Light-blocking polymer films from colloidal templates

Additives such as metal films or absorbing dyes are added to many plastic packaging materials to block short-wavelength light, which is damaging to certain foods and pharmaceuticals. Although effective at blocking light, these additives make recycling difficult and contaminate polymer waste streams. We have developed a different approach to making light-blocking polymer films that relies on scattering light instead of absorbing it. We make these materials by incorporating a colloidal template into a polymer film, then selectively removing the template. By controlling the size and structure of the colloidal template, we can make polymer films that selectively scatter short-wavlength light while remaining transparent at longer wavelenghts. Because the colloidal template is completely removed, these light-blocking films contain only polymer and are therefore recyclable. I will discuss the physical principles underlying the fabrication and properties of these materials.