D. Dadarlat, C. Neamtu, V. Tosa, M. Streza

National R&D Institute for Isotopic and Molecular Technologies, 65-103 Donath Street, POB 700, 400293 Cluj-Napoca, Romania.
Tel.: +40 264 584037,
Fax: +40 264 420042,
E-mail: dadarlat@s3.itim-cj.ro.

Abstract
The suitability of the photopyroelectric (PPE) calorimetry for detection of molecular associations in binary liquid mixtures was investigated. Accurate PPE measurements in two detection configurations (using the information contained only in the phase of the PPE signal) were performed to obtain the values of thermal diffusivity and effusivity. The limits of the method were tested by detecting isotopic effects in H₂O–D₂O and DMSO(6H)–DMSO(6D) mixtures. The composition behaviour of the above mentioned thermal parameters for DMSO(6H)–H₂O mixtures was presented for comparison. Small isotopic effects in thermal diffusivity were observed for H₂O–D₂O and DMSO(6H)–DMSO(6D) mixtures (about 4% and 8%, respectively).

Keywords: photopyroelectric calorimetry, thermal diffusivity, thermal effusivity, molecular associations, isotopic mixtures