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

Nanofiber bundles of TiO 2 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 TiO 2 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 TiO 2 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 TiO 2 spheres of a similar size had an 11 % and 18 % lower ultimate tensile strength and elongation ability, respectively, compared with the prototype hydrogels.