Effect of phase transitions on adsorption properties of thin ferroelectricpoly(vinylidene fluoride-co-trifluoroethylene) films

The adsorption isotherms of water, oxygen, and hexane molecules at the surf ace of poly(vinylidene fluoride-co-trifluoroethylene) films 30 and 5 monola yers thick obtained by the Langmuir-Schaefer technique were measured at var ious temperatures using quartz crystal microbalance. An effect of a ferroel ectric phase transition occurring at a temperatures from 363 to 388 K on th e adsorption activity of the films of the both thicknesses was disclosed. T he highest adsorption was observed at a temperature T approximate to 380 K. In the case of the super-thin copolymer him 5 monolayers thick, one more m aximum of the adsorbability was detected at T approximate to 300 K that cor responded to a low-temperature phase transition, which is typical of only t he copolymer films thinner than 30 monolayers. The effects observed were ex plained by the facilitation of an adsorbate diffusion into the copolymer fi lm upon its structural rearrangement caused by the phase transition. The re sults of this study allowed us to propose a new method for the determinatio n of structural phase transitions based on studying isotherms of molecular adsorption from the gaseous phase.