Features of Coating Deposition Inside a Narrow Cavity in Octafluorocyclobutane Discharge Plasma

High Energy Chemistry -     

Fibroporous polytetrafluoroethylene modified with iron nanoparticles: Structure and electronic and magnetic properties

A method for synthesizing iron-containing nanocomposite based on fibroporous polytetrafluoroethylene (PTFE) is described. Fibroporous PTFE obtained under the radiation of a CO₂ laser on block PTFE is modified in supercritical carbon dioxide (sc CO₂) to form micro- and nanoporous structures. Porous fluoropolymer is treated with a solution of bis(toluene)iron(0) obtained by metal-vapor synthesis (MVS). The composition and structure of iron-containing fluoropolymer is studied by transmission electron microscopy and X-ray photoelectron and Mössbauer spectroscopy. Fe nanoparticles with an average size of 9 nm, consisting of ～30% FeO and ～70% Fe³⁺, are registered in the sample. Fe⁰ nanoparticles are stabilized in fluoropolymer pores and are coated with nanoparticles of nonstoichiometric iron oxides that have superparamagnetic properties.     

Thermomechanical properties of polytetrafluoroethylene in different zones of impact of continuous CO2 laser radiation

The pseudo-network structure of the amorphous block of polytetrafluoroethylene is formed by branching points, the crystallites of low- and high-melting crystalline polymorphs and the cluster segments of macromolecules. The polymer treated by laser irradiation is amorphized, with the degree of amorphization and other changes depending on the radiation fluence. A depression of the molecular flow onset and initial melting temperatures of the crystalline polymorphs, a decrease in the molecular mass, and the disappearance of the crystalline branching points characteristic of the original polymer have been observed in the irradiated polymer. Areas with different degrees of modification of the molecular structure appear in the dynamic mode with moving boundaries during continuous CO₂ laser irradiation. The difference in absorbance of the crystalline and amorphous portions of the polymer at the laser emission wavelength and a relatively high transmittance make laser-induced degradation differ from thermolysis in contact with a hot surface.     

Account of the Cross-Sectional Deplanation of a Composite Bar in Determining the Critical Force

A method for determining the critical force for an axially compressed composite bar with account of deplanation of its cross sections is considered. It is proposed to consider the cross-sectional deplanation, which decreases the critical force, by lowering the basic flexural stiffness of the bar by the value resulting from this effect. General relationships for calculating this value for composite bars are obtained. Numerical results are presented, which show the decrease in the critical force as a function of some parameters for transversely isotropic bars of rectangular cross section.     

Laser ablation of polytetrafluoroethylene

Anomalous behavior of polytetrafluoroethylene (PTFE) under the action of CO₂ laser radiation in vacuum is discussed. A feature of the ablation process is formation of polymer fibers which quantity depends on the target preliminary treatment and the ablation conditions. Experimental results are set out and possible mechanisms of the polymer fibering are discussed. A conclusion is made concerning two dynamic polymer components differ by the resistance to the laser beam action, appearing in the ablation crater. A method is proposed for producing unique fiber-porous polytetrafluoroethylene materials and other useful products as well as for the polytetrafluoroethylene wastes recycling. The results of industrial application of these new fiberporous materials are discussed.     

Influence of IR Laser Radiation on the Surface of Polytetrafluoroethylene Containing Small Amounts of Perfluoropropyl Vinyl Ether Units

High Energy Chemistry - The surface of chemically modified polytetrafluoroethylene, obtained by introducing 1 mol % perfluoropropyl vinyl ether in the polytetrafluoroethylene macromolecule chain,...     

The effect of continuous CO<Subscript>2</Subscript> laser radiation on the thermal and molecular—Topological properties of polytetrafluoroethylene

The impact of high-intensity laser radiation on a polymer in vacuum is accompanied by the release of gaseous products of degradation and, in some cases, of clusters of the partially destroyed polymer. Polytetrafluoroethylene (PTFE) exhibits an abnormal behavior in this process: being exposed to continuous CO₂ laser radiation, it degrades at a high rate and its clusters have a fibrous form. Depending on the irradiation conditions, the fibrous fraction forms two types of product, “cotton wool” and “felt”. Polytetrafluoroethylene and its laser-modified “cotton wool“ product have a semicrystalline topological structure. The preliminary γ-irradiation of PTFE enhances the laser ablation process.     

Effect of Gamma-Ray Pre-Irradiation on the Ablation of Polyethylene and Ethylene-Propylene Copolymer Under Continuous CO<Subscript>2</Subscript> Laser Radiation

We report the effect of preliminary γ-irradiation of polyethylene (PE) and ethylene-propylene copolymer (CEP) on the kinetics of polymer ablation under CO₂ laser irradiation. The rate of PE ablation exceeds the rate of CEP ablation at all doses of γ-irradiation. The ablation rate of the polymers can be approximated by a linear function in the initial stage, and the rate reaches a constant value in the second stage of ablation. The rate of laser ablation increases linearly with the dose of preliminary γ-irradiation in both stages of the kinetics. For PE ablation, the duration of the linear increase in rate decreases with increase in preliminary radiolysis dose. The morphology of the crater surface formed during the laser ablation of γ-irradiated polymers is characterized by a more diverse structure.