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Seminar on rheology

Guideline to 45 minutes

complete rheological characterization

2

45 minutes complete rheological characterization

Oscillation amplitude sweep

Oscillation frequency sweep

Creep and recovery

Yield point test

Thixotropic loop

Steady state viscosity curve

3

Oscillation amplitude sweep

Start stress

End stress

Frequency

Distribution

Approx. 2 minutes

CS sweep

4

Oscillation amplitude sweep – Test 1

lg Tau (Pa)

lg M

odulu

s (

Pa)

Non-linear behavior Depends on used frequency

The slope of the curve gives

information about the MWD or if the

structure breaks at once or partially

The steeper the slope, the narrower

the MWD. For a structured product

the bonds are breaking all on the

same force.

Higher values for G’ and G” show that

the product has a higher ηo value.

A higher ηo value means a high Mw or

longer structures.

5

Oscillation frequency sweep

Mode

Stress / deformation

Start frequency

End frequency

Distribution

Approx. 15 minutes

6

Oscillation frequency sweep – Test 2

A cross-over point at lower frequency means

a higher Mw and that the product is less

elastic at higher impact

A higher modulus at the

cross-over point indicates a

narrower MWD lg M

odulu

s (

Pa)

lg Frequency (Hz)

7

Creep and recovery

Stress

Duration

Approx. 10 minutes

Break criteria

8

Creep and recovery – Test 3

The amount

of recovery is

related to the

amount of

creep in the

sample

A steeper line means more

deformation in time, so ηo is lower

lower Mw

more sagging

The faster the structure

recovers, the shorter the

relaxation time.

De

form

ation

(-)

Time (s)

9

Yield point

Start stress

End stress

Distribution

Duration

Approx. 3 minutes

Break criteria

10

Yield point – Test 4

lg Tau (Pa)

lg D

efo

rma

tio

n (

-)

At low forces only

deformation in the LVR

occurs.

At high forces a

flow is obtained.

The point from deformation in the LVR

towards flow is the Yield point.

A higher Yield point means:

Less sagging

Less leveling

More resistance to flow

11

Thixotropy loop

Start shear rate

End shear rate

Distribution

Duration

Approx. 2 minutes

12

Thixotropy loop – Test 5

Shear Rate (1/s)

Sh

ea

r S

tre

ss (

Pa

)

The bigger the area the more

thixotropic (time dependent) behavior.

Note : there is no information about

the time of recovery and if the product

recovers to its initial state.

13

Structure recovery – Test 6

Partial recovery G’>G” : elastic behavior

Structure is rebuild and material will behave

solid like again (no flow)

Initial state

Faster recovery means:

Less sagging

Less leveling

Sharper dots (printing)

Oscillation Oscillation Rotation

14

Comparison of the tests

Overview of the obtained results:

If we look at the blue and red sample the next conclusions could be made:

Red Test Results Blue

Low Test 1: LVR High

Low Test 1 + 4: Yield Point High

Low/short Test 1, 2 + 3: Mw <-> length of structure High/long

High Test 1 + 2: MWD <-> difference in bond strength Low

Long Test 3: Relaxation time Short

Low Test 1 + 3: Zero shear viscosity High

Long Test 6: Thixotropic recovery time Short

The red sample could be a paint, we need

leveling, a yield point to be stable and a

longer thixotropic behavior. With those

habits the paint is good for application and

as result a flat smooth surface is obtained

The Blue sample could be an offset ink, we do not

want leveling, we need a high yield point to be

stable and a short thixotropic behavior. With those

habits the ink is good for application and as result

sharp dots are obtained

15

Steady state viscosity curve

Start shear rate

End shear rate

Distribution

and ….

Approx. 3 - 35 minutes

16

… Equilibrium definition

= 45 minutes

Steady state viscosity curve

17

Thank you for your attention

Any questions ?