A calorimetric study on the configurational enthalpy and low-energy excitation of ground amorphous solid and liquid-quenched glass of 1, 3, 5-tri--naphthylbenzene

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Abstract
An amorphous solid of 1, 3, 5-tri--naphthylbenzene (TNB) was prepared by grinding the crystalline sample with a vibrating mill. Heat capacities of the ground amorphous solid (GAS), liquid-quenched glass (LQG) and crystal of TNB were measured with an adiabatic calorimeter in the temperature range 10 - 330 K for the GAS and 5 - 370 K for the LQG and crystal. The heat capacities of the LQG and GAS were 0.5 - 1% larger than that of the crystal. The heat capacity of the GAS agreed with that of the LQG between 30 and 330 K but was 1 - 4% larger than that of the LQG below 30 K. The heat capacity difference in the low-temperature region can be attributed to the difference in low-energy excitation which is known as a universal property of amorphous materials. A glass transition occurred at 342 K for the LQG. For the GAS, however, a large exothermic effect due to crystallization appeared from 315 K, which is 25 K lower than of the LQG. The configurational enthalpy of GAS determined from the enthalpy of crystallization was much larger than that of the LQG. This result indicates that the structure of the GAS is much more disordered and strained than that of the LQG.