Introduction to Polymer Rheology
Shi-Qing Wang
Department of Polymer Science, University of Akron, Ohio44325 Introduction
The missions of polymer rheology
phenomenological <Maxwell level>, linear viscoelasticity
a> characterization tools
structural <molecular level>, i.e., molecular weight, MWD,
chain architecture <branching, functional moieties>, thus
heavily model dependent and theoretically intensive
nonlinear aspects
b> a sub-field of polymer science fluid mechanics of polymers – numerically intensive
processing behavior
i. Fluid dynamics/mechanics - study flow behavior of simple <Newtonian> fluids in
complex geometries and complex flow conditions including turbulent flow and thermal convection.
ii. Polymer rheology- explore flow behavior of polymeric <viscoelastic/non-
Newtonian> fluids in simple geometries.
iii.Fluid mechanics of polymers <relevant to processing> - investigate flow behavior of viscoelastic polymeric liquidsin complex geometries
PART A RHEOLOGY AS CHARACTERIZATION METHODS
I. Phenomenological linear viscoelasticity
1. Mechanical deformations
a. Step strain
b. Startup flow
c. Small amplitude oscillatory shear <SAOS>
2. Linear responses
a. Elastic Hookean solids
b. Viscous Newtonian liquids
c. Viscoelastic Maxellian responses
3. Classical rubber elasticity
III. Rheometry
Shear - A combination of extension and rotation
1. Flow due to boundary displacement
a. Linear displacementi. Sliding parallel platesii. Co-cylinder piston
b. Rotational motioni. Parallel disksii. Cone-plateiii. Couette
2. Flow driven by pressure
a. Capillary die
b. Channel slit
Extension
1. Instron type stretcher
2. Extender at fixed length
PART B RHEOLOGY AS SCIENCE
IV. Phenomenological accounts
1. Shear thinning
2. Strain softening
3.Wave distortion
4. Extrudate swell
5. Melt fracture
V. Homogeneous flow
1. Basic principle for rheometry
2. Equivalence between controlled-rate and controlled-stress shear
3. Flow homogeneity in diffusion limit – terminal flow
4. Non-entangled and weakly entangled polymers
VI. Wall slip – a case of inhomogeneous shear
1. Spurt and flow oscillatory
2. Navier-de Gennes extrapolation length b
3. Stick-slip transition
a. capillary flow
b. drag flow
4. Theoretical accounts
a. limit of small surface coverage - Brochard-de Gennes theory
b. saturated adsorption –disentanglement picture
VII. Flow inhomogeneity – strongly entangled polymers
1. New considerations based on viscoelasticity concept
2. Cohesion of entanglement network
3. Elastic yielding
4. Scaling characteristics of stress overshoot – a moving target
5. Deformation-induced structural disintegration – yield phenomenon
6. Case studies
i. Startup shear
ii. Large amplitude oscillatory shear
7. Uniaxial extensional flow
VIII. Experimental Approaches
1. Conventional rheometry
a. Finite size effects
i. free surface at meniscus in rotational rheometryii. entry flow in capillary rheometryb. Improved setupsi. Cone-partitioned plate for shear ii. Counter-rotation drums for extension
2. Rheo-optical <in situ> methods
a. Flow birefringencei. Stress optical rule <SOR>ii.Breakdown of SOR
b. Scattering
c. Spectroscopy <NMR, fluorescence, IR, Raman, dielectric>
3. Particle tracking velocimetry。