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The combustion-synthesized silica particles possess low metal impurity and present excellent surface properties. In this paper, silica particles were first prepared by hexamethyldisiloxane (HMDSO) combustion and then SEM, XPS, XRD and ICP were used to characterize the surface characteristics of silica particle. Finally, ReaxFF molecular dynamics simulations were conducted to investigate the formation mechanism of particle surface groups during HMDSO combustion. Effects of the temperature on surface group formation were also investigated. High-purity and spherical silica nanoparticles were prepared. The experimental and simulation results show that the type of surface groups at silica particle surface included the methyl group (-CH3), aminocarbonyl group (-O-C-OR), hydroxyl group (-OH), carbonyl group (-CO) and aldehyde group (-CHO). The hydroxyl and methoxyl groups were formed at oxygen sites of the silica particle by adsorption of free radicals H and CH3. The adsorptions of free radicals CH3 and CHO as well as carbon monoxide molecule at silicon sites lead to the formation of methyl group, aldehyde group and carbonyl group. The results of ReaxFF simulations also showed that the hydrophobic groups were dominant at low temperatures such as 500 K, and hydrophilic groups played more important role at high temperatures such as 1300 K. [ABSTRACT FROM AUTHOR]

Organosiloxanes are industrially produced worldwide in millions of tons per annum and are widely used by industry, professionals, and consumers. Some of these compounds are PBT (persistent, biaccumulative and toxic) or vPvB (very persistent and very bioaccumulative). If organosiloxanes react at all in the environment, Si–O bonds are hydrolyzed or Si–C bonds are oxidatively cleaved, to result finally in silica and carbon dioxide. In strong contrast and very unexpectedly, recently formation of new Si–CH3 bonds from siloxanes and methane by the action of microorganisms under mild ambient conditions was proposed (in landfills or digesters) and even reported (in a biotrickling filter, 30 °C). This is very surprising in view of the harsh conditions required in industrial Si–CH3 synthesis. Here, we scrutinized the pertinent papers, with the result that evidence put forward for Si–C bond formation from siloxanes and methane in technical microbiological systems is invalid, suggesting such reactions will not occur in the environment where they are even less favored by conditions. The claim of such reactions followed from erroneous calculations and misinterpretation of experimental results. We propose an alternative explanation of the experimental observations, i.e., the putative observation of such reactions was presumably due to confusion of two compounds, hexamethyldisiloxane and dimethylsilanediol, that elute at similar retention times from standard GC columns. [ABSTRACT FROM AUTHOR]

Published data on the effect of low-temperature plasma on polydimethylsiloxane have been analyzed. Changes in the contact properties, chemical structure, and morphology of the modified polymer surface have been revealed using modern research techniques (contact angle measurement, X-ray photoelectron spectroscopy, Fourier-transform IR spectroscopy, atomic force and scanning electron microscopy). It has been shown that modification by plasma results in the formation of a hybrid material that has the surface layer consisting mainly of silicon oxide. Plasma-enhanced chemical vapor deposition processes of hexamethyldisiloxane polymerization on various substrates are considered and the formation of similar hybrid materials containing a significant amount of silicon oxide is shown. Data on the use of such materials in biology, medicine, membranes, humidity sensors, and other fields of science and technology are presented. [ABSTRACT FROM AUTHOR]

Surface properties of SiO2-like films deposited from plasma polymerization of HMDSO + O2 mixture have been investigated. Plasma of the gas mixture was produced using repetitive high voltage pulses at − 3 kV with varied frequency from 100 to 500 Hz. The films were characterized by means of atomic force spectroscopy, spectroscopic ellipsometry, contact angle measurement, and X-ray photoelectron spectroscopy. The film thickness increased linearly with the pulse frequency in the range of 100–400 Hz where the system was in energy-deficient domain. A further increase in the pulse frequency led to the monomer-deficient domain and the linear dependence of the deposition rate terminated. Refractive index of the films were similar to that of SiO2. Refractive index and extinction coefficient values suggested that the films had high density which is related to high fraction of suboxide structure. The total surface energy of the films was not significantly different when varied pulse frequency was used. The surface energy contained high polar component indicating that the polar Si–O groups were dominant in the structure. [ABSTRACT FROM AUTHOR]

The coating deposition inside tubes becomes increasingly important for fluidic applications, in which inner surfaces are chemically and mechanically strained by the flowing liquid and by scratching of particles. The developed process for tube coating, presented in this work, is based on the discharge in the precursor gas atmosphere between two mesh electrodes at the ends of the tube. The gas mixture is introduced on one end and pumped through the electrode on the other end. Igniting plasma inside the tube, the tube walls are the barrier to the atmosphere. Especially pulsed DC discharges for plasma polymerization in this alignment lead to good coating results, which is shown in this work focusing on deposition in pure and mixed hexamethyldisiloxane, ethyne, and oxygen atmospheres. Chemical binding, wetting, and ageing are strongly influenced by the choice of the gas mixtures. Sufficient oxygen partial pressure in the deposition atmosphere leads to hydrophilic behavior of the SiO-like polymer-like carbon coatings, all other applied atmospheres to generally hydrophobic behavior of pure and Si-doped plasma polymers, respectively. [ABSTRACT FROM AUTHOR]

Herein, we present a simple method for fabricating plasma polymerized hexamethyldisiloxane films (pp-HMDSO) possessing superhydrophobic characteristics via arc discharge. The pp-HMDSO films were deposited on a soda-lime-silica float glass using HMDSO monomer vapor as a precursor. A detailed surface characterization was performed using scanning electron microscopy and atomic force microscopy. The growth process of the pp-HMDSO films was investigated as a function of deposition time from 30 to 300 s. The non-wetting characteristics of the pp-HMDSO films were evaluated by means of contact angle (CA) measurements and correlated with the morphological characteristics, as obtained from microscopy measurements. The deposited films were found to be nano-structured and exhibited dual-scale roughness with the static CA values close to 170°. Fourier transform infrared spectroscopy analysis was carried out to investigate chemical and functional properties of these films. Methyl groups were identified spectroscopically to be present within the pp-HMDSO films and were proposed to result in the low surface energy of material. The synergy between the dual-scale roughness and low surface energy resulted in the superhydrophobic characteristics of the pp-HMDSO films. A possible mechanism for the pp-HMDSO film formation is proposed. [ABSTRACT FROM AUTHOR]

n atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film deposition process. The DBD device is enclosed in a vacuum chamber and one of the electrodes is a rotating cylinder. Thus, this device is able to simulate continuous processing in arbitrary deposition condition of pressure and atmosphere composition. A deposition process of thin organosilicon films has been studied reproducing a nitrogen atmosphere with small admixtures of hexamethyldisiloxane (HMDSO) vapours. The plasma discharge has been characterized with optical emission spectroscopy and voltage-current measurements. Thin films chemical composition and morphology have been characterized with FTIR spectroscopy, atomic force microscopy (AFM) and contact angle measurements. A strong dependency of deposit character from the HMDSO concentration has been found and then compared with the same dependency of a typical low pressure plasma enhanced chemical vapour deposition process. [ABSTRACT FROM AUTHOR]

The retention behavior of aclarubicin and doxycycline has been examined on silica gel 60 WF254s, RP-18 F254s, cellulose F, and polyamide 11 F254 TLC plates and on silica gel 60 F254 and RP-18 WF254s HPTLC plates. Wide-range (from 0 to 100%, v/v) mixtures of n-alcohols with dimethyl sulfoxide (DMSO), hexamethyldisiloxane (HMDSO), acetonitrile, and water were used as mobile phases. The effect of mobile and stationary phases on the chromatographic behavior of the compounds was studied. [ABSTRACT FROM AUTHOR]

Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and three stable molecules, CH4, C2H2 and C2H6, in radio frequency plasmas (f=13.56 MHz) containing hexamethyldisiloxane (HMDSO). The methyl radical concentration and the concentration of the stable hydrocarbons, produced in the plasma, have been measured in pure HMDSO discharges and with admixtures of Ar, while discharge power (P=20–200 W), total gas pressure (p=0.08–0.6 mbar), gas mixture and total gas flow rate (Φ=1–10 sccm) were varied. The methyl radical concentration was found to be in the range of 1013 molecules cm-3, while methane and ethane are the dominant hydrocarbons with concentrations of 1014–1015 mol cm-3. Conversion rates to the measured stable hydrocarbons (RC(CxHy): 2×1012–2×1016 molecules J-1 s-1) could be estimated in dependence on power, flow, mixture and pressure. Under the used experimental conditions a maximum deposition rate of polymer layers of about 400 nm min-1 has been found. [ABSTRACT FROM AUTHOR]

Plasma copolymerization of hexamethyldisiloxane (HMDSO,(CH3)3-Si-O-Si-(CH3)3) and C4F8 was performed using an RF plasma enhanced chemical vapor deposition method for application to low dielectric constant intermetal dielectrics. Structure of the films was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The film composition was controlled gradually from fluorinated carbon to organic siloxane by changing the mixing ratio of HMDSO/Ar. Dielectric constant of the films ranged from 2–3.3. Thermal stability of the films, which was characterized by intensity loss of IR absorbance peak around 1000–1500 cm−1 corresponding to C-F n, Si-O-Si and Si-(CH2)n-Si bonds, was inferior to that from C2F4/HMDSO/Ar. In situ gasphase FT-IR spectroscopy revealed that there was a marked difference between the gas phase of C4F8/HMDSO/Ar and that of C2F4/HMDSO/Ar discharges. The IR spectrum of the former combination plasma contained a peak at 1250 cm−1 with full width at half maximum as large as 150 cm−1, which suggests that fluorocarbon particles and/or dusts are formed in the plasma. This suggests also that deposition precursors are not only CF n ( n = 1, 2, and 3) but also larger precursors such as C xF y ( x > 1, y < 2 x + 2) in C4F8/HMDSO/Ar discharges, which is presumably the cause of difference in thermal stability of the films prepared from C4F8/HMDSO/Ar and C2F4/HMDSO/Ar mixtures. [ABSTRACT FROM AUTHOR]

Hexamethyldisiloxane (HMDS) was polymerized onto metallic and insulating substrates in a parallel-plate DC reactor. The limits of the DC reactor with respect to pressure and power were determined for deposition of PP-HMDS films. In all conditions ranging from 5 Pa/0.3 W to 100 Pa/50 W, solid films were deposited. No powders or oily films were obtained under any condition in this operating range. The films were polymeric in nature, i.e., they were neither carbon-like nor SiO x -like films. The structures and crosslink densities of the plasma films dependend strongly on the deposition conditions. The highest deposition rates, up to 2 μm per minute (or 0.3 mg/cm2 min), were obtained at high power, pressure, and flow rate conditions. An efficiency ɛ is introduced, defined as the fraction of the monomer that is retained in the form of a polymer deposited on the substrate. Efficiencies as high as 25% could be obtained in certain conditions. Pulsing the discharge power increased the conversion efficiency markedly, but the effect depended strongly on the monomer used. In addition to HMDS, plasma polymers were also deposited from pyrrole in pulsed conditions for comparison. A method is described for depositing films on insulators from a DC glow discharge using two wire meshes held at a negative potential. [ABSTRACT FROM AUTHOR]