Rault Jacques
Physique des solides, Université de Paris-Sud, 91405, Orsay, France,
Eur Phys J E Soft Matter. 2015 Aug;38(8):91. doi: 10.1140/epje/i2015-15091-6. Epub 2015 Aug 31.
The dynamical properties of glass formers (GFs) as a function of P, V, and T are reanalyzed in relation with the equations of state (EOS) proposed recently (Eur. Phys. J. E 37, 113 (2014)). The relaxation times τ of the cooperative non-Arrhenius α process and the individual Arrhenius β process are coupled via the Kohlrausch exponent n S(T, P). In the model n S is the sigmoidal logistic function depending on T (and P, and the α relaxation time τ α of GFs above T g verifies the pressure-modified VFT law: log τ α ∼ E β /nsRT, which can be put into a form with separated variables: log τ α ∼ f(T)g(P). From the variation of n S and τ α with T and P the Vogel temperature T 0 (τ α → ∝, n S = 0) and the crossover temperature (also called the merging or splitting temperature) T B (τ α ∼ τ β, n S ∼ 1) are determined. The proposed sm-VFT equation fits with excellent accuracy the experimental data of fragile and strong GFs under pressure. The properties generally observed in organic mineral and metallic GFs are explained: a) The Vogel temperature is independent of P (as suggested by the EOS properties), the crossover is pressure-dependent. b) In crystallizable GFs the T B (P) and Clapeyron curves T m(P) coincide. c) The α and β processes have the same ratio of the activation energies and volume, E*/V* (T- and P-independent), the compensation law is observed, this ratio depends on the anharmonicity Slater-Grüneisen parameter and on the critical pressure P* deduced from the EOS. d) The properties of the Fan Structure of the Tangents (FST) to the isotherms and isobars curves log τ versus P and T and to the isochrones curves P(T). e) The scaling law log τ = f(V (Λ) ) and the relation between Γ and γ. We conclude that these properties should be studied in detail in GFs submitted to negative pressures.
结合最近提出的状态方程（EOS）（《欧洲物理杂志E》37, 113 (2014)），重新分析了玻璃形成剂（GFs）作为压力（P）、体积（V）和温度（T）函数的动力学性质。协同非阿仑尼乌斯α过程的弛豫时间τ和单个阿仑尼乌斯β过程通过科尔劳施指数n S(T, P)耦合。在该模型中，n S是依赖于T的S形逻辑函数（以及P，且T g以上GFs的α弛豫时间τα验证压力修正的VFT定律：log τα ∼ Eβ /nsRT，其可转化为分离变量形式：log τα ∼ f(T)g(P)。根据n S和τα随T和P的变化，确定了Vogel温度T 0（τα → ∝，n S = 0）和交叉温度（也称为合并或分裂温度）T B（τα ∼ τβ，n S ∼ 1）。所提出的sm - VFT方程以极高的精度拟合了压力下脆性和强GFs的实验数据。解释了在有机、矿物和金属GFs中普遍观察到的性质：a）Vogel温度与P无关（如EOS性质所暗示），交叉温度与压力有关。b）在可结晶的GFs中，T B(P)和克劳修斯曲线T m(P)重合。c）α和β过程具有相同的活化能与体积比E*/V*（与T和P无关），观察到补偿定律，该比值取决于非谐性斯莱特 - 格律内森参数和从EOS推导的临界压力P*。d）等温线和等压线曲线log τ对P和T的切线的扇形结构（FST）性质以及等时线曲线P(T)的性质。e）标度律log τ = f(V (Λ) )以及Γ和γ之间的关系。我们得出结论，对于承受负压的GFs，应详细研究这些性质。
