Photodeposition of molecular layers on nanoparticle substrates

We report the photodeposition of polymeric layers of nanometer scale thickn ess onto silica nanoparticle substrates. This was accomplished by ultraviol et irradiation of a solution of functionalized diacetylene monomers in whic h the silica nanoparticles were suspended. Following photodeposition, the c oated nanoparticles were analyzed using transmission electron microscopy an d UV-visible spectroscopy. Highly regular polydiacetylene films with thickn esses from 2.5 to 25 nm were produced. The thickness measurements were faci litated by the attachment of small gold nanoparticles onto the surface of t he silica nanoparticle substrates prior to photodeposition, to provide cont rast in the final TEM image. W-visible spectroscopy of the deposited films indicates that approximately 40% less conjugation is present relative to th at of macroscopic polydiacetylene thin films grown with the same approach. This process yields a unique "nanolaminate" coating which may be useful in the modification of the physical, chemical, or optical properties of nanopa rticles.