Measuring the temperature of fluid in a micro-channel using thermochromic liquid crystals

Thermochromic liquid crystal (TLC) thermometry, which has been previously used at the macro-scale, is applied quantitatively in a microfluidic device for the first time. Much like the micro-scale version of the PIV technique, TLC thermometry implementation at the micro-scale must account for constraints on imaging and illumination configurations and the proximity of the measurements to interfaces and surfaces from which light scatters. Unlike μPIV, TLC thermometry requires the use of white light, so unwanted reflections are managed using circular polarization filtering, which is implemented for the first time and may also have applications at the macro-scale. The validity and precision of the TLC thermometry technique are tested by imposing a linear temperature gradient along a micro-channel filled with stationary fluid. Additional work is required to develop the technique into a fully functional form and to realize the potential for use in various microfluidic applications including “lab-on-a-chip” devices, MEMS switches, inkjet printer nozzles, and for use with simultaneous velocity measurements.