Development of ac Calorimetric Method for Thermal Diffusivity Measurement IV: Films with Low Thermal Diffusivity and Very Thin Films

In the ac calorimetric thermal diffusivity measurement of a thin film with low thermal diffusivity and a very thin film, it happens that the atmosphere surrounding the films significantly affects thermal diffusivity measured when the contribution of propagation of ac temperature waves in the atmosphere is not neglected. In fact, the measurement in a polymer film or in a very thin film should be carried out under vacuum, in which ac temperature waves no longer propagate. The experimental tests were made for polypropylene films and a borosilicate glass plate. The measurement under vacuum is not always required for every kind of film. The condition which is required for the measurement in the air is discussed. In addition, various problems which occur in the measurement of thin films with low thermal diffusivity and very thin films are considered.