Silicone rubber and other rubber-like materials have a wide variety of uses, but in almost every case they must be reinforced with particles to make them stronger or less permeable to gases or liquids. University of Cincinnati (UC) chemistry professor James Mark and colleagues have devised a technique that strengthens silicone rubber with nanoscale particles, but leaves the material crystal clear.
Silicone rubber is often reinforced by tiny particles of silica (the primary component of sand and the mineral quartz). However, those silica particles can cloud the silicone rubber, which is a problem for protective masks, contact lenses and medical tubing that rely on silicone rubber's transparency.
Mark, along with graduate student Guru Rajan, UC professor Dale Schaefer, UC associate professor Gregory Beaucage and Yeungnam University (Korea) professor Gil Sur reported on their new technique in the August 15 issue of the Journal of Polymer Science Part B: Polymer Physics.
The technique infuses silicone rubber with nanoparticles up to five times smaller than the silica particles formed by comparable methods while still providing the same level of reinforcement and maintaining the silicone rubber's clarity.
Variations on the technique might also be used to enhance other properties of silicone rubber and similar materials, affecting such traits as impermeability to gases or liquids. This could lead to better masks or suits to protect against agents that might be used in terrorist attacks.
The team's technique is an improvement over related methods that use a chemical reaction to create silica particles within the silicone polymers. By generating the required catalyst in place from a tin salt and by restricting the amount of water to only that absorbed from water vapor in the air, the silica particles remain smaller—only 30 nm to 50 nm across—and are evenly dispersed throughout the silicone rubber. At that size, smaller than the wavelength of ultraviolet and visible light, the silica nanoparticles are essentially invisible.