surfactants, micelles, solubilisation

Question 1

what is an interface

Answer 1

boundary between 2 phases

Question 2

categorise interfaces

Answer 2

liquid liquid = emulsion
liquid vapour = suspension/emulsion
solid vapour = tablet
solid liquid = suspension

Question 3

what is surface tension

Answer 3

force acting over surface of a liquid perpendicular to the force

Question 4

what causes surface tension/why is there an even distribution in bulk

Answer 4

uneven distribution of forces lead to a net inward force that drives the molecule to decrease the surface area of the system

Question 5

what minimises the overall free energy

Answer 5

spontaneous contraction of the surface

Question 6

what is the surface free energy of a liquid defined as

Answer 6

work needed to expand the surface by an area of 1m^2

Question 7

what do surfactants do

Answer 7

lower surface tension of an interface, increase stability of high surface area pharmaceutical formulations, also called surface active agents and amphiphiles

Question 8

structure of a surfactant

Answer 8

2 regions, hydrophilic head and hydrophobic tail , can be saturated or unsaturated hydrocarbon, hydrophilic region can be anionic/cationic/non ionic

Question 9

difference between a diagram of a ionic and non ionic surfactant

Answer 9

hydrophilic head of ionic is a circle, non ionic is a squiggly line

Question 10

example of anionic surfactants

Answer 10

sodium dodecyl sulphate, sodium dodecanoate

Question 11

example of cationic surfactants

Answer 11

cetrimide

Question 12

example of non-ionic surfactants

Answer 12

polysorbate, cetomacrogol 1000

Question 13

describe the orientation of surfactants at interfaces

Answer 13

hydrophilic head in the water and hydrophobic tail outside, minimises free energy of system, more surfactants together decreases free energy

Question 14

toxicity of surfactants

Answer 14

ability to penetrate and disrupt biological membranes, can change fluidity/permeability of membrane affecting active transport, some surfactants not cleared rapidly, some cause hypersensitivity reactions

Question 15

difference between ionic and non ionic surfactants

Answer 15

ionic- small hydrophilic group with intense electrostatic field, powerful surfactant, toxic for in vivo due to membrane disruption, pH dependent ionisation, incompatible with other ingredients

non ionic- large hydrophobic group, less surface active, less toxic, can be used in injections, not pH sensitive, compatible

Question 16

what are micelles

Answer 16

tiny aggregates

Question 17

what does micelle formation allow

Answer 17

allows more surfactant molecules to enter liquid phase by wrapping the hydrophobic region in an oil core, this is a colloid

Question 18

what is a colloid

Answer 18

mixture of small particles suspended in another medium, contains aggregates/particles of molecules surrounded by solvent molecules

Question 19

difference between solution and colloid

Answer 19

colloid contains aggregates surrounded by solvent molecules, in solution every molecule is separate

Question 20

when do micelles start to form

Answer 20

critical micelle concentration (CMC)

Question 21

describe structure of micelle

Answer 21

sphere of ionic surfactant molecules (o~~) with the o facing outwards and ~ inwards, charged, attracts counterions in electrolyte solution

Question 22

what is critical micelle concentration

Answer 22

concentration of surfactant where micelles start to form

Question 23

what happens to the properties of the system at the critical micelle concentration

Answer 23

surface tension stops decreasing and turbidity (clarity) increases

Question 24

structure of non ionic micelles

Answer 24

palisade layer- hydrophilic layer, circle of ~~~~

Question 25

what does the palisade layer do in non ionic micelles

Answer 25

trap water molecules due to hydrogen bonding

Question 26

how does the structure of hydrophobic region affect cmc and micelle size

Answer 26

increase hydrocarbon chain decreases cmc
log[cmc]=A-Bm
A and B= homologous series of surfactants
m= number of carbons in a chain

Question 27

how does the nature of hydrophilic region affect cmc and micelle size

Answer 27

non ionic have lower cmc than ionic, non ionic can form large non spherical structures, no repulsion in non ionics so less surfactant needed for micelle formation, ionic has electrostatic repulsion that stops surfactant molecules from entering micelle

Question 28

how does the nature of counter ions affect cmc and micelle size in ionic surfactants

Answer 28

as concentration of counter ions increases, neutralisation of head group charge is improved so more charged molecules can pack together, weakly hydrated counter ions lose their water molecule more easily so neutralise easier, counter ions reduce the reulsion

Question 29

how does temperature affect cmc and micelle size

Answer 29

small effect on ionic surfactants, major effect on non ionic bc interaction of hydrophilic group and water is temperature dependent

temp increase= cmc decreases then increases
=micelle size increase

Question 30

factors that affect critical micelle concentration and micelle size

Answer 30

structure of hydrophobic region- increasing length of hydrocarbon chain decreases the cmc
log[cmc]=A-Bm
A and B= homologous series of surfactants
m= number of carbons in a chain

nature of hydrophilic group- non ionic have lower cmc than ionic, non ionic can form large non spherical structure as theres no repulsion so less surfactant needed

nature of counter ion- (only for ionic) counter ion conc increases neutralisation of head group so charge is improved so more charged molecules can pack together, counter ion reduces repulsion

Question 31

what is solubilisation

Answer 31

use of surfactants/micelles/other agents to enhance dissolution