Readily available titania nanostructuring routines based on mobility and polarity controlled phase separation of an amphiphilic diblock copolymer

Abstract

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.

Morphology Phase Diagram of Slot‐Die Printed TiO2 Films Based on Sol–Gel Synthesis

“…One possible reason is that spin‐coating is a nonequilibrium process with ultrafast speed, which can freeze‐in structures within fractions of seconds . In contrast, printing provides sufficient time with polymer chain mobility during solvent evaporation, and finally an equilibrium structure can be formed according to a study about the effect of evaporation time on the phase separation behavior of the block copolymer, in which the final TiO 2 morphology becomes stable after 80 s evaporation time . Furthermore, the resulting morphology greatly depends on the different parameters of the spin‐coating process such as acceleration and spinning speed, in addition to the nature of the sol–gel solution .…”

“…On the one hand, pore sizes of titania films in the range ≈40 nm could decrease the possibility of exciton recombination . On the other hand, the larger pore sizes are favorable for the infiltration with hole‐transporting materials .…”

“…Due to these advantages, they contribute to a wide range of applications, such as in the field of photocatalysis, gas sensing, lithium‐ion batteries, supercapacitors, and biomaterials . In addition, nanostructured TiO 2 , especially in its anatase polymorph, has attracted great attention in the field of photovoltaics due to its wide bandgap, high electron mobility, and long charge‐carrier lifetime . As electron transport layer in solid‐state dye‐sensitized solar cells and hybrid solar cells, nanostructured TiO 2 films with a high surface‐to‐volume area and interconnected network are desirable because they hold the potential to improve the generation of charge carriers and inhibit electron–hole recombination .…”

Waterproof and Breathable Electrospun Nanofibrous Membranes

“…Dip coating could provide a quite good uniform hydrophobic layer to the nanofibers, but this process is usually time consuming, and thickness of the formed hydrophobic layer is uncontrollable . Therefore, blade coating has become another effective approach to adjust wettability of electrospun membranes to prepare W&B nanofibrous membranes, which presents precisely controllable thickness, durable hydrophobic property, and good scale‐up potential . Most prominently, the hydrophobic modifiers could be partly filled into the membranes other than to only enwrap the external fibers, which is significantly important for W&B performance of electrospun membranes …”

Key Factors for Template‐Oriented Porous Titania Synthesis: Solvents and Catalysts

“…In the case of organic–inorganic hybrid solar cells, the exciton diffusion length within typical backfilling materials is typically less than 20 nm. Mesoporous titania with uniform pore arrangement provides an excellent basis to suppress recombination losses of excitons . Although many achievements have been reached in the preparation of porous metal oxide materials, current synthetic methods still have several inherent drawbacks from the perspective of thin film nanotechnology, such as time consuming processing conditions and the ill‐defined powder form product .…”