability of solid surface is significant in a wide range of applications. The surface wettability would be affected by a number of factors, such as chemical composition, heterogeneity, surface roughness, and the properties of droplet/bubble. The variation of the contact angle with the size of bubble/droplet in a three phase contact system can be ascribed to the influence of the line tension. Understanding the evolution of contact angle and pseudo-line tension between a heterogeneous surface and bubble with different size is significant in guiding the applications of heterogeneous surfaces. In this work, heterogeneous surfaces with different hydrophobic area fractions were prepared. These surfaces consisted of discrete hydrophilic dots and interconnected hydrophobic background. The contact angles between the heterogeneous surface and bubble were measured at different bubble sizes and the pseudo-line tensions were calculated. Meanwhile, a model was developed to estimate the pseudo-line tension on the heterogeneous surface. The model predicted that the pseudo-line tension would increase with the increase of the hydrophobic area fraction and the vector would point to the liquid phase, which was consistent with the experimental results.