Monomer diffusion assisted preparation of polymer gratings: A nuclear microprobe study

Polymers with an ordered molecular structure can be applied in optical systems for e.g. data transport, data storage and displays. Patterned UV photo-polymerization is used to prepare polymer gratings from a mixture of two acrylate monomers. A 3 MeV proton microprobe is used to study these gratings, prepared from two different monomers, each containing a different easily detectable label element, e.g. Cl, Si or F. During the preparation process, the difference in reactivity and mobility of these two monomers in combination with polymer-monomer interaction results in diffusion of monomers. Since this diffusion process takes place on length scales of micrometers, a scanning ion microprobe is a powerful tool for the quantitative analysis of the polymer films, obtained after complete polymerization. The microprobe is equipped with PIXE, PIGE and RBS, to quantify both the label elements and C and O. This makes it possible to determine the concentration of monomer units as a function of position and thus to study the diffusion process. Two combinations of different monomers are studied. In the case of a 0.5:1 mixture of a monofunctional and a difunctional monomer, both monomers migrate to the illuminated areas and large thickness variations are observed. When a 1:1 mixture of two difunctional monomers is used, opposite migration of the two monomers is observed, while the film shows no variation in thickness