Coatings

892 KiB

Open AccessArticle

Low Loss Sol-Gel TiO₂ Thin Films for Waveguiding Applications

by Tahar Touam, Lamia Znaidi, Dominique Vrel, Iva Ninova-Kuznetsova, Ovidiu Brinza, Alexis Fischer and Azzedine Boudrioua

Coatings 2013, 3(1), 49-58; https://doi.org/10.3390/coatings3010049 - 11 Mar 2013

Cited by 32 | Viewed by 9487

Abstract

TiO₂ thin films were synthesized by sol-gel process: titanium tetraisopropoxide (TTIP) was dissolved in isopropanol, and then hydrolyzed by adding a water/isopropanol mixture with a controlled hydrolysis ratio. The as prepared sol was deposited by “dip-coating” on a glass substrate with a controlled withdrawal speed. The obtained films were annealed at 350 and 500 °C (2 h). The morphological properties of the prepared films were analyzed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The optical waveguiding properties of TiO₂ films were investigated for both annealing temperature using m-lines spectroscopy. The refractive indices and the film thickness were determined from the measured effective indices. The results show that the synthesized planar waveguides are multimodes and demonstrate low propagation losses of 0.5 and 0.8 dB/cm for annealing temperature 350 and 500 °C, respectively. Full article

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4373 KiB

Open AccessArticle

Continuous Convective-Sedimentation Assembly of Colloidal Microsphere Coatings for Biotechnology Applications

by Jessica S. Jenkins, Michael C. Flickinger and Orlin D. Velev

Coatings 2013, 3(1), 26-48; https://doi.org/10.3390/coatings3010026 - 6 Feb 2013

Cited by 14 | Viewed by 9609

Abstract

Continuous convective-sedimentation assembly (CCSA) is a deposition method that constantly supplies the coating suspension to the meniscus behind the coating knife by inline injection, allowing for steady-state deposition of ordered colloids (which may include particles or cells or live cell-particle blends) by water evaporation. The constant inflow of suspended particles available for transport to the drying front yields colloidal arrays with significantly larger surface areas than previously described and thus expands the ability of convective assembly to deposit monolayers or very thin films of multiple sizes of particles on large surfaces. Using sulfated polystyrene microspheres as a model system, this study shows how tunable process parameters, namely particle concentration, fluid sonication, and fluid density, influence coating homogeneity when the meniscus is continuously supplied. Fluid density and fluid flow-path sonication affect particle sedimentation and distribution. Coating microstructure, analyzed in terms of void space, does not vary significantly with relative humidity or suspended particle concentration. This study evaluated two configurations of the continuous convective assembly method in terms of ability to control coating microstructure by varying the number of suspended polymer particles available for transport to the coating drying front through variations in the meniscus volume. Full article

(This article belongs to the Special Issue Advancing Coatings with Biotechnology)

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1036 KiB

Open AccessArticle

Polyurethane Coatings Reinforced by Halloysite Nanotubes

by Xin Li, Irina Nikiforow, Katja Pohl, Jörg Adams and Diethelm Johannsmann

Coatings 2013, 3(1), 16-25; https://doi.org/10.3390/coatings3010016 - 18 Jan 2013

Cited by 18 | Viewed by 9619

Abstract

The pencil hardness of a two-component polyurethane coating was improved by adding halloysite nanotubes to the recipe at a weight fraction of less than 10%. The pencil hardness was around F for the unfilled coating and increased to around 2H upon filling. It was important to silanize the surface of the filler in order to achieve good coupling to the matrix. Sonicating the sample during drying also improved the hardness. Scanning electron micrographs suggest that the nanotubes are always well immersed into the bulk of the film. With a thickness between 10 and 20 µm, the optical clarity was good enough to clearly read letters through the film. The films can be used in applications where transparency is required. Full article

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192 KiB

Open AccessReview

Coating and Surface Treatments on Orthodontic Metallic Materials

by Santiago Arango, Alejandro Peláez-Vargas and Claudia García

Coatings 2013, 3(1), 1-15; https://doi.org/10.3390/coatings3010001 - 27 Dec 2012

Cited by 57 | Viewed by 14902

Abstract

Metallic biomaterials have been extensively used in orthodontics throughout history. Gold, stainless steel, cobalt-chromium alloys, titanium and its alloys, among other metallic biomaterials, have been part of the orthodontic armamentarium since the twentieth century. Metals and alloys possess outstanding properties and offer numerous possibilities for the fabrication of orthodontic devices such as brackets, wires, bands, ligatures, among others. However, these materials have drawbacks that can present problems for the orthodontist. Poor friction control, allergic reactions, and metal ionic release are some of the most common disadvantages found when using metallic alloys for manufacturing orthodontic appliances. In order to overcome such weaknesses, research has been conducted aiming at different approaches, such as coatings and surface treatments, which have been developed to render these materials more suitable for orthodontic applications. The purpose of this paper is to provide an overview of the coating and surface treatment methods performed on metallic biomaterials used in orthodontics. Full article

(This article belongs to the Special Issue Advances in Dental Biomaterials and Coatings)

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Coatings, Volume 3, Issue 1 (March 2013) – 4 articles , Pages 1-58

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