Spray-On Particles Waterproof Paper

Protecting posters, newspapers, and important documents from wet weather is now as simple as spraying them with a solution of nanoparticles. Hitoshi Ogihara and coworkers at Tokyo Institute of Technology developed the new method for preparing superhydrophobic paper (Langmuir, DOI: 10.1021/la204492q). Their approach requires no expensive instruments, extreme conditions, or exotic materials. The researchers take 25-nm-diameter SiO₂ nanoparticles and treat them with dodecyltrichlorosilane, which coats the nanoparticles’ surface with dodecyltrichloro groups to impart hydrophobicity. They then suspend the particles in ethanol, spray the suspension onto paper, and let it dry. The resulting transparent coating creates a microscale roughness to the paper so that when water strikes the surface the liquid beads up and rolls off, rather than sinking into the paper’s cellulose. Treated paper retains its superhydrophobicity upon folding or touching with bare hands. “If somebody needs waterproof paper for some reason at a particular place, they can make it by on-the-spot spraying,” Ogihara points out. He also notes the spray works on other types of cellulosic fibers, such as cotton, so clothes and shoes could also be made super­hydrophobic via this method.