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

Polymers with an ordered molecular structure can be applied in optical syst ems for e.g. data transport, data storage and displays. Patterned UV photo- polymerization is used to prepare polymer gratings from a mixture of two ac rylate monomers. A 3 MeV proton microprobe is used to study these gratings, prepared from two different monomers, each containing a different easily d etectable label element, e.g. Cl, Si or F. During the preparation process, the difference in reactivity and mobility o f these two monomers in combination with polymer-monomer interaction result s in diffusion of monomers. Since this diffusion process takes place on len gth scales of micrometers, a scanning ion microprobe is a powerful tool for the quantitative analysis of the polymer films, obtained after complete po lymerization. The microprobe is equipped with PIXE, PIGE and RBS, to quanti fy 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 s tudy 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 migra te to the illuminated areas and large thickness variations are observed. Wh en a 1:1 mixture of two difunctional monomers is used, opposite migration o f the two monomers is observed, while the film shows no variation in thickn ess. (C) 2001 Elsevier Science B.V. All rights reserved.