Presentación de PowerPoint - Nanbiosis · 2017. 12. 14. · Creep > 0 Recovery = 0 (after steady...
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Creep > 0 Recovery = 0 (after steady state) Recoverable strain Introduction Rheology is the science that studies flow and deformation of materials under the effect of an applied force Flow Oscillation Creep and recovery Viscosity () is the “ resistance to flow”. depends on shear rate. Creep: slow deformation of a material, usually measured under a constant stress. The creep test gives a measure of elastic, viscoelastic and viscous components. The compliance is defined as the ratio of the strain to the applied stress (J ). Oscillatory measurements are used to measure the viscoelastic properties of a material. A stress or strain is applied and the corresponding response (strain or stress) is measured. Ideal solids They flow. The energy is dissipated in the form of heat. The energy required for the deformation is fully recovered when the stresses are removed. reversibly Deform Ideal liquids irreversibly Geometries Rheology applications Yield stress Some samples require a certain stress to flow. Thixotropy Bingham (Newtonian with yield) Bingham Plastic (shear thinning with yield) Pseudo-plastic (shear thinning) Newtonian Dilatant (shear thickening) Shear rate (1/s) . Thixotropy is a time - dependent shear thinning property, which is used to characterize structure change reversibility. : stress (Pa) ሶ : shear rate (1/s) : Viscosity: (Pa·s) Storage Modulus G’ (Elastic parameter) Loss Modulus G” (Viscous parameter) tan ′ = ∗ cos " = ∗ sin tan = " ′ Complex Modulus G* A strain sweep is used to measure the linear viscoelastic region (LVR). From a strain sweep cohesive energy (CE) can be calculated to determine stability. The larger the cohesive energy the more stable is the sample. ∗ = ′ + " G’ = References Ge l point : represents the point where behaviour changes from viscous (liquid- like) to elastic (solid-like). Quality control of polymers Improvement of the processing behaviour Optimization of the end product = 1 2 ′ 2 The greater the compliance the more the material can be strained under the application of a certain shear stress. (1) H.A. Barnes, J. F. Hutton, K. Walters F.R.S.,An Introduction to Rheology, Elsevier, Amsterdam, 1993. (2) F. Chambon, J. Winter, J. Rheol. 3 (8), 683-697, 1987. (3) www. tainstruments.com. Yield stress ( ) Stress Bingham (Newtonian with yield) Bingham Plastic (shear thinning with yield) Pseudo-plastic (shear thinning) Newtonian Dilatant (shear thickening) Shear rate ሶ (1/s) Viscosity (Pa·s) = ሶ Concentric cylinders Very low to medium viscosity Cone and plate Very low to high viscosity Parallel plates Low viscosity to soft solids Storage Transport Sedimentation Sagging Levelling Dipping Pouring Mixing Roller coating Spraying Extrusion Pumping Brushing High Low Viscosity 10 -6 1 10 6 Shear rate Deform at rest under shear Viscosity of different processes vs shear rate
Transcript of Presentación de PowerPoint - Nanbiosis · 2017. 12. 14. · Creep > 0 Recovery = 0 (after steady...
Creep > 0 Recovery = 0 (after steady state)
Recoverable strain
IntroductionRheology is the science that studies flow and deformation of materials
under the effect of an applied force
Flow
Oscillation
Creep and recovery
Viscosity () is the “resistance to flow”.
depends on shear rate.
Creep: slow deformation of a material, usually
measured under a constant stress. The creep test
gives a measure of elastic, viscoelastic and viscous
components.
The compliance is defined as the ratio of the
strain to the applied stress (J ).
Oscillatory measurements are used to measure the viscoelastic properties of a material. A stress or strain is applied and
the corresponding response (strain or stress) is measured.
Ideal solids
They flow. The energy is dissipated in the form of heat.
The energy required for the deformation is fully recoveredwhen the stresses are removed.
reversiblyDeform
Ideal liquids irreversibly
Geometries
Rheologyapplications
Yield stress
Some samples require a certain
stress to flow.
Thixotropy
Bingham (Newtonian with yield)
Bingham Plastic (shear thinningwith yield)
Pseudo-plastic (shear thinning)
Newtonian
Dilatant (shear thickening)
Shear rate (1/s).
Thixotropy is a time-dependent shear thinningproperty, which is used to characterize structure change
reversibility.
: stress (Pa)
ሶ𝛾: shear rate (1/s)
: Viscosity: (Pa·s)
Storage Modulus G’(Elastic parameter)
Loss Modulus G”(Viscous parameter)
tan
𝐺′ = 𝐺∗ cos 𝛿
𝐺" = 𝐺∗ sin 𝛿
tan 𝛿 =𝐺"
𝐺′
Complex Modulus G*A strain sweep is used to measure the linear
viscoelastic region (LVR).
From a strain sweep cohesive energy (CE)can be calculated to determine stability.
The larger the cohesive energy
the more stable is the sample.
𝐺∗ = 𝐺′ + 𝑖𝐺"
G’
𝐽 =𝑆𝑡𝑒𝑎𝑑𝑦 𝑠𝑡𝑎𝑡𝑒 𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑎𝑏𝑙𝑒 𝑠𝑡𝑟𝑎𝑖𝑛
𝑠𝑡𝑟𝑒𝑠𝑠
References
Gel point : represents the point where
behaviour changes from viscous (liquid-
like) to elastic (solid-like).
Quality control of polymers
Improvement of the processing behaviour
Optimization of the end product
𝐶𝐸 =1
2𝐺′𝛾𝑐
2
The greater the compliance the more the
material can be strained under the application of
a certain shear stress.
(1) H.A. Barnes, J. F. Hutton, K. Walters F.R.S., An Introduction to Rheology, Elsevier, Amsterdam, 1993.
(2) F. Chambon, J. Winter, J. Rheol. 3 (8), 683-697, 1987.
(3) www. tainstruments.com.
Yie
lds
tre
ss
()
Stress
Bingham (Newtonian with yield)
Bingham Plastic (shear thinning with yield)Pseudo-plastic (shear thinning)
Newtonian
Dilatant (shear thickening)
Shear rate ሶ𝜸 (1/s)
Vis
co
sit
y
(Pa
·s)
=𝜎
ሶ𝛾
Concentric
cylinders
Very low to
medium viscosity
Cone and
plate
Very low to high
viscosity
Parallel
plates
Low viscosity to
soft solids
Storage Transport
SedimentationSagging
Levelling
DippingPouring Mixing
Roller coating
Spraying
ExtrusionPumpingBrushing
High
Low
Vis
cosi
ty
10-6 1 106
Shear rate
Deform
at rest under shear
Viscosity of different processes vs shear rate
