Rheology

Introduction to Rheology:

Introduction to Rheology By: Vikramjit Singh Email: vicky_5593@yahoo.com Presented to:Dr.Nawazish Alam Department of pharmaceutics H.O.D, S.B.S. college of Pharmacy, Patti,tarn-taran 4/10/2011 1 vikramjit singh

What is Rheology?:

What is Rheology? Study of flow and deformation behavior of materials Examples: Liquid Foods: Flow of water, ketchup, mayonnaise, salad dressings etc. Solid Foods: Creep of apples, grains, cheese etc. 4/10/2011 2 vikramjit singh

Examples of Rheological Properties:

Examples of Rheological Properties Viscosity Power law parameters Elasticity Stress relaxation function Creep compliance function 4/10/2011 3 vikramjit singh

Applications of Rheology:

Applications of Rheology Geology and mining Concrete technology Soil mechanics Plastics industry Tribology (study of lubrication) Food industry 4/10/2011 4 vikramjit singh

Why we want to study rheology of Foods?:

Why we want to study rheology of Foods? Design/select equipment such as pumps, pipelines, extruders, mixers, heat exchangers etc. Rheological behavior relates to food texture and sensory data To determine ingredient functionality in product development Shelf life testing To obtain some information about atomic and molecular scale phenomena To obtain constitutive relations 4/10/2011 5 vikramjit singh

Two Extremes of Material Flow Behavior:

Two Extremes of Material Flow Behavior Most Foods Newtonian Liquids Elastic Solids 4/10/2011 6 vikramjit singh

Stress and Strain:

Stress and Strain Elastic Spring Force, F Area, A L  L 4/10/2011 7 vikramjit singh

SI Units of Stress and Strain:

SI Units of Stress and Strain Stress: Pa (N/m 2) Strain: ? 4/10/2011 8 vikramjit singh

Liquid Foods:

Liquid Foods h  L Force Area 4/10/2011 9 vikramjit singh

Dynamic Viscosity:

Dynamic Viscosity 1 centi-Poise = milli Pascal-second SI Unit: Pascal-second Shear stress Shear rate Lack of slipperiness Resistance to flow Interlayer friction 4/10/2011 10 vikramjit singh

Slide 11:

Typical Viscosities (Pa . s) Asphalt Binder --------------- Polymer Melt ----------------- Molasses ---------------------- Liquid Honey ----------------- Glycerol ----------------------- Olive Oil ----------------------- Water -------------------------- Acetic Acid -------------------- 100,000 1,000 100 10 1 0.01 0.001 0.00001 Courtesy: TA Instruments 4/10/2011 11 vikramjit singh

Measuring Viscosity:

Measuring Viscosity Rotational Viscometers (Low shear rates) Tube Viscometers (High shear rates) Pressure drop Flow Rate 4/10/2011 12 vikramjit singh

Different types of Fluids:

Different types of Fluids Shear stress Shear rate Newtonian Pseudoplastic (or Shear thinning) Dilatant (or Shear thickening) Bingham Plastic Casson Plastic Non Newtonian Fluids 4/10/2011 13 vikramjit singh

Newtonian Foods:

Newtonian Foods Shear stress Shear rate Examples: Water Milk Vegetable oils Fruit juices Sugar and salt solutions 4/10/2011 14 vikramjit singh

Pseudoplastic (Shear thinning) Foods:

Pseudoplastic (Shear thinning) Foods Shear stress Shear rate Examples: Applesauce Banana puree Orange juice concentrate Oyster sauce CMC solution 4/10/2011 15 vikramjit singh

Dilatant (Shear thickening) Foods:

Dilatant (Shear thickening) Foods Shear stress Shear rate Examples: Liquid Chocolate 40% Corn starch solution 4/10/2011 16 vikramjit singh

Bingham Plastic Foods:

Bingham Plastic Foods Shear stress Shear rate Examples: Tooth paste Tomato paste 4/10/2011 17 vikramjit singh

Mathematical Model:

Mathematical Model Herschel Bulkley Model: 4/10/2011 18 vikramjit singh

Model parameters for different types of fluids:

Model parameters for different types of fluids Shear stress Shear rate Newtonian Pseudoplastic (or Shear thinning) Bingham Plastic Casson Plastic Yield stress? 0<n<1 1<n n=1 4/10/2011 19 vikramjit singh

Importance of yield stress:

Importance of yield stress When stress is less than yield stress, material does not flow. It behaves like a solid Important for development of materials like butter, yogurt, cheese spread 4/10/2011 20 vikramjit singh

Pseudoplastic Foods:

Pseudoplastic Foods Their apparent viscosity decreases with increase in shear rate n<1 Shear Rate Apparent Viscosity Importance in Foods Mouth feel Design of pumps 4/10/2011 21 vikramjit singh

Slide 22:

Why Shear Thinning occurs Unsheared Sheared Aggregates break up Random coil Polymers elongate and break Anisotropic Particles align with the Flow Streamlines Courtesy: TA Instruments 4/10/2011 22 vikramjit singh

Slide 23:

Shear Thinning Behavior Shear thinning behavior is often a result of: Orientation of non-spherical particles in the direction of flow. An example of this phenomenon is the pumping of fiber slurries. Orientation of polymer chains in the direction of flow and breaking of polymer chains during flow. An example is polymer melt extrusion Deformation of spherical droplets to elliptical droplets in an emulsion. An industrial application where this phenomenon can occur is in the production of low fat margarine. Breaking of particle aggregates in suspensions. An example would be stirring paint. Courtesy: TA Instruments 4/10/2011 23 vikramjit singh

Viscoelasticity:

Viscoelasticity Viscous + Elastic www.uidaho.edu/~psingh 4/10/2011 24 vikramjit singh

What is Viscoelasticity?:

What is Viscoelasticity? Elasticity deals with mechanical properties of elastic solids (Hooke’s Law) Stress,   L Strain,  =  L/L  L E= / 4/10/2011 25 vikramjit singh

Theory of Hydrodynamics:

Theory of Hydrodynamics In Newtonian Fluids, Stress is proportional to rate of strain but independent of strain itself Newton’s Law 4/10/2011 26 vikramjit singh

Polymeric Materials:

Polymeric Materials Stress-Strain relations are more complex than what can be explained using Hooke’s law or Newton’s Law 4/10/2011 27 vikramjit singh

Energy Storage/Dissipation:

Energy Storage/Dissipation Elastic materials store energy Viscous materials dissipate energy t Energy Energy t E Viscoelastic materials store and dissipate a part of the energy t 4/10/2011 28 vikramjit singh

What causes viscoelastic behavior?:

What causes viscoelastic behavior? Long polymer chains at the molecular scale, make polymeric matrix viscoelastic at the microscale Reference: Dynamics of Polymeric Liquids (1977). Bird, Armstrong and Hassager. John Wiley and Sons. pp: 63. Energy Storage +Dissipation 4/10/2011 29 vikramjit singh

Examples of viscoelastic foods::

Examples of viscoelastic foods: Food starch, gums, gels Grains Most solid foods (fruits, vegetables, tubers) Cheese Pasta, cookies, breakfast cereals Almost all solid foods and fluid foods containing long chain biopolymers 4/10/2011 30 vikramjit singh

Viscoelasticity Experiments:

Viscoelasticity Experiments Static Tests Stress Relaxation test Creep test Dynamic Tests Controlled strain Controlled stress 4/10/2011 31 vikramjit singh

Stress Relaxation:

Stress Relaxation Universal Testing Machine Instron, TA XT2 Force sensor 4/10/2011 32 vikramjit singh

Stress Relaxation Test:

Stress Relaxation Test Time, t Strain Stress Elastic Viscoelastic Viscous fluid 0 Stress Stress Viscous fluid Viscous fluid 4/10/2011 33 vikramjit singh

Viscoelastic Models:

Viscoelastic Models Maxwell Model Kelvin-Voigt Model Used for stress relaxation tests Used for creep tests 4/10/2011 34 vikramjit singh

Why we want to fit models to viscoelastic test data?:

Why we want to fit models to viscoelastic test data? To quantify the data – mathematical representation For use with other food processing applications Some food drying models require viscoelastic properties Design of pipelines, mixing vessels etc., using viscoelastic fluid foods To obtain information at different test conditions Example: Extrusion To obtain an estimate of elastic properties and relaxation times Helps to quantify glass transition 4/10/2011 35 vikramjit singh

Maxwell Model:

Maxwell Model 4/10/2011 36 vikramjit singh

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Strain time Stress 0 time 0 4/10/2011 37 vikramjit singh

Slide 38:

Relaxation time is the time required by biopolymers to relax the stresses 4/10/2011 38 vikramjit singh

Slide 39:

time 0 Viscoelastic Liquids 4/10/2011 39 vikramjit singh

Viscoelastic Solids:

Viscoelastic Solids time 0 4/10/2011 40 vikramjit singh

Slide 41:

n Generalized Maxwell Model 4/10/2011 41 vikramjit singh

Dynamic Mechanical Thermal Analyzer (DMTA):

Dynamic Mechanical Thermal Analyzer (DMTA) 4/10/2011 42 vikramjit singh

Slide 43:

Courtesy: Dr. Osvaldo Campanella 4/10/2011 43 vikramjit singh

Slide 44:

Dynamic Mechanical Testing Response for Classical Extremes Stress Strain  = 0°  = 90° Purely Elastic Response (Hookean Solid) Purely Viscous Response (Newtonian Liquid) Stress Strain Courtesy: TA Instruments 4/10/2011 44 vikramjit singh

Slide 45:

Dynamic Mechanical Testing Viscoelastic Material Response Phase angle 0° < d < 90° Strain Stress Courtesy: TA Instruments 4/10/2011 45 vikramjit singh

Slide 46:

DMA Viscoelastic Parameters: The Complex, Elastic, & Viscous Stress The stress in a dynamic experiment is referred to as the complex stress  * Phase angle d Complex Stress ,  * Strain ,   * =  ' + i  " The complex stress can be separated into two components: 1) An elastic stress in phase with the strain.  ' =  *cos   ' is the degree to which material behaves like an elastic solid. 2) A viscous stress in phase with the strain rate.  " =  *sin   " is the degree to which material behaves like an ideal liquid. Courtesy: TA Instruments 4/10/2011 46 vikramjit singh

Slide 47:

DMA Viscoelastic Parameters The Elastic (Storage) Modulus: Measure of elasticity of material. The ability of the material to store energy. G' = (stress*/strain)cos  G" = (stress*/strain)sin  The Viscous (loss) Modulus: The ability of the material to dissipate energy. Energy lost as heat. The Complex Modulus: Measure of materials overall resistance to deformation. G* = Stress*/Strain G* = G’ + iG” Tan  = G"/G' Tan Delta: Measure of material damping - such as vibration or sound damping. Courtesy: TA Instruments 4/10/2011 47 vikramjit singh

Slide 48:

DMA Viscoelastic Parameters: Damping, tan  Phase angle  G* G' G" Dynamic measurement represented as a vector It can be seen here that G* = (G’ 2 +G” 2 ) 1/2 The tangent of the phase angle is the ratio of the loss modulus to the storage modulus. tan  = G"/G' "TAN DELTA" (tan  )is a measure of the damping ability of the material. Courtesy: TA Instruments 4/10/2011 48 vikramjit singh

Complex and Dynamic Viscosity:

Complex and Dynamic Viscosity The viscosity measured in an oscillatory experiment is a Complex Viscosity much the way the modulus can be expressed as the complex modulus. The complex viscosity contains an elastic component and a term similar to the steady state viscosity. The Complex viscosity is defined as: h * = h ’ - i h ” or h * = G*/ w 4/10/2011 49 vikramjit singh

Slide 50:

Courtesy: Dr. O. Campanella 4/10/2011 50 vikramjit singh

Slide 51:

Frequency Sweep: Material Response Terminal Region Rubbery Plateau Region Transition Region Glassy Region 1 2 Storage Modulus (E' or G') Loss Modulus (E" or G") log Frequency (rad/s or Hz) log G'and G" Courtesy: TA Instruments 4/10/2011 51 vikramjit singh

Dynamic Viscoelastic Properties of Soybeans:

Dynamic Viscoelastic Properties of Soybeans 9% M.C. Ref: Singh et al. (2001). Effect of Temperature and Moisture on Dynamic Viscoelastic Properties of Soybeans . Transactions of the ASAE. (accepted) 4/10/2011 52 vikramjit singh

Slide 53:

Dynamic Temperature Ramp or Step and Hold: Material Response Temperature Terminal Region Rubbery Plateau Region Transition Region Glassy Region 1 2 Loss Modulus (E" or G") Storage Modulus (E' or G') Log G' and G" Courtesy: TA Instruments 4/10/2011 53 vikramjit singh

Applications of rheology in pharmacy:

Applications of rheology in pharmacy Fluids Mixing Particle size reduction of dispersed system which shear emulsions or suspensions. Passage through orifice including pouring and packaging in bottle and passage through hypodermic needle,fluid transfer and flow through pipe. 4/10/2011 54 vikramjit singh

Semi-solids(applications):

Semi-solids(applications) Spreading and adhearence on skin Removal from jar of emulsion from tube. Capacity of solids to mix with misible liquids. Release of drug from the waste. 4/10/2011 55 vikramjit singh

Solids :

Solids Flow of powder from hopper into the dye cavity in tableting and capsulation. Packaging of powders or granular solids. A.PRODUCT DESIGNING: 1.Rheology of emulsions. 2.Rheology of suspensions. 3.Rheology of ointments and gels. Rheology of powders.( micromeritics ) 4/10/2011 56 vikramjit singh

B.PROCESSING:

B.PROCESSING Rheology considerations of material to ensure their proper mixing,i.e . a large impellar operating at low shear rate is required for shear thinning systems. 4/10/2011 57 vikramjit singh

MEASUREMENT OF THIXOTROPY:

MEASUREMENT OF THIXOTROPY A quantitative measurement of thixotropy Can be attempted in several ways. -the most apparent characteristic of a thixotropic system is the hysteresis loop formed by the up and down curves of the RHEOGRAM. 4/10/2011 58 vikramjit singh

DETERMINATION OF RHEOLOGICAL PROPERTIES.:

DETERMINATION OF RHEOLOGICAL PROPERTIES. Capillary rise method:includes 1.ostwald viscometer 2.ubbelholde suspended viscometer.(more viscous liquids) Falling and rising sphere viscometer Rotational viscometer:includes 1.cone and plate 2.cup and bob 4/10/2011 59 vikramjit singh

Rotational viscometers:

Rotational viscometers These intruments work on viscous drag exerted on a body when it is rotated on a fluid whose viscosity is to be determined. Advantage Wide range of shear rate can be determined. 4/10/2011 60 vikramjit singh

Cup and bob viccometer:

Cup and bob viccometer 2 types of intruments 1.couette type viscometers 2.searle type viscometers. STORMER VISCOMETER Bob rotates and the cup is stationary. 4/10/2011 61 vikramjit singh

Cone and plate viscometer.:

Cone and plate viscometer. This intrument essentially consist of a flat circular plate with a wide angle cone placed centrally above it. The rate of shear in revolutions per minute is increased and decreased by a selecter dial and the torque i.e.,the shearing stress produced on the cone is measured by reading on the indicator scale. 4/10/2011 62 vikramjit singh

Falling sphere viscometer :

Falling sphere viscometer It is a falling ball instrument which uses a short nearly vertical glass tube of large diameter and a close fitting ball of either steel or glass. A minimum falling time of 30sec. is used for best results. 4/10/2011 63 vikramjit singh

Rising sphere viscometer.:

Rising sphere viscometer. It is an instrument to study yield value of non- newtonian system. stroke’s equation similar to that use for a falling sphere instrument is use to determine the rate of shear or the rate of strain. 4/10/2011 64 vikramjit singh

Thankyou :

Thankyou For listening patiently…… Keep smiling…….. allways .!!! 4/10/2011 65 vikramjit singh