The Adiabatic, Continuous Heating, Differential Specific Heat Measurement System And The Specific Heat Of Polyaniline At Low Temperatures

Specific heat is one of the most important parameters in condensed matter physics. Because the lattice vibration is weak at very low temperature, the contributions of electrics and other low energy excitations become dominant parts of specific heat. Therefore, we can study the micromechanism of many physical phenomena from specific heat measurement. The entropy or number of states of system or subsystem are closely related to interaction of particles and energy level distribution, therefore , to study the temperature dependence of the specific heat may supply some important and useful microscopic information which may play an important role in understanding electronic structure, density of state, phonon spectrum etc. The specific heat measurements at low temperatures also play important roles in the finding of the third law of thermodynamics, the quantum theory of solid and BCS theory for superconducting etc. Moreover, specific heat measurements help us to understand the different kinds of phase transitions (such as: structural phase transition, magnetic phase transition, superconducting phase transition etc.) and the scaling behavior near the critical point. In order to study the change of specific heat of milligram samples with the changing components or other factors, we hope to separate addition part from the total specific heat or lattice contribution. So, we developed the adiabatic, continuous heating, differential specific heat measurement system. This system has several innovations shown as follows:a. We improved the measuring method. We keep the measured sample to have same temperature instead of heating power with the reference sample. At the same time, we use 42 pairs of thermopiles as the temperature sensor to keep the two samples to be at same temperature. It increases not only measurement sensitivity, also is easy to perform continuous heating the samples and improves measurement efficiency.b. We made use of Wheatstone bridge to control ratio of heating power between the samples, Thus , it enable to control and measure the differential heating power accurately. Consequently, it improves sensitivity of the system. The resolution of the measurement can reach from 1:1000 to 1:10000 or better in comparison with the traditional differential technique. At present, this system is one of the similar systems with the highest resolution.c. We installed 20 pairs of thermopiles between the sample holder and the copperheat sink, and 5 pairs of thermopiles between the copper heat sink and inner radiation shield respectively for sample adiabatic. They can monitor temperature difference very well and auto heat the samples.d. The soft ware of temperature control system, data acquisition and data analysis system are designed and written by ourself .Apart from setting up the Specific heat measured system, we investigated the specific heat of self-assembled PANI nanostructures at low temperatures. The specific heat of the emeraldine base form of polyaniline and the emeradine salt of polyaniline has been measured at temperatures between 1.8 and 45K. The experimental results have been interpreted in terms of the contributions from both the crystalline and the amorphous phases characterizing the polymer. Anomaly of the specific heat which is much larger than that would be expected from the Debye theory has been successfully explained by phonon-fracton model at low temperatures. The electronic specific heat has not been observed from the present data.