UC San Diego

A dry deposition method for patterning particles for specific applications of emissive display screens, photocatalysts and nanoparticles, using DuPont Tacky Dot® photopolymer, was developed. This tacky photopolymer, Cromalin®, may be adhered to various substrates and patterned through the polymerization of the adhesive when exposed to UV light. It was found that Cromalin® is activated at a wavelength of 340-370 nm and has a patterning resolution as measured by the USAF 1951 resolution target to be ̃20 [mu]m. Phosphor, alumina, titania, toner and various types of nanometer-sized materials, including carbon nanotubes, mesoporous silica nanoparticles, silver nanowires and magnetic magnetite nanoparticles were adhered to Positive Cromalin®. These particles were shown to become adhered and embedded within the tacky photopolymer layer. Patterning of these nanomaterials was also found to be successful. Particle loading evaluations showed a monolayer of particles was adhered to the surface with an increase in deposit density and coverage when a layer of large diameter particles was followed by a layer of small diameter particles. A tape test showed the adhesion of particles to the surface is adequate (̃50 N) for the investigated applications and is dependent on particle shape. The decomposition properties of this adhesive material were evaluated to be suitable for emissive display screens and photocatalysis processes. The thermal degradation of the polymer in argon at 450 ⁰C was ̃ 83-86 wt.%. Adhesion increased with limited UV exposure and the solubility in water and acetone of Positive Cromalin® decreased. Multiple adhesion mechanisms may contribute to the adhesion of various particle shapes and materials to Positive Cromalin®. The elastic behavior of Cromalin® allows particles to become completely or partially embedded into the photopolymer layer. This intimate contact allows surface forces, such as van der Waals, to act at the interface of the polymer and adhered particle. This elastic behavior also allows for a larger surface area of the particle to achieve contact, as it deforms around the particle and into cavities. The mechanical theory of adhesion plays a role as the embedded particles become trapped in the elastic polymer surface of Positive Cromalin® which hardens through polymerization by UV activation