Surface and interfacial phenomena

Question 1

Interfaces

Answer 1

boundaries between two phases

Question 2

Surface tension

Answer 2

tension between interfaces due to molecules on the surface being attracted more to each other than any other molecules

Question 3

Minimum surface area

Answer 3

with surface tension, molecules want to shrink to the smallest surface area possible and be as close together as possible

Question 4

Factors affecting surface tension

Answer 4

nature of fluid, concentration and nature of dissolved substances, temperature

Question 5

Cohesive

Answer 5

forces of attraction between the same molecules

Question 6

Adhesive

Answer 6

forces of attraction between different molecules

Question 7

Meniscus

Answer 7

depends on adhesion and cohesion factors. Concave meniscus A>C. Convex meniscus C>A

Question 8

Capillary action

Answer 8

small diameter tubes have more relative surface area meaning water can climb up capillaries. Eg, tear ducts, tall trees, pipette

Question 9

Wetting

Answer 9

ability of liquid to maintain contact with solid. Degree depends on adhesive and cohesive factors

Question 10

Contact angle

Answer 10

angle measured through the liquid at the interface.
Angle = arccos(Ysg - Ysl/Ylg)

Question 11

Complete wetting

Answer 11

Angle = 0
SL &laquo_space;SG

Question 12

Complete de wetting

Answer 12

Angle = 90
SG = SL

Question 13

Partial wetting

Answer 13

Between 0 and 90 degrees

Question 14

Wetting agents

Answer 14

surface active ingredients.
reduce surface tension by reducing water molecule cohesion. Ie making them spread more

Question 15

Factors affecting wetting

Answer 15

surface energy/tension/charge, roughness, porosity, capillarity

Question 16

Surface activity

Answer 16

ability of solute to change surface tension

Question 17

Surface inactive substance

Answer 17

increases surface tension of solvent

Question 18

Surface non-active substance

Answer 18

has no effect on surface tension

Question 19

Surface active substance

Answer 19

decreases surface tension

Question 20

Surfactants

Answer 20

surface active agents. Decrease interfacial tension between two phases. Organic compound with hydrophilic head and hydrophobic tail

Question 21

How surfactants reduce interfacial tension

Answer 21

by breaking cohesive bonds, joining two phases together with water loving head and non polar tail

Question 22

Types of surfactants

Answer 22

non-ionic, anionic, cationic, zwitterionic/amphoteric

Question 23

Surfactant functions

Answer 23

Wetting agents, emulsifiers, solubilisers, dispersing/suspending agents, foaming/anti-foaming agents

Question 24

Surfactant saturation

Answer 24

as more surfactant is added, surface tension decreases until the surface is completely covered then micelles start to form. Saturation occurs well before CMC

Question 25

CMC

Answer 25

critical micelle concentration, the point at which micelles start to form. at this point added surfactant does not affect surface tension. Above CMC surfactant molecules are not soluble. Low CMC = micelles form quickly = more stable

Question 26

Micelle purpose

Answer 26

more solubilisation for cleaning products, improve stability, control rheology, foaming and wetting, tailor for surface properties

Question 27

CPP

Answer 27

micelles come in many shapes and sizes. Critical packing parameter describes likeliness to form a micelle and the shape

Question 28

Micelle shape importance

Answer 28

influences ability to solubilise and the stability. helps for controlled release of actives

Question 29

Anionic surfactant

Answer 29

negative charged head. most widely industrially used in soaps. carboxylates, sulfates, sulphonates, phosphates.

Question 30

Cationic surfactant

Answer 30

positive charged head. used with non-ionics and stable to pH change. Most common ammonium salts. Used in softeners and anti-statics

Question 31

Non-ionic surfactant

Answer 31

no charge on head. large bulk of industrial production. Wetting agents, food preparation. Most common ethoxylated surfactants. Low CMC

Question 32

Zwitterionic surfactant

Answer 32

cationic and anionic head. charge changes with pH changing it properties. compatible with other surfactants. Betaines, amphoacetates. Expensive cosmetics

Question 33

Emulsifier selection

Answer 33

max emulsion, min surfactant. different systems require different surfactants and combining of surfactants

Question 34

HLB

Answer 34

hydrophilic-lipophilic balance. predicts the choice of a non-ionic surfactant.
0 = completely lipophilic
20 = completely hydrophilic

Question 35

HLD

Answer 35

hydrophilic-lipophilic difference. looks at system as a whole not just surfactant