Interfacial Phenomena 1

Question 1

Relationship of surfactants to interface

Answer 1

Surfactants stabilise interface by reducing surface free energy

Question 2

Interface Def

Answer 2

boundary between 2 distinct forms of matter (2 phases)

Question 3

What type of molecule interaction is the lowest energy

Answer 3

Molecules of the same type. Requires a lot of energy to break

Question 4

Relationship between the size of an interface and it’s characteristics on dosage form

Answer 4

Larger interface = larger influence on restof dosage form

Question 5

Water bonding at interface with air

Answer 5

Water molecules don’t bond with air molecules (requires too much energy). Water molecules only form bonds with water molecules below and horizontally beside them. Due to molecules not forming as many bonds as in bulk there’s free energy that isn’t used.

Question 6

Free Energy Def

Answer 6

Energy in the system that is used to do work.

Question 7

Relationship between no of interfaces and amount of free energy

Answer 7

Increased no of interfaces = increased free energy = more thermodynamically unstable

Question 8

Where is the most energy in a disperse system

Answer 8

At the interface. Bul = lower energy. Particles fall out of solution = decreasing interfaces = decreasing system energy

Question 9

Attractive forces between molecules at interface and molecules in bulk

Answer 9

Due to most molecules being in bulk of phase molecules at interface don’t have many molecules around them. Molecules at interface experience attractive forces towards molecules in bulk (bonds wanting to be formed). Water contracts away from air (and retreats into bulk). More bonding betweeen molecules (due to attractive forces) = lower free energy (spontaneous reaction)

Question 10

Consequences of water molecules contracting away from interface

Answer 10

Strength of horizontal = increase in surface tension

Question 11

How to decrease surface tension at interface

Answer 11

Add a surfactant. Hydrophilic component holds water in place while hydrophobic component stays in vapour/gas phase (binds with it). Prevents contraction of water into bulk = decreasing of strength of horizontal bonds = decreased surface tension

Question 12

Surface Free Energy Def

Answer 12

Work required to increase substance surface area by 1m^2. Increase in surface area of water exposed to air = increase in potential energy for contraction of water = increase in free energy (thermodynamically unstable. Water forms droplets to minimise contact with air)

Question 13

Surface Free energy association with surface tension

Answer 13

increased surface free energy = increased surface tension (horizontal forces must be stronger then pulling into bulk)

Question 14

Surface Free Energy association change in surface area

Answer 14

increased surface free energy = positive increased change in surface energy

Question 15

Effect of surface free energy on isolated volume of liquid

Answer 15

Water forms a spherical droplet sahpe

Question 16

Surface Tension Def

Answer 16

Force applied per unit length to prevent contraction of water. The higher the surface tension = the stronger the horizontal bonds = the stronger attractive forces from molecules in bulk = mor water wants to contract

Question 17

Surface Tension Formula (sliding bar apparatus)

Answer 17

Surface Tension = (Force required to break film interface) / (2(length of bar in contact with dispersion))

Question 18

4 surface tension measurements

Answer 18

Ring method, Wilhelmy Plate, Drop Weight and Drop Volume and Capillary Rise

Question 19

Wilhelmy Plate Method Outline

Answer 19

Instrument records how much water is required to pull a plate out of water

Question 20

Drop Weight and Drop Volume Outline

Answer 20

Passing water through a syringe. Bigger drop exiting = more surface tension present

Question 21

Capillary Rise Outline

Answer 21

The higher a fixed volume of a substance travels in graduated capillary = higher surface tension

Question 22

Ring Method Def

Answer 22

Force required to remove 3 different rings (each of a different composition) from water.

Question 23

Relationship between surface tension and interfacial tension

Answer 23

surface tension is a type of interfacial tension when 2 phases are liquid and gas/vapour or solid and vapour. Other interfacial tensions are liquid-liquid, solid-solid and liquid-solid. Interfacial tensions do tend to be lower the surface as there are adhesive attractions between liquid-liquid and solid-solids phases

Question 24

Adhesion Def

Answer 24

Forces of attraction between dissimilar molecules

Question 25

Cohesion Def

Answer 25

Forces of attraction between similar molecules

Question 26

Relationship between adhesion and cohesion in liquids

Answer 26

When adhesion > cohesion liquids spread out. When cohesion> adhesion liquids contract forming droplets

Question 27

Manufacturing processes that use interfacial phenomena

Answer 27

wetting, suspension, emulsification, detergency, granulation, foaming and surfactant science

Question 28

Formulation forming interface sin body

Answer 28

dissolution, absorption, distribution and sorption