Plasma-polymerized Hexamethyldisiloxane Films Research Articles

Characterization of Plasma Polymerized Hexamethyldisiloxane Films Prepared by Arc Discharge

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.

Plasma deposition of a silicone-like layer for the corrosion protection of magnesium

Magnesium (Mg) and its alloys are widely used for biodegradable implant materials due to their degradability and mechanical properties similar to bone. However, the high corrosion rate and release of hydrogen gas hinder its clinical application. In this study, plasma-polymerization was used to deposit the hexamethyldisiloxane (HMDSO) polymeric films on Mg surface using low temperature radio frequency discharge plasma. The chemical and physical properties of the HMDSO films were characterized by contact angle measurements, field emission scanning electron microscope, and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Contact angle results show that the contact angle and the plasma discharge powers are strongly correlated. ATR-FTIR results indicate that plasma-polymerized HMDSO films have a chemical structure close to polydimethylsiloxane (PDMS). The weight loss test and electrochemical impedance spectroscopy were performed immersion in 0.9% NaCl solution in order to investigate corrosion protective properties of the coating layer. It was found that HMDSO plasma-polymerized coating layer showed good anti-corrosion properties than that of untreated samples. These results that the polymeric films coated on Mg may be potentially applied for clinical use.

Organic-Inorganic Behavior of Plasma-Polymerized Hexamethyldisiloxane Films Studied by Electron and Photon Induced Ion Desorption

In the present work two thin films, fabricated by plasma-polymerization of hexamethyldisiloxane (HMDSO) monomer, were studied by a combination of electron (ESID) and photon (PSID) stimulated ion desorption techniques. The organic character of the polymer film is evidenced by the high contribution of C2Hn+ species and the absence of high mass fragments in its ESID spectrum. On the other hand, the inorganic character is elucidated by the presence of high mass silicon ionic fragments. NEXAFS and PSID spectra also show clear differences between organic and inorganic films. The marked reduction of CH3+ species for PSID spectra of the organic–polymeric film is in accordance with ESID analysis and may be interpreted by a screening effect of its cross-linked organic structure.

Plasma polymerization of hexamethyldisiloxane: Investigation of the effect of carrier gas related to the film properties

In this work we present the influence of carrier gases in the deposition of low-pressure discharge plasma of hexamethyldisiloxane (HMDSO). Plasma polymerized HMDSO films were deposited with an inductively-coupled discharge reactor using Ar and O2 as carrier gases. The films deposited in Ar contained polymeric structure in the form of SiOxCyHz and could significantly improve the barrier to water vapor of poly(lactic acid) (PLA). The SiOx-like structure of HMDSO films was obtained when using O2 as the carrier gas. However, the films supported some state of residual stress leading to film failures and a significant loss of barrier performance of PLA. The formation of organic and inorganic contents in the films was confirmed by X-ray photoelectron spectroscopy (XPS). The discharge power had an effect on the topography of the films. Rough surface with coarse texture was obtained when the process was done in Ar at high discharge powers. On the other hand, the deposition process in O2 induced smoother surface of plasma‐polymerized films.

Initial biocompatibility of plasma polymerized hexamethyldisiloxane films with different wettability

Understanding the relationships between material surface properties, behaviour of adsorbed proteins and cellular responses is essential to design optimal material surfaces for tissue engineering. In this study we modify thin layers of plasma polymerized hexamethyldisiloxane (PPHMDS) by ammonia treatment in order to increase surface wettability and the corresponding biological response. The physico-chemical properties of the polymer films were characterized by contact angle (CA) measurements and Fourier Transform Infrared Spectroscopy (FTIR) analysis.Human umbilical vein endothelial cells (HUVEC) were used as model system for the initial biocompatibility studies following their behavior upon preadsorption of polymer films with three adhesive proteins: fibronectin (FN), fibrinogen (FG) and vitronectin (VN). Adhesive interaction of HUVEC was evaluated after 2 hours by analyzing the overall cell morphology, and the organization of focal adhesion contacts and actin cytoskeleton. We have found similar good cellular response on FN and FG coated polymer films, with better pronounced vinculin expression on FN samples while. Conversely, on VN coated surfaces the wettability influenced significantly initial celular interaction spreading. The results obtained suggested that ammonia plasma treatment can modulate the biological activity of the adsorbed protein s on PPHMDS surfaces and thus to influence the interaction with endothelial cells.

Gas Sorption of Acetone, Diethyl Ether, Toluene, Acetic Acid, and Ammonia on Plasma-Polymerized Hexamethyldisiloxane Films Coated with Quartz Crystal Microbalance

Gas Sorption of Acetone, Diethyl Ether, Toluene, Acetic Acid, and Ammonia on Plasma-Polymerized Hexamethyldisiloxane Films Coated with Quartz Crystal Microbalance

Photoluminescence from PP-HMDSO thin films deposited using a remote plasma of 13.56 MHz hollow cathode discharge

Room temperature photoluminescence (PL) from plasma-polymerized hexamethyldisiloxane (PP-HMDSO) thin films deposited on silicon wafers has been investigated as a function of both the applied RF power and the monomer flow rate. Films were deposited in a low pressure–low temperature remote plasma ignited in a 13.56 MHz hollow cathode discharge reactor, using pure HMDSO as a monomer and Ar as a feed gas. The substrate temperature during the deposition was as low as 40 °C and the total pressure was about 0.03 mbar. Optical emission spectroscopy (OES) has been used as in situ tool for monitoring the different chemical species present in the plasma during deposition processes. The deposited PP-HMDSO films showed a strong, broad ‘green/yellow’ PL band. The RF power and the flow rate of the HMDSO monomer are found to have a significant impact on the PL intensity of the deposited film. The changes in the chemical bonding of the film as a function of deposition parameters have been investigated by using the Fourier transform infrared (FTIR) spectroscopic analysis and are related to PL and OES results. The ‘green/yellow’ PL band is ascribed to chemical groups and bonds of silicon, hydrogen and/or oxygen constituting the films, in particular, SiH, SiO bonds and silanol Si–O–H groups.

Synthesis and characterization of plasma-polymerized hexamethyldisiloxane films

The deposition rates of plasma-polymerized (pp-) films from hexamethyldisiloxane (HMDSO) monomer were determined by the quartz crystal microbalance technique. Using the several polymerization conditions for HMDSO, these were found that the deposition rates were proportional to the polymerization time. The deposition rate of the pp-HMDSO films increased with the increasing RF power. But for vapor pressure, the deposition rates increased with increasing the vapor pressure until 100 Pa; above it, deposition rates tended to decrease gradually. The maximum deposition rate of pp-HMDSO film was obtained 4.577 μg/min on 150 W of RF power at 100 Pa of monomer pressure.

Characterization and protein-adsorption behavior of deposited organic thin film onto titanium by plasma polymerization with hexamethyldisiloxane

Plasma polymerized hexamethyldisiloxane (HMDSO) thin film was deposited onto titanium using a radio-frequency apparatus for the surface modification of titanium. A titanium disk was first polished using colloidal silica at pH=9.8. Plasma-polymerized HMDSO films were firmly attached to the titanium by heating the titanium to a temperature of approximately 250°C. The thickness of the deposited film was 0.07–0.35 μm after 10–60 min of plasma polymerization. The contact angle with respect to double distilled water significantly increased after HMDSO coating. X-ray photoelectron spectroscopy revealed that the deposited thin film consisted of Si, C, and O atoms. No Ti peaks were observed on the deposited surface. The deposited HMDSO film was stable during 2-weeks immersion in phosphate buffer saline solution. Fourier transform reflection–absorption spectroscopy showed the formation of Si–H, Si–C, C–H, and CO bonds in addition to Si–O–Si bonds. Quartz crystal microbalance-dissipation measurement demonstrated that the deposition of HMDSO thin films on titanium has a benefit for fibronectin adsorption at the early stage. In conclusion, plasma polymerization is a promising technique for the surface modification of titanium. HMDSO-coated titanium has potential application as a dental implant material.

Plasma-polymerized hexamethyldisiloxane films characterized by variable-energy positron lifetime spectroscopy

Nanometer-size holes in plasma-polymerized thin films were characterized by variable-energy positron lifetime spectroscopy for the first time. Hexamethyldisiloxane (HMDSiO) was plasma-polymerized at different discharge powers (30–105 W) and monomer pressures (1.0–4.9 Pa). The positron lifetime spectra of deposited films were collected at positron energies of 1 and 5 keV. All films showed a well-defined long-lived component due to pick-off annihilation of ortho-positronium (o-Ps). The o-Ps lifetime τ3, reflecting the average size of free-volume holes in the film, increased with an increasing ratio of plasma discharge power, W, and monomer flow rate, F. Based on the empirical relationship between the o-Ps lifetime and the cavity radius, hole volumes were estimated to be 0.19–0.36 nm3. We also found that the o-Ps intensity, I3, depends strongly on the same parameter, W/F. Comparison with infrared (IR) absorption spectroscopy data showed that Ps formation is suppressed in films with fewer organic bonds and higher disorder, i.e., those increasingly inorganic in nature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2522–2528, 1999

Plasma-polymerized hexamethyldisiloxane films characterized by variable-energy positron lifetime spectroscopy

Nanometer-size holes in plasma-polymerized thin films were characterized by variable-energy positron lifetime spectroscopy for the first time. Hexamethyldisiloxane (HMDSiO) was plasma-polymerized at different discharge powers (30–105 W) and monomer pressures (1.0–4.9 Pa). The positron lifetime spectra of deposited films were collected at positron energies of 1 and 5 keV. All films showed a well-defined long-lived component due to pick-off annihilation of ortho-positronium (o-Ps). The o-Ps lifetime τ3, reflecting the average size of free-volume holes in the film, increased with an increasing ratio of plasma discharge power, W, and monomer flow rate, F. Based on the empirical relationship between the o-Ps lifetime and the cavity radius, hole volumes were estimated to be 0.19–0.36 nm3. We also found that the o-Ps intensity, I3, depends strongly on the same parameter, W/F. Comparison with infrared (IR) absorption spectroscopy data showed that Ps formation is suppressed in films with fewer organic bonds and higher disorder, i.e., those increasingly inorganic in nature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2522–2528, 1999

An approach to conductometric immunosensor based on phthalocyanine thin film

A new approach to conductometric biosensors utilizing iodine-sensitive phthalocyanine thin films has been proposed. The excellent sensitivity of the tetra-tert-butyl copper phthalocyanine (ttb-CuPc) to free iodine was used for the first time to detect a peroxidase-initiated reaction in an aqueous medium. To minimize the interfering effect of aqueous electrolytes on the impedance responses of the ttb-CuPc film itself, Au/Cr interdigitated planar electrodes bearing ttb-CuPc thin films were protected with hydrophobic gas-permeable membranes, namely thermally evaporated calixarene or plasma polymerized hexamethyldisiloxane films. Impedance spectroscopy data were analyzed in order to define the optimal operating frequency. An enzyme sensor with peroxidase immobilized in a cross-linked albumin matrix was tested. Its impedance responses were studied under variation of the substrate concentration, pH, ionic strength and buffer capacity. These results were used to define conditions for peroxidase-linked immunoassay in subsequent tests. With the developed sensor, concentrations of IgG in 0.2–2 μg/ml range were measured in a competitive mode with satisfactory accuracy. The detection of IgG in both test solutions and blood serum samples has been demonstrated.

Deposition behavior of hexamethydisiloxane films based on the FTIR analysis of Si–O–Si and Si–CH 3 bonds

A-SiCO:H films were prepared from hexamethyldisiloxane in a radio frequency reactor and the incorporation behavior of the Si–O–Si and Si–CH 3 bonds of the monomer into the films was investigated in terms of discharge power. The relative incorporation rate of the chemical bonds was obtained by measuring the infrared absorption intensity for the bonds in the plasma-polymerized hexamethyldisiloxane films using a Fourier transform infrared spectrometer. The incorporation rate of the two bonds decreased with increasing the discharge power. In order to give a quantitative description of the incorporation behavior, a simple model was developed. The model was based on the dissociation of a bond of the monomer by electron impact in the plasma. The concentration of the unbroken bonds in the steady state of the plasma was given as a function of the discharge power. This model was examined with the experimental results and the kinetics of plasma-polymerization was discussed.

Improvement of the partial discharge resistance of polymer films by coating with plasma-polymerized films

The surface of polytetrafluoroethylene (PTFE) and polyethylene terephthalate films was coated with plasma-polymerized hexamethyldisiloxane (PPHMDS) film in a triode glow discharge system. The dielectric properties of PPHMDS films and their durability, the partial discharge characteristics and the surface morphology of coated polymer films were investigated. The lifetime of the coated PTFE films was longer than that of the uncoated PTFE films and varied with the preparation conditions of PPHMDS films. The maximum electrical pulse of the coated polymer film in a partial discharge electrode system was smaller than that of the uncoated polymer film. From observation of the deteriorated surface scars, it was shown that the PPHMDS film is effective for improving the partial discharge resistance.

Correlation between Adhesion Strength of Plasma-Polymerized Hexamethyldisiloxane Films to Polytetrafluoroethylene and Partial Discharge Resistance

Polytetrafluoroethylene (PTFE) films were coated with plasma-polymerized hexamethyldisiloxane (PPHMDS) films in a dc glow discharge system. The correlation between the adhesion of the PPHMDS films to the PTFE films and the partial discharge resistance of the composite films was investigated. The voltage endurance of the composite films in the presence of partial discharges increased with the adhesion of the PPHMDS films. From an observation of the deteriorated surface scars, it was shown that the deterioration is affected by the formation of cracks in the PPHMDS film.

Surface Modification of Polytetrafluoroethylene Films by Discharges

A triode glow discharge system was used for the plasma treatment of polytetrafluoroethylene (PTFE) films and the formation of plasma polymerized hexamethyldisiloxane (PPHMDS) films on PTFE films. The nitrogen plasma increased the surface tension of the PTFE films to about 40 dyn/cm by applying an rf voltage to the substrate electrode. The contact angle of water on the PPHMDS films with the rf voltage was changed to 40°∼90° by corona discharge exposure for 30 s at 6 kV. This reduction is due to the decarbonization and the oxidation of PPHMDS films.

On the origin of the dielectric breakdown mechanism in plasma-polymerized hexamethyldisiloxane films

Dielectric breakdown phenomena of plasma-deposited hexamethyldisiloxane are discussed. We show that the deposition conditions and post-treatment can change the dielectric strength. A lowering of the breakdown field was attributed to reactions with oxygen species during or after deposition.

プラズマ重合シロキサン薄膜をコーティングしたポリ四ふっ化エチレン（ＰＴＦＥ）の耐部分放電性

プラズマ重合シロキサン薄膜をコーティングしたポリ四ふっ化エチレン（ＰＴＦＥ）の耐部分放電性

Adhesion of plasma-polymerized hexamethyldisiloxane films on polytetrafluoroethylene films.

Plasma-polymerized hexamethyldisiloxane (PPHMDS) was deposited on polytetrafluoroethylene (PTFE) films by changing the conditions for the plasma pre-treatment of PTFE surface prior to PPHMDS coating. The adhesion strength measured by the direct pull method increased from about 30 kg/cm2 for the untreated films to about 80 kg/cm2 for the treated ones in Ar and N2 plasmas for 10 minutes. In the case of O2 plasma treatment, the adhesion strength increased to about 70 kg/cm2 by 1 minute treatment, but then decreased rapidly to the value lower than that of the untreated surface. The fracture of PPHMDS/PTFE system took place cohesively in the PTFE films except for the substrate films treated in O2 plasma for about more than 5 minutes. The increase in adhesion strength is due to the sputtering of the surface layers of PTFE films which otherwise might produce weak boundary layers at the interface, while the rapid decrease, in the case of O2 plasma treated PTFE films, is due to the lowering of cohesive force of the surface layers caused by the scission of the polymer chain by atomic oxygen in plasma.