Repulsive forces in thin smectic-C*films on substrates

摘要: X-ray reflectivity studies of spin-coated ultrathin films smectic-${\mathit{C}}^{\mathrm{*}}$ liquid crystals show dramatic variation the smectic layer spacing L as a function number layers n. Results for three different suggest long-range force between interfaces that decays algebraically like 1/${\mathit{n}}^{\ensuremath{\gamma}}$ where \ensuremath{\gamma}=3.0\ifmmode\pm\else\textpm\fi{}0.3. This decay is consistent with van der Waals type force, although its magnitude cannot be explained by existing mechanisms. Interactions electric dipoles and their images well formation ferroelectric domains may provide mechanism to explain force.