Condensation of organic vapours within nanoporous calixarene thin films

Adsorption of vapours of benzene, toluene, p-xylene, aniline, hexane and chloroform in LB films of two novel calix[4]resorcinarene derivatives was studied in situ using quartz-crystal microbalance (QCM), ellipsometry and surface plasmon resonance (SPR) techniques. Isotherms of adsorption obtained by both QCM and SPR show that the adsorption ability depends on the condensed vapour pressures of the adsorbates rather than on a structural coincidence between host cavities and guest molecules. The results were interpreted in terms of capillary condensation of organic vapours in the nanoporous matrix of calixarene LB films accompanied by film swelling. Ellipsometric measurements show changes of both the thickness and refractive index of the LB films caused by adsorption, and thus confirm condensation and further accumulation of liquid adsorbate within the film matrix. Unusual adsorption kinetics were observed only when the vapour injection technique was used and their occurrence is believed to be caused by initial vapour condensation on the film surface. This can be eliminated by measurements under constant vapour flow.