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

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

Concentration vs Viscosity Gum Concentration (%) 10 5 4 3 2 1 0.10 0.5 1.0 Viscosity (cP) ~ 10,000 cP ~ 5,000 cP ~ 300 cP

~ 50 cP ~ 18 cP ~ 5 cP ~ 1.9cP

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

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

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

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

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)

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

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

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

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

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

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

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

Schematic of Ostwald Viscometer

Zahn Viscometers (dripping orifice-type)

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

Nametre Viscometer Probe

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

Types of Flow Newtonian Non-Newtonian Pseudoplastic Thixotropic Dilatant Rheopectic

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)

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

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)

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)

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)

Types of Flow Newtonian Non-Newtonian Pseudoplastic Thixotropic Dilatant Rheopectic

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

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!

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

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

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

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

Gels & Gel Texture Typical Textures of Gels Brittle Elastic

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

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

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

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