Colloidal Dispersions 1

Question 1

What are the properties of colloidal dispersions?

Answer 1

Very small particles (1-500 nm) dispersed in a continuous phase
Very large specific surface (the surface area per unit weight or volume of material)
The color of colloidal dispersions is related to the size of the particles
Not pass through semi-permeable membrane (dialysis, ultrafiltration, electrodialysis)Not visible by naked eye
Have light scattering effects
Not resolve by optical microscope
Visible in electron microscope
Diffuse slowly, exhibits characteristics of molecular solutions (Brownian motion, diffusion)
Not completely dissolved in “solvent” (external phase)

Question 2

What are the types of colloidal systems?

Answer 2

• Lyophilic (solvent loving)
• Lyophobic (solvent hating)
• Association (amphiphilic)

Question 3

What is a lyophilic colloid?

Answer 3

Have a strong affinity with their medium
Form colloidal dispersions, or sols, with relative ease.
Thermodynamically stable
The attraction between the dispersed phase and the dispersion medium, which leads to solvation (he attachment of solvent and dispersed phase molecules )
Hydration: the attachment of media (water) molecule to the dispersed phase
Spontaneous formation
E.g. Jello from gelatin,

Question 4

What is a lyophobic colloid?

Answer 4

Little attraction between particle and media
Thermodynamically unstable
Need a special methods to prepare
Dispersion methods: Ultrasonication, Colloidal Mill, Condensation methods:
e.g. colloidal Silver

Question 5

What is an association colloid?

Answer 5

Formed by the association of dissolved molecules to create larger particles (colloidal dimension), micelle, liposomes and micro-emulsions
Thermodynamically stable

Question 6

Micelles

Answer 6

Amphiphiles or surface-active agents, have two distinct regions of opposing solution affinities within the same molecule.
When present in a liquid medium at low concentrations, the amphiphiles exist separately (sub-colloidal)
As the concentration is increased, aggregation occurs over a narrow concentration range (50 or more monomers)
These aggregates called micelles

Question 7

Shapes of micelles

Answer 7

a) spherical micelle in aqueous media

(b) reversed
micelle in non-aqueous media

(c) laminar micelle, formed at higher amphiphile concentration in
aqueous media.

Question 8

Critical Micelle Concentration (CMC)

Answer 8

Critical micelle concentration (CMC) is the concentration of surfactant monomer at which micelle starts to forms. At CMC, the surface is saturated with surfactants and any further increase in concentration leads the formation of micelle in the bulk.
Aggregation number: The number of monomers that aggregate to form a micelle

Question 9

CMC and Colloidal Properties

Answer 9

Surface tension
Osmotic pressure
Light scattering
Drug solubility
Conductivity 
Density
Detergency

Question 10

Amphiphiles

Answer 10

Amphiphile : a chemical that have both hydrophilic (water-loving, polar) and lipophilic (fat-loving) properties.
Amphiphiles may be anionic, cationic, nonionic, or ampholytic (zwitterionic)

Question 11

How to predict the CMC of a mixture of amphiphiles

Answer 11

Mixtures of two or more amphiphiles are usual in pharmaceutical formulations Assuming an ideal mixture we are able to predict the CMC of the mixture:
1/CMC= x1/ CMC1 + x2/ CMC2

CMC1 and 2: CMC values of the pure amphiphiles
X 1and 2: mole fractions of each in the mixture

Question 12

Solubilization (by micelle)

Answer 12

A: benzene and toluene: nonpolar

B: Salicylic acid: “amphiphilic”
C: para-hydroxy-benzene: more polar

Solubilization is a important micelle application in drug formulation
(refer to slide 23)

Question 13

CERNEVIT (BAXTER)

Answer 13

Multivitamins for i.v. infusion
Mixed micelles formed with glycocholic acid and lecithin

Retinol palmitate.
Colecalciferol 
DL-alpha-tocopherol 
Ascorbic acid 
Cocarboxylase tetrahydrate 
Riboflavin dihydrated sodium phosphate.
Pyridoxine hydrochloride.
Cyanocobalamin 
Folic acid.
Dexpanthenol 
D-Biotin 
Nicotinamide

Question 14

Properties of Colloids

Answer 14

Optical Properties of Colloids
The Faraday-Tyndall effects
Electron microscope
Light scattering
Kinetic Properties of Colloids
Brownian motion
Diffusion
Osmotic pressure
Sedimentation 
Viscosity
Electrical Properties of Colloids
Electrokinetic phenomena
Stability of colloid systems
Sensitization and protective colloidal action

Question 15

Types of Electron Microscopy

Answer 15

Transmission electron microscopy (TEM)
Scanning electron microscopy (SEM)
Reflection electron microscope (REM)
Scanning transmission electron microscope (STEM)

Question 16

Faraday-Tyndall effect

Answer 16

a visible cone, resulting from the light scattering of colloidal particles when strong beam light is passed through a colloidal system
Ultramicroscope used to examine the light points responsible for the Tyndall cone

Question 17

Light Scattering

Answer 17

Depends on the Faraday–Tyndall effect
Widely used for determining the molecular weight of colloids.
Can also be used to obtain information on the shape and size of the particles.