Friction control of elastic materials on glass by means of textured surfaces.

To investigate the friction behaviors of elastomer and polyacetal writing tips sliding on various textured glass surfaces, the influences of the pitch size and height of sub-millimeter to millimeter sized texture on friction were examined via reciprocating friction tests. The friction coefficients of each writing tip could be systematically varied by changing the pitch and height of the texture. These changes in friction were based on the relationship between the convex-concave shapes and the contact parts of the writing tip, and hence, influence the adhesive, abrasive, and deformation frictions. By inducing a surface texture with a pitch smaller than the contact area of the writing tip, the friction coefficient could be reduced effectively. By inducing a surface texture with a larger height, the friction coefficient of the elastomer could be increased due to deformation friction. These behaviors indicate the possibility of controlling the friction by changing the parameters such as the pitch and height of the textured glass surfaces.

Antibacterial activity of silver-doped silica glass microspheres prepared by a sol-gel method.

Various kinds of inorganic substances doped with silver ions have been developed as antibacterial materials, and some have already been commercialized. Previously, we successfully prepared colorless silica glass microspheres doped with silver ions in combination with aluminum ions by a sol-gel method. However, the antibacterial activity of the microspheres was not maintained for long periods in an aqueous environment, since the silver ions were located only in a thin layer near the surface of the microspheres. In this study, silica glass microspheres in which silver ions are uniformly distributed were attempted to be prepared. A tetraethoxysilane ethanol solution was mixed with aqueous silver nitrate and aluminum nitrate solutions to be subjected to almost simultaneous hydrolysis and polycondensation. An ammonia solution was then added, to form microspheres. Monodispersed microspheres about 0.1 microm in diameter were obtained, which did not show coloring even after heat treatment at 600-1000 degrees C, indicating that the silver in the microspheres took the form of Ag(+) ions and not colloid, even after the heat treatments. Microspheres heat-treated at temperatures ranging from 700 to 800 degrees C showed much higher antibacterial activity than commercial antibacterial zeolites and maintained their high antibacterial activities for long periods in an aqueous environment. Polypropylene plates and films mixed with the microspheres heat-treated at 800 degrees C showed excellent antibacterial properties.

Preparation of antibacterial silver-doped silica glass microspheres.

Various types of inorganic substances doped with silver ions have been developed as antibacterial materials, and some have already been commercialized. Colorless and chemically durable materials that slowly release silver ions are, however, still need to be developed. The present authors have previously shown that when a silica glass doped with silver and aluminium ions is prepared using the sol-gel method, the resultant product is colorless, chemically durable, and slowly releases silver ions into water over a long period. The doped silica glass takes a form of microspheres <1 microm in diameter, it is easily mixed with organic polymers, and the mixture can be formed into a thin film or fine fibers, etc. We report on the preparation of silver doped silica glass microspheres having a diameter =1 microm, using the sol-gel method. Initially, tetraethoxysilane was partially prehydrolyzed by water in ethanol, and then aluminium triisopropoxide was added to the solution to form Si-O-Al bonds. Finally, an ammonia solution containing silver nitrate was added to form silica microspheres doped with silver ion together with aluminium ions. The results show monodispersed microspheres 0.4-0.6 microm in diameter were obtained with nominal compositions of Si/Al/Ag = 1/0.01-0.03/0.003-0.03, with a molar ratio of Al/Ag = 1-3.3. The microspheres were colorless, showed a high chemical durability, and slowly released silver ions into water at 37 degrees C. Microspheres with the composition Si/Al/Ag = 1/0.01/0.01 showed excellent antibacterial activity against Escherichia coli. The minimum inhibitory concentration (MIC) of the microspheres was 400, which is less than the MIC value (800) of commercial antibacterial materials.