The interaction of materials with water vapor is of interest to a broad spectrum of science and industry. Almost all materials have some interaction with moisture that is present in their surroundings.The effects of water can be both harmful and beneficial depending on the material and how it is used.
The material properties can change as a function of humidity and temperature and the stability, type, magnitude and the kinetics of interaction are all important in this regard. For most materials it is this interaction with the moisture that must be understood, often the interaction of the sample with moisture leads to spoiling or changing of the sample which is very rarely desirable.
Water sorption is a general term that encompasses the range of possible interactions for water molecules with surfaces and bulk matter: These include physical adsorption, chemical (hydrogen) bonding and hydroxylation. Water sorption can also induce bulk changes such as hydration and amorphous phase transitions
The measurement that is most commonly made is the percentage weight content of moisture retained in the sample at a given relative humidity (% RH) and temperature and it is the measurement of these isotherms over a given range of temperatures that can be used to characterise the sample for defined environmental conditions
Materials are broadly classed as hydrophobic or hydrophilic, but detailed measurements of the interaction are required to investigate a given specimen and this generally requires determination of the water sorption isotherm.