Question

Dynamic vapour adsorption working principle

Answer 1

The water vapour sorption properties of Sitka spruce determined using a dynamic vapour sorption apparatus

Callum AS Hill, Andrew J Norton, Gary Newman

Wood Science and Technology 44 (3), 497-514, 2010

The water vapour sorption properties of Sitka spruce (Picea abies) have been investigated over a range of temperatures (14.2–43.8°C) using a dynamic vapour sorption apparatus. The sorption kinetics behaviour was evaluated using the parallel exponential kinetics model which has been found to give very accurate fits to the data in studies of foodstuffs or plant fibres, but has not been previously applied to sorption studies with wood. Both the adsorption and desorption kinetics curve can be deconvoluted into a fast and slow exponential process. Under conditions of adsorption, the fast process appears to be associated with the formation of monolayer water (determined using the Hailwood Horrobin model) up to a relative humidity of 20%. Under desorption, there is no clear differentiation between fast and slow processes. The area bounded by the sorption hysteresis loop reduced as the temperature at which the isotherm was measured increased, due to movement of the desorption curve only, with the adsorption curve remaining the same at all temperatures. This behaviour is consistent with sorption processes taking place on nanoporous glassy solids below the glass transition temperature. The heat of wetting was determined from the temperature dependence of the desorption isotherms by using the Clausius–Clapeyron equation, yielding results that are consistent with literature values. However, doubts are raised in this paper as to the applicability of using the Clausius–Clapeyron equation for analyses of this type.

Answer 2

Dynamic vapor sorption (DVS) is a gravimetrictechnique that measures how quickly and how much of a solvent is absorbed by a sample: such as a dry powder absorbing water. It does this by varying the vapor concentration surrounding the sample and measuring the change in mass which this produces. Water vapor is most commonly used, but it is also possible to use a wide range of organic solvents.

Dr Daryl Williams, founder of Surface Measurement Systems Ltd, invented Dynamic Vapor Sorption in 1991 and the first instrument was delivered to Pfizer UK in 1992. DVS was originally developed to replace the time and labor-intensive desiccators and saturated salt solutions to measure water vapor sorption isotherms.