Imparting antimicrobial property to the silica-based glasses and mechanical strengthening of glass surfaces by ion exchange treatment

Glasses have become widely used in all aspects of our lives, being no longer just household goods, with new developments in technology. In accordance with the need for developing high quality glasses for different usage areas, the interest in glassy materials showed a rapid increase. Glasses with their aesthetic and durable properties have become indispensable materials in many applications, such as touch screens, glassware, architectural applications, cosmetic industry, textiles and biomaterials with the antibacterial properties imparted to their structure. In the context of antimicrobial materials, many studies had been performed on plastics, ceramics, polymers, composites and fibers. On the other hand, glasses showing antimicrobial property have gained great importance in recent years due to their hardness, forming ability, high chemical durability and long lasting antimicrobial activity. There is a special interest on antimicrobial glassy materials since they can be prepared in different forms such as bulk glass, powder and coating on different substrates. Although there are various techniques available for enhancing glasses with antimicrobial property, ion exchange treatment is an ideal method for this purpose. Ion exchange technique in glass is convenient for modifying the surface composition and properties of the glass surface without changing the bulk glass properties. It is widely applied for altering the optical, mechanical, chemical and electrical properties, so it is used for many different applications such as strengthening of glass, fabrication of gradient index lenses and optical waveguides, coloration and decoration of glass. It is based on the substitution by diffusion of the ions in glass by the ions that are desired to be added into the glass which are generally from the molten salt bath. Ion exchange treatment has the benefit of being applicable not only to bulk glasses but also to the powdered glasses; therefore, it enables both powdered and bulk glasses to have antimicrobial properties. Glasses in bulk form can either be used as worktops, touch screens, bathroom and kitchen surfaces, pharmaceutical and cosmetic bottles etc. or can be applied as an additive in powdered form for textiles, cosmetics, wall and floor coverings, medical applications, food containers etc. In this dissertation, studies were contucted to impart antimicrobial properties to the widely used bulk and powdered silica-based glasses by doping silver, zinc, and copper ions with ion exchange treatment; and to chemically strengthened the bulk glass surfaces by doping potassium ions at the same time. In the experimental studies, many experiments were realized with Corning® 2947 glasses applying different temperatures, times and bath compositions to determine the optimum process parameters. The ion exchange treatment was realized using silver-potassium, zinc-potassium, and copper-potassium baths for the bulk samples, whereas silver-sodium, zinc-sodium, and copper-sodium baths were used for the powdered samples. Then, totally eight different glass compositions were prepared using conventional melt quenching technique with two differing compositions of the soda lime, aluminosilicate, borosilicate and alumina borosilicate glass groups. The effect of the change in the glass composition were investigated by applying ion exchange under certain conditions. The ion exchanged bulk and powdered glass samples were evaluated in terms of the incorporated ions into the glass, ion release behavior into aqueous environment and their antimicrobial properties. In addition, phase analysis was realised for powdered glasses to detect the possible phase formations after the process; surface and mechanical properties such as glass density, transmittance, wettability, hardness, indentation cracking behavior, scratch resistance and bending strength were investigated for the bulk glass samples. As well as doping silver, zinc and copper ions separately, Ag-Zn and Ag-Cu ion exchange treatment was studied for the first time for the bulk and powdered form of Corning® 2947 soda lime glasses. Obtained glass was investigated in terms of their ion release ability and antimicrobial activity. It was obtained that silver, zinc, copper, and potassium ions were incorporated into the glass using the ion exchange treatment, with an increased density rate where the ion exchange rate increased. Based on the transmittance analysis on the visible region, it was revealed that the transmittance of the samples doped silver decreased, whereas no change in transmittance was observed for the samples doped with zinc and copper. Contact angle measurements showed that samples with silver-potassium, zinc-potassium, and copper-potassum had larger contact angle values compared to untreated samples. After the ion exchange treatment, the hydrophobicity of the glass surface showed an increase which means that the wettability of the glass surface was reduced. The Vickers hardness of the treated glasses showed considerable increase compared to the untreated sample. After the ion exchange treatment, crack initiation threshold load was increased, and the crack sizes under a constant load showed a decrease; therefore, the samples showed higher indentation crack formation resistance after the threatment. Remarkable increase was obtained in the scratch resistance and bending strength of the treated glass samples. All the treated glass samples showed ion release ability into aqueus environment, where higher ion release rate was recorded for silver containing samples compared to the zinc and copper containing samples. According to the antimicrobial susceptibility test results, which were realized in compliance with standard test methods, silver-potassium containing bulk glass samples showed antimicrobial activity against Escherichia Coli (E.coli) ve Staphylococcus Aureus (S.aureus) cells. Experiments with the powdered glasses revealed that the incorporation of the silver, zinc, and copper ions into the glass was realized after the ion exchange treatment. While all of the samples were observed to release ions into aqueus environment, zinc and copper exchanged samples were seen to have lower ion release rate. Antimicrobial susceptibility tests using liquid broth medium showed that silver containing powdered glass samples were antimicrobial against E.coli and S.aureus cells. All of the bulk and powdered glass samples subjected to ion exchange treatment using Ag-Zn and Ag-Cu dual bath showed similar silver incorporation into the glass when compared to the glass treated only with Ag bath, while the release rate of silver ions remarkably decreased. Based on the results of antimicrobial susceptibility tests, the bulk and the powdered samples treated with Ag-Zn bath were antimicrobial against E.coli and S.aureus cells; whereas the bulk and the powdered samples treated with Ag-Cu bath showed antimicrobial activity against E.coli and Candida Albicans (C.albicans) cells. As a result of the experimental studies aimed to investigate the effect of the different glass