Dynamic vapour sorption

Dynamic vapour sorption (DVS) is a technique advancing the conduct of an investigation of the micropore and mesopore structure of materials. Analyses use water or solvent molecules carried by a gas close to the material surface and measure the speed of adsorption into the surface. Changes in sample mass observe the adsorption process. It changes according to the variation of partial pressure of the environment during the test period. This method was introduced in 1991, replacing traditional desiccator methods using salts solution. The DVS method has a wide range of uses. The continuous mass measurement significantly increases accuracy and removes systematic errors and distortions. The most common applications are the measurement of sorption isotherms and hysteresis effect in materials. Thanks to the dynamic range of temperatures and partial pressure of the solvent, this method dramatically extends the scale of material characterisation. It is also suited for permeability measurement, measurement of surface area of material or material stability. The temperature range of the device spans from 5°C up to 80°C. The only limitation is the behaviour of probe molecules, which restrict the upper limit of partial pressure for higher temperatures. The partial pressure can be set up to 95 %, but it is set at room temperature for the most common applications. Sample mass depends on the experiment type and sample properties. The most common sample weight used is approximately 10 mg.

Main usage:

Sorption isotherms
 * Sorption and desorption isotherms for water vapour or organic solvents display material reaction with absorbate at specific partial pressure. Simultaneous water sorption and solvent sorption are also possible.

Hysteresis effect and investigation of cyclic loads
 * Irreversible processes, such as the difference between sorption and desorption hysteresis and between series of moisture cycles, can be analysed with DVS. The measurements offer valuable information about the stability of materials for secure processing and storage properties.

Phase transition analysis
 * Most powder compounds change structure with moisture. A glass transition point and recrystallisation region are also described by the thermal analysis of polymers. Transitions are visible on mass change. Video observation is also available and shows material behaviour in high magnification. DVS allows to set the amount of amorphous content.

Heat of sorption
 * The amount of energy absorbed or released when vapours sorb into the sample surface can be set by the DVS method. Samples are measured at different temperatures, and the isosteric sorption heat is set using the Clausius-Clapeyron equation.

Surface area
 * The BET theory requires very low temperatures for applicable measurement, which is not suitable for many materials. DVS enables the measure the surface area taken in the room temperature range.

Permeability
 * Dynamic change of partial pressure and sample mass response are used for the determination of diffusivity properties of materials based on work previously done by Crank and Park.

S. Lowell, Joan E. Shields, Martin A. Thomas Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density

Diffusion in polymers edited by J. Crank and G. S. Park, Academic Press, London and New York, 1968

Brunauer, Stephen; Emmett, P. H.; Teller, Edward. Adsorption of Gases in Multimolecular Layers. Journal of the American Chemical Society.