Immobilizing adsorption of diffusing penetrants is known to occur in a number of polymer membrane systems. It will cause very large increases in the diffusion time lag but will have only minor effects on the steady‐state permeation. This effect may be troublesome in that considerable errors may be incurred when the time lag method is used to analyze quantitatively the sorption and diffusion behavior in such systems. On the other hand, this effect can be utilized in a beneficial way to design very effective protective coatings, packaging materials, timed release mechanisms, etc. for special situations. The time lag in this case can be predicted very accurately from a theoretical result reported previously. This point is demonstrated here by comparing theoretical predictions with experimental time lag data obtained for various gases in a model membrane synthesized by dispersing highly adsorptive molecular sieves into silicone rubber. The agreement is excellent.
SynopsisThe equilibrium and kinetics of gas sorption by a silicone rubber filled with highly adsorptive molecular sieves was studied. Sorption in this system is by two mechanisms: gas is simply dissolved in the polymer matrix according to Heiiry's law, while it is adsorbed by the dispersed sieve phase in accordance with a Langmuir's isotherm. The latter effectively immobilizes the gas molecules preventing their further diffusioii. Ail equilibrium parameters were determined experimentally. Immobilization greatly affects sorption kinet,ics and renders conventional analyses invalid. A theory to account, for this process was adapted from a previoiis analysis by Vieth and Slpdek which assumes that the kinetics of adsorptioii is very fast compared to diffusion. For this situation the kinetics always assume a Fickean form. The experiinental data agreed very well with the predictions of this theory in a comparison where all parameters were defined by independent experiments. I t was found that n single effective diffusion coefficient describes sorption kinetics, steady-state permeation, and lime-lag results once the effects of immobilization are properly accoinited for.
A number of polycyclic aromatic thiones have been prepared from the corresponding ketones. Several of the thiones in which there is a free peri position cyclize, on excitation in the π* ← n band, to give thiophene derivatives. The structures of these were proven by application of physical methods and by desulfurization to the corresponding benzyl derivatives. The formal hydrogen 1,3 migration involved was, in one case, shown to be intermolecular by the incorporation of deuterium, from deuterium oxide, during the irradiation. In the case of the α-naphthyl derivative, the mechanism of the reaction has been investigated and it has been concluded that the n,π* singlet is the responsible entity.
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