Monolayer Packing of Submicrometer Ceramic Spheres by Employing a Langmuir-Blodgett Film of Dicarboxylic Acid

Abstract

A closely packed monolayer of spherical SiO2 or SiO2–TiO2 particles of submicrometer size has been fabricated on a silicon or glass substrate by employing a Langmuir–Blodgett (LB) film of 1,12-dodecanedicarboxylic acid, followed by dehydration–condensation reaction between carboxyl groups of the dicarboxylic acid and surface hydroxyl groups of both the substrate and the ceramic spheres. Deposition of the LB film on the substrate was essential for immobilization of ceramic spheres. The flexibility of an alkyl chain in the dicarboxylic acid may have resulted in better capturing of ceramic spheres compared with surface hydroxyl groups on the substrate. Two-dimensional packing of the ceramic spheres immobilized became dense with decreasing molecular area of the dicarboxylic acid in the LB film and the temperature of the LB medium (water), although partial three-dimensional attachment of ceramic spheres was observed, especially when an LB film of quite small molecular area was used. In addition, the amount of surface hydroxyl groups on the substrate was found to significantly affect the microstructure of the two-dimensionally packed ceramic spheres. The closest two-dimensional packing was observed on a glass substrate by employing an LB film with a molecular area of 0.03 nm2·molecule−1 at 20°C.