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Thermotropic glazings for overheating protection. I. Material preselection, formulation, and light-shielding efficiency



This article presents a systematic strategy for formulation and optimization of thermotropic layers for overheating protection purposes. Specifically, thermotropic systems with fixed domains (TSFD) which consist of a thermotropic additive finely dispersed in a matrix material are considered. Based on systematic material (component) preselection regarding thermoanalytical characteristics and refractive indices, numerous thermotropic layers were formulated. TSFD with thermoplastic matrix were produced by compounding and compression molding. TSFD with resin matrix were produced by UV curing. The thermotropic layers were analyzed as to solar optical properties, threshold temperature, switching process and residual transmittance in the opaque state applying UV/Vis/NIR spectrometry equipped with a heating stage. Best performing materials exhibited solar hemispheric transmittance in the range of 72.2–84.5% and between 59.6 and 83.7% in the clear and opaque state, respectively. Threshold temperatures between 45 and 75°C were realized. Refractive index difference between matrix and additive and solar hemispheric transmittance displayed a close correlation. Hence, refractometry was shown to be an appropriate tool for material preselection. Furthermore, investigations revealed a close correlation of thermal transitions of thermotropic additives recorded by differential scanning calorimetry and threshold temperatures of thermotropic layers formulated therewith. However, thermotropic layers formulated so far have to be optimized with respect to light-shielding performance for efficient overheating protection. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39950.