Finger-Temperature-Detecting Liquid Crystal Composite Film for Anti-Counterfeiting Labels

• Published in: Molecules (Basel, Switzerland) Vol. 25; no. 3; p. 521
• Main Authors: Gao, Yanzi, Feng, Ke, Zhang, Jin, Zhang, Lanying
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 25-01-2020; MDPI
• Subjects: anti-fake; Calorimetry; cholesteric phase; Cooling; Counterfeiting; Crystals; Differential scanning calorimetry; Light microscopy; liquid crystal; Liquid crystal polymers; Liquid crystals; Optical microscopy; Optical properties; Phase transitions; Polymerization; Polymers; Scientific imaging; Self-assembly; side-chain liquid crystal polymers; Temperature; Temperature control; X-ray diffraction; anti-fake; cholesteric phase; side-chain liquid crystal polymers; liquid crystal
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules25030521

The development of the economy has increased the demand for anti-counterfeiting technologies, and with the traditional ones becoming known to the public, new and more effective ones are needed. In this study, a series of liquid crystal mixtures containing side-chain liquid crystal polymers and small-molecular-weight liquid crystals (LCs) were designed and prepared. The phase transition behavior and self-assembling structures of the LC mixtures were investigated by a combination of differential scanning calorimetry, polarized optical microscopy, and small-angle X-ray diffraction. The optical properties of the mixture film were characterized with a UV/VIS/IR spectrum study. The results reveal that the obtained film exhibited different optical modes between transparent, scattering, and selective reflection under finger-temperature control. Therefore, by the introduction of a coexisting thermal- or optical-polymer-dispersed network, a liquid crystal composite film with an integration of apparent optical switching modes and enhanced strength and toughness was successfully demonstrated. This research provides a versatile strategy for the design and preparation of liquid crystal anti-counterfeiting materials for practical use. In this study, a prototype finger-temperature-detecting anti-counterfeiting label was prepared, and its temperature-response property was demonstrated.