Transparent core-sheath composite fibers as flexible temperature sensor based on liquid crystal color change for smart sportswear

The characteristic of color changes in response to external temperature stimuli has made thermochromic fibers a subject of widespread research interest. However, for practical applications, improvements are still needed in terms of color rendering and the prevention of temperature-sensitive material leakage. This study utilized an optimized thermally induced coaxial dry spinning process to prepare a transparent temperature sensing fiber (PCCF) with a core-sheath structure. The sheath layer and the core layer of the PCCF were polydimethylsiloxane (PDMS) and cholesteric liquid crystal (CLC), respectively. The high transmittance exhibited by PCCF was attributed to the pellucid PDMS, which quickly cured in oil bath to form a complete core-sheath structure. The research results indicated that PCCF displayed uniform morphology (average diameter ∼539 μm), excellent tensile properties (elongation at break up to 183 %), as well as good mechanical, thermal, and sweat resistance stability. In addition, the PCCF showed a colorful variation of hues including yellow, green, blue and purple at a very narrow temperature change from 34 °C to 38 °C, attributing to that the molecular pitch was altered to selectively reflect visible light when the CLC was stimulated by temperature. Meanwhile, high sensitivity and short response time were obtained. When the PCCF was directly integrated into sportswear, the remarkable color changes could be observed as the wearer's body temperature increases. PCCF demonstrates a great potential application in smart sportswear and healthcare area.