Introduction to Viscometry and Rheology, Basics...

Introduction to Viscometry and

Rheology, Basics, Rotational

Testing

Basic Seminar

Applied Rheology

2

Contents

Definition of basic rheological parameters

Viscosity and elasticity

Deformation, shear stress and shear rate

Parameters changing viscosity

Temperature, time and pressure

Newtonian and Non-Newtonian flow behavior

Yield stress

Thixotropic and rheopectic flow behavior

3

(Spring) (Dashpot)

Real Systems


Viscosity and elasticity

Rotation and Oscillation Rotation and Oscillation

Viscosity Elasticity

4

Viscosity (dynamic) [Pa∙s]

Shear stress [Pa]

Deformation [-]

Shear rate [1/s].

Calculation of the dynamic viscosity

· =


5

y

A

F v

y

x

= F

A = Pa

N

m2

Force

Area =

= dv

dy =

d

dt =

m

s·m

1 s

·

= x y Distance

Displacement =

m

m



6

Viscosity Shear rate

Shear stress =

Torque Md · Shear factor A

Rotational speed · Shear factor M

= .

Definitionen rheologischer Größen Definition of basic rheological parameters


7

Definitionen rheologischer Größen

Experimental determination of the viscosity

Absolute Measurement

Relative Measurement

The geometry factors A and M can be calculated for the sensor

(Certificate from the manufacture)

The geometry factors A und M can not be calculated for the sensor

(e.q. Brookfield)


8

= Dynamic (shear-)viscosity [Pa∙s] = /

1 Pa∙s = 1000 mPa∙s

1 mPa∙s = 1cP (centi Poise)

= Shear stress [Pa]

= Shear rate [1/s]

Units of viscosity

.

.


9

= Kinematic Viscosity [mm2/s] = /

1 mm2/s = 1 cSt (centi Stokes)

= Density [kg/m3]

rel = Relative Viscosity [-] rel = 1/ 2

e.q. HAAKE-Unit

Units of viscosity


10

* = Complex

dynamic

(oscillatory-) viscosity [Pa∙s]

1 Pa∙s = 1000 mPa∙s

1 mPa∙s = 1 cP (centi Poise)

G* = Complex modulus [Pa]

= Angular frequency [rad/s]

i = Imaginary Unit (= -1)

* = G*/i∙

Units of viscosity


11

e = Extensional viscosity [Pa∙s] e = ( 22- 11)/

= Rate of deformation [1/s]

.

.

Units of viscosity


12

Contents


Temperature, time and pressure

13

Chem./physical composition = f ( S )

Temperature = f ( T )

Pressure = f ( p )

Shear rate = f ( )

Time = f ( t ) Shear time, relaxation time

Miscelaneous e.g. electric, magnetic fiel intensity

Viscosity should always be indicated togehter with the relevant influencing

parameters

Einflussgrößen auf die Viskosität

Viscosity is not a constant

e.q.: = 1,4 Pa∙s (20°C, 100 s-1, after 1 min pre-shear 200 s-1)

.


14

-20 -10 0 10 20

T [°C]

101

102

103

104

30 -30

At 20 °C: ( / )/ T = 0.0504 1/K

Temperature dependence of a mineral oil

Parameters changing viscosity [m

Pa∙s

]

15

Viscosity of fluids measured at 20°C

Water

Fruit juice, wine

Saccharose-solution

Coffee cream

Olive oil

Honey

Bitumen

Fluid Viscosity [mPa∙s]

1

2 - 5

6 (40 g in 100 ml Wasser)

10

100

10 000

100 000 000


16

Pressure depence of viscosity of cruede oil

0 100 200 300 400 500 600 700 800 900 1000 0.1

1.0

[P

as]

Viscosity curve at 15 bar

Viscosity curve at

atmosheric pressure

[1/s] .

Increase of the viscosity of 20 % with a

pressure increase of 15 bar


17

Contents

Newtonian and non-Newtonian flow behavior

18

log shear rate .

Slope of 1

Shear rate


The viscosity is not a

function of the applied

shear rate.

≠ f(

Newtonian flow behavior

Water

Mineral oil

Bitumen

log

vis

co

sit

y

log

sh

ear

str

ess

19

.

Viscosity curve: = f ( ) .

Shear rate


log shear rate .

Slope of 1

Slope > -0.82

Almost every polymer

containing fluid

(melts and solutions)

Shear thinning behavior

Shower gel

Skin cream

Mayonnaise

Aka pseudoplastic flow

behavior

log

vis

co

sit

y

log

sh

ear

str

ess

20

Dis-aggregation Deformation

Newtonsches und nicht-Newtonsches Fließverhalten

Shear thinning flow behavior

Orientation

Ridgid rods

Liquid crystal Polymeric fluids Emulsions Suspensions

Extension

Rest state

Sheared


Random coils Droplets Particles

21

Sedimentation

Storage,

shelf live

Transport

Producing paint

Applying paint

Consistency in

the can

Brushing,

spraying, rolling

Levelling

10-4

10-3

10-2

10-1

100

101

102

103

104

10-1

100

101

102

103

shear rates [1/s] .

Shear rates for different paint applications


vis

co

sit

y

[

Pa∙s

]

22

Applications and typical shear rates

10-6 - 10-4

10-6 - 10-4

10-1 – 101

100 – 102

101 – 102

101 – 102

101 - 103

101 - 104

103 - 104

Sedimentation

Phase separation

Levelling, running

Extrusion

Dip coating

Chewing

Pumping, stirring

Brushing

Spraying

Application .

Shear rate [s-1]


23

log shear rate .

Dilatant flow behavior

PVC-plastisol

Clay dispersions

Quicksand


log

vis

co

sit

y

log

sh

ear

str

ess

24

Contents

Yield stress

25

Shear stress

Yield stress

Microscopic picture

The yield stress 0 is the shear stress required , to

overcome elastic behavior and

obtain stationary flow behavior

26

Bingham flow behavior

shear rate .

0

Extrapolation of the flow curve

Mortar

Yield stress

log

vis

co

sit

y

log

sh

ear

str

ess

27

Plastic flow behavior

shear rate [1/s] .

0

Extrapolation of the flow curve

Chocolate

Tooth paste

Printing ink

Yield stress

log

vis

co

sit

y

log

sh

ear

str

ess

28

Flow behavior

Newton = ·

Bingham = 0 + ·

Shear thinning = K · n (n < 1) Ostwald de Waele

Plastic = 0 + K · n Herschel-Bulkley, Casson

Dilatant = K · n (n > 1)

.

.

.

.

.

Mathematic models

29

Fließverhalten

Overview

log shear rate

log

sh

ear

str

ess

. lo

g v

isco

sit

y

log shear rate .

Newtonian

Shear thinning

Dilatant

Plastic

Bingham

Flow behavior

30

Contents


31

Network-structure

Scherzeitabhängiges Fließverhalten

Decrease of viscosity as a function of time under shear

100% recovery as a function of time without shearing

Primary-Particles Agglomerates

Agglomerates

Thixotropy


32

Recording of initial state (low shear stress, shear rate or oscillation)

Disaggregation at constant shear rate (e.g. 100 1/s) until a constant level

is reached

Re-aggregation (low shear stress, shear rate or oscillation)


Determination

Ramp up, (peak hold) and ramp down

Hysteresis area as a measure for thixotropy

Time curve

Thixotropic-Loop


33


Time curve and structure recovery


Range 1

Initial State

Range 2

Disaggregation

Range 3

Reaggregation

time t

Rotation

(Oscillation)

0 .

Rotation

(Oscillation)

0 .

Rotation

>> 0 .

t1 t2

log

vis

co

sit

y

34


Thixotropic loop


shear rate [1/s] .

peak hold

• fresh building material

sh

ear

str

ess

vis

co

sit

y

35


Rheopexy


shear rate [1/s] .

• Dispersions with high concentration of solids (e.g. Latex)

Real Rheopexy is not observed often

double check whether an artifact is observed

sh

ear

str

ess

vis

co

sit

y

36

Flow behavior

Newtonian flow behavior: f ( )

Non-Newtonian Flow behavior: = f ( )

Bingham (yield stress)

Shear thinning (pseudoplastic)

Plastic (yield stress)

Dilatant (shear thickening)

Time dependant flow behavior: = f (t, )

Thixotropy

Rheopexy

.

.

.

Conclusions

37

Any Questions?

Thank you for your attention!

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