Contact Angles on Spherical Hydrophilic Surfaces

The wettability of a surface is measured through its contact angle. A static contact angle smaller than 90° is defined as hydrophilic and a static contact angle larger than 90° is defined as hydrophobic. Contact angles are usually measured on horizontal surfaces, but given the significance of curved surfaces in biomedical and industrial applications it is important to assess these as well. In this paper we focus on two materials: neodymium and steel. We explore the contact angle measured on these surfaces from a dynamic perspective. To an initial deposited drop, in incremental steps, more water was added. With increased volume, the apparent advancing contact angle grew and at each increment it was measured. Two equations were used to calculate the intrinsic advancing contact angle. The values obtained were compared with intrinsic advancing contact angles measured on flat, horizontal surfaces.