Interfacial Phenomena

Question 1

What is an interface?

Answer 1

a boundary between phases

Question 2

What do interfacial phenomena affect?

4

Answer 2

1. absorption onto solid adjuncts
2. penetration through biological membranes
3. emulsion formulation
4. dispersion (suspensions)

Question 3

Interfacial/surface tension definition

Answer 3

the force that must be applied parallel to the surface to counteract the net inward pull

dyne/cm

Question 4

Interfacial tension

Answer 4

liquid-liquid interfaces

Question 5

Surface tension

Answer 5

liquid-vapor or solid-vapor interfaces

Question 6

Surface free energy

Answer 6

work done in increasing the surface area

Question 7

cohesion

Answer 7

attraction between like substances

Question 8

adhesion

Answer 8

attraction between unlike substances

Question 9

Meaning of spreading coefficient

Answer 9

positive: spreading occurs (free energy of new surface interface is lower than free energy of old surface)
negative: spreading does not occur

Question 10

L2 = gamma D t / 4 n

Answer 10

cookie dunking optimization

Question 11

When do we use spreading coefficients in pharmacy?

3

Answer 11

1. topicals
2. emulsions
3. other liquids

Question 12

Positive adsorption

Answer 12

molecules move toward the surface interface

Question 13

Negative adsorption

Answer 13

molecules move toward the bulk

Question 14

Where are surface active agents used in pharmacy?

3

Answer 14

1. emulsions
2. suspensions
3. foams

Question 15

oil in water (o/w) emulsion examples

Answer 15

Noxema, Eucerin

Question 16

water in oil (w/o) emulsion examples

Answer 16

Lanolin, Nivea

Question 17

Hydrophile-lipophile balance (HLB)

Answer 17

describes surfactants (higher –> hydrophilic)

one surfactant’s HLB should be higher and one surfactant’s HLB should be lower than the RHLB (required HLB)

Question 18

Pharmaceutical relevance of solid-liquid adsorption?

2

Answer 18

1. tablet wetting

2. activated charcoal for overdoses

Question 19

What is the most important action of a wetting agent?

Answer 19

lowering the contact angle

Question 20

Wettability of tablet surfaces influences what?

3

Answer 20

1. disintegration
2. dissolution
3. subsequent release

Question 21

lower contact angle, higher work of adhesion –> better wetting

Answer 21

:)

Question 22

Where are surfactants used in pharmacy?

5

Answer 22

1. emulsions
2. suspensions
3. creams/ointments/lotions
4. antibacterials (are themselves a drug agent)
5. aid absorption