Siloxane Coatings Research Articles

Properties of Siloxane Coatings Deposited in a Reel-to-Reel Atmospheric Pressure Plasma System

techniques. The requirement forthe vacuum process however limits the exploitation ofthis technology to batch processing. As a result, there hasbeen an increasing interest in the use of atmosphericpressure plasmas for continuous processing. In this study,silicon-containing coatings were deposited from four typesof liquid siloxane precursors, with varying molecularstructures, as follows: poly(dimethylsiloxane) (PDMS),tetraethylorthosilicate (TEOS), octamethylcyclotetrasilox-ane (OMCTS) and hexamethyldisiloxane (HMDSO). Theobjective of this study was to evaluate both the influenceof siloxane precursor structure and the level of exposure ofthe precursor to the plasma, on the properties of thedeposited coatings. Amongst the properties evaluatedwere deposited coating thickness, surface energy, mor-phology and coating siloxy chemistry and elementalcomposition.

Analysis and surface energy estimation of various model polymeric surfaces using contact angle hysteresis

Wetting of hydrophobic polymer surfaces commonly employed in electronic coatings and their interaction with surfactant-laden liquids and aqueous polymer solutions are analyzed using a contact angle hysteresis (CAH) approach developed by Chibowski and co-workers. In addition, a number of low surface tension acrylic monomer liquids, as well as common probe liquids are used to estimate solid surface energy of the coatings in order to facilitate a thorough analysis of surfactant effects in adhesion. Extensive literature data on contact angle hysteresis of surfactant-laden liquids on polymeric surfaces are available and are used here to estimate solid surface energy for further understanding and comparisons with the present experimental data. In certain cases, adhesion tension plots are utilized to interpret wetting of surfaces by surfactant and polymer solutions. Wetting of an ultra-hydrophobic surface with surfactant-laden liquids is also analyzed using the contact angle hysteresis method. Finally, a detailed analysis of the effect of probe liquid molecular structure on contact angle hysteresis is given using the detailed experiments of Timmons and Zisman on a hydrophobic self-assembled monolayer (SAM) surface. Hydrophobic surfaces used in the present experiments include an acetal resin [poly(oxymethylene), POM] surface, and silane, siloxane and fluoro-acrylic coatings. Model surfaces relevant to the literature data include paraffin wax, poly(methyl methacrylate) and a nano-textured surface. Based on the results, it is suggested that for practical coating applications in which surfactant-laden and acrylic formulations are considered, a preliminary evaluation and analysis of solid surface energy can be made using surfactant-laden probe liquids to tailor and ascertain the quality of the final coating.

N-halamine biocidal coatings

Novel N-halamine siloxane and epoxide coatings are described. The coatings can be rendered biocidal by exposure to dilute bleach. Once the bound chlorine is lost from the coatings, it can be regenerated by further exposure to dilute bleach. Synthetic schemes and biocidal efficacy data are presented. The stabilities of the bound chlorine on the surfaces are also addressed. Substrates employed include sand, textiles, and paint. Potential uses for the technology are discussed.

Antimicrobial properties of novel n-halamine siloxane coatings

Antimicrobial coatings on a wide variety of hard and soft substrates were prepared by exposing surfaces treated with novel N-halamine siloxane precursor monomers and macro-monomers to oxidative halogen solutions. Suspensions of a range of bacterial, viral, fungal and yeast micro-organisms were applied to the halogen-charged coatings for defined intervals, before recovery and quantification of surviving microbes using appropriate neutralisation and culture techniques. The biocidal surfaces exhibited powerful, broad-spectrum antimicrobial properties, inactivating most challenge microbes in contact times measured in minutes to hours, rather than the extended contact incubation periods usually associated with substrate-bound antimicrobial agents. Antimicrobial effects were also demonstrated to prevent odour caused by bacterial generation of ammonia in an experimental simulation of a urine-soaked nappy pad. Contact times for efficacy were related to bound halogen concentrations per unit of surface area. Potential benefits of these novel rechargeable biocidal surfaces cover a range, from limiting contamination of environmental surfaces with disease agents in healthcare or food service facilities, to controlling odour and mildew in bathrooms, and preventing odour formation in incontinence pads. They also confer antimicrobial protective functions on textiles and non-woven filter media for air and water.

Influence of interfaces on the rates of crosslinking in poly(dimethyl siloxane) coatings

AbstractWe have determined with infrared spectroscopic ellipsometry how the nature of the interface between a thin poly(dimethyl siloxane) (PDMS) coating and its substrate affects the rate of PDMS crosslinking reactions. Reactions between vinyl (CHCH2) end groups on PDMS and silyl (SiH) groups in a crosslinker (hydrosilylation) and between SiH groups and silanol (SiOH) groups, during the so‐called postcure crosslinking stage, have been probed in situ. The overall consumption of SiH follows first‐order reaction kinetics. The first‐order reaction coefficient (k1) for the hydrosilylation crosslinking reaction is the same for coatings on three different substrates: native oxide on silicon (SiO2/Si), polystyrene (PS), and poly(ethylene terephthalate). For the slower postcure reactions, however, the rate of SiH consumption depends on the substrate. In 2.5‐μm PDMS coatings on PS, k1 is about seven times greater than k1 in the same coating on SiO2/Si. In PDMS coatings on a PDMS substrate, when the effect of the interface is thus minimal, k1 is 16 times higher than on SiO2/Si. The dependence of k1 on the type of interface is probably the result of the interfacial segregation and complexation of the Pt catalyst for the postcure reactions. We propose that polar surfaces more strongly attract Pt and form complexes that inhibit the postcure reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1421–1431, 2004

Protein-resistant coatings for glass and metal oxide surfaces derived from oligo(ethylene glycol)-terminated alkyltrichlorosilanes

This paper describes the preparation of oligo(ethylene glycol)-terminated alkyltrichlorosilanes, Cl 3Si(CH 2) 11(OCH 2CH 2) n OCH 3 ( n=2, 3 ), and their use in the formation of self-assembled monolayers on an oxide surface. The adsorption of the trichlorosilanes from solution produces densely packed, oriented monolayer films that are 2–3 nm in thickness. The trichlorosilyl group anchors the molecules to the surface, and the resulting film exposes the ethylene glycol units at its surface, as noted by its moderate hydrophilicity ( θ a(H 2O)≈68°). The films are robust with stabilities similar to those of other alkylsiloxane coatings. These oligo(ethylene glycol)-terminated silane reagents produce films that notably exhibit resistances against the non-specific adsorption of proteins from solution that are better than for films prepared from octadecyltrichlorosilane. With insulin, lysozyme, albumin, and hexokinase, no adsorption was observed with the oligo(ethylene glycol)-siloxane coatings whereas protein films of approximately a monolayer formed on surfaces-treated with octadecyltrichlorosilane. With fibrinogen, complete resistance was not possible with either coating; however, the oligo(ethylene glycol)-siloxane coatings exhibited greater resistance against non-specific adsorption. The oligo(ethylene glycol)-siloxane coatings offer performance advantages over available systems and could easily provide a direct and superior replacement in protocols that presently use silane reagents to generate hydrophobic, ‘inert’ surfaces.

Chemical behaviour of siloxanes at metal interfaces-2

Further evidence on the nature of siloxane films on metal substrates is presented in this paper in the form of experimental results which support the theory that the case of formation of bonded siloxane coatings is related to the ease of oxidation of the metal substrate. The evidence also shows that film thickness is closely related to the molecular geometry of the siloxane used.

Chemical behaviour of siloxanes at metal interfaces

The apparently anomalous behaviour of siloxanes as lubricants is discussed and a reason for this behaviour is suggested. This paper also includes a study of the nature of the surface film produced at elevated temperatures and a method of differentiating between chemically bonded coatings and surface lacquers is suggested.