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1、聚合物流变学导论聚合物流变学导论 复习复习 Rheology is “ the study of the flow and deformation of all forms of matter.” 1. Rheology?1. Rheology?= “the science of flow“ 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) 法林效应法林效应(F-L(F-L效应效应 ) ) 1931年，Fahraeus 和Lindqvist发现，
2、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。 法林效应法林效应(F-L(F-L效应效应 ) ) 法林效应的重要性法林效应的重要性 G Shear ModulusE Elastic Modulus 简单拉伸简单减切 Ideal Solids Fluids exhibits no re
3、sistance to flow “Pressure in liquid is the same in all directions” - Pascal (1663) Hydrodynamics (流体力学) Bernoulli (1738), Euler(1755) (1) Inviscid (非粘性) or Pascalian fluid Ideal Fluids (2) Newtonian (or viscous) Fluids (2) Newtonian (or viscous) Fluids - Sir. Issac Newton, - Sir. Issac Newton, 1687
4、1687 “ “The resistance which arises from the lack of The resistance which arises from the lack of slipperiness originating in the fluid is slipperiness originating in the fluid is proportional to the velocity by which the proportional to the velocity by which the parts of the fluid are separated fro
5、m each parts of the fluid are separated from each other.other.” ” Viscoelasticity ( Viscoelasticity (粘弹性粘弹性) ) 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 appl
6、ied force is removed. Energy is stored by the system, then released. Ideal Elastic Solids Viscoelasticity These 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
7、such materials, the necessary rheological properties must be related to the flow or stress conditions during processing and application. flow behavior of different liquidflow behavior of different liquid Time Independent liquids Newtonian Nonnewtonian shear thinning shear thickening yield stress Tim
8、e Dependent liquids thixotropic (触变性) rheopectic (震凝性) Basic Concepts in RheologyBasic Concepts in Rheology Newtonian Newtonian and Non-Newtonian Fluidsand Non-Newtonian Fluids h0 h0：零切粘度 ha：表观粘度 Rheopexy (work hardening, Rheopexy (work hardening, 震凝性震凝性) ) A rheopectic material becomes more viscous
9、 with increasing time of applied force. This effect is the opposite of thixotropy, and is sometimes called work hardening. Viscoelastic Viscoelastic ( (粘弹性粘弹性) ) Behavior Behavior of Polymerof Polymer In between elastic and viscous behavior lies the real world of most substances, which are viscoelas
10、tic materials. uPolymer Melts uPolymer Solution uEmulsions uSuspensions uSlurry Plastic (Plastic (塑性塑性) and Pseudoplastic) and Pseudoplastic（假塑性）（假塑性） shear thinningshear thinning（剪切变稀）（剪切变稀） PLASTIC materials initially resist deformation, until a yield stress is reached. When that stress is exceede
11、d, the shear rate becomes 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 (Newtonian) behavior at the highest levels of stress and shea
12、r rate. Plastic Plastic Dilatancy fluidDilatancy fluid（膨胀流体）（膨胀流体） -Shear thickening (-Shear thickening (剪切变稠剪切变稠) ) A dilatant material resists deformation more than in proportion to the applied force. For example, the more effort you put into stirring a dilatant material, the more resistant it bec
13、omes to stirring. This is usually an indication that the applied force is causing the material to adopt a more ordered structure Concentrated colloidal suspensions Example: A thick slurry of wet beach sand is often dilatant Thixotropy (Thixotropy (触变性触变性) ) A thixotropic material becomes more fluid
14、with increasing time of applied force. The applied force could be stirring, 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 u Quicksand (流沙) u Paint u Unsaturate
15、d Polyester Special Viscoelastic Flow Behavior of Special Viscoelastic Flow Behavior of PolymersPolymers 1.Rod Climb-up (Weissenberg Effect) 2.Elastic Recoil (弹性回复) 3.Secondary Flow （次级流动） 4.Tubeless Siphon (无管虹吸) 5.Die Swell (Banus Effect) （挤出胀大） 6.Sharkskin, Flow Instability and Melt fracture 7.Ho
16、le Pressure Error (孔压误差) 8.Drag Reduction (Toms Effect) （湍流减阻效应 ） 影响挤出破裂的因素 q 口模长度的影响 q 挤出速度的影响 q 温度的影响： 温度升高有利于减少挤出破裂； q 分子量分布的影响： 相同重均分子量的聚合物，分子量分布大时，挤出破裂现象减弱； q 添加润滑剂的影响 q填料的影响： 填料有利于减少挤出破裂 关于挤出不稳定现象的小结关于挤出不稳定现象的小结 1. 当挤出速度或者压力大于临界值时,出现挤出不 稳定现象; 2. 分子结构对挤出不稳定行为具有重要影响: 带 大的侧基或长支化链的聚合物(LDPE、PS、 SBS、PDMS)与线性高分子链(HDPE、 LLDPE、PBI等)挤出不稳定行为不同,其根 源在于后者容易发生分子链缠结; 3. 工艺参数、模具材料、添加剂等因素对挤出不 稳定行为具有重要影响。 8. Drag Reduction (Toms 8. Drag Reduction (Toms Effect)Effect) 湍
