Dynamic shear-modulus data are presented for the two silicone oils DC704 and DC705 for frequencies between 1 mHz and 10 kHz at temperatures covering more than five decades of relaxation-time variation. The data are fitted to the alpha part of a phenomenological model previously shown to describe well the dynamic shear modulus of squalane, which has a large beta process [Hecksher \textit{et al.}, J. Chem. Phys. \textbf{146}, 154504 (2017)]; that model is characterized by additivity of the alpha and beta shear compliance and by a high-frequency decay of the alpha process in proportion to $ω^{-1/2}$ in which $ω$ is the angular frequency. The fits of the alpha part of this model to the DC704 and DC705 data are compared to fits by a Havriliak-Negami type model, the Barlow-Erginsav-Lamb model, and a Cole-Davidson type model. At all temperatures the best fit is obtained by the alpha part of the squalane model. This strengthens the conjecture that so-called $\sqrt{t}$-relaxation, leading to high-frequency decays proportional to $ω^{-1/2}$, is a general characteristic of the alpha relaxation of supercooled liquids [Dyre, Phys. Rev. E {\bf 74}, 021502 (2006); Nielsen \textit{et al.}, J. Chem. Phys. \textbf{130}, 154508 (2009); Pabst \textit{et al.}, J. Phys. Chem. Lett. \textbf{12}, 3685 (2021)].
Using extensive numerical simulations, we investigate the flow behaviour of a model glass-forming binary mixture whose constituent particles have a large size ratio. The rheological response to applied shear is studied in the regime where the larger species are spatially predominant. We demonstrate that the macroscopic rigidity that emerges with increasing density occurs in the regime where the larger species undergo a glass transition while the smaller species continue to be highly diffusive. We analyse the interplay between the timescale imposed by the shear and the quiescent relaxation dyna…
The phase behaviour of soft colloids has attracted great attention due to the large variety of new phenomenologies emerging from their ability to pack at very high volume fractions. Here we report rheological measurements on interpenetrated polymer network microgels composed of poly(Nisopropylacrylamide) (PNIPAM) and polyacrylic acid (PAAc) at fixed PAAc content as a function of weight concentration. We found three different rheological regimes characteristic of three different states: a Newtonian shear-thinning fluid, an attractive glass characterized by a yield stress, and a jamming state. W…
Rheological constitutive equation for model of soft glassy materials
我们精确地求解并详细地描述了泡沫、乳状液、泥浆等的低频剪切流变学的简化标量模型。Lequeux，P. Hebraud，M. E. Cates，Phys. Rev. Lett. 78，2020（1997）]。该模型将这种“软玻璃质材料”流变学的相似性归因于结构无序和亚稳性的共同特征。通过关注介观元素的动力学，它保留了一个通用的字符。相互作用由平均场噪声温度x表示，玻璃化转变发生在x=1（以适当的单位表示）。该模型的精确解采用将应力与应变历史相关联的本构方程的形式，从该本构方程可以导出所有流变性质。对于线性响应，我们发现储能模量G'和损耗模量G“都随频率ω^{x-1}（1<x<2）变化，在玻璃化转变附近变得平坦。在玻璃相，老化的模量预测。稳态剪切流动曲线显示x<2的幂律流体行为，玻璃相中具有非零屈服应力; Cox-Merz规则在该非牛顿状态下不成立。单阶和双阶应变进一步探讨了模型的非线性行为，这是不能很好地表示的BKZ关系。最后，我们考虑在有限应变幅γ下G'和G“的测量。在玻璃化转变附近，随着应变扫描中γ的增加，G“呈现最大值。由于非线性效应，它的值可能会被严重高估，即使当应力响应非常接近谐波时也会出现这种效应。在最大应变γ_c处，测量仍能探测到线性响应，这一点与频率无关。
Employing wide-angle neutron spin echo spectroscopy, we measured the Q-dependent coherent intermediate scattering function of the prototypical ionic glass former Ca0.4K0.6(NO3)1.4, in the equilibrium and supercooled liquid states beyond the hydrodynamic regime. The data reveal a clear two-step relaxation: an exponential fast process, and a stretched exponential slow alpha process. de Gennes narrowing is observed in all characteristic variables of the alpha process: the relaxation time, amplitude, and stretching exponent. At all length scales probed, the relative amplitude of the alpha-relaxati…
Anomaly of the non-ergodicity parameter and crossover to white noise in the fast relaxation spectrum of a simple glass former
本文报道了玻璃形成体α-甲基吡啶（13 K < T <320 K）的准弹性光散射（LS）谱和介电谱（DS）。在高温下，极化率极小值的演化可用模耦合理论（MCT）很好地描述，得到临界温度T_c = 162 K +-5 K。当T_c > T > T_g时，在DS谱中发现了α过程的过剩翼，并在LS谱中重新发现了其幂律指数c。引入几种玻璃形成者的DS数据所建议的c = c[lg（tau_{alpha}）]的普遍演化，挑选出快速动力学谱，允许确定非遍历性参数f（T）。后者也显示了预测的尖点状异常，识别T_c。在T_g处，f（T）的另一个不连续变化被观察到.快动力学谱表现出向"白噪声“（T < T_c）的交叉。关于快动力学，我们得出的结论是，理想化的MCT预测甚至低于T_c。
We study the shear induced fluidization of amorphous solids subjected to external loading by investigating the relaxation dynamics of the deformed states using computer simulation. A simple shear deformation is employed at constant rate to the thermal glassy materials. The shear localization and the plastic deformation heterogeneity with strain is investigated in terms of the non-affine displacement field. The mean square displacement shows an enhanced mobility of the particles with strain, indicating the fluidization of the material. Using the time correlation function we estimate the relaxat…
Frequency dependent heat capacity within a kinetic model of glassy dynamics
近年来，人们对过冷液体的比热随频率变化的研究重新引起了人们的兴趣，计算机模拟研究探索了整个弛豫频率范围。因此，模拟研究可以补充现有的实验结果，以提供一个深入了解能源景观动态。在这里，我们调查的动态热容量行为的景观范式内的合作动力学的动力学模型。在这幅图中，β过程被建模为一个热激活事件在一个两能级系统和α过程被描述为一个β弛豫介导的合作过渡在一个双阱。该模型提供了一个描述的能量景观中的激活跳跃的跳跃事件的合作性质密切相关。为了选择合适的参数，该模型预测了反映两步驰豫行为的频率相关热容量。虽然实验获得的过冷液体的比热谱到目前为止不能捕捉到的两步弛豫行为，这已被观察到在计算机模拟研究Scheidler等。等人[Phys.Rev.B63，104204（2001）]。由于α-弛豫，低频峰的位置的温度依赖性示出了如Birge和Nagel [Phys. Rev. Lett. 54，2674（1985）]。然而，发现α峰的形状与温度无关，与模拟结果一致。高频峰的振幅比α峰大得多。我们尝试一个合理的理由，这一观察结果是在对比的介电谱所揭示的一般功能。
We apply our recently-developed mean-field 'SL-TS2' (two-state Sanchez-Lacombe) model to simultaneously describe dielectric alpha-relaxation time and pressure-volume-temperature (PVT) data in four polymers (polystyrene, poly(methylmethacrylate), poly(vinyl acetate) and poly(cyclohexane methyl acrylate)) and four organic molecular glass formers (ortho-terphenyl, glycerol, PCB-62, and PDE). Previously, it has been shown that for all eight materials, the Casalini-Roland thermodynamical scaling, /tau_{/alpha} = f(TV_{sp}^{/gamma}) (where T is temperature and V_{sp} is specific volume), (Casalini, …
