Siloxane Coatings Research Articles

Molecular assembly of nanolayers of water-repellent siloxane coatings on the surface of fibers

We demonstrate the feasibility of chemical modification of the surface of fibers and fabrics by layer-by-layer molecular assembly of a water-repellent polysiloxane coating, involving covalent anchoring of nanolayers of a poly(chloromethyl)siloxane coating on the surface of the fibers, followed by grafting a monomolecular finishing layer of long-chain alkyl radicals. The method makes it possible to achieve a high degree of water resistance (wetting contact angle up to 128°) for a concentration of the waterproofing agent equal to 24-98 μmoles per gram of fabric.

Modification of siloxane coatings with boron and aluminum compounds

Modification of siloxane coatings of protective materials with boron (boric acid, boric anhydride, triethyl borate) and aluminum (aluminum butylate, oxide, hydroxide) compounds was studied with the aim to enhance the fireproofing and physicomechanical properties of the materials.

Deposition of Hybrid Organic–Inorganic Composite Coatings Using an Atmospheric Plasma Jet System

The objective of this study is to investigate the influence of alcohol addition on the incorporation of metal oxide nanoparticles into nm thick siloxane coatings. Titanium oxide (TiO2) nanoparticles with diameters of 30-80 nm were incorporated into an atmospheric plasma deposited tetramethylorthosilicate (TMOS) siloxane coating. The TMOS/TiO2 coating was deposited using the atmospheric plasma jet system known as PlasmaStream. In this system the liquid precursor/nanoparticle mixture is nebulised into the plasma. It was observed that prior to being nebulised the TiO2 particles agglomerated and settled over time in the TMOS/TiO2 mixture. In order to obtain a more stable nanoparticle/TMOS suspension the addition of the alcohols methanol, octanol and pentanol to this mixture was investigated. The addition of each of these alcohols was found to stabilise the nanoparticle suspension. The effect of the alcohol was therefore assessed with respect to the properties of the deposited coatings. It was observed that coatings deposited from TMOS/TiO2, with and without the addition of methanol were broadly similar. In contrast the coatings deposited with octanol and pentanol addition to the TMOS/TiO2 mixture were significantly thicker, for a given set of deposition parameters and were also more homogeneous. This would indicate that the alcohol precursor was incorporated into the plasma polymerised siloxane. The incorporation of the organic functionality from the alcohols was confirmed from FTIR spectra of the coatings. The difference in behaviour with alcohol type is likely to be due to the lower boiling point of methanol (65 degrees C), which is lower than the maximum plasma temperature measured at the jet orifice (77 degrees C). This temperature is significantly lower than the 196 degrees C and 136 degrees C boiling points of octanol and pentanol respectively. The friction of the coatings was determined using the Pin-on-disc technique. The more organic coatings deposited with octanol and pentanol exhibited friction values of 0.2, compared with approx. 0.8 for the coatings deposited from TMOS/TiO2 mixture (with and without methanol). Wear performance comparison between the two types of coating again indicated a significant organic component in the coatings deposited from the higher boiling point alcohols.

Innovative Siloxane Coating Formulations: The Experimental Assessment of the Durability of Colour

Maintenance programming of civil and industrial buildings is a relevant problem, especially in a global situation where natural resources are increasingly limited. Accurately knowing the durability of building products and components, essential for a sustainable use of resources, becomes more and more important after the recent 18 January 2011 resolution of the European Parliament, which introduced the seventh requirement on construction products, specifically regarding the sustainability and therefore the durability of such. This study concerns the evaluation of the durability of some innovative coatings based on acrylic-siloxane resins containing several pigments, used for building external decorative finishing, applied in thin thickness and of different basic components. The parameters investigated are: the surface appearance and the maintenance of the original colour, significant for the aesthetic quality of the architecture. The paper presents the first results of the experimental study on coating materials, produced by Hydrate Ltd, performed according to ISO 15686, aimed at defining the Reference Service Life, by monitoring the behaviour over time of artificially aged samples in the climatic chamber and external exposed samples, as well as the monitoring of a case study.

Effect of Atomic Oxygen Exposure on Si Implanted Siloxane Coatings in Low Earth Orbit Environment

To improve the AO erosion resistance of siloxane coating, the Si ion implantation with nominal dosage of 7×1016 ions/cm2 in siloxane coatings on the polyimide substrate was carried out by using the plasma immersion ion implanter. The Si implanted siloxane coatings before and after AO exposure in the ground-based AO simulation facility were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The results of mass measurement shown that, in initial stage of AO exposure the implanted sample had a small mass change, and then was stabilized. The erosion yield of the implanted siloxane coating decreased by a factor of more than two orders of magnitude compared with that of the polyimide film, and decreased by a factor of more than an order of magnitude than that of unimplanted siloxane coatings. The results through SEM and XPS indicated that a continuous high-quality protective SiO2 surface layer was formed on the implanted siloxane coatings after the AO exposure. It can prevent further degradation of the underlying polymer with increased exposure to the AO flux and provide high-quality erosion protection for these materials. The Si implanted materials have a markedly increased erosion resistance than unimplanted siloxane coatings in AO environment.

Enhancing the Mechanical Properties of Superhydrophobic Atmospheric Pressure Plasma Deposited Siloxane Coatings

AbstractSurfaces with water contact angles above 150° are regarded as superhydrophobic. In this study the use of atmospheric pressure plasma jet system called PlasmaStreamTM to deposit superhydrophobic coatings is investigated. The coatings were deposited from the following liquid precursors: hexamethyldisiloxane (HMDSO), tetramethyl cyclotetrasiloxane (Tomcats) and a mixture of Tomcats and fluorosiloxane. The objective of the study is to investigate how precursor type and deposition conditions, influences the morphology and mechanical performance of the deposited superhydrophobic coatings. Optical profilometry, AFM, SEM, Ellipsometry, XPS, Water contact angle and FTIR techniques were used to evaluate the surface roughness, morphology, thickness and chemical functionality of the deposited coatings. The mechanical properties were evaluated using the Nano Tribometer, Nano Scratch, Ultra Nanoindentation and ultrasonic abrasion tests. Superhydrophobic coatings deposited from a precursor mixture of Tomcats and fluorosiloxane yielded a substantial enhancement in coating adhesion and mechanical durability compared to the superhydrophobic coatings obtained with either Tomcats or HMDSO precursors alone. magnified image

Correlation Between the Electrical and Optical Properties of an Atmospheric Pressure Plasma During Siloxane Coating Deposition

The effect of varying process parameters on atmospheric plasma characteristics and properties of nanometre thick siloxane coatings is investigated in a reel-to-reel deposition process. Varying plasma operation modes were observed with increasing applied power for helium and helium/oxygen plasmas. The electrical and optical behaviour of the dielectric barrier discharge were determined from current/voltage, emission spectroscopy and time resolved light emission measurements. As applied power increased, multiple discharge events occurred, producing a uniform multi-peak pseudoglow discharge, resulting in an increase in the discharge gas temperature. The effects of different operating modes on coating oxidation and growth rates were examined by injecting hexamethyldisiloxane liquid precursor into the chamber under varying operating conditions. A quenching effect on the plasma was observed, causing a decrease in plasma input power and emission intensity. Siloxane coatings deposited in helium plasmas had a higher organic component and higher growth rates than those deposited in helium/oxygen plasmas.

Evaluation of the anti-fouling properties of nm thick atmospheric plasma deposited coatings

Both organic and inorganic fouling are significant problems for stainless steel surfaces used in industrial applications as diverse as shipping and paper making. The objective of this study is to evaluate the anti-fouling properties of a range of fluoropolymer, fluorinated and non-fluorinated siloxane coatings on stainless steel substrates. These nm thick coatings were deposited using the atmospheric plasma jet system called PlasmaStream™. The surface properties of the plasma polymerised coatings were examined using optical profilometry, SEM–EDX, ellipsometry, contact angle measurement and FTIR. Accelerated wear testing of the coated heat exchangers indicated that coating durability was a significant issue for the nanometre thick coatings investigated. A crystallization fouling study was carried out using a laboratory scale heat exchanger test apparatus. In this the heated steel surface was in contact with flowing fluid containing CaCO 3 particles. The coated steel exhibited both a delay before fouling was initiated and in addition a decrease in the fouling rate. A lubricant oil fouling study was also carried out involving a comparison between both coated and uncoated stainless steel separator discs over a 30 day period, in the engine of a passenger ferry. A significant reduction in the level of oil fouling was observed for the fluorosiloxane and fluoropolymer coated separator discs compared with the uncoated discs.

Corrosion resistance of new epoxy–siloxane hybrid coatings. A laboratory study

Traditional multilayer epoxy/polyurethane type anticorrosive paint systems are widely employed in the protection of steel structures due to their high efficiency against atmospheric corrosion. However, the use of isocyanate in the curing process, and the high volatile organic compound (VOC) content of such systems, makes it necessary to search for new isocyanate-free paints. Hybrid organic–inorganic coatings, such as epoxy–siloxane coatings, represent a step forward in the field of paint coatings for atmospheric corrosion protection. These new isocyanate-free hybrids present low VOC levels – due to the high solid content associated with their low viscosity – along with good heat and UV radiation stability and excellent chemical resistance. With the new polysiloxane inorganic resins it is hoped to improve the anticorrosive behaviour of traditional organic binders. This work assesses the anticorrosive performance of one-layer epoxy–siloxane coatings compared to traditional two-layer epoxy/polyurethane coatings, in paint systems with and without an epoxy or silicate-type zinc-rich primer. The anticorrosive properties of these coatings applied on steel substrates have been evaluated using a wide range of experimental techniques, namely measurement of water vapour and oxygen permeability in free films, 3-year outdoor testing, accelerated corrosion testing (condensing humidity, Kesternich, salt fog and Prohesion), and electrochemical impedance spectroscopy (EIS). Hybrid epoxy–siloxane films show the lowest oxygen and water vapour permeability, capacitance values, and the highest ionic resistance values, along with excellent behaviour in humidity and Kesternich tests, outperforming traditional epoxy/polyurethane paints, while the behaviour of both types of coatings is similar in the salt fog, Prohesion and short-term outdoor tests. This type of paint requires the presence of zinc-rich primers to optimise its anticorrosive behaviour.

Mechanism of Photolytic Decomposition of N-Halamine Antimicrobial Siloxane Coatings

Generally, antimicrobial N-halamine siloxane coatings can be rehalogenated repetitively upon loss of their biocidal efficacies, a marked advantage over coatings containing other antimicrobial materials. However, the N-halamine materials tend to slowly decompose upon exposure to ultraviolet irradiation as in direct sunlight. In this work the mechanism of photolytic decomposition for the N-halamine siloxanes has been studied using spectroscopic and theoretical methods. It was found that the N-chlorinated coatings slowly decomposed upon UVA irradiation, whereas the unhalogenated coatings did not. Model compound evidence in this work suggests that upon UVA irradiation, the N-Cl bond dissociates homolytically, followed by a Cl radical migration to the alkyl side chain connected to the siloxane tethering group. An alpha and/or beta scission then occurs causing partial loss of the biocidal moiety from the surface of the coated material, thus precluding complete rechlorination. NMR, FTIR, GCMS, and computations at the DFT (U)B3LYP/6-311++G(2d,p) level of theory have been employed in reaching this conclusion.

Effect of Surface Wettability and Topography on the Adhesion of Osteosarcoma Cells on Plasma-modified Polystyrene

Biomaterials interact with the biological environment at their surface, making accurate biophysical characterization of the surface crucially important for understanding subsequent biological effects. In this study, the surface of polystyrene (PS) was systematically altered in order to determine the effect of plasma treatment and surface roughness on cell adhesion and spreading. Surfaces with water contact angle from hydrophilic (12°) to superhydrophobic (155°) were obtained through a combination of modifying surface roughness (R (a)), the deposition of siloxane coatings and the fluorination of the PS surface. R (a) values in the range of 19-2365 nm were obtained by grinding the PS surface. The nanometer-thick siloxane coatings were deposited using an atmospheric pressure plasma system, while the fluorination of the PS was carried out using a low-pressure radio frequency (RF) plasma. The siloxane coatings were obtained using a liquid poly(dimethylsiloxane) precursor that was nebulized into helium or helium/oxygen plasmas. Water contact angles in the range of 12-122° were obtained with these coatings. Cell adhesion studies were carried out using human MG63 osteosarcoma cells. It was observed that higher polymer surface roughness enhanced cell adhesion, but had a negative effect on cell spreading. Optimum cell adhesion was observed at ∼64° for the siloxane coatings, with a decrease in adhesion observed for the more hydrophilic and hydrophobic coatings. This decrease in cell adhesion with an increase in hydrophobicity was also observed for the fluorinated PS surfaces with water contact angles in the range of 110-155°.

Effect of Titanium Oxide Nanoparticle Incorporation into nm Thick Coatings Deposited Using an Atmospheric Pressure Plasma

This study reports on the use of an atmospheric plasma technique to incorporate metal oxide nanoparticles into nm thick siloxane coatings. Titanium dioxide (TiO2) particles with diameters of 30-80 nm, were mixed with a number of different siloxanes-polydimethylsiloxane, hexamethyldisiloxane and tetraethylorthosilicate (TEOS). The TiO2/TEOS mixture was found to give the most stable suspension, possibly due to the higher surface tension of TEOS compared with the other siloxanes. TiO2/TEOS mixtures with 2 to 10% by weight of the metal oxide were prepared and were then nebulised into a helium/oxygen atmospheric plasma. Polyethylene terepthalate (PET) and silicon wafer substrates were passed through this plasma using a reel-to-reel substrate manipulation system. SEM combined with EDX was used to examine the distribution of the metal oxide particles in the resultant coatings. The TEOS coating thickness without TiO2 addition was 9 nm. The composite coating consisted of a relatively homogeneous distribution of small agglomerates of the TiO2 nanoparticles in TEOS. A linear increase in the titanium surface concentration was observed with increase in the quantity of TiO2 added into the siloxane precursor. The chemical functionality of the siloxane coating was examined using FTIR spectroscopy and no significant spectrum differences was observed with the incorporation of the different concentrations of TiO2 into the polymer. There were also no changes observed in coating surface energy with TiO2 incorporation. Coating morphology was examined using optical profilometry and surface roughness (Ra) values increased from typical values of 0.8 nm for the TEOS coating to 4.1 nm for the TiO2/TEOS coating. The adhesion of the deposited coatings was compared using fragmentation tests. These were carried out through uniaxial tensile loading. The coating cracking pattern after applied strain of 20% was not observed to change significantly with the addition of TiO2 into the siloxane.

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.

Evaluation of Cell Behaviour on Atmospheric Plasma Deposited Siloxane and Fluorosiloxane Coatings

For developing functional biomaterials, an understanding of the biological response at material surfaces is of key importance. In particular, surface chemistry, roughness and cell type influence this response. Many previous reports in the literature have involved the study of single cell types and their adhesion to surfaces with a limited range of water contact angles. The objective of this study was to investigate the adhesion of five cell lines on surfaces with contact angles in the range of 20° to 115°. This range of water contact angles was obtained using siloxane and fluorosiloxane coatings deposited using atmospheric plasma deposition. These nm thick coatings were deposited by nebulizing liquid precursors consisting of poly(dimethylsiloxane) (PDMS) and a mixture of perfluorodecyl acrylate/tetraethylorthosilicate (PPFDA/TEOS) into the atmospheric plasmas. Cell adhesion studies were carried out with the following cell types: Osteoblast, Human Embryonic Kidney (HEK), Chinese hamster ovary (CHO), Hepatocytes (HepZ) and THP1 leukemic cells. The study demonstrated that cell adhesion was significantly influenced by the type of cell line, water contact angle and coating chemistry. For example, the sensitivity of cell lines to changes in contact angle was found to decrease in the following order: Osteoblasts > Hepatocytes > CHO. The HEK and THP-1 inflammatory cells in contrast were not found to be sensitive to changes in water contact angle.

Effect of Process Parameters on Chemistry, Growth Rate and Nano-Sized Particulate Formation of Atmospheric Plasma Deposited, nm Thick Siloxane Coatings

Nano-thick siloxane coatings with thickness in the range 1-33 nm were deposited using a reel-to-reel atmospheric plasma coating system. The coatings were deposited from a tetraethoxysilane (TEOS) precursor which was nebulised into a helium plasma. An issue influencing coating performance is the incorporation of particulates, which are formed during the deposition process. By systematically varying the process parameters such as plasma power, TEOS flow rate, gas flow rates (He, O2, and N2), a correlation was obtained between the deposition conditions and particulate formation. The effect of process parameters on growth rate, changes in coating chemistry and particulate formation on the deposited nm-thick films were studied by spectroscopic ellipsometry, contact angle/surface energy measurements, optical profilometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR), Scanning electron microscopy (SEM) and Atomic force microscopy (AFM). Larger numbers of particulates were formed under the conditions of higher plasma power, with the addition of O2 or N2 into the He plasma and also at both very low and high TEOS flow rates in the range 10-200 microl/min. Low plasma input power and moderate precursor flow rates (approx. 25 microl/min) significantly reduced particulate formation.

Influence of Atmospheric Plasma Source and Gas Composition on the Properties of Deposited Siloxane Coatings

AbstractSiloxane coatings were deposited using two different atmospheric plasma systems namely a reel‐to‐reel atmospheric plasma liquid deposition system called Labline™ and an atmospheric plasma jet system called PlasmaStream™. Both systems combine an atmospheric plasma, with the use of liquid precursors. The influence of the plasma source and processing conditions on the deposited coating properties were studied. The coatings were deposited onto Vycor glass and silicon wafer substrates from a liquid tetraethyl orthosilicate (TEOS) precursor which was nebulized into both He and He/O2 plasmas. Higher film growth rates were obtained using the plasma jet system; however, the reel‐to‐reel system facilitated the larger area coating of webs. The thickness (spectroscopic ellipsometry measurements) and water contact angle profile of the films deposited using the jet system on silicon wafer substrates in static mode were investigated. Amongst the other coatings characterization techniques used to evaluate the deposited coatings were optical profilometry, XPS, SEM, and AFM. The formation of particulates due to excess gas‐phase reactions during the atmospheric plasma deposition of coatings has been widely reported. In this study, larger number of particulates were observed under the conditions of higher plasma power, with the addition of O2 into the He plasma and also at low TEOS flow rates. The introduction of N2 into the He/O2 plasma, during the deposition of siloxane coatings led to a significant reduction in the number of particulates generated for both plasma sources. Nitrogen gas flow rate was varied systematically and a correlation was obtained on the influence of the flow rate of this gas on surface roughness and particulate formation.

Deterioration and damage evaluation of rendering mortars exposed to sulphuric acid

Renders and plasters are usually employed for restoration, consolidation and decorative purposes. This paper looks at a rapid method based on conductivity measurements to evaluate the damage caused by sulphuric acid on cement renders. Exposure of the renders to 0.1% w/w sulphuric acid solutions resulted, as expected, in the formation of gypsum and no signs of ettringite were observed. The samples were also treated with siloxane coatings (polydimethylsiloxane) to investigate the waterproofing role on acid protection. A linear correlation was found between the time of immersion and change in conductivity. Finally, the results were supported by water absorption tests, scanning electron microscopy, X-ray diffraction and ion chromatography.

Deposition parameters to improve the fouling-release properties of thin siloxane coatings prepared by PACVD

A range of SiO x -like coatings was deposited on glass slides from a hexamethylsiloxane precursor by plasma-assisted CVD. The effect of varying deposition parameters, specifically ion cleaning time and HMDSO/O 2 ratios, on the coating properties and antifouling performance was investigated. At low HMDSO/O 2 ratios, the resulting coatings were close to SiO 2. Carbon content in the bulk of the coatings increased with increasing HMDSO/O 2 ratio. Coatings deposited at high HMDSO/O 2 ratios and with the longest cleaning time (30 min), elevated the relative carbon content to 25 atomic %. Surface energies (22–43 mJ/m) were correlated with the degree of surface oxidation and hydrocarbon content. With the exception of the most polar coatings the apolar component of the surface energy ( γ LW) was the dominant component. In the most hydrophilic coatings, the Lewis base component of the surface energy ( γ −) was dominant. Significantly improved antifouling performance was detected with the most reduced coatings deposited using the extended ion cleaning times. For both, the removal of sporelings of the marine green alga, Ulva linza and the initial adhesion of the freshwater bacterium, Pseudomonas fluorescens, there was a strong, positive correlation between strength of attachment and ion cleaning time. Increased ion cleaning time will elevate the deposition temperature, increasing decomposition rates and thus the crosslinking of the polymer. Increased cross-linking may render these coatings less permeable to penetration and mechanical interlocking by the adhesive polymers used by these organisms, thus reducing their adhesion. Films with improved biological performance have potential for use as coatings in the control of biofouling in applications such as heat exchangers, where thin films are important for effective thermal transfer, or optical windows where transparency is important.

Effect of Alkyl Derivatization on Several Properties of N-Halamine Antimicrobial Siloxane Coatings

Variation of alkyl substitution at position 5 on the hydantoin ring of a series of N-halamine siloxane derivatives has been employed to better understand the biocidal activities of these compounds for use in preparing antimicrobial coatings. The alkyl derivatization of the hydantoin ring at its 5 position, while an essentially constant chlorine loading is maintained at the 1 position, has shown that there is little dependence of the antimicrobial efficacy against Escherichia coli O157:H7 on the alkyl chain length, in contrast to reported observations for biocidal quaternary ammonium salt derivatives. The stabilities of the derivatives toward hydrolyses and ultraviolet light exposure have also been found to not be dependent upon the nature of the alkyl substituent group. These observations led to the conclusion that the 5,5-dimethyl derivative would be recommended for use, since it is the least expensive alternative.

A methodology for curve‐fitting of the XPS Si 2p core level from thin siloxane coatings

AbstractPlasma‐enhanced coating processes are recognised as a route to well‐adhered, conformal coatings, and are often used as a means of modifying the surface properties of materials, while having a minimal effect on the bulk characteristics of the substrate. Here, a method for providing an understanding of the chemistry of siloxane coatings prepared by plasma liquid deposition in atmospheric pressure (AP) is described.An iterative Si 2p–C 1s method for curve‐fitting the C 1s and Si 2p core levels of siloxane coatings thinner than the depth of analysis of XPS has been developed when the substrate is poly(ethylene terephthalate) (PET) film. In addition to the determination of unambiguous binding energy positions for four siloxy environments, this has allowed the elemental composition of the coating to be determined in isolation of the substrate.Application of the binding energies to the Si 2p core levels of industrially relevant materials where the composition is not known by any other means can now be carried out. This can be used to provide understanding of the relationship between coating chemistry and plasma parameters, which is essential in the development of novel processes such as AP plasma liquid deposition, and will result in the deposition of coatings with controlled properties. Copyright © 2007 John Wiley & Sons, Ltd.