Rheology

Question 1

change in shape or apparent size /dimension of an object or substance under the influence of an applied stress

Answer 1

Deformation

Question 2

the continuous deformation of a liquid on an unconfined surface (spreading ) or through a confined system (tubes) or through an orifice under the influence of an active stress

Answer 2

Flow

Question 3

the load beyond which the material no longer behaves elastically.

Answer 3

Elastic limit

Question 4

Why is perfect elastic deformation is difficult to attain

Answer 4

because 100% recovery of an object’s dimensions following a stress may not be feasible.

Question 5

What is Strain Hardening used for

Answer 5

used in industries to strengthen metals and polymers.

Question 6

What is the name given to spaces that metal atoms undergoing deformation are forced to move and occupy

Answer 6

Defects

Question 7

How is the energy exerted in plastic deformation used

Answer 7

most of the energy given to a solid is given off as heat, while only a small part is used in changing its dimensions.

Question 8

the study of the flow properties of fluids (liquids and semi-solids).

Answer 8

Rheology

Question 9

Who suggested the term Rheology

Answer 9

Bingham and Crawford.

Question 10

What is the order of flowability of linear branched and cross linked molecules

Answer 10

Linear > Branched molecules >cross-linked molecules

Question 11

What factors affect flow of fluids

Answer 11

Viscosity
Magnitude of stress
Temp
Molecular chain characteristics of fluid

Question 12

What is the relationship btn viscosity and flow

Answer 12

𝑉𝑖𝑠𝑐𝑜𝑠𝑖𝑡𝑦 ∝ 1/𝑟𝑎𝑡𝑒 𝑜𝑓 𝑓𝑙𝑜𝑤

Question 13

Shear rate( D) formula and unit

Answer 13

D= 𝑣𝑓/H

ms-1/m or s-1

Question 14

Shear stress(τ) formula and unit

Answer 14

τ=𝐹/𝐴

Newton per metre square ( Nm-2) or the Pascal (Pa)

Question 15

Dynamic viscosity(ŋ) formula and unit

Answer 15

ŋ = τ/D

Nm-2s or Pascal seconds (Pas)

Question 16

Kinematic viscosity (v) formula and unit

Answer 16

V = ŋ/ρ

Shear stress/ density

The SI units of v is m2s-1

Question 17

Relative viscosity formula and definition

Answer 17

ŋr = ŋsol/ŋs

the ratio of the solution viscosity to solvent viscosity

IT HAS NO UNITS

Question 18

Specific viscosity(ŋsp) formula

Answer 18

ŋsp= ŋsolute/ ŋs

the ratio of solute viscosity (ŋsolute) to that of the solvent (ŋs )

Question 19

What is the relationship between specific viscosity and relative viscosity

Answer 19

ŋsp= ŋr -1

Question 20

What are the three formulas in intrinsic viscosity

Answer 20

1.Einstein’s colloidal equation
𝜂𝑠𝑜𝑙 = 𝜂𝑠 (1 + 2.5∅)

∅= volume fraction of colloidal phase

2. ŋsp/c=k

ŋsp/c is the viscosity number, c= concentration

3. Intrisic viscosity is the y-intercept if a graph is specific viscosity against concentration

Question 21

Units😢

Answer 21

Dynamic
Pas
Dyn cm-2 s
Poise (P)=0.1 Pas

Kinematic
m2 s-1
Cm2 s-1
Stoke (St) = 10- 4m2s-1

Question 22

What Liquids whose flow characteristics are in consonance with Newton’s law of flow ( shear stress is proportional to shear rate)

Answer 22

Newtonian liquids or systems

Question 23

Give egs of Newtonian liquids

Answer 23

Castor oil-1000

Chloroform-0.563

Ethyl alcohol-1.19

Glycerin 93%-400

Olive oil-100

Water-1.0019

Question 24

They are heterogeneous solutions of solids in liquids as such, most pharmaceutical liquid dosage and don’t obey Newton’s law of flow

Answer 24

non-Newtonian liquids

Question 25

How can you find dynamic viscosity in a Rheogram

Answer 25

Inverse of the slope

The slope is flowvity of the material

Question 26

What are plastic systems

Answer 26

concentrated suspensions containing flocculated Particles that are held by Van der Waal forces.
A plastic material does not flow until a minimum force sufficient to overcome the Van der Waal forces is applied

Question 27

What is yield value in plastic flow liquids

Answer 27

Minimum force needed to over come the van der waal forces

Question 28

How do you determine plastic viscosity

Answer 28

Reciprocal of the slope ( mobility)

Equation
U= F -f/D

F=Applied stress in dynes/cm2
f= yield value in dynes/cm2
D= shear rate in s^-1

Question 29

What polymers exhibit pseudoplastic flow

Answer 29

Acacia
dispersions of tragacanth, 
methyl and ethyl cellulose, 
sodium alginate and 
carboxymethyl cellulose.

Question 30

In pseudoplastic system The degree of alignment and the corresponding decrease in viscosity depend on what

Answer 30

Magnitude of stress

Question 31

The viscosity determined at a given shear stress and shear rate of pseudoplastic system

Answer 31

apparent viscosity of the pseudoplastic material.

Question 32

Pseudoplastic liquids have different viscosity at different rates and how does this affect its rheogram diagram

Answer 32

The reogram will have no linear portion and therefore the liquid can’t be described by a single viscosity material

Question 33

What is dilatant flow

Answer 33

Flow of suspensions with high solid fraction. When stress it applied they form spaces and flow
After they loss lubrication and flow reduces

Question 34

What is shear thickening materials exhibit it

Answer 34

When a particle under force flows but loses its lubrication later making the flow reduce

Question 35

What is the relationship btn shear stress and viscosity of a dilatant flow

Answer 35

Viscosity increases with increasing shear stress

Question 36

What is thixotropy

Answer 36

Slow recovery of consistency lost as a result of shearing

It forms a hysteresis loop on its rheogram

Question 37

What is importance of thixotrophy in pharmacy

Answer 37

Preparations that are thixotrophic settle down slowly after agitation( therefore accurate dose can be taken)
But non thixotrophic settle rapidly

Question 38

What structures are being talked about in plastic pseudoplastic and dilatant

Answer 38

Plastic- flocculated suspensions