OIA1008 OVERVIEW DISPERSE SYSTEMS

Disperse System

A system where one substance (dispersed phase) is distributed within another (dispersion medium).

Dispersed Phase

The particulate matter present in a disperse system.

Dispersion Medium

The continuous phase in which the dispersed particles are distributed.

Molecular Dispersion

Particle size <1 nm

Invisible under an electron microscope, passes through filters.

Example: Oxygen molecules, glucose.

Colloidal Dispersion

Particle size 1 nm – 1 µm

Visible under an electron microscope, does not pass through semi-permeable membranes.

Example: Colloidal silver sols, polymeric dispersions.

Coarse Dispersion

Particle size >1 µm

Visible to the naked eye, does not pass through filter paper.

Example: Sand grains, red blood cells, emulsions, suspensions.

Colloidal System

A disperse system where at least one dimension of the dispersed phase is between 1 nm – 1 µm.

Sol

A colloidal dispersion of a solid in a liquid or gas.

Example: Hydrosol (water-based sol), Aerosol (gas-based sol).

Lyophilic Colloids (Solvent-Loving)

Strong interaction between dispersed phase and medium.

Thermodynamically stable, reversible system.

Example: Acacia, gelatin, insulin.

Lyophobic Colloids (Solvent-Hating)

Weak interaction, particles tend to aggregate.

Thermodynamically unstable, irreversible system.

Example: Sulfur, gold, silver chloride dispersions.

Association Colloids (Amphiphilic Colloids)

Surfactants that form micelles above the Critical Micelle Concentration (CMC).

Example: Sodium lauryl sulfate.

Dispersion Methods

Reducing coarse particles to colloidal size using colloid mills, ball mills, homogenizers.

Peptization

Breaking up aggregates into smaller particles using peptizing agents (e.g., Na lauryl sulfate for charcoal).

Condensation Methods

Supersaturation leads to colloid formation via chemical reactions or solvent changes.

Hydrolysis Method

Example: AlCl₃ + H₂O → Al(OH)₃ (colloid) + HCl.

Optical Properties

Tyndall Effect: Light scattering by colloidal particles.

Kinetic Properties

Brownian Motion: Random zig-zag movement of particles.

Osmotic Pressure

Governed by the van’t Hoff equation:

π=cRT\pi = cRT

π\pi = Osmotic pressure

cc = Concentration

RR = Gas constant

TT = Absolute temperature.

Diffusion

Movement from high to low concentration.

Sedimentation

Stokes’ Law: Sedimentation rate depends on particle size and density.

Donnan Membrane Effect

Large non-diffusible colloidal ions influence the diffusion of smaller ions across a membrane.

Electrical Stability

Zeta Potential: The charge difference stabilizing colloids.

Flocculation vs. Coagulation

Flocculation: Loose aggregates that can be redispersed.

Coagulation: Permanent aggregation, destroying the colloidal system.

Electrostatic Stability

Colloidal particles have an electrical charge, preventing aggregation.

Solvation Stability

A hydrated layer forms around particles, preventing aggregation.

Salting Out Effect

High salt concentration removes hydration, leading to coagulation.

DLVO Theory

Balance between electrostatic repulsion (VR) and Van der Waals attraction (VA) determines stability.

Effect of Electrolytes

Adding salts compresses the electric double layer, promoting flocculation.

Steric Stabilization

Polymers adsorbed onto particles prevent aggregation.

Drug Delivery Systems

Nanoparticles for targeted drug delivery.

Suspensions & Emulsions

Colloidal suspensions improve drug solubility.

Protein-Based Drug Formulations

Albumin-based nanoparticles for drug transport.

Coacervation in Microencapsulation

Used in controlled drug release formulations.

Emulsification

Surfactants stabilize emulsions in liquid medications.

Microencapsulation Process

The coating of small particles for drug stability.

Coating Materials

Gelatin, acacia, synthetic polymers.

Colloidal Silver

Used as an antimicrobial agent.

Colloidal Gold

Used for diagnostic imaging.

Colloidal Mercury

Used for syphilis treatment.

Natural Polymers in Pharmaceuticals

Acacia, starch, cellulose used in excipients.