We have investigated bottom-up chemical synthesis of quaternary ammonium (QA) groups exhibiting antibacterial properties on stainless steel (SS) and filter paper surfaces via nonequilibrium, low-pressure plasma-enhanced functionalization. Ethylenediamine (ED) plasma under suitable conditions generated films rich in secondary and tertiary amines. These functional structures were covalently attached to the SS surface by treating SS with O 2 and hexamethyldisiloxane plasma prior to ED plasma treatment. QA structures were formed by reaction of the plasma-deposited amines with hexyl bromide and subsequently with methyl iodide. Structural compositions were examined by electron spectroscopy for chemical analysis and Fourier transform infrared spectroscopy, and surface topography was investigated with atomic force microscopy and water contact angle measurements. Modified SS surfaces exhibited greater than a 99.9% decrease in Staphylococcus aureus counts and 98% in the case of Klebsiella pneumoniae. The porous filter paper surfaces with immobilized QA groups inactivated 98.7% and 96.8% of S. aureus and K. pneumoniae, respectively. This technique will open up a novel way for the synthesis of stable and very efficient bactericidal surfaces with potential applications in development of advanced medical devices and implants with antimicrobial surfaces.
Surface rich in covalently-bonded amine groups have wide end use applications in biomaterials. This article describes functionalization of stainless steel (SS) surface with reactive chemical groups using RF-cold-plasma polymerization of ethylene diamine (ED), acrylonitrile (AN), and acetonitrile (AcN). The effect of RF plasma power and frequency (40 kHz and 13.56 MHz) on surface chemistry was investigated by electron spectroscopy for chemical analysis (ESCA) and FTIR. It was demonstrated that all the plasma-deposited films consist of secondary and tertiary amines, imines, and amides with a small concentration of nitrile groups present in AN plasma. Significant changes in ED, and AN plasma-induced molecular fragmentation occur as the plasma conditions are varied. However, AcN plasma polymer chemistry is observed to be independent of RF frequency. Films deposited at 13.56 MHz RF power in continuous mode have higher concentrations of CÀ ÀN linkages, with maximum in ED plasma-polymerized films.
The structure and rheological properties of xanthan gum (XG) modified in a cold plasma environment were investigated. XG was functionalized in a capacitively coupled 13.56-MHz radio frequency dichlorosilane (DS)-plasma conditions and, consecutively, in situ aminated by ethylenediamine. The surface structure of modified XG was evaluated on the basis of survey and high-resolution ESCA, FTIR, and fluorescence labeling techniques. The types of species generated in DS-plasma were reported using residual gas analysis (RGA). The aqueous solutions of modified XG were cross-linked and cured at room temperature to form stable gels. The dynamic rheological characteristics of virgin XG and functionalized and cross-linked XG were compared. It was found that parameters such as plasma treatment time and concentration of solutions can be optimized to form stable gels of XG. Thus, cold plasma technology is a novel, efficient, and nonenzymatic route to modify XG.
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