Preparation of Ultrathin Silsesquioxane Nanofilms via Polymer Langmuir−Blodgett Films

This Article describes a unique approach to building silsesquioxane nanoassemblies based on the Langmuir−Blodgett (LB) technique. Poly(N-dodecylacrylamide-co-3-methacryloxypropyl-T8-heptatrifluoropropyl (or heptaphenylpropyl) POSS)s (p(DDA/SQ)s) were synthesized through free radical copolymerization using propyl methacrylate-substituted polyhedral oligomeric silsesquioxane (POSS) monomers containing seven nonreactive trifluoropropyl or phenyl groups (R₇(Si₈O₁₂)(CH₂CH₂CH₂OCOCH₃CCH₂) (where R is either trifluoropropyl (SQF) or phenyl (SQPh)) and amphiphilic copolymers. The p(DDA/SQ)s formed stable monolayers at the air/water interface. The monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. The polymer LB films had a well-defined layer structure and a surface flatness (rms values < 1 nm in 1 μm²). The high heat-resistant properties of the p(DDA/SQ) LB films were demonstrated using UV−vis spectroscopic reflectometry and FT-IR. The refractive index and the thickness of the p(DDA/SQ) LB films were measured as functions of temperature. Upon heating, the refractive index of the p(DDA/SQPh) LB films increased from 1.43 (200 °C) to 1.49 (270 °C), whereas that of poly(N-dodecylacrylamide) (pDDA) decreased from 1.38 (200 °C) to 1.28 (220 °C), indicating a densely packed configuration of silsesquioxane units in thin films. A control experiment with pDDA LB films showed domain structures at temperatures greater than 200 °C, although the p(DDA/SQ) LB films remained uniform and smooth after heating to 320 °C. This bottom-up approach is promising for coating with organic and inorganic nanomaterials for optoelectric nanodevice applications.