Hexamethyldisiloxane Thin Films Research Articles

Large-Scale Plasma-Polymerized Hexamethyldisiloxane Thin Films: Role of Interelectrode Distance and Excellent Corrosion Resistance.

In comparison to the more traditional anticorrosion thin film coatings, the plasma polymerization approach offered a more efficient, dry, and straightforward procedure that made it possible to create dense films of several hundred nanometers in thickness, which has potential applications in metallic implant materials. In this paper, large-scale plasma polymerized hexamethyldisiloxane (ppHMDSO) thin film coatings were deposited on stainless steel substrates at different electrode distances to improve their corrosion resistance. The physicochemical properties and corrosion resistance of the ppHMDSO thin films as prepared at different electrode distances were characterized and gauged utilizing various characterization means. The results indicate that decreasing electrode distance accelerates monomer fragmentation and increases the oxidation process. The deposition rate and roughness of the ppHMDSO films both decreased as the electrode distance increased, while the carbonaceous group and hydrophobicity of the films enhanced. The ppHMDSO film prepared at an electrode distance of 40 mm obtained excellent elastic recovery and wear resistance and had an improved corrosion resistance, resulting in a reduction of 75% of the original corrosion behavior against the corrosion in Hank's solution. The resulting large-scale ppHMDSO thin film coatings can be further employed in implants for tissue engineering and biomaterials.

Effect of surface modification on the properties of plasma‐polymerized hexamethyldisiloxane thin films

Plasma‐polymerized hexamethyldisiloxane (pp‐HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma‐enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as‐grown thin films have been post treated in two types of reactive plasmas produced in SF6 and O2 gases. The effect of this surface modification on different properties of the as‐grown pp‐HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF6 plasma and O2 plasma surface modifications of the as‐grown pp‐HMDSO thin film induce property changes different from each other. SF6 plasma converted the as‐grown pp‐HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O2 plasma induced a lowering of film electrical resistivity of about two orders of magnitude.

Single step synthesis of Janus nano-composite membranes by atmospheric aerosol plasma polymerization for solvents separation

Solvent permeation across membranes is limited due to physical resistance to diffusion from the selective layer within the membrane and to plasticizing effects generated by the solvent molecules onto the polymeric macromolecular matrix. Nano-composite thin film membranes provide promising routes to generate controlled microstructural separation materials with higher selectivities and permeabilities. Here, the fabrication of nano-composite based on octamethyl-polyhedral oligomeric silsesquioxane - hexamethyldisiloxane thin film membranes is demonstrated by aerosol assisted atmospheric plasma deposition onto pre-formed nano-porous membrane supports for the first time. Stable, atomically smooth and continuous solid films with controllable thickness down to 50 nm were achieved. The deposition process allowed for the control of the wettability of the surfaces to water and organic solvents, leading to the generation of hydrophobic but alcohol-philic surfaces. The liquid entry pressure of the films to water was found to be 8 bar from plasma polymerization as oppose to 3 bar for the bare nano-porous support only. In addition, the ideal separation selectivity for ethanol to water, up to 6.5, highlight the impact of both the surface energy and level of cross-linking of the hexamethyldisiloxane nanostructures on the diffusion mechanisms. This new atmospheric plasma deposition strategy opens-up cost-effective and environmentally friendly routes for the design of the smart Janus membrane with customizable properties and performance.

Hexamethyldisiloxane thin films as sensitive coating for quartz crystal microbalance based volatile organic compounds sensors

Hexamethyldisiloxane (HMDSO) thin films coated quartz crystal microbalance (QCM) electrodes have been characterized for the detection of volatile organic compounds (VOCs). The sensitive coatings were plasma polymerized in pure vapor of HMDSO and HMDSO/O2 mixture. The sensor sensitivity was evaluated by monitoring the frequency shift (∆f) of the coated QCM electrode exposed to different concentrations of VOC vapors, such as ethanol, methanol, benzene and chloroform. The isotherm response characteristics showed good reproducibility and reversibility. For all types of analyte, ∆f were found to be linearly correlated with the concentration of VOC vapor. It was shown that it is possible to tune the chemical affinity of the sensor by changing the oxygen ratio in the deposition gas mixture. Contact angle measurements (CA), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to study surface wettability, chemical composition and surface morphology of the coated QCM electrodes. ATR-FTIR analysis showed the presence of methyl groups around 840cm−1 due to Si(CH3)3 rocking vibration making the elaborated sensor surface hydrophobic. When the coating is performed in HMDSO/O2 mixture, AFM and SEM images showed an increase in the effective specific surface area of the sensor due to the increase in surface roughness. Surface morphology combined with chemical composition significantly affects the sensitivity of the QCM-based sensor.

Preparation and characterization of thin films by plasma polymerization of hexamethyldisiloxane

Plasma polymerized hexamethyldisiloxane thin films were produced using an electrode capacitively coupled apparatus. Fourier transform infrared spectroscopy analysis indicated that the thin film spectra are composed not only of the corresponding monomer bands but also of several new bands. Auger electron spectroscopy analysis indicated that the permeation depth of aluminum into the films is ca. 30 nm when top electrode is deposited by evaporation aluminum. The increase of relative dielectric constant and decrease of dielectric loss tangent with the discharge power is originated from high cross-link of the films.

A SEM study of plasma-polymerized hexamethyldisiloxane thin films

Plasma-polymerized layers were obtained from hexamethyldisiloxane (HMDSO) in a parallel plate diode operated at 400 V 50 Hz and at a current density of 3.0 mA/cm 2 with a gas pressure of 133 Pa in a dynamic type system. The polymers were used as humidity sensors and to increase their sensitivity the polymer was modified in an ammonia plasma. An SEM study was made of the polymer layer to fix the effect of the polymerization conditions and modification by the ammonia plasma. It was shown that the polymer layers were uniform, dense and had a good adhesion to the substrate.