A Simple New Way To Account for Free Volume in Glassy Dynamics: Model-Free Estimation of the Close-Packed Volume from PVT Data
A Simple New Way To Account for Free Volume in Glassy Dynamics: Model-Free Estimation of the Close-Packed Volume from PVT Data
复制标题
解释玻璃动力学自由体积的一种简单新方法：根据 PVT 数据对密堆积体积进行无模型估计
DOI：
10.1021/acs.jpcb.1c01620
复制
发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Lipson, Jane E.
中科院分区：
文献类型：
--
作者：
White, Ronald P.;Lipson, Jane E.
在这篇文章中，我们专注于定义明确的自由体积（Vfree）在规定的玻璃形成液体和聚合物熔体的结构弛豫时间，τ，的重要作用。我们定义Vfree =V-Vhc，其中V是系统的总体积，这意味着Vfree的使用取决于Vhc的确定，Vhc是系统在极限紧密堆积状态下的体积。拒绝历史上妥协的使用ofVfree作为一个动态相关的拟合函数，我们已经成功地应用了一个明确的基于动力学的路线到Vhc使用局部相关晶格（LCL）模型状态方程（EOS）。然而，在这项工作中，我们更进一步，并表明，Vhc可以定义，而不使用状态方程的直接线性外推的一个V（T）的高压等压线下降到零温度（T）。在十几个实验系统上测试的这条路线的结果产生了ln τ vs 1/Vfree等温线，它们与T依赖的斜率呈线性关系，与我们先前描述的一般ln τ f（T）×（1/Vfree）行为形式一致。这种功能形式也通过实施一个简单的机械解释，通过合作自由体积（CFV）速率模型，它假设动态松弛都是热激活的，它需要分子链段协同。由于后者的程度以及活化能由自由体积的可用性决定，我们在这里展示的确定Vfree的新路线扩展了理解和预测玻璃形成材料中局部动态弛豫的潜力。
In this article we focus on the important role of well-defined free volume (Vfree) in dictating the structural relaxation times, τ, of glass-forming liquids and polymer melts. Our definition ofVfree=V–Vhc, whereVis the total system volume, means the use ofVfreedepends on determination ofVhc, the system’s volume in the limiting closely packed state. Rejecting the historically compromised use ofVfreeas a dynamics-dependent fitting function, we have successfully applied a clear thermodynamics-based route toVhcusing the locally correlated lattice (LCL) model equation of state (EOS). However, in this work we go further and show thatVhccan be defined without the use of an equation of state by direct linear extrapolation of aV(T) high-pressure isobar down to zero temperature (T). The results from this route, tested on a dozen experimental systems, yield ln τ vs 1/Vfreeisotherms that are linear withT-dependent slopes, consistent with the general ln τ ∼f(T) × (1/Vfree) form of behavior we have previously described. This functional form also results by implementing a simple mechanistic explanation via the cooperative free volume (CFV) rate model, which assumes that dynamic relaxation is both thermally activated and that it requires molecular segmental cooperativity. With the degree of the latter, and thus the activation energy, being determined by the availability of free volume, the new route we demonstrate here for determination ofVfreeexpands the potential for understanding and predicting local dynamic relaxation in glass-forming materials.