From partial to complete optical erasure of azobenzene-polymer gratings: effect of molecular weight

The ability to control surface functionality by optical inscription and erasure of surface patterns is highly appealing, since it opens up the possibility for the design of complex, spatially varying surface topographies. We show through a supramolecular approach, which allows us to attach nominally equal amounts of azobenzene into polymers of varying molecular weight, that the completeness of optical erasure of high-modulation-depth surface-relief gratings on polymer-azobenzene complexes depends on the molecular weight of the polymer, and therefore on the glass transition temperature of the material used. The optical erasure is further applied to realize surface patterns with varying grating vector directions through masking. All patterning is done at a temperature well below the glass transition temperatures of the materials, which allows different patterning steps to be frozen into the material.