Glossary: Isotherm

Measurement of the amount sorbed as a function of sorbate pressure at constant temperature. The pressure may be the absolute pressure referenced to vacuum (IGA-001), the relative pressure referenced to saturation vapor pressure P₀ (IGA-002), the partial pressure (IGA-003) or relative density (e.g. humidity) for dynamic water sorption experiments using the IGAsorp. Isotherms may be measured at different temperatures to map phase diagrams or to enable calculation of the differential enthalpy and entropy of sorption using the Clausius-Clapeyron equation or van ‘t Hoff relation.

The amount sorbed is expressed in a range of units such as mmol/g and percentage uptake. It is also referred to as uptake, coverage, composition and concentration.