M. Yu. Yablokov

Adhesive properties of plasma-modified polytetrafluoroethylene films

A procedure was developed for the determination of the adhesion characteristics of the modified surface of thin polymer films, including those treated in a low-temperature plasma, with the use of the Scotch® 810 adhesive tape. The procedure comprises coating the surface to be studied by physical vapor deposition with an aluminum layer of ∼100 nm thickness, making an adhesive joint of the film with the Scotch® 810 tape, and T-peel testing of the specimen. Using this procedure, the peel resistance of the initial PTFE film and the film modified at the cathode and the anode in dc discharge was measured.

Detection of scintillation light in liquid xenon by multipixel avalanche Geiger photodiode and wavelength shifter

A multipixel avalanche Geiger photodiode with a p-terphenyl wavelength shifter in front of it has been tested in the liquid xenon to detect the 175-nm scintillation light. The detection efficiency of about 10% is obtained. A poly-para-xylylene film was used for protection of the liquid xenon detection medium from p-terphenyl pollution. The film has shown very good and stable adhesion at the low temperatures both to the p-terphenyl surface and to the surface of the stainless steel flange.

Microwave plasma in liquid n-heptane: A study of plasma-chemical reaction products

It has been found that a microwave discharge in liquid n-heptane leads to the formation of a solid phase in the form of carbonaceous nanoparticles. The composition and size of the particles have been determined by means of scanning electron microscopy with energy dispersive analysis and Raman spectroscopy. Using electronic absorption and luminescence spectroscopy, it has been shown that the discharge treatment results in the formation of polycyclic aromatic hydrocarbons in liquid n-heptane.

Determination of modified-layer thickness of glow-discharge-treated polytetrafluoroethylene film

It is known that treatment of polymer films with lowtemperature plasma is an effective surface modi� fication process resulting in improvement in the con� tact and adhesion properties, which can significantly extend the range of their use. An undoubted advantage of the process is that structural changes occur in a thin surface layer, whereas the bulk of the polymer remains intact, retaining the initial mechanical, physicochem� ical, and electrical properties of the material (1-3). We have shown that low values of the contact angle of water ( ~30°) can be achieved by treating PTFE films in dc discharge (4, 5). The XPS data obtained showed significant changes in the chemical structure of the surface: a decrease in the concentration of fluo� rine atoms (F/C ratio in the polymer decreased from 1.98 to 1.6) and the presence of various oxygencon� taining groups (C=O, C-O-, C(O)-F-, etc.), although the original film did not contain oxygen atoms (4, 5). The thickness of the affected layer in a plasma� treated polymer is an issue of great theoretical and experimental importance. In the literature, there are only indirect estimates of the layer thickness based on some unobvious approximations and related to differ� ent treatment conditions that do not allow the data to be compared and analyzed (1). Previously, we attempted to determine the thickness of the modified layer of a PTFE sample (plate of 10 mm thickness, treatment at the anode in dc discharge) by IR spectroellipsometry (6). However, this method does not provide direct experimental results, since it suggests model building and fitting the experimentally obtained parameters with the use of the Bruggeman equation for a twocomponent material (7). The aim of this study was direct experimental mea� surement of the thickness of the modified layer in a dc dischargetreated PTFE film. The object of study was a PTFE film of 50 µm in thickness (GOST (State Standard) 24222�80, Plast� polimer, St. Petersburg) treated on the anode in dc dis� charge at a plasma gas (air) pressure in the reaction chamber of ~20 Pa and a discharge current of 50 mA for 60 s. The thickness of the modified layer was deter� mined using a combination of Xray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The ion etching of the modified PTFE film was carried out directly in the XPS spec� trometer. During etching, XPS spectra were periodi� cally recorded; as a result, the dependence of the atomic concentrations of elements on the etching time was obtained. To determine the film etching rate, ion etching was carried out in the same mode, but with the imposition of a mask to cover half the sample etching area. The depth of the pit formed by ion etching was measured by AFM, and the etching rate was found as the ratio of the pit depth to the etching time. Based on the obtained value for the etching rate, we transformed the dependence of the atomic concentration of oxygen in the film on the etching time into the relation of the atomic concentration of oxygen to the pit depth.

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.

Alteration in the surface properties of direct-current discharge-treated tetrafluoroethylene-ethylene copolymer films

A change in the contact properties of the surface of a tetrafluoroethylene-ethylene copolymer film by treatment of its samples mounted on the cathode and anode in a dc discharge has been studied. It has been shown that the modification leads to a significant improvement in the contact properties of the films owing to the appearance of oxygen-containing polar groups on the polymer surface. The formation of such groups has been proved by X-ray photoelectron spectroscopy. The peel strength of both the untreated and modified films was measured by the T-peel test method.

Surface modification of vinylidene fluoride-hexafluoropropylene copolymer films by direct-current discharge treatment

Changes in the contact properties of the surface of a vinylidene fluoride-hexafluoropropylene copolymer film by dc discharge treatment were studied. It was found that the modification considerably improved the contact properties of the films because of the appearance of oxygen-containing polar groups on the polymer surface. The formation of these groups was detected by X-ray photoelectron spectroscopy and Fourier-transform IR spectroscopy.

Modification of Tetrafluoroethylene-Hexafluoropropylene Copolymer Films in Direct-Current Discharge

The effect of dc discharge treatment at the anode and cathode on the surface properties of tetrafluoroethylene-hexafluoropropylene copolymer films was studied. It was found that the modification of the films under conditions that ensure the separation of the discharge active species acting on the polymer materials makes it possible to achieve substantially lower values for the contact angle and higher values for the work of adhesion and surface energy than in the case of other modes of discharge. A change in the composition and structure of the films was studied by means of IR and X-ray photoelectron spectroscopy. It was found that new oxygen-containing groups are formed on the polymer surface as a result of plasma discharge treatment.

Micro- and nanofluidic diodes based on track-etched poly(ethylene terephthalate) membrane

The work is devoted to fabrication of micro- and nanofluidic diodes, devices that are polymer composite membranes with asymmetric conductivity. To this end, a polytetrafluoroethylene layer has been applied by electron beam sputter deposition on one side of a poly(ethylene terephthalate) track-etched membrane used as a porous substrate. It has been shown that the resulting effect of conductivity asymmetry is due to not only a significant decrease of the diameter of pores and a change in their geometry in the deposited polytetrafluoroethylene layer, but also the existence of an interface between the initial membrane and the hydrophobic polymer layer in the pores. Devices of this kind can be used for directional ion transport.

Modification of tetrafluoroethylene-perfluoropropylvinyl ether copolymer films in direct-current discharge

Changes induced in the surface properties of films of a tetrafluoroethylene copolymer with perfluoropropylvinyl ether by direct-current discharge have been investigated, depending on the discharge parameters. It has been shown that the treatment of the films at the anode is more effective than at the cathode. A change in the contact properties of the modified films during their storage in air under ambient conditions and upon heating to 150°C has been examined. The chemical composition of the surface of the films after modification, storage, and heating has been studied by X-ray photoelectron spectroscopy and Fouriertransform IR spectroscopy. It has been found that dc discharge treatment significantly improves the adhesion properties of the films and barely affects their light transmission.