Subject sorption constant

Modeling relaxation-influenced processes has been the subject of much theoretical work, which provides valuable insight into the physical process of solvent sorption [119], But these models are too complex to be useful in correlating data. However, in cases where the transport exponent is 0.5, it is simple to apply a diffusion analysis to the data. Such an analysis can usually fit such data well with a single parameter and provides dimensional scaling directly, plus the rate constant—the diffusion coefficient—has more intuitive significance than an empirical parameter like k. 

In principle, the Henry constant may be predicted theoretically by evaluation of the configuration integral for an occluded molecule. Such calculations are subject to the considerable uncertainties implicit in theoretical potential calculations (17), and the utility of this approach is now limited to simple spherical molecules such as the inert gases (18, 19). A fair estimate of the standard entropy of sorption or of the value of K0 may, however, be obtained from a simple idealized model. 

Sorption Kinetics. The adsorption and desorption data were analyzed in terms of a model based on the following main assumptions. Micropore diffusion within the sieve crystals is the rate-controlling process. Diffusion may be described by Fick s law for spherical particle geometry with a constant micropore diffusivity. The helium present in the system is inert and plays no direct role in the sorption or diffusion process. Sorption occurs under isothermal conditions. Sorption equilibrium is maintained at the crystal surface, which is subjected to a step change in gas composition. These assumptions lead to the following relation for the amount of ethane adsorbed or desorbed by a single particle as a function of time (Crank, 4). 

The unstirred layer adsorption model can be generalized by the introduction of surface concentration dependent sorption rate constants k and This subject is currently being studied as well as the existence of a second, irreversible, surface reaction following reversible initial adsorption for fibrinogen and prothrombin on a 60% DOPS/40% DOPC mixture. 

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