The amphiphilic diblock copolymer polystyrene-block-polyethylene oxide is combined with sol-gel chemistry to control the structure formation of blade-coated foam-like titania thin films. The influence of evaporation time before immersion into a poor solvent bath and polarity of the poor solvent bath are studied. Resulting morphological changes are quantified by scanning electron microscopy (SEM) and grazing incidence small angle X-ray scattering (GISAXS) measurements. SEM images surface structures while GISAXS accesses inner film structures. Due to the correlation of evaporation time and mobility of the polymer template during the phase separation process, a decrease in the distances of neighboring titania nanostructures from 50 nm to 22 nm is achieved. Furthermore, through an increase of polarity of an immersion bath the energetic incompatibility of the hydrophobic block and the solvent can be enhanced, leading to an increase of titania nanostructure distances from 35 nm to 55 nm. Thus, a simple approach is presented to control titania nanostructure in foam-like films prepared via blade coating, which enables an easy upscaling of film preparation.
With the aim of obtaining nanostructured titania thin films for the potential use in hybrid or dye sensitized solar cells, the amphiphilic diblock copolymer polystyrene-b-poly(ethylene oxide) is employed as a structure directing template in combination with sol− gel chemistry. For easy upscaling, spraying is used as a deposition technique. In situ grazing incidence small-angle X-ray scattering (GISAXS) measurements are performed during spraying and show that most titania structures are already formed within the solution prior to deposition. However, structural rearrangement is enabled during the deposition period when small amounts of hydrochloric acid (HCl) are used as a catalytic additive to the spray solution. This behavior is ascribed to an altering of the reaction dynamics and phase separation in the presence of HCl, which significantly improves the templating effect of the employed diblock copolymer. With HCl as an additive the final nanoscale morphologies exhibit smaller pore sizes and strongly enhanced order as compared to thin films sprayed from solutions that do not contain HCl as quantified with atomic force microscopy, scanning electron microscopy, and GISAXS.
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