Applicability of 8OCB for temperature calibration of temperature modulatedcalorimeters

Calibration of temperature modulated calorimeters (TMC) is essential becaus e it is often not possible to calculate heat capacity and sample temperatur e directly from the quantities measured. The question arises whether temper ature 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 o f the whole system (calorimeter, sample, transition) must be linear. Some l ow energy liquid crystal transitions behave in this way, under certain cond itions, 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 calibrati on is shown for temperature modulated DSC, AC calorimeter, 3 omega method a nd photo-acoustic method. (C) 2000 Elsevier Science B.V. All rights reserve d.