Fabrication of microlens arrays by localized hydrolysis in water droplet microreactors

We report a facile self-assembly strategy for fabricating TiO2 microlens arrays by localized hydrolysis of TiCl4 precursor in water droplets. Microcontact printing was used to define hydrophilic areas on a substrate for space resolved hydrolytic reaction. The water droplets served as the templates, reactant, and microreactors. Highly ordered TiO2 microlens arrays could be produced, which exhibit excellent ability to focus light. Because both size and shape of the final TiO2 microlens can be controlled by the printed chemical pattern and the precursor concentration, it is possible to define TiO2 microlens arrays with different imaging properties. This new method shows attractive features of simplicity, low cost, and requires no heating process, hence is suitable for a range of applications.