The method of sorption calorimetry is designed for studies of
hydration of complex organic and biological materials. It has been applied for studies of
surfactants
Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a blend of "surface-active agent",
coined in 1950. As t ...
,
lipids
Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins Vitamin A, A, Vitamin D, D, Vitamin E, E and Vitamin K, K), monoglycerides, diglycerides, phospholipids, and others. The fu ...
,
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
,
nanomaterials
Nanomaterials describe, in principle, chemical substances or materials of which a single unit is sized (in at least one dimension) between 1 and 100 nm (the usual definition of nanoscale).
Nanomaterials research takes a materials science ...
and other substances. A sorption calorimetric experiment is performed at isothermal regime, but different temperatures can be studied in separate experiments.
In a sorption calorimetric experiment, a two-chamber calorimetric cell is inserted into a double-twin microcalorimeter.
Water evaporates, diffuses through the tube connecting two chambers of the calorimetric cell and is absorbed by the studied substance.
The amount of evaporated water is calculated from the thermal power registered in the vaporisation chamber:
:
From the same data, the activity of water in the sample can also be calculated:
:
From the thermal powers registered in the two chambers one can calculate the partial molar
enthalpy
Enthalpy () is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant extern ...
of mixing of water.
During the sorption experiment the water content in the sample increases until it reaches a value high enough to make the process of diffusion of water vapor between the chambers very slow. Then the sorption experiment can be stopped.
For studies of hydration at very high relative humidities, a special modification of the method of sorption calorimetry – the
desorption calorimetric method
Desorption is the physical process where Adsorption, adsorbed atoms or molecules are released from a surface into the surrounding vacuum or fluid. This occurs when a molecule gains enough energy to overcome the activation barrier and the binding e ...
– was developed. A desorption experiment starts with a fully hydrated sample which is placed in the sample chamber (the top chamber in the figure). In the bottom chamber a salt solution is injected. During the desorption experiment the sample is being slowly dehydrated and the salt solution takes up the water evaporated from the sample.
See also
*
Isothermal microcalorimetry
Isothermal microcalorimetry (IMC) is a laboratory method for real-time monitoring and dynamic analysis of chemical, physical and biological processes. Over a period of hours or days, IMC determines the onset, rate, extent and energetics of such pr ...
*
Isothermal titration calorimetry
In chemical thermodynamics, isothermal titration calorimetry (ITC) is a physical technique used to determine the Conjugate variables (thermodynamics), thermodynamic parameters of interactions in Solution (chemistry), solution. ITC is the only tec ...
*
Pressure perturbation calorimetry
References
{{Reflist
External links
Vitaly Kocherbitov: Sorption calorimetry (Malmö University)
Calorimetry
Heat transfer