Assessment of Early Fracture Risk Using Thermochromic Cholesteric Liquid Crystal Systems

Liquid Crystals (LCs) have been extensively studied, due to their features, namely their capability to alter their properties, such as their color, as a response to external inputs, such as humidity, temperature and pressure, presenting a promising class of materials to be employed in stimuli-responsive and smart-sensing applications. Within the different phases which LCs can exhibit, cholesteric LCs (CLCs) have attracted growing interest, attributed to their tunability and capability to selectively reflect circularly polarised light, which enables the control of the reflected wavelength. Given that the deterioration of civil structures is influenced by environmental factors, this study aimed to develop CLC-based temperature-sensitive devices for continuous temperature monitoring, which allows the inference of the risk of early fracture formation. For this effect, polymer-dispersed CLC (PDCLC)-based thermochromic devices were produced. CLC microdroplets were first prepared by mixing cholesteryl oleyl carbonate (COC) and 4-cyano-4’-pentylbiphenyl (5CB) and were then dispersed onto different matrices – polyurethane, polydimethylsiloxane (PDMS), cellulose acetate (CA), acetoxy propyl cellulose (APC) and APC/PDMS. The sensorial capabilities of the devices were tested by subjecting them to thermal cycles to assess whether it led to a change in color. It was concluded that apart from the dispersion in polyurethane, all devices exhibited a temperature-dependent color change, with the most pronounced shift being observed in the PDMS-based systems.