Three‐Dimensionally Branched Titanium Dioxide with Cheek‐Brush Morphology: Synthesis and its Application to Polymer Composites

Nanofiber bundles of TiO2 with a unique cheek-brush morphology were prepared by simple, rapid, one-pot, single-step, and template-free solvothermal treatment of a titanium alkoxide and aromatic ester in methanol. The solvothermal reaction was performed by heating a mixture of titanium tetraisopropoxide and dimethyl phthalate in methanol to 300 °C. The precursor solution had to be kept at room temperature for 20 min before heating the solution to obtain a cheek-brush morphology. The heating rate (5–6 °C/min), final reaction temperature (300 °C), and holding time at the final temperature (10 min) were also crucial for formation of the cheek-brush morphology. A systematic study of additives in the precursor solution showed that aromatic esters such as diethyl phthalate and methyl benzoate gave cheek-brush morphologies. The cheek-brush TiO2 assemblies were used to crosslink a poly(N-isopropylacrylamide) hydrogel; the brushes enhanced the physical adhesion properties of the hydrogel. The hydrogel prepared from a 20wt% polymer containing 0.02wt% of the cheek-brush TiO2 assemblies had an 11 % and 9.1 % higher ultimate tensile strength and elongation ability, respectively, compared with a prototype hydrogel without a crosslinker. A hydrogel prepared using TiO2 spheres of a similar size had an 11 % and 18 % lower ultimate tensile strength and elongation ability, respectively, compared with the prototype hydrogels.