第5届全国大学生化学实验邀请赛(试卷C3)实验C3 粘度的测定及应用

一、实验目的(1)掌握用乌氏粘度计测定粘度的方法。(2)测定一未知高聚物的平均分子量。二、实验原理及实验内容1实验原理高聚物是由单体分子经加聚或缩聚过程而合成的,其聚合度不一定相同,一般高聚物是摩尔质量大小不同的大分子混合物,摩尔质量常在103~107之间,通常所测的高聚物摩尔质量是一个统计平均值。高聚物溶液的粘度是它流动过程中内摩擦力的反映。粘度比较大是高分子溶液的基本特征之一,并且其特性粘度与平均摩尔质量有关,可利用这一关系测定其摩尔质量。有关粘度的定义式如下:相对粘度ηr:ηr=ηη0(1)式中,η为高聚物溶液的粘度,…     

特性粘数测定中的动能改正问题

液体的粘度这个物理量是表征流体在受到切应力后在层流情况下对流动的阻力,是流体的一个重要物理常数。当高聚物溶解在溶剂中,其溶液有一个很明显的特征,那就是即使高聚物在溶液中的浓度非常小,溶液的粘度增加很多,可以大大超过原来纯溶剂的粘度。1930年斯陶丁格(Staudinger)提出此浓粘度(单位浓度的溶液粘度的增值百分数)η_(sp)/C 与高聚物的分子量成正比,从而可以由粘度来测定分子量。这个方法经过不断改善和充实后得到了很大的成功,溶液粘度法已程成为目前应用最广泛的高聚物分子量测定     

一组新的高分子溶液粘度与浓度关系函数式

<正> 粘度法是测定高聚物分子的大小与结构最简便、最常用的方法.在用粘度法测定高聚物分子大小与结构时,需求得极限粘数[η].为此,需确立高分子溶液粘度与浓度的关系,文献中有过种种不同的函数式.通常,将ηsp/c、logηsp/c、lnηr/c对c或ηsp/c对ηsp作图外推到c为零或ηsp为零得[η].Heller对各种外推方法进行了详细的研究,可是到目前为止,采用的成对外推公式不多,且有明显的缺陷.     

流变光学方法研究结晶高聚物的形变机理(摘要)

用光学方法研究结晶高聚物的形变和流动过程称为流变光学(Rheo-opties)。通常研究结构用的光学方法与动态力学试验装置相结合,还可观察其动态形变过程中相应的结构变化。 X射线衍射法可以测定高聚物形变过程中晶粒的取向。我们发现:聚乙烯随拉伸程度的增长昌区的取向程度也增加,但晶区的取向滞后于非晶区的取向且随晶区取向的增加其非晶区的取向逐渐松弛。因此,     

用凝胶渗透色谱谱图计算氯化氯丁胶的粘度方程常数

众所周知,分子量对高聚物的使用性能和加工性能有重要的影响。测定高聚物的分子量是控制生产和了解产品性能的重要分析手段之一。而粘度法测定分子量,仪器简单,数据处理简便,是目前应用最广泛的测定分子量的方法之一。但是,为了从粘度数据得到分子量的确切数值,需要已知Mark-Houwink方程的K、a值,一般确定K、a值,需要将样品分级,并用绝对方法测定各个级分的分子量及测定各级分的[η]。用log[η]对     

小形变时杨氏模量等于三倍的剪切模量

尽管高聚物是黏弹性材料,具有时间依赖性和温度依赖性,但在小形变时,弹性理论中的一些假定和定理仍能用来讨论黏弹性高聚物的形变。应力与应变之比是模量,在小形变时,单向拉伸的杨氏模量约等于三倍的剪切模量,E≈3G。     

快速测定聚合物特性粘数的对半法

概述粘度法测定高聚物的分子量,设备简单,操作方便,并能较快地知道结果。因此,在生产和研究部门中是应用最广泛的一种方法。习惯上,它是以四、五个浓度下将η_(sp)/C 和 lnη_r/C对 C 作图外推至 C 为0,而求得[η]。然后再按     

高聚物温度-形变曲线全自动测定仪

测定温度-形变曲线是研究高聚物力学性质的一种重要方法。在高聚物试样上加以一定的荷重,并改变温度测定在各温度条件下的相对形变,再以形变对温度作图即可得到温度-形变曲线。在曲线的两个转折范围内可以定出玻璃化转变温度 T_g 和流动温度 T_f,从而可以估计被测试样材料的适用范围和加工条件。此外曲线还可以用来配合高聚物结构的研究和估计分子量。必须指出,T_g 和 T_f 仅标志高聚物分子运动状态的区分。在 T_g 以上分子链段开始作局部运动,因此高分子表现为高弹状态,而在 T_f 以上整个分子可以     

高聚物拉伸形变中的声发射

对一系列高聚物进行了单轴拉伸过程中声发射的观察,包括玻璃态高聚物、结晶高聚物、共聚物、共混高聚物和一种交联橡胶。非晶态高聚物拉伸时声发射次数很少,伴随银纹和微裂缝的产生而出现。结晶高聚物在屈服成颈时出现强的声发射,在颈部拉伸的初期声发射较少或不出现,拉伸到接近试件断裂前声发射强烈,次数急剧增多。相同高聚物但试件加工成形历史不同会在声发射上得到反映。交联的顺丁橡胶拉伸时声发射很弱,但可以观察到,在拉力-形变曲线开始偏离线性后出现,没有Kaiser效应。共混高聚物拉伸时声发射很多。高耐冲击共混接枝塑料在断裂前不出现强烈的声发射。如试样和试件加工成形条件相同,声发射现象的重演性是相当好的。     

高聚物从高弹态到流体态的转变

将高聚物由高弹态转变为流体态的转变温度命名为流动温度Tf,该转变温度与高聚物分子量密切相关.在高聚物从高弹态转变为流体态的研究中,由于T1.1的概念忽视对高聚物分子量的依赖性,因此采用Tf的概念更为合理.本文对高聚物的流动温度Tf的讨论涉及高聚物温度-形变曲线、高弹态温区、高聚物熔体剪切粘度.从高聚物凝聚态观点来看,高聚物熔体中凝聚缠结网络中的凝聚结点是分子链的局部向列相互作用使链单元间产生平行凝聚而形成的,而高聚物从高弹态到流体态的转变正是反映了高聚物熔体中凝聚缠结网络的物理交联点,即凝聚结点状态的变化.高聚物熔体可以流动,说明熔体中凝聚网络中的凝聚结点至少是可以在瞬间内打开的,升温使凝聚结点的解凝聚状态存在的时间加长,凝聚状态存在时间减短,当升高到某一温度时,在凝聚结点解凝聚状态的时间内,分子链通过内旋转使质量中心在外加力的方向上可以发生位移,此时高聚物从高弹态转变为流体态,而此时的温度就是流动温度Tf.对高聚物流体弛豫网络的研究,是一个很有前景的研究课题.     

Effects of drawing on creep parameters of polyoxymethylene-drawn fibers

The effects of drawing on creep parameters (modulus, viscosity, and retardation time) of polyoxymethylenedrawn fibers were examined on the basis of a series-parallel, four-element, mechanical model. These parameters increased with the draw ratio. The change in the modulus was the same between the series and parallel components. This was true also for the viscosity, although the change in the viscosity was much greater than that in the modulus. This means that the series and parallel components are deformed in the same mode by drawing. The parallel viscosity increased with elapsed loading times according to an experimental power function; this was also derived from the usual rate equation for viscosity change in the amorphous component. In contrast, the series viscosity remained unchanged over the short creep range due to an extremely larger value than that of the parallel. © 1995 John Wiley & Sons, Inc.     

在确定的热力学状态下测量气体导热系数与黏度

气体的导热系数和黏度是重要的热物性参数,其数值大小取决于所处的热力学状态。在目前的导热系数和黏度主要测量方法中,待测工质在测量时需经历非定常的过程或处于具有物性梯度的非平衡态之下,使得待测工质的物性在时间或者空间上不处于一个确定的热力学状态。本文利用圆柱定程干涉法,通过分析气体导热系数和黏度导致的声波能量耗散,结合气体输运理论中对稀疏气体的描述,探索了在确定的热力学状态下同时测量气体导热系数和黏度的方法,并以氩(Ar)为例进行了实验验证。测量结果与已有文献一致性较好,初步证实了方法的可行性。     

Polymer crystallinity and its effect on the non-linear bending creep rate for a polyphenylene sulphide thermoplastic composite

Recent developments have led to the introduction of advanced thermoplastic composites such as Polyphenylene Sulphide (PPS), which can be used structurally at higher temperatures. Because of its thermoplastic nature, it can also be hot worked by bringing the working temperature considerably above the glass transition temperature. However, such annealing processes also affect its degree of crystallinity, which in turn affect the properties of the material. This paper reports on the effect of matrix crystallinity on the rate of creep deformation in three point bending of some reinforced PPS composites. This work was based on a non-linear approach based on a Power law creep model creep deformation analysis. The effect of annealing on the non-linear creep deformation of the PPS composite specimens has been analysed using a Power Law creep model. Results indicate that the creep deformation for both 20 and 40% reinforced samples were relatively similar despite the difference in the amount of fibre reinforcement. In contrast, the value of the creep component decreased exponentially with the % crystallinity. for both 20 and 40%, reinforced samples.     

Viscoelastic behavior of low molecular weight polystyrene

The shear creep and creep recovery behavior of narrow molecular weight distribution polystyrene samples of low molecular weight, 1.1 × 10³, 3.4 × 10³, and 1.57 × 10⁴ are reported as a function of temperature, near and above the glass temperature. Time-temperature equivalence for the total creep compliance is found to be nonapplicable, and in fact the steady-state recoverable compliance, J_e, is a strong function of temperature. The time-scale shift factors for the recoverable compliance are analyzed in the light of free volume theory. Viscosity data are presented for samples with molecular weights between 1.1 × 10³ and 6.0 × 10⁵. The temperature dependence of the characteristic time constant ηJ_e can be explained in terms of free volume concepts whereas that of viscosity η cannot. Effects of residual molecular weight heterogeneity are demonstrated.     

Effect of homogenization (microfluidization) process parameters in mechanical production of micro- and nanofibrillated cellulose on its rheological and morphological properties

The rheological properties of microfibrillated cellulose (MFC)/nanofibrillated cellulose (NFC) suspensions have an important role during processing and mixing. In this work, the process parameters for MFC/NFC production within a microfluidizer (i.e., the size of interaction chamber and number of passes) were varied to investigate the influences on morphology, zeta potential, chemical properties and rheological features including viscosity, creep, strain recovery and yield stress behavior. The stability and appropriate viscosity of the fiber suspensions can be controlled by optimizing the processing conditions, resulting in a reduction in fiber diameter and most negative zeta potential value. The viscosity increased with higher amount of fibrillation by using a smaller chamber or higher number of passes, but intermediate plateau values are characteristic for temporary aggregation and breaking-up of the fiber network. The creep response and yield stress have been described by parameters of the Burger model and Herschel–Bulkley model, respectively, showing a more prominent effect on yield stress of chamber size than number of passes. The network formation leads to lower creep compliance and step-like strain recovery. The transition from gel-like to liquid-like behavior as characterized by the dynamic yield point at a specific strain, is almost independent of the processing conditions. Most important, the total number of passes applied in production can be directly related to the rotational Péclet number, which combines rheological and morphological data.     

A two-stage stress-dependent creep mechanism in plasticized poly(vinyl chloride) (PVC)

The temperature dependence of tensile creep of plasticized poly(vinyl chloride) (PVC) was tested under differently applied stresses. The steady creep rate showed two distinct stages, depending on stress and temperature. At relatively low stresses the activation energy (0.2 eV) which characterized the steady creep mechanism of stage I, showed no stress sensitivity. Under high stresses (stage II) the energy-activating steady creep was of the order of 1 eV and increased excessively with increasing stress. The model for plastic flow of PVC suggested here assigns the extension of the twisted zigzag molecular conformation to creep in stage I. In stage II creep is controlled by the reorientation of molecular segments by rotation from initially random orientations in a direction parallel to the principal tensile axis. γ Irradiation of the samples before testing increased the steady creep rate and reduced the creep lifetime. This was attributed to chain scission and greater mobility of the molecular segments.     

Detection of long-chain branches in polyethylene via rheological measurements

The detection of long-chain branches(LCB) in polyethylene is of considerable importance as the processing properties of polyethylene are strongly affected by even a small amount of LCB. While the conventional characterization techniques such as GPC-MALS and13 C NMR fail or take very long time to detect low content of LCB, we turn to the rheological method, which is more sensitive to LCB. In our study, we performed oscillatory shear test, creep test and stress relaxation test on two series of metallocene linear low density polyethylene(LLDPE), revealing that the resins with LCB show higher zero-shear-rate viscosity, retarded relaxation and higher flow activation energy than those without or with less LCB. The resins with LCB showed shear thinning at very low shear rate and their zero-shear-rate viscosities were obtained via creep test. The content of LCB was quantitatively estimated from the flow activation energy. In addition, the modulus-time curves during stress relaxation of melt of the different resins obeyed the power law. The exponent of the resins with more LCB was 0.7, different from that of the resins with less LCB, around 1.7.     

Entanglement between dissimilar chains in compatible polymer blends: poly(methyl methacrylate) and poly(vinylidene fluoride)

The plateau modulus and zero-shear melt viscosity of binary compatible blends of poly(methyl methacrylate) and poly(vinylidene fluoride) were measured by dynamic oscillation and shear creep, and used to analyze the entanglement between dissimilar chains and its effect on melt viscosity. It is found that dissimilar chains are less likely to entangle with each other than similar chains, resulting in a large reduction of zero-shear melt viscosity in this system.     

Rheological properties of polymer melts

A new method of treating experimental data on the viscous and viscoelastic properties of various polymer melts is suggested. The dependence of the apparent viscosity on the molecular weight, temperature and shear stress can be represented as the product of three independent functions, each of them having a single argument. All three functions are universal, at least in first approximation, and the dependence of the apparent viscosity on the variables indicated is determined by two parameters (glass transition temperature and critical molecular weight), characteristic of each homologous polymer series. The viscoelastic characteristics (dynamic, relaxation, creep, as well as relaxation and retardation spectra) of polymer melts are universal in shape in the linear region and contain only one individual polymer parameter, viz., maximum Newtonian viscosity. It is shown that upon normalization of certain nonlinear characteristics with respect to the maximum Newtonian viscosity, they can also be represented in the universal form.     

Creep behavior of ultrahigh-modulus polyethylene: Influence of draw ratio and polymer composition

The creep behavior of ultrahigh-modulus polyethylene monofilaments has been studied over the temperature range 20–70°C. A wide range of samples was examined in an attempt to determine the influence of draw ratio, molecular weight, copolymerization, and crosslinking by γ irradiation Prior to drawing. Results are also presented for a solution-spun fiber. It is proposed that the permanent flow creep arises from a combination of two creep processes, one of which is associated with the crystalline regions of the oriented structure and the other with a molecular network.