Abstract

Liquid crystal thermography (LCT) provides a colour response proportional to the temperature of a heated surface in contact with the crystals. Thermochromic liquid crystals (TLC) are offered in the form of an emulsion, polymer sheet or latex support. Wider adoption of this technology has been limited due to response time, pressure sensitivity and imaging equipment. It is important to characterise TLC based on their chemical composition, colour play interval, spatial density and repeatability. This paper presents results for three forms of TLC material in terms of the effects of incident lighting, pressure sensitivity and hysteresis. Data are presented in the form of hue versus temperature calibration curves. Hue versus temperature curve shifts towards higher hue values for the identical temperature producing a maximum change of 15–20% in hue when the lighting intensity is changed from minimum to maximum. Hysteresis in the calibration curve occurred when the liquid crystals were heated above the colour play range producing a maximum temperature change of 1°C for R25C5W TLC sheet. This hysteresis was not permanent. The authors recommend using liquid crystals within their colour bandwidth to overcome hysteresis effects. The results may be helpful in developing LCT for various biomedical applications.