Applicability of 8OCB for temperature calibration of temperature modulated calorimeters

Calibration of temperature modulated calorimeters (TMC) is essential because it is often not possible to calculate heat capacity and sample temperature directly from the quantities measured. The question arises whether temperature calibration used in conventional calorimetry is also valid for TMC's. To prove this, a well defined transition is needed which does not disturb the temperature profile within the sample during modulation. The response of the whole system (calorimeter, sample, transition) must be linear. Some low energy liquid crystal transitions behave in this way, under certain conditions, and can be used for temperature calibration in TMC's. The procedure is demonstrated for the nematic to smectic-A transition in a cyanobiphenyl liquid crystal (80CB). The applicability of 80CB for temperature calibration is shown for temperature modulated DSC, AC calorimeter, 3 omega method and photo-acoustic method. (C) 2000 Elsevier Science B.V. All rights reserved.