An apparatus for measuring specific heat capacity of solids from liquid-helium temperature 4.2K up to ∼200K has been constructed. For the measurement, the thermal relaxation method was adopted, instead of the conventional Nernst, pulse heating, or ac methods. When the present method is compared with other ones, the advantages are: small amount of sample required, relatively short measuring time, easy operation, and relatively high accuracy of measurement. The minimum amount and dimensions of sample are typically about 30mg and 100μm thick, 10mm in diameter. The measuring time for each measurement is as short as 3min. Experimental results for sapphire and KBr single crystals are shown, and their agreements with the existing data are excellent. As an example of polymer, the specific heat capacity of polyethylene has been measured, and the preliminary data are presented.

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The effect of pressure on miscibility and phase separation in blends of two kinds of random copolymers consisted of styrene and para-fluorostyrene, P(S-co-p-FS), and ortho-and para-fluorostyrene, P(o-FS-co-p-FS), and poly(2, 6-dimethyl-1, 4-phenylene oxide), PPO, has been studied bydifferential thermal analysis (DTA) at pressures up to 300MPa. P(S-co-p-FS) copolymers less than 36mole% p-FS are miscible with PPO in all proportions irrespective of pressures, using the customary criterion of a single calorimetric glass relaxation. P(S-co-p-FS) copolymers containing 40 to 50mol% p-FS undergo phase separation upon annealing at elevated temperatures, indicating the existence of a lower critical solution tempratures (LCST). In the PPO/P(S-co-p-FS) blends, pressure displaces the phase boundary associated with the LCST to higher temperatures causing an apparent increase in polymer miscibility. The phase diagram for the PPO/P(S-co-46p-FS) containing 46mol% p-FS, shows that the critical composition at about 50wt% PPO does not change with pressure, but the consolute temperature T_c increases with increasing pressure. The pressure dependence of the LCST of this system is about 0.35°C/MPa of dT_c/dP. On the other hand, the P(o-FS-co-p-FS) copolymers containing from 10 to 38mole% p-FS are miscible with PPO below 230°C. When the phase behaviors of the 50/50wt% blends are examined as a function of temperature and copolymer composition, a symmetric miscibility “window” can be observed in the resulting temperature-composition diagram with a maximum at about 22mol% p-FS. The pressure dependence of the phase diagram for the PPO/P(o-FS-co-29p-FS) blend containing 29mol% p-FS shows that the critical composition is at about 50wt% PPO and is independent of pressure. The T_c increases at about 0.10°C/MPa up to 200MPa and then becomes independent of pressure to reach an asymptotic value at around 270°C. Similar behavior is also observed for blends in which the copolymer composition contain either 16 or 23mol% p-FS. The decrease of dT_c/dP at higher pressure may indicate that the negative volume of mixing approaches zero above 200MPa.

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