The response time of a surface thermometer employing encapsulated thermochromic liquid crystals

Abstract

A time-varying surface temperature may be measured by a thin film of encapsulated thermochromic liquid crystal applied to the surface. The work reported in this paper has assessed, for engineering purposes, the response of such a film to a rapidly increasing surface temperature. Rates of increase in temperature of greater than 2000 degrees C s -1 were employed in these tests. The experiments show that the delay between the time at which the surfaces reaches the steady-state colour display temperature and the occurrence of the colour display is no more than a few milliseconds. The particular type of film used employed a micro-encapsulated chiral nematic thermochromic liquid crystal which was supplied by BDH and applied to the surface by a screen printing technique to a thickness of approximately 10 mu m. The conduction of heat into the film is analysed, but this would not appear to explain the observed response time of the thermometer.