MEASURING METHOD FOR DIFFUSION COEFFICIENT

PURPOSE:To measure a diffusion coefficient highly precisely by using a hot wire densiometer and finding the diffusion coefficient on the basis of a change with the lapse of time in volatile component concentration in an atmosphere inside a sample chamber and a diffusion equation. CONSTITUTION:A high molecular material of a sample S is provided in the inside of a sample chamber 11 to be melted while an atmosphere 12 inside the sample chamber 11 is kept in constant temperature and constant pressure condition. Under this condition, the inside of a hot wire density probe 13 is sucked by a vacuum pump 16 of the hot wire densiometer H to be a critical condition, while an impressed voltage to the hot wire is controlled so that the temperature of the hot wire of the probe 13 is kept constant by a constant temperature type hot wire control circuit of a hot wire control unit 17. When a volatile component is diffused to the atmosphere from the sample S containing the volatile component inside the sample chamber 11, concentration of the volatile component is varied according to the lapse of time. On the basis of this change with the lapse of time and a diffusion equation, the diffusion coefficient of the volatile component can be found precisely.