Development of measuring apparatus for thermophysical properties in a very small qyuantity of substances by means of ac calorimetric method

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A light-irradiation-type ac calorimeter has been developed for obtaining thermophysical properties in a small quantity of materials.One of the aims in the present study is to measure the heat capacity of a small quantity of liquid. The sample cell is made of a very fine stainless steel tube, for instance, 130mum in inside diameter, 17Omum in outside diameter and 39mm long, which is filled with 0.52mul of a liquid sample. To obtain the absolute value of the heat capacity, evaluation of the heat capacity of the empty cell and the amplitude of ac heat flux supplied to the cell is necessary. For this purpose, the amplitude of ac temperature of the empty cell, the cell filled with a standard liquid and the cell filled with a liquid sample. From them, the heat capacity per unit volume of the liquid sample is obtained. In this measurement, the absolute value of heat capacity in liquid sample is determined within an accuracy of 1%. Using this method, the heat capacity of phospholipids in aqueous suspension was measured. The heat capacity in dipalmitoylphosphatidylcboline (DPPC)-cholesterol with cholesterol, concentrations up to 7 mol%. The heat capacity in DPPC-dimyristoylphosphatidylicholine (DMPC) mixtures was measured with special attention to the condition for the appearance of metastable state, which appears in pure DPPC and does not appear in pure DMPC. It was found that the metastable state no longer appears at the DMPC concentrations more than 50 mol%.The measurement of thermal diffusivity or thermal conductivity is desirable to know the thermophysical properties of a small quantity of materials. A light-irradiation-type ac calorimetry was also applied to the measurement of thermal diffusivity in not only thin films but also fine wires.