Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur Campus, Bangalore 560 064, India.
J Chem Phys. 2011 Nov 21;135(19):194503. doi: 10.1063/1.3660201.
We study the influence of the softness of the interparticle interactions on the fragility of a glass former by considering three model binary mixture glass formers. The interaction potential between particles is a modified Lennard-Jones type potential, with the repulsive part of the potential varying with an inverse power q of the interparticle distance, and the attractive part varying with an inverse power p. We consider the combinations (12,11) (model I), (12,6) (model II), and (8,5) (model III) for (q,p) such that the interaction potential becomes softer from model I to III. We evaluate the kinetic fragilities from the temperature variation of diffusion coefficients and relaxation times, and a thermodynamic fragility from the temperature variation of the configurational entropy. We find that the kinetic fragility increases with increasing softness of the potential, consistent with previous results for these model systems, but at variance with the thermodynamic fragility, which decreases with increasing softness of the interactions, as well as expectations from earlier results. We rationalize our results by considering the full form of the Adam-Gibbs relation, which requires, in addition to the temperature dependence of the configurational entropy, knowledge of the high temperature activation energies in order to determine fragility. We show that consideration of the scaling of the high temperature activation energy with the liquid density, analyzed in recent studies, provides a partial rationalization of the observed behavior.
我们通过考虑三种模型二元混合物玻璃形成体来研究粒子间相互作用的柔软度对玻璃形成体脆性的影响。粒子间相互作用势是一种改进的 Lennard-Jones 型势，势的排斥部分随粒子间距离的逆幂 q 变化，而吸引力部分随逆幂 p 变化。我们考虑了 (q,p) 的组合 (12,11) (模型 I)、(12,6) (模型 II) 和 (8,5) (模型 III)，以使相互作用势从模型 I 到 III 变得越来越软。我们从扩散系数和弛豫时间随温度的变化来评估动力学脆性，从构型熵随温度的变化来评估热力学脆性。我们发现，动力学脆性随势的柔软度增加而增加，这与这些模型体系的先前结果一致，但与热力学脆性相反，后者随相互作用的柔软度增加而减小，这也与早期结果的预期不一致。我们通过考虑完整的 Adam-Gibbs 关系来解释我们的结果，该关系除了要求构型熵随温度的变化之外，还需要了解高温激活能，以便确定脆性。我们表明，考虑最近研究中分析的高温激活能与液体密度的标度，为观察到的行为提供了部分解释。
