Colloidal

Question 1

What is a colloid?

Answer 1

Homogeneous non crystalline substance composed of molecules or ultramicroscopic particles of 1 substance dispersed through another (particles don’t settle and cant be separated by simple filtration)

Question 2

What is an interface

Answer 2

High energy barrier between 2 phases - it brings together 2 substances that don’t readily form productive interactions

Question 3

What is a liquid in liquid colloid? and why are the 2 liquids immiscible

Answer 3

Emulsion
No favourable interactions between hydrocarbon and H2O, Hydrogen bonding is limited at the interface = surface tension.

Question 4

What is a surfactant?

Answer 4

Is a molecule which is partially soluble in both phases which organises itself at the interface between 2 phases and lowers the energy. Allows tiny droplets of 1 phase to exist suspended in the other.

Question 5

What happens when surfactant in water?

Answer 5

1) at low conc surfactant is found at air-water interface with hydrophobic chains in air
2) Once air-water interface is full as the conc of surfactant increases they go into bulk water
3) at CMC the energy cost of free surfactants in water too high so form micelles.

Question 6

Thermodynamics of micelle formation

Answer 6

3D water structure reestablished -ΔH
Ordered water release from hydrophobic chains +ΔS
Inside micelle hydrophobic chains mobile +ΔS
Monomer cant move freely -ΔS
Charged polar headgroups close together and repel each other +ΔH

Question 7

What is Critical Micelle Concentration?

Answer 7

The concentration of surfactant at which the energetics of micelle formation become favoured (i.e. ΔG < 0)

Question 8

Ways to determine the CMC?

Answer 8

1) Surface tension
2) Conductivity (only for ionic surfactants)
3) Fluorescence

Question 9

How does surface tension change with surfactant concentration?

Answer 9

Surface tension decreases as surfactant builds up at air-water interface, at CMC no change in surface tension as all surfactant is now forming micelles

Question 10

How does conductivity change with surfactant concentration?

Answer 10

Conductivity increases as more ions are present in solution, at CMC additional surfactant forms micelles which are less mobile so conductivity doesn’t increase at same rate

Question 11

How does Fluorescence change with surfactant concentration?

Answer 11

Fluorescent chromophore that fluoresces in organic solvent so will only fluorese once micelles form at CMC.
However the presence of the chromophore can affect the CMC by encouraging or discouraging micelle assembly

Question 12

What effect does hydrophobic chain length have on CMC?

Answer 12

As hydrophobic chain length increases the CMC decreases
The hydrophobic effect increases allowing self assembly at lower surfactant concentration

Question 13

What effect does a non-ionic head group have on CMC?

Answer 13

Significantly decreases CMC as there is no repulsion between the polar head groups so assembly is more favoured

Question 14

What effect does having a higher charger counter ion have on the CMC

Answer 14

Better interactions with the anionic micelle surface and therefore assists with surfactant packing and micelle assembly lowering the CMC

Question 15

Limitation of simple surfactants

Answer 15

Require relatively high conc of surfactant to assemble limiting applications for drug delivery

Question 16

Alternative to simple surfactants

Answer 16

Polymer Micelles
Block copolymer, with one hydrophobic monomer and one hydrophilic polymer

Question 17

Benefits of polymer micelles

Answer 17

1) Lower cost of translational energy
2) Large apolar chains = strong hydrophobic effect = v stable micelles which form at lower CMC
3) Higher kinetic stability - larger energy barrier to removal from the micelle
4) Larger interior volume is good for drug delivery

Question 18

Main surfactant morphologies

Answer 18

Spherical
Cylindrical
Bilayer
Reverse

Question 19

For spherical micelles what is v/lmaxa?

Answer 19

v/lmaxa < 1/3

Question 20

For cylindrical micelles what is v/lmaxa

Answer 20

1/3 < v/lmaxa < 1/2

Question 21

For bilayer vesicles what is v/lmaxa

Answer 21

1/2 < v/lmaxa > 1

Question 22

What is a solid in liquid colloid called?

Answer 22

Gel

Question 23

4 types of gel

Answer 23

1) crosslinked polymer gels
2) associative polymer gel
3) inorganic network gels
4) Molecular gels

Question 24

What are low molecular weight gelators

Answer 24

Small molecules that self assemble into non-covalent polymers (e.g. hydrogen bonds) that form an extended network and trap solvents

Question 25

What is the hierarchal assembly?

Answer 25

1) Molecules freely dissolved
2) molecules form non covalent interactions and form fibrils
3) fibrils bundle non covalently to form fibres
4) Nanofibres form interactive sample spanning network
5) Network makes bulk gel

Question 26

Minimum gelation concentration

Answer 26

Critical concentration above which gelation occurs
(as little as 0.1% gelator)

Question 27

Maximum gelation concentration

Answer 27

Critical concentration above which gelation will not occur, gelator cannot be dissolved in the solvent

Question 28

Considerations to take when selecting gelator

Answer 28

Cannot be too soluble or no gel will form, if too insoluble will just ppt out of solution.
Must dissolve with stimulus e.g. heating then when stimulus is removed must be insoluble enough to form a gel

Question 29

What structure does DBS have and how to make it soluble in water?

Answer 29

Has hydrogen bonding between sugar bodies and 𝜋-𝜋 stacking of aromatic wings
Is insoluble in pure water so to form gels have to modify wing tips with hydrophillic groups eg. COOH or CONHNH2

Question 30

How to analyse macroscopic behaviour of gels

Answer 30

1) Rheology
2) Vial inversion method
3) Ball dropping method

Question 31

What is rheology?

Answer 31

Investigates flow and elasticity properties
G’ = storage modulus, associated with energy stored in elastic deformation (solid like)
G’’ = loss modulus, measure of flow under stress (liquid like)

Question 32

How to assess nanoscale behaviour?

Answer 32

1) Electron microscopy - uses e- instead of light so shorter 𝛌 means can see smaller structures - freeze sample with liquid nitrogen then evaporate solvent in vacuo - gel solid structure doesn’t collapse
2) IR spectroscopy - do before and after gelation - can she shifts in C=O or N-H stretches due to non-covalent interactions of gelation
3) NMR - do before and after gelation - can interpret what has gone from liquid into solid phase

Question 33

Laundry detergent composition

Answer 33

1) Builders (50%) - Chelating agents that remove Ca2+ or Mg2+ ions that would usually cause SDS to ppt
2) Surfactant (15%) hydrophobic dirt goes inside of micelles = clean clothes
3) Bleach = oxidises organic stains
4) Enzymes = remove biological stains e.g. fats, proteins

Question 34

How can surfactants be used in drug delivery?

Answer 34

Water insoluble drugs can be solubilised within the hydrophobic centre of a micelle

Question 35

What benefits do surfactants have in drug delivery?

Answer 35

Minimise drug degredation
prevent harmful side effects
Enahance amount of drug at zone of interest

Question 36

Alternative to simple micelles for drug delivery as they have poor thermodynamic stability

Answer 36

Hollow vesicles - bilayer micelle with hydrophillic exterior + interior

Question 37

Benefits of Bilayer vesicles in drug delivery e.g Doxil

Answer 37

Has PEG lipids around exterior ‘stealth effect’ - shields structure from the body extending circulation time and limiting breakdown
High drug loading - only releases at tumor as cannot pass normal membrane so circulates round body until finds tumor

Question 38

Gels in the lubrication industry

Answer 38

Used for chariot grease - animal fat and limestone (CaCO3) - poor thermal stability (100°c) so used Na+ instead of Ca2+ stable to 120°c
Aviation needed better grease Lithium grease - more stable
1950s onwards - Low molecular weight ureas - synthetic grease can tune properties

Question 39

In vivo gels in tissue engineering

Answer 39

Materials for use in reconstructive surgery - enable better recovery of damaged tissues/ integration of synthetic materials into body

Question 40

In vitro gels in tissue engineering

Answer 40

Materials to grow stem cells and then control their differentiation into different types of cells
More stiff gell => bone, cartilage
Softer gel => fat tissue