Faasivaheline

Faasivaheline is a term used to describe the boundary between two distinct phases of matter within a system, such as solid–liquid, liquid–liquid, or gas–liquid interfaces. This interfacial region is characterized by properties that differ from those of the bulk phases and by the presence of an interfacial tension or surface energy.

The interfacial tension is the excess free energy per unit area associated with the interface. It depends on temperature, composition, and the nature of the phases involved. Interfaces can be flat or curved, and curvature leads to a pressure difference across the interface described by Laplace’s law. How a phase wets a surface is described by the contact angle, which influences the shape and stability of droplets, films, and pores.

Interfacial phenomena include adsorption of surfactants or impurities at the boundary, which can lower interfacial tension and modify flow along the interface (the Marangoni effect). Mass transport across interfaces occurs by diffusion, and interfacial rheology describes how the boundary behaves under shear or deformation.

Measurement and study of faasivaheline properties employ methods such as tensiometry (Du Noüy ring, Wilhelmy plate), pendant-drop and spinning-drop techniques for interfacial tension, and interfacial rheometers for viscoelastic properties. Microscopy and spectroscopy help visualize and characterize the interface in situ.

Applications span emulsions and foams, coatings and printing, electrochemistry, catalysis, and environmental science. The Estonian term faasivaheline translates to interfacial or phase-boundary, highlighting its role as the boundary zone between two phases.