Chemical and physical surface modification of PTFE films—an approach to produce stable electrets

The thermal stability of positive charge has been investigated in chemically and physically treated polytetrafluoroethylene (PTFE) films. It has been found that virgin films, oriented by the manufacturer, display an increase in thermal stability of positive charge with an increase of the initial value of surface potential. Such an anomalous behavior is explained by the influence of a negative tribocharge, trapped some small distance below the surface. In PTFE samples treated with orthophosphoric acid and with tetraethoxysilane, a?considerable improvement of positive charge stability has been achieved, but no influence of the initial value of surface potential has been observed. However, this influence should be kept in mind when comparing charge stability in virgin and modified samples. In nonoriented PTFE films, no influence of the initial value of surface potential on charge stability has been observed. This could be due to the fact that these films did not possess a noticeable negative tribocharge. After the treatment in glow-discharge defluorination, oxidation and appearance of polar groups have been detected on the surface. These changes in chemical composition of a PTFE surface resulted in a noticeable improvement in thermal stability of positively charged electrets. This improvement is attributed to the formation of deeper traps on the modified surface.     

Effect of direct-current discharge treatment on the surface properties of chitosan-poly(L,L-lactide)-gelatin composite films

The surface of films made from a chitosan-poly(L,L-lactide)-gelatin mixture stabilized with a grafted-copolymer fraction has been modified by dc discharge treatment, as well as that of films made of the individual components. The surface properties of the films (wettability, surface energy), the chemical structure of surface layers, and their morphology have been examined by goniometric measurement of contact angles, X-ray photoelectron spectroscopy, and scanning electron microscopy.     

Structural aspects of the deposition of metal coatings on polymer films

An electron-microscopic study of the formation of thin metal coatings (gold and aluminum) on a PET film is performed. During the deposition of gold coatings, a well-pronounced interfacial polymer/metal layer is formed, while, in the case of aluminum coatings, the polymer/metal interface is well-defined. The assumption is made that this effect is caused by different chemical activities of metals deposited on the polymer.     

Transport properties of the LaSrNiO4 ± δ ceramics

The temperature dependence of electrical resistivity in LaSrNiO_{4 ± δ} ceramics synthesized using various techniques and subjected to heat treatment is studied. The occurrence of a metal-semiconductor transition is shown to be accounted for by the Anderson carrier localization originating from the random arrangement of oxygen vacancies.