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A polyorganosiloxane thin film was deposited on an optically transparent poly(ethylene 2,6-naphthalate) (PEN) film using plasma-enhanced chemical vapor deposition (PECVD) at room temperature to improve the moisture barrier property of the PEN film. In the PECVD process, hexamethyldisiloxane (HMDSO) was used as the monomer. Argon or oxygen and their mixture gases were used as the plasma carrier gas. Poly(HMDSO) thin film was successfully deposited through plasma-induced radical polymerization reaction on the surface of PEN film. It was observed that the mixture ratio of argon-oxygen carrier gas significantly affected the surface and the moisture barrier properties of the resulting poly(HMDSO) film. Chemical structures of the poly(HMDSO) were confirmed using FT-IR analysis. Surface properties of the poly(HMDSO) thin film were investigated by water contact angle measurement and atomic force microscopy (AFM). Water vapor transmission rate (WVTR) value was obtained by an electrical calcium test (Ca test) at 85 °C and 85% relative humidity condition. It was confirmed that the poly(HMDSO) thin film exhibited excellent water vapor barrier capability. WVTR value of the PEN film coated with poly(HMDSO) deposited with a mixture of argon and oxygen (Ar: O2 = 2: 8) was 5.09 g/m2-day, which is much lower than 18.4 g/m2-day of a bare PEN film. [ABSTRACT FROM AUTHOR]

Chemical sensors generally suffer from the cross-sensitivity problem. For this purpose, the identification of volatile organic compounds (VOCs) using unselective sensor requires a combination of sensors followed by pattern recognition methods. In the current study, four quartz crystal microbalances (QCMs) were coated by plasma-enhanced chemical vapor deposition (PECVD) with the pure vapor of hexamethyldisiloxane (HMDSO) at monomer pressures ranging from 5 to 40 Pa. The coated QCM-based sensors were used for the detection of volatile organic molecules. The sensor responses toward different VOCs showed the possibility to tune the chemical affinity of the sensors by changing only the monomer pressure during the sensitive layer deposition process. Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used to investigate chemical composition and surface morphology of the coated QCM sensors, respectively. The sensor responses have been used as a database for the identification of VOCs using pattern recognition methods such as principal component analysis (PCA) and artificial neural networks (ANNs). PCA is a linear method that allowed the identification of ethanol only among two other VOCs. Complete identification and accurate quantification of the studied VOCs have been achieved by the combination of PCA for data preprocessing and ANN for pattern recognition. [ABSTRACT FROM PUBLISHER]

Hydrophobic volatile methyl siloxanes (VMS), such as hexamethyldisiloxane (L2) and octamethylcyclotetrasiloxane (D4), present a low solubility in water. An alternative treatment by absorption into hydrophobic absorbents was therefore studied. For this purpose, three different absorbents, motor oil, cutting oil and a water-cutting oil mixture, were selected with the aim of re-using a waste product. The set of experiments was carried out in a bubble column, where parameters such as inlet concentration, residence time and temperature were studied. The best performance for the removal of both siloxanes, in terms of absorption capacity, was observed for motor oil, particularly for D4. In fact, motor oil removal efficiency for D4 was 80%, whereas for L2 it was 60%, indicating that D4 is more easily absorbed than L2. In the case of water-cutting oil, this showed a mass transfer enhancement from the gas phase to the liquid phase compared with water alone. Furthermore, a removal efficiency of 70% was observed for D4, showing that the addition of an oil fraction to a water system improves the absorption of VMS. These results show that VMS absorption into oils could be a promising way to achieve their abatement. [ABSTRACT FROM PUBLISHER]

Siloxanes are widely used in different applications: health care, dry cleaning, household products, paints and coatings, paper, personal care, for example. This explains their prevalence in the environment. Because of their volatile nature, most of the time they are dispersed in the atmosphere, but they can also be present in the slurry from landfills. During anaerobic digestion, when the temperature goes up to 60 °C, siloxanes are volatilized, forming part of the biogas. Operational problems using biogas to produce energy, heat and hydrogen have been identified. At high temperatures the siloxanes are transformed into silicate dioxide (commonly called sand transmission). These white deposits may adhere to metal or catalytic substrate surfaces, seriously reducing equipment efficiency, and this can be a reason for changing equipment warranties. Consequently, elimination of siloxanes has become very important. Unfortunately, relatively little information can be found on this subject. Nevertheless some authors have described different analytical methods for siloxane quantification, and recent studies have looked at the presence of siloxanes in landfills and the restriction on the energy recovery equipment using the biogas produced. The growing consumption of siloxanes and silicones in industrial processes consequently increase their prevalence in the environment, hampering the use of biogas as a source of 'green energy'. Therefore, the principal focus of this study is the treatment of siloxanes. Their elimination was carried out using an adsorption process with four different porous materials: activated carbon cloths (ACC), granular activated carbon (GAC), zeolite and silica gel. Two representative siloxane compounds were used in this study, hexamethyldisiloxane (L2) and octamethylcyclotetrasiloxane (D4). Adsorption kinetics and isotherms in batch reactors were performed. It was observed that the mass transfer into the porous material was more rapid for the activated carbon than for the zeolite and silica gel, congruent with the porous structure of the material. Moreover, it was found that D4 is more adsorbable than L2, due to possible interactions between the solid surface and the physical structure of the cyclic compound (D4). The influence of humidity and temperature were also studied. The increase in the temperature reduced the adsorption capacities. The influence of humidity on the adsorption was investigated under dry air and humid air at 70%. No significant difference in the adsorption capacities was found for the activated carbon and for the zeolite, but for the silica gel the mass transfer decreased considerably. For the adsorption isotherms, the maximal capacity of elimination was obtained with the activated carbon materials and was directly related to the porous structure. Thus activated carbon cloth was chosen to design the adsorption- desorption processes in a dynamic system. Thermal heating was used to achieve the regeneration process. Initial cycles have been accomplished and show the stability of the process. [ABSTRACT FROM AUTHOR]

Plasma treatment at atmospheric pressure using a dielectric barrier discharge was carried out to increase the surface hydrophilicity of wood and wood-based materials. Surface energy determination by contact angle measurement revealed an increase in the polar component of surface energy and in total surface energy following plasma treatment. X-ray photoelectron spectroscopy revealed the generation of polar groups and consequently an increase in O/C ratio. The feasibility of plasma polymerization on wooden substrates at atmospheric pressure to create water-repellent characteristics was also investigated. An atmospheric-pressure plasma jet using hexamethyldisiloxane as precursor and air as process gas was used for thin-layer deposition. Treatment parameters for the layer deposition were investigated, as well as the layer topography and chemical composition. Atomic force microscopy revealed a closed surface layer consisting of silicon, oxygen, carbon and hydrogen that exhibited low water permeability. [ABSTRACT FROM AUTHOR]

Three-component reaction of an enolizable compound, such as acetophenone, methyl acetoacetate, 4-hydroxycoumarin, 2-naphthol, or 3-hydroxy-2-naphthoic acid; an aromatic aldehyde, and acetonitrile induced by phosphorus pentoxide and hexamethyldisiloxane leads to 2-acetylamino ketones, methyl 3-(acetylamino aryl methyl)-3-oxobutanoates, 3-(acetylamino aryl methyl)-4-hydroxycoumarins, 1-(acetylamino aryl methyl)-2-naphthols, or 4-(acetylamino aryl methyl)-3-hydroxy-2-naphthoic acids in excellent yields. [ABSTRACT FROM AUTHOR]

Hexamethyldisiloxane (HMDS) is a volatile linear siloxane dimer used in many applications, including precision cleaning, active ingredient carrier, and as a manufacturing intermediate. The purpose of this study was to characterize the subchronic vapor inhalation toxicity of the material as part of a comprehensive toxicology program. Groups of 20 male and 20 female Fischer 344 (F344) rats were exposed to nominal (and mean actual) vapor concentrations of 0, 50 (50), 200 (194), 600 (593), 1500 (1509) and 5000 (5012) ppm of HMDS, 6 hours per day, 5 days per week, for 13 weeks. No treatment-related signs of clinical toxicity or mortality, statistically significant effects upon body weight gain or food consumption, ophthalmoscopic changes, gross macroscopic necropsy findings, or organ weight changes were noted. Minor hematological, clinical biochemical, and urinalysis changes were seen but were not considered to be of toxicological relevance. Histological lesions in the kidney apparently consistent with male rat–specific α -2- urinary globulin nephropathy were observed in male rats exposed to 593, 1509, and 5012 ppm of HMDS, accompanied by slightly increased plasma urea and creatinine concentrations. No other treatment-related histological changes were seen in HMDS-exposed rats. [ABSTRACT FROM AUTHOR]