¹Kyiv National University of Technologies and Design,
2, Nemirovich-Danchenko str., 01011 Kyiv, Ukraine
E-mail: akoval@knutd.com.ua
²National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”
37, prospect Peremohy, 03056 Kyiv, Ukraine
³Institute of Physics, NAS of Ukraine
46, prospect Nauky, 03680 Kyiv, Ukraine
⁴V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
41, prospect Nauky, 03680 Kyiv, Ukraine

Abstract. Within the frequency range 10…10⁶ Hz, the frequency dependences of the real (ε') and imaginary (ε") components of the complex dielectric permittivity of medical thermal indicators based on polyvinyl acetate and mixtures of cholesteric liquid crystals have been studied. In them, the selective reflection of electromagnetic waves visible to the human eye occurs at normal (36.6 °C) and elevated (38.2 °C) human body temperatures. Being based on the comparison of the ε' frequency dependences for the studied in this work dispersions of nematic liquid crystals prepared using the same technology and with the same polymer, it has been shown that, already on the basis of analysis of frequency dependences for ε', it is possible to ascertain the difference in characteristics for two types of thermal indicators. From the comparison of frequency dependences for ε", the main reasons of a difference between dielectric properties of the investigated medical thermal indicators for various temperatures of a human body have been ascertained.

Keywords: liquid crystal thermal indicator, selective light reflection, cholesteric liquid crystal, nematic liquid crystal, polymer matrix, dielectric spectroscopy.

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