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arXiv 1111.5912cond-mat.softcond-mat.mtrl-scicond-mat.stat-mech
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剪切条件下高过冷液体中的动力学异质性

Dynamical Heterogeneity in a Highly Supercooled Liquid under a Sheared Situation

Hideyuki Mizuno Ryoichi Yamamoto

摘要:

在本研究中,我们进行了分子动力学模拟和研究动态不均匀性下的稳定剪切流的过冷液体。动态异质性可以用三个量来表征:相关长度$ξ_4(t)$、强度$χ_4(t)$和寿命$τ_\text{hetero}(t)$。我们通过粒子动力学的相关函数量化了所有三个量,即,四点相关函数,并推广到剪切条件。这里,为了定义局部动力学,我们使用两个时间间隔$t=τ_α$和$τ_{\text{ngp}}$ ; $τ_α$是$α$ -弛豫时间,而$τ_{\text{ngp}}$是Van Hove自相关函数的非高斯参数最大化的时间。我们发现,所有三个量($ξ_4(t)$,$χ_4(t)$,和$τ_\text{hetero}(t)$)减少的剪切速率$\dotγ$的稳定剪切流的增加。对于时间间隔$t=τ_α$,获得缩放$ξ_4(τ_α) \sim \dotγ^{-0.08}$、$χ_4(τ_α) \sim \dotγ^{-0.26}$和$τ_\text{hetero}(τ_α) \sim \dotγ^{-0.88}$。定常剪切流抑制了非均匀结构,同时也抑制了动力学非均匀性的寿命。此外,我们的研究结果表明,$α$ -弛豫时间$τ_α$依赖的三个量符合那些在平衡。这意味着所有三个数量的动力学不均匀性可以映射到那些在平衡状态通过$τ_α$。

英文摘要:

In the present study, we performed molecular-dynamics simulations and investigated dynamical heterogeneity in a supercooled liquid under a steady shear flow. Dynamical heterogeneity can be characterized by three quantities: the correlation length $ξ_4(t)$, the intensity $χ_4(t)$, and the lifetime $τ_\text{hetero}(t)$. We quantified all three quantities by means of the correlation functions of the particle dynamics, i.e., the four-point correlation functions, which are extended to the sheared condition. Here, to define the local dynamics, we used two time intervals $t=τ_α$ and $τ_{\text{ngp}}$; $τ_α$ is the $α$-relaxation time, and $τ_{\text{ngp}}$ is the time at which the non-Gaussian parameter of the Van Hove self-correlation function is maximized. We discovered that all three quantities ($ξ_4(t)$, $χ_4(t)$, and $τ_\text{hetero}(t)$) decrease as the shear rate $\dotγ$ of the steady shear flow increases. For the time interval $t=τ_α$, the scalings $ξ_4(τ_α) \sim \dotγ^{-0.08}$, $χ_4(τ_α) \sim \dotγ^{-0.26}$, and $τ_\text{hetero}(τ_α) \sim \dotγ^{-0.88}$ were obtained. The steady shear flow suppresses the heterogeneous structure as well as the lifetime of the dynamical heterogeneity. In addition, our results demonstrated that the $α$-relaxation time $τ_α$ dependences of three quantities coincide with those at equilibrium. This means that all three quantities of the dynamical heterogeneity can be mapped onto those in the equilibrium state through $τ_α$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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