Contact Angle Measurement in the Environmental Scanning Electron Microscope (ESEM)

Abstract

The ESEM uses a novel differential pumping system combined with a pressure-limiting aperture to achieve relatively high pressures of up to 10 torr in the specimen chamber. Using this system allows samples to be imaged in the presence of water vapour or other gases. Conveniently the saturated water pressure at 275K lies within this range, allowing the stabilisation of hydrated samples, condensation from water vapour and evaporation to be performed in situ within the microscope chamber.Wetting of surfaces is of fundamental importance in many different areas of science, from textiles to petroleum engineering. The ESEM now provides an opening for high-resolution studies of these phenomena without the problematic depth-of-field limitations that optical methods present. The contact angle, θ, is defined as the angle between the tangent to the liquid-fluid interface and the tangent to the solid interface. It provides a ready indication to the wetting properties of a system.