聚合物流變學(xué)-復(fù)習(xí)

1、聚合物流變學(xué)導(dǎo)論復(fù)習(xí),Rheology is “ the study of the flow and deformation of all forms of matter.”,1. Rheology?,= "the science of flow",E. C. Bingham, M. ReinerApril, 29, 1929,Heraclitus (赫拉克利特, 紀(jì)元前五世紀(jì)的希臘哲學(xué)家)“Everythin

2、g Flows” (萬物皆流),,法林效應(yīng)(F-L效應(yīng) ),1931年，F(xiàn)ahraeus和Lindqvist發(fā)現(xiàn)，血液粘度隨血管半徑的減小而降低;　微血管范圍內(nèi)，血管越細，血液粘度越低，這有利于血液順利通過微血管。,一種看法是血液流經(jīng)較細的血管時，近管壁處易形成無紅細胞的血漿層，從而降低了流動阻力,在病理情況下，紅細胞變形性降低或聚集性增高，均可導(dǎo)致臨界半徑顯著增大，甚至高達正常的幾十倍，此時，由于多數(shù)微血管內(nèi)血液粘度急驟增高，必將導(dǎo)

3、致微循環(huán)的嚴(yán)重障礙。,法林效應(yīng)(F-L效應(yīng) ),法林效應(yīng)的重要性,G… Shear Modulus,E… Elastic Modulus,簡單拉伸,簡單減切,Ideal Solids,Fluids exhibits no resistance to flow“Pressure in liquid is the same in all directions”

4、 - Pascal (1663) Hydrodynamics (流體力學(xué)) – Bernoulli (1738), Euler(1755),(1) Inviscid (非粘性) or Pascalian fluid,Ideal Fluids,(2) Newtonian (or viscous) Fluids,- Sir. Issac Ne

5、wton, 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.”,Viscoelasticity (粘彈性),ideal N

6、ewtonian liquidsNewton LawDeformation ceases when the applied force is removed. Energy dissipated in flow.,Viscoelasticity,Hooke LawDeformation reverses spontaneously when an applied force is removed.Energy is store

7、d by the system, then released.,Ideal Elastic Solids,Viscoelasticity These materials may be called complex fluids (復(fù)雜流體) for which the viscosity and elasticity are not material constants but rather are complex fun

8、ctions 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.,flow behavior

9、of different liquid,Time Independent liquids NewtonianNonnewtonian －shear thinning －shear thickening －yield stress Time Dependent liquids thixotropic (觸變性)rheopectic (震凝性),Basic Concepts i

10、n Rheology,Newtonian and Non-Newtonian Fluids,h0：零切粘度ha：表觀粘度,Rheopexy (work hardening, 震凝性),A rheopectic material becomes more viscous with increasing time of applied force. This effect is the opposite of thixotropy, a

11、nd is sometimes called ‘work hardening’.,Viscoelastic (粘彈性) Behavior of Polymer,In between elastic and viscous behavior lies the real world of most substances, which are viscoelastic materials.,Polymer MeltsPolymer Solu

12、tionEmulsionsSuspensionsSlurry,Plastic (塑性) and Pseudoplastic（假塑性） shear thinning（剪切變?。?PLASTIC materials initially resist deformation, until a yield stress is reached. When that stress is exceeded, the shear rate be

13、comes measurable. Further stress leads finally to linear (Newtonian) behavior.PSEUDOPLASTIC materials exhibit shear thinning without the initial resistance to deformation. Like plastic materials, they also show linear

14、(Newtonian) behavior at the highest levels of stress and shear rate.,Plastic,Dilatancy fluid（膨脹流體）-Shear thickening (剪切變稠),A dilatant material resists deformation more than in proportion to the applied force. For exampl

15、e, the more effort you put into stirring a dilatant material, the more resistant it becomes to stirring. This is usually an indication that the applied force is causing the material to adopt a more ordered structure..,Co

16、ncentrated colloidal suspensions Example: A thick slurry of wet beach sand is often dilatant,Thixotropy (觸變性),A thixotropic material becomes more fluid with increasing time of applied force. The applied force could be s

17、tirring, pumping or shaking. This effect is sometimes called ‘work softening’.It is often reversible, so that if left undisturbed for some time a thixotropic slurry regains its viscosity.,Examples Quicksand (流沙) Pain

18、t Unsaturated Polyester,Special Viscoelastic Flow Behavior of Polymers,Rod Climb-up (Weissenberg Effect)Elastic Recoil (彈性回復(fù))Secondary Flow （次級流動）Tubeless Siphon (無管虹吸)Die Swell (Banus Effect) （擠出脹大）Sharkskin, Flow

19、 Instability and Melt fractureHole Pressure Error (孔壓誤差)Drag Reduction (Toms Effect) （湍流減阻效應(yīng)）,影響擠出破裂的因素 口模長度的影響 擠出速度的影響 溫度的影響： 溫度升高有利于減少擠出破裂； 分子量分布的影響： 相同重均分子量的聚合物，分子量分布大時，擠出破裂現(xiàn)象減弱； 添加潤滑劑的影響填料的影響：

20、 填料有利于減少擠出破裂,關(guān)于擠出不穩(wěn)定現(xiàn)象的小結(jié),當(dāng)擠出速度或者壓力大于臨界值時,出現(xiàn)擠出不穩(wěn)定現(xiàn)象;分子結(jié)構(gòu)對擠出不穩(wěn)定行為具有重要影響: 帶大的側(cè)基或長支化鏈的聚合物(LDPE、PS、SBS、PDMS)與線性高分子鏈(HDPE、LLDPE、PBI等)擠出不穩(wěn)定行為不同,其根源在于后者容易發(fā)生分子鏈纏結(jié);工藝參數(shù)、模具材料、添加劑等因素對擠出不穩(wěn)定行為具有重要影響。,8. Drag Reduction (Toms Eff

21、ect)湍流減阻效應(yīng),Drag,Basic Concepts in Polymer Rheology,Stress (應(yīng)力), Strain (應(yīng)變)ViscosityFlow Behavior of Non-Newtonian LiquidStress Tensor (應(yīng)力張量)Normal Stress (法向應(yīng)力) Deviatoric Stress (偏應(yīng)力張量)First Normal Force Differe

22、nce（第一法向應(yīng)力差）Second Normal Force Difference（第二法向應(yīng)力差）,Rheometry (流變測量),Viscometer(粘度計) , Rheometer (流變儀) Viscosity testing: Ford Cup Falling Ball Viscometer (落球粘度計) Capillary rheometer Rotational Viscometer

23、 Coaxial Cylinder Viscometer (rheometer)Cone and Plate Viscometer(rheometer)Parallel plate viscometer(rheometer) Dynamic Rheometer Extensional ViscometerViscosity Relative viscosity (相對粘度) Steady V

24、iscosity (穩(wěn)態(tài)粘度) Dynamic Viscosity (動態(tài)粘度) Extensional Viscosity　(拉伸粘度)Normal Stress Differences　(法向應(yīng)力差)Loss ModulusStorage ModulusLoss Tangent (tan d),Apparent Viscosity,Entrance Pressure Drop (Bagley Correction ),I

25、nfluence of Wall Slip,用入口壓力降表征PVC塑化程度,雙管毛細管流變儀,◆,◆,◆,◆,◆,Capillary Rheometer,Types of the Coaxial Cylinder (Couette) Viscometer,內(nèi)筒旋轉(zhuǎn)式,外筒旋轉(zhuǎn)式,單筒式,涂料, 油漆, 乳液… 高分子熔體 水泥,流變儀的選用,Haake Rheomixer,P

26、olyLab - Rheomix Mixer – System The PolyLab System from Thermo Haake used together with the Rheomix mixer sensor produces rheograms that provide production-related information such as: dynamic viscosity depending o

27、n the shear load, melt behavior in the extruder, the influence of additives, and temperature and shear load behavior. The mixer is suitable for highly viscous substances such as thermoplastics, thermosets and rubbers to

28、 name a few.,,1,2,3,Applications of Haake Rheomixer --- Summary,轉(zhuǎn)矩流變儀用途：樣品的制備；模擬密煉、擠出(裝擠出式測量裝置)等工藝過程；評價溫度，轉(zhuǎn)速對加工行為的影響評價材料組成對加工行為的影響,在聚合物加工研究中具有重要應(yīng)用價值。,Extensional Flow and Extensional Viscosity,Contraction Flow (injec

29、tion, extrusion. etc.)Fiber spinningFilm blowingBlow FormingThermo forming (Vacuum forming, Pressure forming, etc. )pumping, filling, blending, spreading, ink-jets,,Industrial processing conditions always have some

30、form of extensional deformation,拉伸及剪切粘度與形變速率之間的關(guān)系,A類 (如低密度聚乙烯、聚異丁烯、聚苯乙烯)由于熔體中有局部弱點，在拉伸過程中形變趨于均勻化，又由于應(yīng)變硬化，因而h隨 g增大而增大;B類 (如有機玻璃、ABS、尼龍、聚甲醛、聚酯)的h與g無關(guān); C類 (如某些類型的高密度聚乙烯、聚丙烯)因局部弱點在拉伸過程中引起熔體的局部破裂，所以h隨 g增大而下降。,拉伸硬化,,拉伸流變行為的研

31、究方法,Stretching method,Spinning,Converging flow method,Capillary break up,DMA,電磁流變液體，定義、組成、應(yīng)用,拉伸共振，影響因素、臨界拉伸比DR,光學(xué)在流變學(xué)中的應(yīng)用,殘余應(yīng)力的分布; 分子的取向; 流速的分布; 相區(qū)的尺寸和形變; 球晶的大小和形變.,上述問題由傳統(tǒng)的流變學(xué)測試是無法完成的,必須依賴于光學(xué)技術(shù),即所謂的流變光學(xué).,聚合物產(chǎn)生雙折射的原因

32、１．residual stress (殘余應(yīng)力),Definition of residual stress:內(nèi)應(yīng)力是塑料制品在無外界作用力的情況下，樣品內(nèi)部的應(yīng)力，原因是物質(zhì)的原子或分子偏離其平衡態(tài)．或者分子鏈上鍵角的非平衡變化，分子鏈段以及超分子結(jié)構(gòu)之間相互位置的非平衡等形成的。由內(nèi)應(yīng)力所引起的形變具有能彈性質(zhì)．限制這一形變的外在條件一旦除去．形變隨即發(fā)生。,２．Orientation (取向),流動狀態(tài)下快速冷卻；,,粘度