Test 3- Rheology/Dispersed Systems

Question 1

Rheology

Answer 1

the study of deformation and the flow of matter

Question 2

Why study rheology?

Answer 2

1. understanding uniformity of liquid and semi-solid dosage forms
2. affects patient’s acceptability of the product
3. pharmaceutical manufacturing
4. needed to determine the type of packaging required

Question 3

viscosity

Answer 3

the resistance of a fluid to flow; the higher the viscosity, the greater the resistance

Question 4

How does viscosity relate to temperature?

Answer 4

they are inversely related

Question 5

Newtonian flow

Answer 5

the rate of flow of a liquid (G) was directly proportional to the applied force (F), where n is the viscosity

Question 6

Shearing

Answer 6

When the top layer of a cube is subjected to force, each lower layer moves with velocity directly proportional to its distance from the bottom layer

Question 7

Shear rate

Answer 7

the difference in velocity (dv) between the two planes of liquid separated by distance (dr); this is equivalent to flow rate; difference between moving plane and stationary phase

Question 8

Shear stress

Answer 8

force per unit area required to bring about the flow

Question 9

Liquids that demonstrate Newtonian flow

Answer 9

water, ethanol, glycerin (Pure liquids); syrup, normal saline, 5% dextrose (Molecular solutions)

Question 10

Non-Newtonian flow

Answer 10

the viscosity of non-Newtonian fluids changes under stress; can cause the fluid to get runnier or thicker

Question 11

3 types of non-Newtonian flow

Answer 11

1. Plastic flow
2. Pseudoplastic flow
3. Dilantin flow

Question 12

Plastic flow

Answer 12

-does not flow at low values of force
-when force reaches the yield value, the liquid will flow proportionate to the applied force
-the rheogram does not pass through the origin
-at stresses below the yield value, behaves like a solid
-e.g. semi-solid creams and ointments

Question 13

Pseudoplastic flow

Answer 13

-do not need to reach a yield value
-termed “shear thinning”
-as greater force is applied, the viscosity of the liquid decreases
-e.g. suspensions, liquid emulsions, hydrophilic polymers in aqueous solutions

Question 14

Shear thinning

Answer 14

the viscosity of a liquid decreases with increasing shear stress

Question 15

Dilantin flow

Answer 15

-viscosity increases as force applied increases
-termed shear thickening
-e.g. suspensions with high concentrations of undissolved solids (>40%) demonstrate dilantin flow

Question 16

Shear thickening

Answer 16

the viscosity of a liquid increases with increasing shear stress

Question 17

Solutions

Answer 17

mixtures of ions or small molecules that form a single phase that is homogenous down to the molecular level

Question 18

Disperse system

Answer 18

-consists of a disperse phase dispersed as particles or droplets throughout the continuous phase
-the solubility of the dispersed phase within the continuous phase is low

Question 19

Molecular solutions

Answer 19

-homogenous down to molecular level
- <1 nm
- e.g. syrups, elixirs, solutions for injection, nasal, otic, ophthalmic solutions
-solutes exhibit Brownian motion
-diffuse easily from an area of high concentration to an area of low concentration
-do not scatter light
-demonstrate Newtonian flow

Question 20

Colloidal

Answer 20

-Large MW compounds or aggregates of smaller MW compounds
-1nm to 0.5 micrometer
-e.g. gels and vehicles for suspensions
-exhibit Brownian motion
-diffuse from an area of high concentration to an area of low concentration
-scatter light
-exhibit non-Newtonian flow
-do not settle due to gravity

Question 21

Coarse dispersions

Answer 21

-contains particles large enough to see with the naked eye
- >5 micrometer
-e.g. suspensions, emultions, foams, aerosols
-too large to exhibit Brownian motion
-too large to diffuse
-scatter light
-exhibit non-Newtonian flow
-dispersed particles tend to aggregate (can cause stability issues)

Question 22

Brownian motion

Answer 22

random kinetic motion of particles

Question 23

Hydrophilic polymers

Answer 23

-large chains of macromolecules in solutions
-swell when they become hydrated (will increase the viscosity of solution)
-reform upon rest
-associations untangle upon shaking