Long‐Range Interactions in Thin Smectic Films on Substrates: X‐Ray Reflectivity Studies

摘要: Long-range forces between interfaces of thin and ultrathin smectic films are responsible for their thickness stability. We present here X-ray reflectivity studies the in spin-coated three different commercial liquid crystal (LC) mixtures as well main-chain LC polymers based on polysiloxane. All these materials possess a C* phase at room temperature. demonstrate spontaneous molecular self-assembly after spin coating into nearly perfect layer structure various substrates. However, annealing temperature is essential to achieve an equilibrium state. Measurements annealed show dramatic variation spacing, L, function number layers, n (or film thickness, d). The functional dependence L(n) all suggests long-range interaction that decays algebraically 1/nκ where κ = 2 ± 0.3. This decay consistent with van der Waals type interaction, although its magnitude cannot be explained by existing mechanisms. X-ray thick polysiloxane allow determination phases, transition temperatures, tilt angle phase. Thin (300 A 600 A) far above bulk smectic–isotropic formation film–substrate interface due surface freezing phenomena. Preliminary investigations indicate algebraically, exponent 1.5 0.5.