参考教材 聚合物流变学导论 - 中国流变网 ... · e. c. bingham, m. reiner april, 29,...

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聚合物流变学导论 师:彭 E-mail: [email protected] Tel: 0571-87953075 Adds: 高分子大楼413 Department of Polym. Sci. & Eng. Zhejiang University, Hangzhou, China 参考教材 高分子材料流变学导论吴其晔,化学工业出版社 固体高聚物的力学性能I.M.沃德,科学出版社 屈服、破坏、线性粘弹理论、粘弹性测量等 非牛顿流体力学及其应用沈崇棠等,高等教育出版社 流变测量、聚合物减阻*高聚物流变学导论王玉忠,郑长义四川大学出版社 Rheology is “ the study of the flow and deformation of all forms of matter.” 1. 什么是流变学? E. C. Bingham, M. Reiner April, 29, 1929 Heraclitus (赫拉克利特, 纪元前五世纪的希腊哲学家) “Everything Flows” (万物皆流) Chapter One Introduction to Rheology 流变学是物理学的一个分支,它主要研究材料在外界作用 (应力、应变、温度、电场、磁场、辐射等)下的变形和流 动的科学。 2. Examples for Applications of Rheology Plastics; Rubbers; Fibers; Adhesives; Coatings; Paints; Inks Medicament(药剂); Blood (Hemorheology) ; Muscle … * Polymer * Foodstuff - Melts: Injection; Extrusion; Spinning; Thermoforming ...... - Solids: Mechanical Properties ; Deformation; Fracture...... * Biology, Medicine * Chemical Engineering - Chemicals, Personal care products; Cosmetics … * Geology: Rock * 其它: Drilling muds, Cement, Solder Pastes (焊锡) States of Matter GAS - Rotates, vibrates, translates(扩散), in an ideal system there are no attractive forces between units. LIQUID - Flows, posses viscosity due to interactions between units. There is still translation but of a more restricted form. SOLID - Crystalline lattice with 3D order. No translation of units in the crystal. Small molecules Polymer Much more complex behavior 古典物理中对物质的描述 (2) Elastic Solids (弹性固体) (1) Rigid Solids (刚性固体) Ideal Solids Ideal Fluids (1) Inviscid (非粘性) or Pascalian Fluids (2) Newtonian (or viscous) Fluids

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聚合物流变学导论

教 师:彭 懋

E-mail: [email protected]: 0571-87953075Adds: 高分子大楼413

Department of Polym. Sci. & Eng.Zhejiang University, Hangzhou, China

参考教材高分子材料流变学导论,吴其晔,化学工业出版社

固体高聚物的力学性能,I.M.沃德,科学出版社

屈服、破坏、线性粘弹理论、粘弹性测量等

非牛顿流体力学及其应用,沈崇棠等,高等教育出版社

流变测量、聚合物减阻*等

高聚物流变学导论,王玉忠,郑长义,四川大学出版社

Rheology is “ the study of the flow and deformation of all forms of matter.”

1. 什么是流变学?

E. C. Bingham, M. ReinerApril, 29, 1929

Heraclitus (赫拉克利特, 纪元前五世纪的希腊哲学家)

“Everything Flows” (万物皆流)

Chapter One Introduction to Rheology

流变学是物理学的一个分支,它主要研究材料在外界作用(应力、应变、温度、电场、磁场、辐射等)下的变形和流动的科学。

2. Examples for Applications of Rheology

Plastics; Rubbers; Fibers; Adhesives; Coatings; Paints; Inks

Medicament(药剂); Blood (Hemorheology) ; Muscle …

* Polymer

* Foodstuff

- Melts: Injection; Extrusion; Spinning; Thermoforming ......

- Solids: Mechanical Properties ; Deformation; Fracture......

* Biology, Medicine

* Chemical Engineering- Chemicals, Personal care products; Cosmetics …

* Geology: Rock

* 其它: Drilling muds, Cement, Solder Pastes (焊锡)

States of Matter

GAS - Rotates, vibrates, translates(扩散), in an ideal system there are no attractive forces between units.LIQUID - Flows, posses viscosity due to interactions between units. There is still translation but of a more restricted form.SOLID - Crystalline lattice with 3D order. No translation of units in the crystal.

Small molecules Polymer

Much more complex behavior

古典物理中对物质的描述

(2) Elastic Solids (弹性固体)

(1) Rigid Solids (刚性固体)

• Ideal Solids

• Ideal Fluids

(1) Inviscid (非粘性) or Pascalian Fluids

(2) Newtonian (or viscous) Fluids

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(1) Rigid Solids (刚性固体)

Archimedes (~250BCE) claimed that he can move the world if he were provided a right leverage.

In Euclidean Geometry (欧几米德几何)and Solid Mechanics (固体力学) ,

ideal solids don’t undergo deformation

?

• Ideal Solids(理想固体) (2) Elastic Solids (弹性固体)

“The power of any spring is in the same proportion with the tension thereof, i.e. the stress is proportional to the strain”

- Robert Hooke (1678)

εδ ⋅= Eδ − Stressε − StrainE –Elastic (Young’s) Modulus

An intrinsic property of materials

固体在小应力, 小应变下符合虎克定律

G… Shear ModulusE… Elastic Modulus

简单拉伸 简单减切

形变的各种方式 •Contraction (压缩)

A spring, shortened by acompressional stress S1, has its length reduced fro L0 to L1. A plot of the strain (L0-L1)/Lo as a function of stress produces a straight line.

A cylinder of rock subjected to a confining stress by a tight metal jacket, and shortened by a compressional stress S1has its volume reduced from V0 to V1. A plot of strain (V0-V1)/V0 as a function of stress produces a straight line.

Bend 弯曲

Rotation 扭曲

Fluids exhibits no resistance to flow

Hydrodynamics (流体力学)– Bernoulli (1738), Euler(1755)

“Pressure in liquid is the same in all directions”- Pascal (1663)

(1) Inviscid (非粘性) or Pascalian fluid

• Ideal Fluids

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(2) Newtonian (or viscous) Fluids

- Sir. Issac Newton, 1687

“ The resistance which arises from the lack of slipperiness originating in the fluid is proportional to the velocity by which the parts of the fluid are separated from each other.”

随着科学与技术的发展,学者们在研究橡胶、塑料、油漆、玻璃、混凝土,以及金属等工业材料;岩石、土、石油、矿物等地质材料;以及血液、肌肉骨骼等生物材料的性质过程中,发现使用古典弹性理论、塑性理论和牛顿流体理论已不能说明这些材料的复杂特性,于是就产生了流变学的思想。

3. Viscoelasticity (粘弹性)

ideal Newtonian liquids• Newton Law• Deformation ceases

when the applied force is removed.

• Energy dissipated in flow.

Viscoelasticity

• Hooke Law• Deformation reverses

spontaneously when an applied force is removed.

• Energy is stored by the system, then released.

Ideal Elastic Solids

ViscoelasticityThese materials may be called complex fluids(复杂流体) for which the viscosity and elasticity are not material constants but rather are complex functions of stress, strain, and strain history.

For such materials, the necessary rheological properties must be related to the flow or stress conditions during processing and application.

* 粘弹性流体的类型将在以后做详细介绍

Time Dependent Viscoelastic Behavior of PDMS (polydimethyl siloxane)

At long flow times (or high temperatures), PDMS acts like a viscousliquid, similar to honey. However at short flow times (or low temperatures) it acts like an elastic solid, similar to rubber. In other words, if you leave some PDMS on a surface overnight (long flow time), it will flow to cover the surface and mold to any surface imperfections. However if you roll the same PDMS into a sphere and throw it onto the same surface (short flow time), it will bounce like a rubber ball.

short time ( <1 sec )long time ( about 24 hrs)

Polymer Biological Materials Liquid crystallineColloidal (胶体) suspensionsEmulsions (乳液)Gels (凝胶)

Soft Condensed Matter De Gennes

1. Responsive to weak environmental stimuli2. Made up of particles or structures on the

mesoscopic length scale (1nm - 1um) 3. The softness of interactions in these systems leads

to complex phase behavior and dynamical phenomena

* 此类材料的流变行为更加复杂,对流变学的发展提出了更多的难题和更加丰富的研究内容。

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Clepsydra (漏壶,刻漏 ) - Amenemhet (Egypt, ~1600BCE)- 中国,<<周礼>>,公元前500年

The clepsydra or water clock was invented to be used at night or on overcast days. It is much more consistent than sundials ( 日 晷 )because it does not rely on a changing factor.

People realized that its consistency changes when the water is too cold, too hot or too dirty.

Amenemhet made corrections to the influence of temperature to the viscosity of water.

Genesis(起源)of Rheology英国物理学家麦克斯韦和开尔文很早就认识到材料的变化与时间存

在紧密联系的时间效应。

麦克斯韦在1869年发现,材料可以是弹性的,又可以是粘性的。对于粘性材料,应变相同的情况下,应力不能保持恒定,而是以某一速率减小到零,其速率取决于施加的起始应力值和材料的性质。这种现象称为应力松弛。许多学者还发现,应力虽然不变,材料棒却可随时间继续变形,这种性能就是蠕变或流动。

经过长期探索,人们终于得知,一切材料都具有时间效应,于是出现了流变学,并在20世纪30年代后得到蓬勃发展。1929年,美国在宾汉教授的倡议下,创建流变学会;1939年,荷兰皇家科学院成立了以伯格斯教授为首的流变学小组;1940年英国出现了流变学家学会。当时,荷兰的工作处于领先地位,1948年国际流变学会议就是在荷兰举行的。法国、日本、瑞典、澳大利亚、奥地利、捷克斯洛伐克、意大利、比利时等国也先后成立了流变学会。

Genesis of Rheology

Genesis of Rheology

After 1929

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电流变磁流变

液晶高分子

流变学的发展同世界经济发展和工业化进程密切相关。现代工业需要耐蠕变、耐高温的高质量金属、合金、陶瓷和高强度的聚合物等,因此同固体蠕变、粘弹性和蠕变断裂有关的流变学迅速发展起来。核工业中核反应堆和粒子加速器的发展,为研究由辐射产生的变形打开新的领域。

在土木工程中,建筑的土地基的变形可延续数十年之久。地下隧道竣工数十年后,仍可出现蠕变断裂。因此,土流变性能和岩石流变性能的研究日益受到重视。

5 Important Rheology Branches

旨在研究血液及其组分的流动和变形特性,以及这种特性对循环功能,乃至全身功能和代谢影响的科学;血液的粘弹性、触变性、红细胞的变形性和聚集性以及血小板的粘附和聚集性等等,对于循环功能,尤其是微循环,有着十分重要的作用。

心脑血管疾病

(1) Hemorheology(血液流变学)法林效应(F-L效应 )

1931年,Fahraeus和 Lindqvist发现,血液粘度随血管半径的减小而降低; 微血管范围内,血管越细,血液粘度越低,这有利于血液顺利通过微血管。

一种看法是血液流经较细的血管时,近管壁处易形成无红细胞的血浆层,从而降低了流动阻力

  在病理情况下,红细胞变形性降低或聚集性增高,均可导致临界半径显著增大,甚至高达正常的几十倍,此时,由于多数微血管内血液粘度急骤增高,必将导致微循环的严重障碍。

法林效应(F-L效应 )

法林效应的重要性

(2) Geological Rheology(地质流变学)

• 矿产的形成规律

• 工程建设选址

• 自然灾害的防止:

如山体滑坡、地震、泥石流的预防等

在地球科学中,人们很早就知道时间过程这一重要因素。流变学为研究地壳中极有趣的地球物理现象提供了物理-数学工具,如冰川期以后的上升、层状岩层的褶皱、造山作用、地震成因以及成矿作用等。对于地球内部过程,如岩浆活动、地幔热对流等,现在则可利用高温、高压岩石流变试验来模拟,从而发展了地球动力学。

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(3) Food Rheology(食品流变学)

食品流变学是研究食品在力的作用下变 形的科学.测定食品的流变性对于改善和控制食品的质量,设计,改善有关加工设备具有 重要的意义

食品的物质形态

胶体;凝胶;泡沫;溶液;悬浮液等各种复杂流体等

食品的加工方法

Extensional Rheology of DoughIn the process of baking bread, gas cells

trapped within the dough during mixing expand. This expansion is driven by the release of carbon-dioxide from the reaction with yeast and the release of water due to the increase in temperature. This expansion increases the overall volume of the dough and is known as the rise. During rise, the dough between gas cells are stretched and at a critical point, undergo an instability leading to rupture , forming the open foam structure of baked bread.

The stability of the dough during stretching is in turn related to its rheology, and some studies have indeed shown a correlation between the rheology of the uncooked dough to the final loaf volume.

The objective of this project is to understand the relationship between microstructure,rheology and stability. To do this, we will need to develop an accurate and reproducible method for measuring the relevant properties of the dough

通过研究建筑物在地震中受到的破坏程度和破坏方式的规律,寻找建筑物抗震及修复的方法。

(4)建筑The Tacoma Narrows Bridge Collapse

At the time it opened for traffic in 1940, the Tacoma Narrows Bridge was the third longest suspension bridge in the world. It was promptly nicknamed "Galloping Gertie," due to its behavior in wind. Not only did the deck sway sideways, but vertical undulations also appeared in quite moderate winds.

Drivers of cars reported that vehicles ahead of them would completely disappear and reappear from view several times as they crossed the bridge. Attempts were made to stabilize the structure with cables and hydraulic buffers, but they were unsuccessful. On November 7, 1940, only four months after it opened, the Tacoma Narrows Bridge collapsed in a wind of 42 mph -- even though the structure was designed to withstand winds of up to 120 mph.

Technical experts still disagree on the exact cause of the bridge's destruction, but most agree the collapse had something to do with a complex phenomenon called resonance: the same force that can cause a soprano's voice to shatter a glass.

Today, wind tunnel testing of bridge designs is mandatory. As for the Tacoma Narrows bridge, reconstruction began in 1949. The new bridge is wider, has deep stiffening trusses under the roadway and a narrow gap down the middle -- all to dampen the effect of the wind.

(5) Polymer Rheology

SolutionMolten Polymers

Solution Suspensions Emulsion

• Polymer Synthesis

• Processing

PlasticsRubberComposites

• Applications

3. 聚合物流变学的主要内容研究方法:

A 理论模拟(结构流变学)主要有宏观与微观两种:

• 宏观法 即经典的唯象研究方法,是将聚合物看作由连续质点组成,材料性能是位置的连续函数,研究材料的性能是从建立粘弹模型出发,进行应力-应变或应变速率分析。(注:对于纯弹性物体,可以用胡克定律来描述,即应力与应变成正比。对于牛顿流体,可以用应力=粘度×应变速率来描述。但是现实中的固体存在不符合胡克定律的塑性变形,液体也全是非牛顿流体。特别对于高分子,具有粘弹性性质,情况复杂。其数学模型主要借助于连续介质力学。目前对于一般流体的简单流动,理论模拟效果较好,但是对于复杂流道,由于存在很多复杂的边界效应,目前

的计算能力还无法给出比较好的结果,这也成为近来流变学研究的重要方向)

• 微观法 即分子流变学方法,是从分子运动的角度出发,对材料的力学行为和分子运动过程进行相互关联,提出材料结构与宏观流变行为的联系。

结构流变学对于聚合物流变学以及高分子凝聚态物理基础理论的研究具有重大价值

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3. 流变学的研究方法:

B 实验流变学 常用的仪器主要有:

• 挤出式流变仪(毛细管流变仪、熔体指数仪)

• 转动式流变仪(同轴圆筒粘度计、锥板式流变仪)

• 振荡式流变仪、

• 转矩流变仪

• 拉伸流变仪等。

C 加工流变学•加工条件与产品流动行为的关系

•聚合物加工操作单元的流变学分析(挤出、注射、纺丝、吹塑)

•异常流变行为(挤出胀大、熔体破裂、拉伸共振等等)

•多相高分子体系的流变学规律

•模具、机械设计中与材料流动性、传热有关的问题

聚合物主要流变行为: 聚合物的流动性、弹性、形变和断裂特性

流动性 以粘度的倒数表示流动性。按作用方式的不同,流动可分为剪切流动和拉伸流动,相应地有剪切粘度和拉伸粘度。前者为切应力与切变速率之比;后者为拉伸应力与拉伸应变速度之比。聚合物的结构不同,流动性(或粘度)就不同。对于聚合物熔体,大多数是属于假塑性液体,其剪切粘度随剪切应力的增加而降低,同时测试条件(温度、压力)、分子参数(分子量及其分布、支化度等)和添加剂(填料、增塑剂、润滑剂等)等因素对剪切粘度-剪切应力曲线的移动方向均有影响。对于拉伸粘度,当应变速率很低时,单向拉伸的拉伸粘度约为剪切粘度的 3倍,而双向相等的拉伸,其拉伸粘度约为剪切粘度的6倍。拉伸粘度随拉伸应力增大而增大,即使在某些情况下有所下降,其下降的幅度远较剪切粘度的小。因此,在大的应力作用下,拉伸粘度往往要比剪切粘度大一二个数量级,这可使化学纤维纺丝过程更为容易和稳定。

弹性 由于聚合物流体流动时,伴随有高弹形变的产生和贮存,故外力除去后会发生回缩等现象,例如:塑料、橡胶挤出后和纤维纺丝后会发生断面尺寸增大而长度缩短的离模膨胀现象,或称弹性记忆效应;搅动时流体会沿杆上升,这种爬杆现象称韦森堡效应或法向应力效应。此外,聚合物加工时,半成品或成品表面不光滑,出现“橘子皮”和“鲨鱼皮”,出现波浪、竹节、直径有规律的脉动、螺旋形畸变甚至支离破碎等影响制品质量的熔体破裂和不稳定流动等现象,这些现象主要与熔体弹性有关。

断裂特性 是影响聚合物(尤其是橡胶)加工的又一流变特性。它主要是指生胶的扯断伸长率、以及弹性与塑性之比。扯断伸长率与弹塑比要适当地配合,一般都希望两者均大些为好,以便有利于炼胶等工艺的顺利进行。

研究聚合物流变学的意义

① 可指导聚合,以制得加工性能优良的聚合物。例如:合成所需分子参数的吹塑用高密度聚乙烯树脂,则所成型的中空制品的冲击强度高,壁厚均匀,外表光滑;增加顺丁橡胶的长支链支化和提高其分子量,可改善它的抗冷流性能,避免生胶贮存与运输的麻烦。

② 对评定聚合物的加工性能、分析加工过程、正确选择加工工艺条件、指导配方设计均有重要意义。例如:通过控制冷却水温及其与喷丝孔之间的距离,可解决聚丙烯单丝的不圆度问题;研究顺丁橡胶的流动性,发现它对温度比较敏感,故需严格地控制加工温度。

③ 对设计加工机械和模具有指导作用。例如:应用流变学知识所建立的聚合物在单螺杆中熔化的数学模型,可预测单螺杆塑化挤出机的熔化能力;依据聚合物的流变数据,指导口模的设计,以便挤出光滑的制品和有效地控制制品的尺寸。