准静态条件下的玻璃化转变中的等自由体积的理论解释

发布时间：2018-04-13 17:25

  本文选题：玻璃化转变 + 等自由体积　； 参考：《西南石油大学》2017年硕士论文

【摘要】：玻璃化转变问题是一个广泛而深刻的物理难题。几乎所有的物质都有玻璃化转变行为,却并未有任意一种的材料的玻璃化转变理论被认为是完全成功的。玻璃化转变对材料性能有着十分显著的影响,例如光散射性、力学强度和模量、介电常数、松弛时间等等。并且其过程受热历史的影响很大,特别的,玻璃化转变温度与结晶转变温度不同,会随着温度变化速率的高低而改变。实验上,玻璃化转变的研究越来越深入。实验参量包括分子量、主链结构、支链结构、支化度等化学参量,以及变温速率、外压等物理参量。实验手段从过去的体积膨胀法、差示扫描量热仪(DSC,Differential Scanning Calorimeter)、动态机械热分析(DMA,Dynamic Thermomechanical analysis)等发展到正电子湮灭技术(PAT,Positron annihilation technique)。不同的实验数据往往支持不同的理论,除了一个经验方程—WLF方程。这使得WLF方程理论化显得尤为重要。理论上,层出不穷的旧理论和新理论被相继提出。旧理论包括Adam-Gibbs理论、Cohen-Grest自由体积理论和Random First-order Transition理论等。新理论则包含动力学理论和LCL模型等。在比较理论和实验结果的匹配度后,这些理论都比不上WLF方程。WLF方程是基于Flory等自由体积理论推导构建的,可以说,证明了 Flory的等自由体积猜想,就等于证明了 WLF方程的基础理论。基于上述考虑,本文从严格的准静态热力学模型出发,首先从Doolittle的自由体积与粘度方程中定义了玻璃化转变,然后证明了玻璃化转变区域中,理想单链体系在常压下的自由体积比例是一个定值,与其他物理参数、化学参数无关。在比较实验结果和理论结果的过程中,许多模型被我们不断的推演和重构,其中大多数并未对我们理解玻璃化转变带来多少帮助。本文最后采用的玻璃化转变理论建立在松弛格子模型—RLM之上。除了 RLM以外,本文还推导了一个在理论证明过程中有启示作用的模型—溶液析出模型。RLM模型的推演思路是:首先引入参数描述松弛过程和自由体积,然后求解熵函数。在对熵函数的极值和极点进行分析时,使用了小剪刀思想实验的方法,通过在小剪刀思想实验中设计热力学路径消去了中间参量,得到了 Flory早已预言却从未在理论上证明的等自由体积比例β,该值为(?)。同时证明了在玻璃化转变中,熵函数对温度的一阶导数不连续但函数值连续。此外,对高交联度和高温高压条件下的系统进行了理论解析。研究表明,其玻璃化转变行为可以通过RLM进行预测,其结果表达为一个三维相图。
[Abstract]:The glass transition is an extensive and profound physical problem.Almost all materials have glass transition behavior, but no glass transition theory of any material is considered to be completely successful.The glass transition has a significant effect on the properties of the materials, such as light scattering, mechanical strength and modulus, dielectric constant, relaxation time and so on.In particular, the glass transition temperature is different from the crystallization transition temperature, and will change with the change rate of temperature.In the experiment, the glass transition is studied more and more deeply.The experimental parameters include molecular weight, main chain structure, branched chain structure, branching degree, and physical parameters such as temperature change rate, external pressure and so on.The experimental methods have been developed from volume expansion method, differential Scanning calorimeter and dynamic Thermomechanical analysis to positron positron annihilation technique.Different experimental data tend to support different theories, except for one empirical equation--WLF equation.This makes it particularly important to theorize the WLF equation.In theory, the old theory and the new theory have been put forward one after another.The old theories include Adam-Gibbs theory, Cohen-Grest free volume theory and Random First-order Transition theory.The new theory includes kinetic theory and LCL model.After comparing the matching degree of the theoretical and experimental results, none of these theories can be compared with that of WLF equation. WLF equation is derived from Flory's equal free volume theory. It can be said that Flory's conjecture of equal free volume is proved.The basic theory of WLF equation is proved.Based on the above considerations, this paper starts from the strict quasi-static thermodynamic model, defines the glass transition from the free volume and viscosity equations of Doolittle, and then proves that the glass transition region is in the glass transition region.The free volume ratio of the ideal single-chain system under atmospheric pressure is a constant value independent of other physical and chemical parameters.In the process of comparing the experimental results with the theoretical results, many models have been continuously deduced and reconstructed, most of which have not done much to help us understand the vitrification transition.The glass transition theory is based on the relaxation lattice model-RLM.In addition to RLM, this paper also deduces a model, solution precipitation model, in the process of theoretical proof. The deductive idea of RLM model is as follows: firstly, parameters are introduced to describe relaxation process and free volume, then entropy function is solved.In the analysis of extremum and extremum of entropy function, the method of small scissors thought experiment is used, and the intermediate parameter is eliminated by designing thermodynamic path in the thought experiment of small scissors.The iso-free volume ratio 尾, which has been predicted by Flory but never proved in theory, is obtained.It is also proved that the first derivative of entropy function to temperature is discontinuous but the value of function is continuous in the vitrification transition.In addition, the system with high crosslinking degree and high temperature and high pressure was analyzed theoretically.The results show that the glass transition behavior can be predicted by RLM and the results are expressed as a three dimensional phase diagram.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB30
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本文编号：1745486