分子机器中链状分子热膨胀性质的理论研究

Theoretical Study on Thermal Expansions of Chain Molecules in Molecular Machines

运用晶格动力学理论推导了分子机器中链状分子中原子间距热膨胀和链状分子热膨胀系数公式,并进行了数值计算。数值计算结果表明,在低温下,当短的链状分子的长度增加时,其原子间距热膨胀快速减小而热膨胀系数快速增加,从而分别快速接近无限长的链状分子的原子间距热膨胀及热膨胀系数,所以链状分子热膨胀性质呈现明显的尺寸效应;随温度升高,链状分子的热膨胀性质的尺寸效应明显减弱,直至在高温极限下消失。低温下必须考虑链状分子热膨胀性质的尺寸效应。

The formulas to describe thermal expansions of interatomic distances and thermal expansion coefficients of chain molecules in molecular machines were derived based on the lattice dynamics, and then the numerical calculations were carried out. The numerical results show that at the low temperature, when the length of short chain molecule increases, the thermal expansion of interatomic distance increases rapidly and the thermal expansion coefficient decreases rapidly, and they approach to the corresponding values of the chain molecule with infinite length rapidly. Therefore, there are size effects in the thermal expansion properties of chain molecules;the size effects of thermal expansion properties of chain molecules are weakened obviously when temperature increase and finally disappeared at high temperature limit. It is concluded that the size effects of thermal expansion properties of chain molecules must be considered at low temperature.