Mohamed A. Bourham

Modifying Nylon and Polypropylene Fabrics with Atmospheric Pressure Plasmas

Polypropylene and nylon 66 fabrics are subjected to atmospheric pressure He and He-O2 plasmas for selected exposure time intervals. Scanning electron microscopy anal ysis of the fabrics shows no apparent changes in the plasma-treated nylon fiber surfaces, but significant surface morphological changes for the polypropylene. Surface analyses of the nylon filaments reveal small differences in the surface carbon and oxygen contents between the treated and control groups. The surface oxygen and nitrogen content of the polypropylene fabric increases significantly after treatment in both He and He-O2 plasmas. There is a slight decrease in nylon fabric tensile strength after treatment in He plasma for 3 minutes, while. there is no significant change in tensile strength of the nylon fabric treated with He-O2 after exposure times of up to 8 minutes.

One-step synthesis of silver nanoparticle-filled nylon 6 nanofibers and their antibacterial properties

A novel and facile one-step approach to in situ synthesize silver nanoparticle-filled nylon 6 nanofibers by electrospinning is reported. The method does not need post-treatments and can be carried out at ambient conditions without using additional chemicals. It employs the electrospinning solvent as a reducing agent for in situ conversion of AgNO3 into silver nanoparticles during the solution preparation. The resultant silver nanoparticle-filled nylon 6 hybrid nanofibers show an excellent fibrous structure (fiber diameter at 50–150 nm), with narrow size 2–4 nm silver nanoparticles uniformly dispersed throughout the nylon 6 matrix. DSC analysis shows that the in situ incorporation of silver nanoparticles increased the Tg and crystallinity of the resultant nanofibers. These silver nanoparticle-filled nylon 6 nanofibers exhibit a steady and long-lasting silver ion release behavior, and robust antibacterial activity against both Gram-positive B. cereus and Gram-negative E. coli microorganisms.

Plasma and antimicrobial treatment of nonwoven fabrics for surgical gowns

Plasma treatments are gaining popularity in the textile industry due to their numerous advantages over conventional wet processing techniques. In this study, the nonwoven fabric Sontara®, commonly used for surgical gowns, is treated with antimicrobial finishes and a plasma containing fluorocarbon gas. Treated samples are evaluated for changes in physical and functional characteristics. The plasma treatment does not alter the weight, thickness, stiffness, air permeability, and breaking strength and elongation. Plasma-treated and water-repellent Sontara samples show higher blood and water resistance compared to other treatments. Plasma-treated samples also show a zone of inhibition for Staphylococcus aureus, thus providing a barrier against microbes. There is no zone of inhibition for the water repellent Sontara, untreated, and wet control samples. This implies that the nonwoven fabric treated with plasma can provide a better barrier against microbes than commonly available surgical gown fabric with a fluorocarbon finish.

Numerical simulation and experiment of plasma flow in the electrothermal launcher SIRENS

An electrothermal plasma source (ET) may be used as a launcher by itself, or as a preinjector for electromagnetic launchers (railguns) or electrothermal-chemical (ETC) launchers. The characteristics of the injected plasma may affect the performance of the plasma armature (EMs) or the combustion process (ETCs). A 1-D, time-dependent fluid dynamics code, ODIN, has been developed to model the plasma formation and flow in the source and the barrel of the ET launcher SIRENS. The code models the energy transport, particle transport, plasma resistivity, plasma viscosity, and the equation-of-state. The measured mass ion of the ablating liner in the source section is in good agreement with predicted by the code. Comparisons between the measured and predicted pressures inside the barrel are in good agreement. >

Vapor shielding and erosion of surfaces exposed to a high heat load in an electrothermal accelerator

The experimental and theoretical verification of the vapour shield concept in an electrothermal accelerator is reported. Measurements of the ablation mass loss of the insulator material (Lexan) demonstrate that the energy transmission factor through the vapor shield is of the order of 10%. If enough vapor is produced under high heat flux, the vapor shield mechanism will help limit the surface erosion in electromechanical devices. The erosion of the barrel material (aluminum) has a strong axial dependence, and the erosion depth increases with input energy. >

A Study of Plasma Parameters in a Capillary Discharge With Calculations Using Ideal and Nonideal Plasma Models for Comparison With Experiment

A study of the plasma parameters in a capillary discharge was conducted using an experimental electrothermal plasma facility. The experimental results are compared to calculations using ideal and nonideal formulas of the Coulomb logarithm in the plasma electrical conductivity model to determine the nature of the plasma regime. Calculations are compared to the measured ablated mass, the measured electrical conductivity. Other calculated parameters are compared to results from similar and typical discharges. The measured ablated mass falls in between the ideal and nonideal calculations suggesting that the plasma is neither ideal nor nonideal; however, the linear fit of the experimental and calculated values shows divergence in the ideal calculations at higher peak currents. Measured plasma electrical conductivity is close to the ideal model predictions at lower values of the peak discharge current and approaches the nonideal model predictions at higher peak currents; the shape of the measured conductivity follows that of the nonideal model.

Surface Modification of Organic Polymer Films Treated in Atmospheric Plasmas

The effect of plasma treatment on surface characteristics of polyethylene terephthalate films was investigated using helium and oxygenated-helium atmospheric plasmas. Sample exposure to plasma was conducted in a closed ventilation test cell inside the main plasma chamber with variable exposure times. The percent weigh loss of the samples showed an initial increase followed by decrease with extended exposure time, indicating a combined mechanism of etching and redeposition. The wettability as measured by the contact angle showed a sharp initial increase followed by a steady-state trend with increased exposure time, suggesting a change in surface functionality. Atomic force microscopy analysis revealed increase in surface roughness, as well as evidence of redeposition of etched volatiles. Functionality changes were measured using X-ray photoelectron spectroscopy and these changes were correlated to the new plasma-induced properties.

Visible light emission measurements from a dense electrothermal launcher plasma

Measurements of the visible light emission from dense, weakly nonideal plasmas have been performed on the experimental electrothermal launcher device SIRENS. The plasma is created by the ablation of a Lexan insulator in the source, which then flows through a cylindrical barrel which serves as the material sample. Visible light emission spectra have been observed both in-bore and from the muzzle flash of the barrel, and from the flash of the source. Recent measurements along the axis of the device indicate time-averaged plasma temperatures in the barrel of about 1 eV for lower energy shots, which agree with experimental measurements of the average heat flux and plasma conductivity along the barrel. Measurements of visible emission from the source indicate time-averaged temperatures of 1 to 2 eV which agree with the theoretical estimates derived from ablated mass measurements and calculated estimates derived from plasma conductivity measurements. >

Multifunctional ZnO/Nylon 6 nanofiber mats by an electrospinning-electrospraying hybrid process for use in protective applications.

Abstract ZnO/Nylon 6 nanofiber mats were prepared by an electrospinning–electrospraying hybrid process in which ZnO nanoparticles were dispersed on the surface of Nylon 6 nanofibers without becoming completely embedded. The prepared ZnO/Nylon 6 nanofiber mats were evaluated for their abilities to kill bacteria or inhibit their growth and to catalytically detoxify chemicals. Results showed that these ZnO/Nylon 6 nanofiber mats had excellent antibacterial efficiency (99.99%) against both the Gram-negative Escherichia coli and Gram-positive Bacillus cereus bacteria. In addition, they exhibited good detoxifying efficiency (95%) against paraoxon, a simulant of highly toxic chemicals. ZnO/Nylon 6 nanofiber mats were also deposited onto nylon/cotton woven fabrics and the nanofiber mats did not significantly affect the moisture vapor transmission rates and air permeability values of the fabrics. Therefore, ZnO/Nylon 6 nanofiber mats prepared by the electrospinning–electrospraying hybrid process are promising material candidates for protective applications.

Semi-analytical modelling and simulation of the evolution and flow of Ohmically-heated non-ideal plasmas in electrothermal guns

In this paper, the Ohmic power input to the discharge capillary is recovered and used to analyse the basic processes involved in electrothermal (ET) plasma devices operated in an ablation-controlled-arc regime. Such an interplay between theory and experiment is necessary to reduce the number of reasons which might be responsible for the reported discrepancies between theory and experiment, as well as to illuminate the subject of ablation controlled arcs. A consistent methodology for determining detailed composition and thermodynamic functions of the non-ideal plasma generated in such devices is presented and used in the present computations. Different non-ideality effects, due to Debye-Huckel corrections in the Gibbs free energy, which have been ignored in prior publications, have been taken into account. A semi-analytical model for an ET plasma source with non-ideal effects is described and incorporated into a comprehensive computer code to simulate plasma evolution and flow in the discharge capillary. The model is one-dimensional, time dependent and uses the recovered Ohmic power input in the source term of the energy equation. The developed code has been used to investigate the ablation process and has shown the inappropriateness of a widely used ablation model. Code predictions for different plasma parameters are presented, discussed, and compared to available experimental data.