Rheology

Question 1

Study of flow or deformation of matter under influence of stress

Answer 1

Rheology

Question 2

Resistance of a fluid to flow

Answer 2

Viscosity (η)

Question 3

Internal friction in the fluid

Answer 3

Viscosity

Question 4

Unit of Viscosity

Answer 4

Poise/ Centipoise
Stokes/ Centistokes

Question 5

Force applied per unit area required to bring about flow

Answer 5

Shear Stress (F)
Unit: dyme/cm2

Question 6

The velocity gradient between two planes of a body that are separated by a small distance

Answer 6

Rate of Shear (G)

Question 7

Reciprocal of viscosity

Answer 7

Fluidity

Question 8

Types of Flow

Answer 8

• Absolute Viscosity
• Kinematic Viscosity
• Relative Viscosity

Question 9

Fluid in which there is direct proportionality betwen shear stress and shear rate.

Answer 9

Newtonian Flow

Question 10

Viscosity stays ________ as the applied force changes

Answer 10

Viscosity stays constant as the applied force changes

Constant viscosity with Increasing rate

Question 11

Kinematic Viscosity

Answer 11

Kinematic Viscosity = Absolute Viscosity / Density

Unit: Stokes

Question 12

Ratio of viscosity of dispersion to that of solvent

Answer 12

Relative Viscosity

Unitless

Question 13

Fluids with no direct linear relationship between shear stress and shear rate

Answer 13

Non-Newtonian Flow

Question 14

Time-Independent / Shear-Dependent

Answer 14

Plastic Flow
Pseudoplastic Flow
Dilatant Flow

Question 15

Time-Dependent Non-newtonian Flow

Answer 15

Thixotropy
Rheopexy

Question 16

Aka Bingham Bodies

Answer 16

Plastic Flow

Question 17

No flow occurs in response to shear stress until a certain transition point is reached

Answer 17

Plastic Flow

Above the Yield Value, they behave as Newtonian Systems (Bingham Flow)

Question 18

Minumum shear stress required by the system before it deform and begins to flow

Answer 18

Yield Value

Question 19

Examples of Plastic Flow

Answer 19

Suspensions
Gels, Ointments, Pastes, Creams
Cataplasm cerates
Butter, Margarine

Question 20

Pseudoplastic Flow

Answer 20

Shear-Thinning System

Question 21

Liquids become thinner on the application of stress

↑ shear stress; ↓ viscosity

Answer 21

Pseudoplastic flow

Question 22

Examples of Pseudoplastic Flow

Answer 22

Gums, tragacanth, Na alginate, methyl cellulose
Aqueous Solution of Polymers (CMC, HPMC in Water)

Question 23

Dilatant Flow

Answer 23

Shear-Thickening Flow

Question 23

Dilatant Flow

Answer 23

Shear-Thickening Flow

Question 24

Liquids become **thicker**, or flow with **increased resistance** with application of **stress** ↑ shear stress; ↑ viscosity

Answer 24

Dilatant Flow

Question 25

Examples of Dilatant Flow

Answer 25

Whipcream Corn starch Susp High Solid Content Suspension Paint Susp

Question 26

**Gradual decrease** of the viscosity under *constant shear stress* followed by **gradual recovery** when the **stress is removed**

Answer 26

Thixotropy

Question 27

Reversible and isotherma transformation of **gel to sol**

Answer 27

Thixotropy | Shaking: Sol Standing: Gel

Question 28

**Increased viscosity** with time under constant **shear rate/stress**, followed by gradual **recovery** when the **stress/rate is removed**

Answer 28

Rheopexy | Sol-Gel Formation Shaking: Gel Standing: Sol

Question 29

Factors affecting Viscosity

Answer 29

↑ temp, ↑ η (Gases) ↑ MW, ↑ η + organic substance, ↑ η ↑ Dispersed Phase Content, ↑ η Spherical Shape ↓ η ↑ temp, ↓ η (liquids) + electrolytes, ↓ η

Question 30

Measurement of Viscosity

Answer 30

**A. Single Shear Rate Instruments** - used for Newtonian 1. Capillary Viscometer (Ostwald) 2. Falling Sphere (Hoeppler) **B. Multipoint, Rotational Instruments** - both 1. Cup & Bob (Coutte, Mac Michael, Searle ‘Brookefield –rotating spindle/ Bob’ ) 2. Plug Flow 3. Cone & Plate (Ferranti-Shirley) Others: Penetrometers - Ointment