COLLOIDAL DISPERSION

COLLOIDAL DISPERSION

•  Particle size is 1 nm to 500 nm (0.5 mm) 

• May be detected under ultramicroscope and visible in an electron microscope

• Pass-through filter paper but do not pass through a semipermeable membrane 

• Diffuse very slowly

Dialysis

• a separation method 

• using a semi-permeable membrane, the pore size of which will prevent the passage of colloidal particles, yet permit small molecules and ions, such as urea, glucose, and NaCl to pass through.

Ultrafiltration

• a separation and purification process of colloidal material 

• that allows filtration under negative pressure through a dialysis membrane supported in a Buchner funnel.

Lyophilic Colloids (Solvent-Loving Colloids)

Systems with colloidal particles that interact well with the dispersion medium forming colloidal dispersions or solutions.

Solvation

the attraction between the dispersed phase and the dispersion medium

Hydrophilic colloids (solvation is termed hydration

• in an aqueous dispersion media. 

• Examples are gelatin, acacia, insulin, albumin in water 

• Acacia and gelatin are polymers (molecules in chain) 

• Insulin and albumin are proteins 

• The four of them are macromolecules (large enough to classify as colloids).

Lipophilic colloids

• in non-aqueous, organic solvents. 

• Examples are rubber and polystyrene dissolved in benzene.

Lyophobic Colloids (Solvent-Hating)

• Composed of materials that have little attraction for the dispersion medium. 

• Examples are inorganic particles dispersed in water, such as gold, silver, sulfur, silver iodide. 

• These colloids do not like solvents. 

• They are less stable; therefore, a stabilizing agent is often used to make this system stable.

Amphiphiles

characterized by having two distinct regions of opposing solution affinities within the same molecule or ion.

Advantage

can combine both with polar and non- polar solvent

Anionic

sodium lauryl sulphate, dodecyl sulfate

Cationic

cetyl trimethyl-ammonium bromide

Nonionic

tweens or polyoxyethylene lauryl ether

Ampholytic (zwitterionic)

dimethyldodecylammoniopropane sulfonate

Micelles

aggregates of 50 or more monomers of amphiphiles, has a size of 50 nm – colloidal size

Critical micelle concentration (CMC)

concentration of monomer at which micelles are formed.

Aggregation number

number of monomers (amphiphiles) that aggregate to form a micelle

Amphiphiles in water

hydrocarbon chains face inward into the micelle to form, surrounding it are the polar portions pf the amphiphiles associated with the water molecules.

Amphiphiles in nonpolar liquids

the polar heads facing inward while the hydrocarbon chains are associated with the nonpolar phase.

Gegenions

a certain number of the sodium ions that are attracted to the surface of the micelle, reducing the overall negative charge.

Faraday-Tyndall effect (optical)

• formation of a visible cone (resulting from the scattering of light by the colloidal particles) when a strong beam of light passed through a colloidal sol. This may be examined by an ultramicroscope (light points).

• scattering light

1. Brownian motion

2. Diffusion

3. Sedimentation

4. Viscosity

Kinetic

Brownian motion

random, irregular, zigzag movements of colloidal particles caused by the bombardment of the particles by the molecules of the dispersion medium.

Large particle size

decreased velocity

Small particle size

increased velocity

Diffusion

spontaneous movement of particles from a region of higher concentration to one of lower concentration until the concentration of the system is uniform throughout.

Fick’s First Law of Diffusion

• ↓ particle size = ↑ diffusion 

• ↑ temperature = ↑ diffusion 

• ↓ viscosity = ↑ diffusion

↓ particle size

↑ diffusion

↑ temperature

↑ diffusion

↓ viscosity

↑ diffusion

Sedimentation

based on Stoke’s Law

Viscosity

resistance to flow under applied stress

Spherocolloids

low viscosity

Linear

high viscosity

1. Nernst potential / Electrothermodynamic Potential'

2. Zeta Potential / Electrokinetic Potential

Electric

Nernst potential / Electrothermodynamic Potential

Difference between actual surface and the electroneutral region of the solution