1. Lecture XII Solutions/Gels Rheology/Texture
Lecture #12 - Solutions & Gels; Rheology/Texture of gum systems

2. Introduction/Rheology of Polysaccharides I
PS Functions
Provide viscosity
Gelation
PS Terminology
Starch vs other PSs
Usage levels

3. Concentration vs Viscosity
Gum Concentration (%) 10 5 4 3 2 1
Viscosity (cP)
~ 10,000 cP
~ 5,000 cP
~ 300 cP

4. ~ 50 cP
~ 18 cP
~ 5 cP
~ 1.9cP

6. Rheology Definitions I
Science of Flow and Deformation
Liquids
Gels/semisolids
Properties
Stress
Strain
Time effects

7. Rheology Definitions II
Stress
Intensity of force components
Units = force/area
Strain
Change in size or shape
Nondimentional (a ratio)
Time effects
Impt in describing rates

8. Rheology Definitions III
Viscoelasticity
Viscous elements
Elastic elements
Modes of Deformation
Elastic
Plastic
Viscous

9. Rheology Definitions IV
1 meter/sec
1 sq. meter
1 Newton (force)
liquid
1 meter
back
1 sq. meter
front
Diagram for Rheological Definitions

11. Rheology Definitions V
Shear Stress (t) = Force required to move
a given area of the fluid
(Units = Newtons/m2, aka Pascals)
Shear Rate ( ) = velocity diff between plates
distance between plates
(Units = sec-1 (1 m/sec/m of fluid))  .
Viscosity (h) = ratio of shear stress/shear rate
(Units = Newton•sec/m2, or Pascal•seconds)

12. Viscosity Units
Viscosity (h or m) = ratio of shear stress/shear rate
(Units = Newton • sec/m2, or Pascal seconds)
Another common unit of viscosity = the Poise (dyne • sec/cm2).
1 centiPoise = 1 milliPascal • sec
(1 cP = 1 mPa • s) or
1000 cP = 1 Pa • s

13. Importance of Rheology
Evaluate performance of liquids
Suspension
Mouthfeel
Flow characteristics (pumping, spraying, painting, etc)
Ability to cling/coat
Choose proper polymer to modify rheology of system

14. Importance of Rheology A Suspension Example
Oil field fluids
Used to transport solids
Used to suspend solids
Stokes Law
V = 2r2g D r 9m
V = velocity of particle
movement
r = radius of particle
g = force of gravity
Dr = difference in density
m = viscosity

15. Rheology Measurement Viscometers and rheometers I
Rotational (Haake, Hercules, Brookfield)
Tube (capillary, orifice, pipe)
Oscillatory
Falling ball
Rising bubble

16. Brookfield Viscometers (courtesy of Brookfield)
Rheology Measurement
Brookfield Viscometers (courtesy of Brookfield)

17. Schematic of cone & plate viscometer
Rheology Measurement
Viscometers and rheometers I
Rotational (Ferranti-Shirley)
Schematic of cone & plate viscometer

18. Rheology Measurement Viscometers and rheometers II Rotational
Tube (capillary, orifice, pipe)
Oscillatory
Falling ball
Rising bubble

19. Schematic of Ostwald Viscometer

20. Zahn Viscometers (dripping orifice-type)

21. Rheology Measurement Viscometers and rheometers II Rotational
Tube (capillary, orifice, pipe)
Oscillatory (Nametre Viscometer) Falling ball
Rising bubble

22. Nametre Viscometer Probe

23. Simple falling-ball viscometer (note glass marble falling through liquid)

24. Types of Flow Newtonian Non-Newtonian Pseudoplastic Thixotropic
Dilatant
Rheopectic

25. Types of Flow Newtonian Newtonian fluids include:
Water & watery beverages such as tea, coffee, beer, carbonated beverages, sugar syrups honey, edible oils, filtered juices, milk
Idealized representation of Newtonian solution rheology: viscosity as a function of shear rate and time (CHO Chem-Whistler & BeMiller)

26. Types of Flow Newtonian Non-Newtonian (e.g., most gum “solutions”)
Pseudoplastic
Thixotropic
Dilatant
Rheopectic

27. Types of Flow Non-Newtonian Pseudoplastic
Idealized representation of pseudoplastic solution rheology: viscosity as a function of shear rate and time (CHO Chem-Whistler & BeMiller)

28. Types of Flow Non-Newtonian Thixotropic
Idealized representation of thixotropic solution rheology, showing time dependence of the viscosity change with a change in shear rate. (CHO Chem-Whistler & BeMiller)

29. Types of Flow Non-Newtonian Effect on Mouthfeel
Effect of shear rate on apparent viscosity of gum solutions. Group C = very slimy; Group B = somewhat slimy; Group A = nonslimy (From Szczesniak & Farkas, 1962)

30. Types of Flow Newtonian Non-Newtonian Pseudoplastic Thixotropic
Dilatant
Rheopectic

31. Types of Flow Non-Newtonian Rheopectic Viscosity Time Rheopectic
Thixotropic
Time
Viscosity
Newtonian

32. Gels & Gel Texture What is a Gel?
A continuous, 3-dimensional network of connected molecules or particles, entrapping a large volume of a continuous phase
Gels have both liquid & solid characteristics - wide variety of textures!

33. Gels & Gel Texture Requirements for HC Gel formation Types of HC Gels
Controlled “precipitation”
Examples
Types of HC Gels
H-Bonded
Ionic
Hydrophobic
Melting
Non-Melting

34. OK NOT OK IN / OUT / GELLED
Three Possible States for Gelling Hydrocolloids
IN SOLUTION
(Dissolved, Hydrated)
NOT OK OK
GELLED
(Half in & Half out of Solution)
OUT OF SOLUTION
(precipitated, dried)
Complements of Mr. Andy Hoefler

35. Gel Formation 1. Cool hot HC solution 2. Add specific ions
3. Cool hot solution w/ ions added
HC Solution
junction zones
Gel

36. Gels & Gel Texture Requirements for HC Gel formation Types of HC Gels
Controlled “precipitation”
Examples
Types of HC Gels
H-Bonded
Melting
Ionic
Non-melting
Hydrophobic

37. Gels & Gel Texture
Typical Textures of Gels
Brittle
Elastic

38. Gel Texture Testing Gel Strength TPA - Texture Profile Analysis
Modulus
Hardness
Brittleness
Elasticity
Cohesiveness

39. The Bloom Gelometer. (Courtesy of Precision Scientific Co.)

40. Texture Profile Analysis I
Area 1
Area 2
Hardness
FORCE
CYCLE #1
Down Up
CYCLE #2

41. Texture Profile Analysis II
Modulus
Cohesiveness =
Area 1
Area 2
Hardness
FORCE
Elasticity
Brittleness
CYCLE #1
Down Up
CYCLE #2