Highly ordered TiO2 nanostructures by sequential vapour infiltration of block copolymer micellar films in an atomic layer deposition reactor

Sequential vapour infiltration operated in an atomic layer deposition (ALD) reactor was used to controllably deliver precursors of TiO2 into the cores of micellar films of the amphiphilic block copolymer, poly(styrene-block-4-vinylpyridine) (PS-b-P4VP). Vaporized precursors diffused through the PS corona and were exclusively enriched into the P4VP cores. Arrays of hexagonally arranged TiO2 nanoparticles were produced by burning off the polymeric components after UV-crosslinking the TiO2-incorporated micellar films. The size of the TiO2 particles was tunable simply by repeating the cycle numbers, and the interparticle distances were dictated by the distances between neighboring micelles of the original micellar films and could be changed by using block copolymers with different molecular weights. Compared to the extensively used solution impregnation method, the sequential vapour infiltration strategy was distinct in terms of the simplicity accompanying the "dry" process and precise control in particle sizes. More importantly, growth of TiO2 particles inside micellar cores was not limited by the available pyridyl groups as TiO2 continued to grow on preformed TiO2 particles after the pyridyl groups were consumed. Consequently, the particle sizes could be tuned in a much broader range compared to the solution impregnation method in which the particle size was limited by the saturation of impregnated precursors bound to the pyridyl groups. Furthermore, we demonstrated the versatility of this sequential vapour infiltration strategy in producing nanostructures with different morphologies and chemical compositions.