The method of sorption calorimetry is designed for studies of

hydration Hydration may refer to: * Hydrate, a substance that contains water * Hydration enthalpy, energy released through hydrating a substance * Hydration reaction, a chemical addition reaction where a hydroxyl group and proton are added to a compound * ...

of complex organic and biological materials. It has been applied for studies of

surfactants Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsion#Emulsifiers , ...

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

, DNA,

nanomaterials * Nanomaterials describe, in principle, 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-based approach to nan ...

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: :

n_w= \frac

From the same data, the activity of water in the sample can also be calculated: :

a_w=1-\frac

From the thermal powers registered in the two chambers one can calculate the partial molar

enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...

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 a previously adsorbed substance is released from a surface. This happens when a molecule gains enough energy to overcome the activation barrier of the bounding energy that keeps it in the surface. There ...

Kocherbitov, V. and L. Wadsö, A Desorption Calorimetric Method for Use at High Water Activities. Thermochimica Acta, 2004. 411(1): p. 31-36. – 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.

References

{{Reflist

External links

Vitaly Kocherbitov: Sorption calorimetry (Malmö University)
Calorimetry Heat transfer

See also

References

External links