A NOVEL ESR APPROACH TO ACCURATELY PROBE TRANSITION-TEMPERATURES IN LIQUID-CRYSTALLINE SYSTEMS

Using the spin probe euterated-2,2,6,6-tetramethyl-4-piperidone-N-oxid e (PD-Tempone) at mole fractions about 10(-5) the transition temperatu res of 'pure' 4-cyano-4'-n-pentylbiphenyl (5CB) and four dilute soluti ons of 3,3-diethylpentane (Et(4)C) at mole fractions between 0.02 and 0.08 in 5CB were determined. This fast approach relies on the smaller coupling constant obtained for the spin probe in the orientationaly or dered nematic phase relative to the isotropic phase. Using an especial ly designed sample holder in conjunction with a temperature control an d monitoring system the temperatures of our samples were controlled to within +/- 0.02 degrees C. The results were used to obtain the phase diagram for the 5CB-Et(4)C system in the concentration range studied.