Mixture Of Hexamethyldisiloxane Research Articles

Photocatalytic Investigation of Aerosol-Assisted Atmospheric Pressure Plasma Deposited Hybrid TiO2 Containing Nanocomposite Coatings.

We report on the aerosol-assisted atmospheric-pressure plasma deposition onto a stainless-steel woven mesh of a thin nanocomposite coating based on TiO2 nanoparticles hosted in a hybrid organic−inorganic matrix, starting from nanoparticles dispersed in a mixture of hexamethyldisiloxane and isopropyl alcohol. The stainless-steel mesh was selected as an effective support for the possible future technological application of the coating for photocatalytically assisted water depollution. The prepared coatings were thoroughly investigated from the chemical and morphological points of view and were demonstrated to be photocatalytically active in the degradation of an organic molecule, used as a pollutant model, in water upon UV light irradiation. In order to optimize the photocatalytic performance, different approaches were investigated for the coating’s realization, namely (i) the control of the deposition time and (ii) the application of a postdeposition O2 plasma treatment on the pristine coatings. Both strategies were found to be able to increase the photocatalytic activity, and, remarkably, their combination resulted in a further enhancement of the photoactivity. Indeed, the proposed combined approach allowed a three-fold increase in the kinetic constant of the degradation reaction of the model dye methylene blue with respect to the pristine coating. Interestingly, the chemical and morphological characterizations of all the prepared coatings were able to account for the enhancement of the photocatalytic performance. Indeed, the presence of the TiO2 nanoparticles on the outmost surface of the film confirmed the accessibility of the photocatalytic sites in the nanocomposite and reasonably explained the enhanced photocatalytic performance. In addition, the sustained photoactivity (>5 cycles of use) of the nanocomposites was demonstrated.

Characterization of Gaseous Plasma Sustained in Mixtures of HMDSO and O2 in an Industrial-Scale Reactor

Optical emission spectroscopy and mass spectrometry was used to characterize gaseous plasma in an industrial reactor of volume 5 m3 during deposition of protective coatings. Plasma was created in mixtures of hexamethyldisiloxane (HMDSO) and oxygen at the powers between 1 and 8 kW. The plasma density was somehow below 1014 m−3. The flows of both gases were varied up to 200 sccm while the effective pumping speed was adjusted by changing the roots pump rotation speed between 250 and 4000 rpm. At such conditions the HMDSO was only partially dissociated to fragments. The behaviour of optical emission lines and mass ion currents was well correlated indicating that even one single technique was sufficient to monitor the behaviour of plasma at various discharge conditions. The optical emission spectroscopy as a simple and economic method is therefore suitable for controlling key processing parameters in such a plasma reactor.

DBD‐based plasma polymerization from monomer‐argon mixtures: Analytical model of monomer reactions with excited argon species

Experimental studies of DBD‐based atmospheric‐pressure plasma polymerization from mixtures of hexamethyldisiloxane (HMDSO) with argon are presented and interpreted using an analytical model of the plasma‐chemical kinetics. Gradient films are obtained using a special DBD‐PACVD reactor. Growth‐rate profiles and their monomer fraction dependence show that long‐living excited Ar species play a major role in the deposition mechanism. Reactions of HMDSO with metastable and resonance argon atoms as well as argon excimers are considered within the presented model which may be simplified by introducing a lumped excited argon species Ar*. Model predictions are compared with experimental results. Recombination reactions must be included in order to reproduce characteristic features of the measured growth‐rate curves.

Aging effect of atmospheric air on lithium disilicate ceramic after nonthermal plasma treatment

Statement of problemNonthermal plasma (NTP) treatment is an alternative technique for promoting the adhesion of resin cement to lithium disilicate ceramic. However, no study has evaluated whether the surface modifications are affected by atmospheric air aging. PurposeThe purposes of this in vitro study were to characterize the lithium disilicate surface after depositing an organosilicon film with NTP treatment and to verify the surface energy before and after atmospheric air aging up to 30 days. Material and methodsSixteen lithium disilicate disks (10×3 mm) were prepared, and their surfaces were treated with a mixture of hexamethyldisiloxane and argon, followed by oxygen plasma treatment, both for 30 minutes. The lithium disilicate surface was characterized through scanning electron microscopy, energy-dispersive spectroscopy, and atomic force microscopy. Surface energy analysis was performed before (T0) and immediately after NTP treatment (T1) and after atmospheric air aging for 7 (T2), 15 (T3), and 30 days (T4). Data were submitted to analysis of variance followed by the Tukey HSD test (α=.05). ResultsCarbon, oxygen, and silicon were identified on the disilicate surface after NTP treatment, suggesting organosilicon film adhesion. Air aging did not modify the film morphology. At T1, the surface energy was significantly higher compared with other periods, and the water contact angle on the disilicate surface was reduced to 0 degrees. Similar surface energy was observed for T0, T2, T3, and T4. ConclusionsOn the basis of the results of this in vitro study, NTP treatment can promote bonding to lithium disilicate surfaces because of its high surface wettability. However, after air aging, the wettability was not durable.

Structure and diffuse-boundary in hydrophobic and sodium dodecyl sulfate-modified silica aerogels

Small-angle X-ray scattering (SAXS) and nitrogen adsorption were used to study ambient pressure drying (APD) silica aerogels prepared from hydrolysis of tetraethoxysilane (TEOS) with additions of sodium dodecyl sulfate (SDS). The surfactant-extracted precursor wet gels have presented mass-fractal structure with typical fractal dimension 2.25 in a SAXS characteristic length scale from ∼10 nm to ∼0.35 nm. Hydrophobic APD aerogels with typical specific surface of 800 m2/g and bulk density of 0.20 g/cm3 were obtained after silylation of the precursor wet gels with a mixture of hexamethyldisiloxane (HMDSO) and trimethylchlorosilane (TMCS). The pore volume and the mean pore size of the APD aerogels increased with increasing the SDS quantity. APD aerogels presented most of the mass-fractal characteristics of the precursor wet gels at large length scales. The radius of gyration of the clusters of the APD aerogels (typically 17nm) increased with increasing the SDS quantity, while the radius of the silica primary particles (typically 2.0 nm) increased at first with the addition of SDS (with respect to the sample without SDS) and decreased regularly afterward with increasing the SDS quantity. The primary particles presented yet some internal inhomogeneity and a diffuse-boundary interface with thickness of about 0.7 nm, according to a linear-gradient model for the diffuse boundary.

Effect of Ion Irradiation on the Structural Properties and Hardness of a-C:H:Si:O:F Films

Amorphous carbon-based thin films, a-C:H:Si:O:F, were obtained by plasma immersion ion implantation and deposition (PIIID) from mixtures of hexamethyldisiloxane, sulfur hexafluoride and argon. For PIIID the sample holder was biased with negative 25 kV pulses at 60 Hz. The main system parameter was the proportion of SF6 in the reactor feed, Rsf. To allow comparison to growth without intentional ion implantation, some films were also grown by plasma enhanced chemical vapor deposition (PECVD). The objectives were to investigate the effects of fluorine incorporation and ion implantation on the film's chemical structure, and principally on the surface contact angle, hardness and friction coefficient. Infrared and X-ray photo-electron spectroscopic analyses revealed that the films are essentially amorphous and polymer-like, and that fluorine is incorporated for any non-zero value of Rsf. Choice of RSF influences film composition and structure but ion implantation also plays a role. Depending on Rsf, hydrophilic or hydrophobic films may be produced. Ion implantation is beneficial while fluorine incorporation is detrimental to hardness. For ion implanted films the friction coefficient falls about one third as Rsf is increased from 0 to 60%. Films prepared by PIIID without fluorine incorporation present fairly low friction coefficients and hardnesses greater than those of conventional polymers.

Deposition of thick polymer or inorganic layers with flame-retardant properties by combination of plasma and spray processes

Mixtures of hexamethyldisiloxane (HMDSO) and oxygen have been used for deposition of SiO2-like layers by plasma polymerization under low-pressure conditions onto polyethylene and polystyrene used as basecoat. Water glass was cast onto these 0.5μm plasma thick siloxane-like layers with a thickness of 5 to 40μm. The adhesion of these bilayer systems and their flame resistance were tested.The effect of different plasma parameters such as monomer/gas ratio, pressure and power input into the discharge on the deposition rate and the composition of the formed layers was studied. Characterization and chemical composition of the formed films were performed using infrared, X-ray photoelectron and solid state nuclear magnetic resonance spectroscopy.Peel strengths of composites were measured and the locus of peel front propagation was detected. Thermal properties of composites were analyzed by thermo-gravimetric analysis. Finally, the fire-retardant properties of thick coated polymers were determined by exposure to flames and the behavior of coatings on the polymers during flaming was observed visually.

Plasma deposited polymers as gas sensitive films

The possibility is presented of producing thin plasma polymers with desired properties by using nanofillers. Composite films are synthesized from a mixture of hexamethyldisiloxane (HMDSO) and detonation nanodiamond particles (DNDs). The chemical structure of the composite consists of DNDs distributed in the polymer matrix. The effect of DNDs on the humidity and ammonia sorptive properties of the polymers obtained is studied by measuring the mass changes as a result of gas sorption by using a quartz crystal microbalance (QCM). The results show that, in view of building a sensing element for measuring humidity, ammonia or other gases, it is possible to maximize the sensor sensitivity to a certain gas by using an appropriate concentration of DNDs in HMDSO. Thus, a high degree of sensor sensitivity, together with short response time and minimum hysteresis, can be achieved. Composites of plasma-polymerized HMDSO with DNDs can be used as gas sensitive layers for the development of quartz resonator sensors.

Synthesis and characterization of MQ silicone resins

AbstractMQ silicone resins, which represent a broad range of hydrolytic condensation products of monofunctional silane (M) and tetrafunctional silane (Q), were synthesized by reaction of water glass with hexamethyldisiloxane. The optimum reaction time and the optimal reaction temperature is 30 min and 30–40°C, respectively. Concentrated hydrochloric acid is the best one among those catalysts tested. In large‐scale experiments (420–1680 mL), the favorable feeding order is catalyst first, and then water glass, the mixture of hexamethyldisiloxane and ethanol last and most MQ silicone resin was observed. The structure of MQ silicone resin was characterized by FT‐IR and GPC spectra. The MQ silicone resin shows narrow molecular weight distribution and the number average molecular weight of MQ silicone resin is 2917. The silicone pressure sensitive adhesive prepared from as‐synthesized MQ resin has good tack (29#) and 180° peel adhesion (5.630N/20 mm). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Chemical and Morphological Characterization of Low‐k Dielectric Films Deposited From Hexamethyldisiloxane and Ethylene RF Glow Discharges

AbstractLow‐k dielectric films were deposited by PECVD from mixtures of hexamethyldisiloxane (HMDSO), ethylene, and oxygen. After deposition the films were thermally annealed in order to reduce their permittivity. Different deposition conditions were investigated in order to accomplish the best trade‐off between low permittivity and low thickness loss upon annealing. Soft plasma conditions were required in order to allow organic species incorporation in the film and achieve dielectric constant as low as 2.2 with a thickness loss of 14% upon thermal annealing treatment. Results were also compared to those obtained with divinyltetramethyldisiloxane, which is similar in structure to HMDSO but with two vinyl groups replacing methyl ones. The morphological analysis showed that feeding the plasma with a large amount of ethylene, CHx‐enriched nanodomains were obtained over a siloxane matrix. Finally, the plasma phase composition was also investigated by infrared spectroscopy and correlated with the film chemistry. magnified image

Optimisation of the properties of siloxane coatings as anti-biofouling coatings: Comparison of PACVD and hybrid PACVD–PVD coatings

Plasma-assisted chemical vapour deposition (PACVD) siloxane coatings from a mixture of hexamethyldisiloxane (HMDSO) and O2, and hybrid coatings deposited by simultaneous sputtering of silicon and plasma polymerisation of HMDSO + O2 were prepared on glass and steel substrates. The effect of the addition of sputtered silicon was investigated for coatings with different HMDSO/O2 ratios. The microstructure and composition of coatings were affected by the coating parameters used. Silicon content was roughly the same for all coatings; carbon content decreased while oxygen content and surface energy increased with decreasing HMDSO/O2 ratio in hybrid coatings. Hardness and modulus were higher for hybrid coatings and increased with decreasing HMDSO/O2 ratio. Hybrid coatings showed much better scratch and wear resistance than PACVD coatings. All coatings showed good fouling-release performance with the freshwater bacterium Pseudomonas fluorescens.

Effects of Deposition Plasma Power on Properties of Low Dielectric-Constant Plasma Polymer Films Deposited Using Hexamethyldisiloxane and 3,3-Dimethyl-1-butene Precursors

We investigated the effects of deposition plasma power on the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of hexamethyldisiloxane and 3,3-dimethyl-1-butene as the precursor, which are referred to as plasma polymerized hexamethyldisiloxane:3,3-dimethyl-1-butene (PPHMDSO:DMB) films. As the deposition plasma power was increased from 15 to 60 W, the relative dielectric constants k of PPHMDSO:DMB films, increased from 2.67 to 3.19. After annealing at 450 °C, the films deposited at a deposition plasma power of 15–60 W showed k values of 2.27–2.64. With increased deposition plasma power, the as-deposited and annealed films showed increased values of hardness and Young's modulus. For as-deposited films, deposited at a plasma power of 15–60 W, the films showed a hardness of 0.13–2.0 GPa, and a modulus of 2.25–17.27 GPa. Annealed films, deposited at a plasma power of 15–60 W, showed a hardness of 0.05–2.07 GPa and a modulus of 1.66–14.4 GPa. The change in the k value and hardness of plasma polymer films as a function of deposition plasma power was correlated with fourier transform infrared (FT-IR) absorption peaks of C–Hx, Si–CH3, and Si–O related groups. The as-deposited and annealed PPHMDSO:DMB films showed decreased intensities of C–Hx and Si–CH3 peaks as the deposition plasma power increased. The reduction in the dielectric constant after annealing is mainly due to hydrocarbon removal in the film. Deconvolution of Si–CH3 bending peaks of PPHMDSO:DMB films was performed to relate mechanical properties to chemical structures. The relative oxygen content in the O–Si–(CH3)x structure is analyzed in detail. Improvements in hardness and modulus of our films are attributed to an increased amount of O3Si–(CH3) in the Si–CH3 structure.

Water Molecule Sensitive Layers Deposited from Hexamethyldisiloxane/Oxygen Mixture at Low Temperature

Humidity sensors are widely used in industry production, process control, environment monitoring, medical and electrical applications. In this study, water molecule sensitive layers have been elaborated by plasma enhanced chemical vapor deposition PECVD technique, from a mixture of hexamethyldisiloxane (HMDSO) and oxygen (O2) in different proportions. The films were deposited on a comb-shape aluminum electrode evaporated on glass substrate. Electrical and structural characteristics of the elaborated humidity sensors were evaluated by humidity-impedance characteristics, infrared spectroscopy FTIR and ellipsometric analysis. Electrical analysis showed that the elaborated humidity sensor exhibited a detectable response to relative humidity ranging from 35 to 95%. However, increasing O2 concentration in the mixture during deposition, leads to a significant decrease of the sensor sensibility. A sensor elaborated with pure vapor of HMDSO exhibited a better sensibility. FTIR analysis revealed that increasing O2 concentration induces a decrease of methyl groups CH3 and the formation of Si-O groups leading to film densification. Besides, the values of the refractive index deduced from ellipsometric data indicated that the refractive index increases with increasing the O2% in the mixture. This observation may be considered as further evidence to film densification.

Characterization of SiOF Thin Films Deposited by PECVD from Hexamethyldisiloxane in Mixture with Oxygen and CF<sub>4</sub>

Thin SiOF films were elaborated in microwave excited DECR plasma reactor (Distributed Electron Cyclotron Resonance) from a mixture of hexamethyldisiloxane (HMDSO) and oxygen (O2) (in 1: 9 proportion) with the presence of various CF4 concentrations. The fluorine contents in the films composition were adjusted by the CF4 gas flow ratio (in the range of 10 - 70%). The refractive index and the deposition rate were estimated from ellipsometric data and the film chemical structure was studied by FTIR analysis technique. The deposition rate increases with increasing CF4 flow and then decreases after reaching a maximum value for 20% of CF4. The decrease in the deposition rate may be attributed to the etching effect by CF4 plasma during the deposition process. As the additive fluorine concentration increases, the intensity of Si–F peak stretching vibrations located at 930 cm-1 increases and the frequency of the Si–O stretching vibration mode centered at 1060 cm-1 shifts towards higher wavenumber.

Synthesis by plasma-enhanced chemical-vapor deposition and characterization of siliconlike films with hydrophobic functionalities for improved long-term geometric stability of fiber-reinforced polymers

Amorphous siliconlike films with hydrophobic functionalities have been deposited by plasma-enhanced chemical-vapor deposition on carbon-fiber-reinforced polymer (CFRP) unidirectional laminates used for micromechanical applications where high strength-to-weight and high stiffness-to-weight ratios are required. To improve long-term geometrical stability in ultrahigh-precision machine structures, hydrophobic CFRP materials are desirable. Three layers have been grown with different plasma-process parameters from a mixture of hexamethyldisiloxane, O2, and Ar. Chemical composition, water contact angle, surface energy, morphology, and tribological properties have been evaluated to choose the one that best fulfills hydrophobicity, wear, and scratch resistance. Wear tests have also been carried out on CFRP laminates coated with a polyurethane layer to compare the wear performance of the above specimens with that of a conventional hydrophobic coating. Scanning electron microscope images show a very good adhesion of the films to the composite substrate because the failure of the film and of the substrate (such as fiber failure) take place simultaneously.

Deposition of silicon-like hybrid films by PECVD on carbon-fiber-reinforced polymers for high-precision engineering applications

Hybrid silicon-like films have been deposited by PECVD on the surface of carbon-fiber-reinforced polymer (CFRP) laminates, used for micro-mechanical engineering applications where high strength-to-weight and high stiffness-to-weight ratios are required, to prevent structural distortions induced by the absorption of water vapour and water in liquid phase (hygroscopic behaviour). The films are made up of two layers: the inner layer was deposited from a mixture of hexamethyldisiloxane (HMDSO) as monomer, O2 and Ar in conditions of high monomer fragmentation to confer the material barrier properties against moisture absorption while the most superficial layer was deposited from the same monomer and feed gases in conditions of low monomer fragmentation to confer the material hydrophobic properties against the absorption of water during machining operations. Three films, made up of the same barrier layer and of three different hydrophobic layers have been grown to choose the one which best fulfils impermeability, hydrophobicity, wear and scratch resistance.

A comparative study on the effect of VUV radiation in plasma SiO x-coated polyimide and polypropylene films

Wettability of polyimide (PI) and polypropylene (PP) films have been improved using SiO x -like thin layers deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen in a microwave distributed electron cyclotron resonance plasma reactor. The films wettability evolution behaviors were evaluated through the results of contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The plasma depositions of SiO x thin layers in presence of VUV radiation induce a contact angle decrease to about 7° and 35° for PI and PP films, respectively. XPS data showed that such difference in wettability is attributed to the increase of hydrophilic group's proportion at the surface of coated PI films due to VUV irradiation. AFM images showed that the PI surface topography remains relatively smooth when coated in presence of VUV radiation. However, in the case of PP films, AFM images revealed the growth of irregular structure due to a substrate etching effect supported by VUV radiation. For polymers coated without VUV irradiation, the deconvolution of the C1s peaks showed a significant decrease of C O bonds for both PI and PP substrates.

Deposition of polysiloxane‐like nanofilms onto an aluminium alloy by plasma polymerized hexamethyldisiloxane: characterization by XPS and contact angle measurements

AbstractIn this work, aluminium (Alclad 2024‐T3) substrates were cleaned by an r.f. (13.56 MHz) plasma, using argon (Ar), oxygen (O2) and a mixture of O2/Ar (50:50) gases. The effectiveness of plasma cleaning was checked in situ using X‐ray photoelectron spectroscopy (XPS) and ex situ using water contact angle measurements. XPS O/Al surface atomic ratios are in excellent agreement with those of the crystalline boehmite and the pseudoboehmite. Oxygen O 1s peak‐fitting was used to quantify the proportion of hydroxyl ions and the functional composition on the aluminium surface: the surface cleaned with O2 plasma contains 50% of aluminium hydroxides, the ones cleaned with Ar plasma and with Ar/O2 plasma contain, respectively, 25 and 37% hydroxyl ions. The binding energy separation between Al 2p and O 1s is characteristic of AlO(OH). Thin SiOx films were subsequently deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen. In the absence of oxygen, a hydrophobic (Θ≥ 100° ) film characteristic of polydimethylsiloxane (PDMS) is formed: polysiloxane‐like thinner films (SiOx) are obtained with the introduction of oxygen. XPS and contact angle measurements confirmed both the composition and the structure of these films. More importantly, contact angle measurements using different liquids and interpreted with the van Oss‐Good‐Chaudhury theory allowed determination of the surface free energy of the deposited films: the calculated values of surface tension of the film formed from HMDSO/O2: (50/50) are in excellent agreement with those of reference silica‐based materials such as a silicon wafer and cleaned glass. Copyright © 2007 John Wiley & Sons, Ltd.

Organosilicon thin films deposited by plasma enhanced CVD: Thermal changes of chemical structure and mechanical properties

Thin organosilicon and silicon oxide films were deposited in r.f. capacitively coupled discharges from a mixture of hexamethyldisiloxane (HMDSO) and oxygen. The concentration of HMDSO was in the range 5–17%. Even for such relatively high dilution of HMDSO the organic–inorganic crossover of the film character was observed due to changes of the HMDSO concentration, but other factors, such as pressure and d.c. self-bias should also be taken into account. When annealed the films changed their composition, chemical structure and mechanical properties. We observed desorption of water, methane and CO or CO 2 from the SiO 2-like films. The hardness of the SiO 2-like film, containing 5% carbon and 25% hydrogen, increased with the increase of annealing temperature from 5.9 (as deposited) to 11.3 GPa ( 500 ∘ C ) . Simultaneously, its fracture toughness was significantly improved. These effects were explained by dehydration and cross-linking of the film. However, the mechanical properties of highly cross-linked SiO 1.9 C 1.6 H 0.6 plasma polymer were superior over the SiO 2-like film containing impurities and such film can be used as a protective coating with a hardness above 9.6 GPa up to the temperature of 400 ∘ C .

Poole-Frenkel conductivity in SiOxHyCz coatings prepared by PECVD

The aim of the present work is to investigate the electrical properties of SiOxHyCz coatings prepared in a capacitively coupled r.f. glow discharge (13.56 MHz) from mixtures of hexamethyldisiloxane (HMDSO) and oxygen under several different deposition conditions. V-A characteristics of the films were measured. All electrical measurements were performed in a separate vacuum system at a pressure of 10−1 Pa and the temperature varied from 237 K to 286 K. Complex analysis of the obtained I–V data was done. It is well known that SiOxHyCz coatings prepared by plasma enhanced chemical vapor deposition (PECVD) exhibit Poole-Frenkel conductivity, although space-charge-limited conductivity has been occasionally also observed.