Preparation and characterization of anti bacterial, anti scratch and easy to clean multifunctional coatings by sol gel method

Developments of science and technology help us to understand the relationship between microstructure and material properties. Materials gain new properties by decreasing their particle size from micro to nano scale. Nowadays, thin film coatings on solid surface are developing by various physical and chemical coating methods. In order to show functionality, thin coatings must have homogeneous thickness and composition throughout the coating layer. Coating methods are generally divided as physical and chemical coating methods. Among the coating methods, sol-gel method come forward as a chemical method to develop multifunctional coatings. In general, sol gel is defined as the transition from a liquid sol phase to solid gel phase. Sol-gel process does not require high process temperatures and in this process, there is a control of the material from precursor to final product at molecular level. It is a low cost process, capable to coat flat or geometric shapes and large areas as well. In addition, it allows us to produce organic-inorganic hybrid polymers, thanks to its high purity and homogenity. In hybrid compositions, organic polymers bring well adhesion and flexibility whereas inorganic molecules brings hardness. With these compositions, various functions such as thermal and chemical stability, antibacterial property, hardness, anti scratch, anti wear, wettability... etc, can be reached. In addition, hybrid coatings can easily be bonded to ceramic or glass surfaces, thanks to their covalent binding property. Organofunctional silanes are the most suitable precursors for the preparation of organic - inorganic sol gel films. Alkyl groups which contain a functional groups such as epoxy, amino or vinyl are employed as cross linking agents in polymerization reactions. Meanwhile, non reactive groups of precursors do not participate polymerization reactions and they form porous structure in the silica network. This porous structure controls optical and mechanical properties of the films such as fracture or cracking. Since, the final product may have various characteristics depending on chemical composition of precursors, hydrolysis time, the addition order of materials into solution,etc..,sol-gel method requires close monitoring of each step. In this study, various compositions containing (3-glycydyloxypropyl)trimethoxysilane (GLYMO), Titanium(IV)isopropoxide and AgNO3 were prepared by sol-gel process. It is well known from the literature, coatings having Ag+ on the surface present antibacterial properties. An experimental design of 27 different compositions were prepared by changing the amount of titanium(IV)isopropoxide, hydrolysing water and hydrolysis time. Glass substrates were coated by sol-gel dip coating method at 15 cm/min withdrawal rate. Wet coatings were cured in oven at 150°C for 30 min. For all set of coating compositions, physical tests such as, pencil hardness test, linear abrasion test,adhesion test and nanoindentation tests were employed to find the most scratch resistant coating. The effect of the amount of last hydrolysing water on gel formation was investigated by percent solid test. From the exprerimental design set, it is found that, as the amount of Titanium(IV)isopropoxide decreases, the transparency and scratch resistance of the coatings decreased as well. For all the samples, a trend of decrease in solid % according to the increase in the amount of last hydrolysing water was obtained. Coatings which have high transparency were selected. Hydrolysis and polymerisation reactions of coating solutions and thin films were investigated by FTIR and silver absorbance during redox reactions were followed by UV absorbance spectroscopy. Micro and nano structural characterization of coatings were analyzed by SEM-EDS and AFM. Viscosity measurements in specific periods were done to determine the shelf life of the coating solutions. As a result of physical tests, the hardest and the most transparent samples were chosen to improve their easy to clean property. Fluorosilane was added to the most scratch resistant coating composition in two different route and easy to clean property of the coatings was determined by contact angle measurements. The anti bacterial activity of the coatings against Gram negative Eschericia Coli (E.Coli) and Gram positive Staphylococcus Aureus (S.aureus) was examined. Consequently, antibacterial (log5), scratch resistant (8N), and easy to clean (CA = 98-108°) multi-functional sol-gel coatings were developed.