Chemical nano-heterogeneities detection by contact angle hysteresis: theoretical feasibility

The theoretical feasibility of detecting chemical nanoheterogeneities on solid surfaces by measurement of contact angle hysteresis (CAH) was studied, using simplified models of cylindrical (2D) and axisymmetric (3D) drops on corresponding models of chemically heterogeneous, smooth solid surfaces. This feasibility depends on the ratio between the external energy input to the drop and the energies needed to deform its liquid-gas interface and move the contact line across energy barriers. A ubiquitous source of external energy is building vibrations, since most contact-angle measurements are done in buildings. The energy barriers that oppose the motion of the contact line were numerically calculated for various parameters of the two systems. The variations of the liquid-gas interfacial energy are discussed in terms of orders of magnitude. By comparing these energies, it is concluded that under regular ("barely perceptible") building vibrations CAH measurements may detect chemical heterogeneities at the few nanometers scale.