dispersed systems

1. Types of Mixtures

  • Solutions: Monophasic systems with homogeneous molecular/ionic mixtures.

    • Solute: Present in lesser quantity.

    • Solvent: Present in greater quantity.

  • Dispersions: Biphasic systems with non-miscible substances.

    • Dispersed phase: Discontinuous component.

    • Continuous phase: Medium in which the dispersed phase is distributed.

  • Classification by Particle Size:

    • Emulsions, Suspensions: Particle size > .

    • Colloidal Systems: Particle size between and .

2. Colloidal Systems

  • Two-phase systems where one phase is dispersed in the other as particles (0.5 mm - 1 nm).

  • Colloidal Particles: Dispersed particles in a substance.

  • Colloidal State: Extreme subdivision of dispersed substances.

  • Surface Area: Large interfacial surface area between dispersed and dispersing phases.

  • Types:

    • Sol: Solid in liquid/gas (e.g., hydrosol, aerosol).

    • Gel: Liquid dispersed in solid (e.g., hydrogel, aerogel).

3. Types of Colloids

Lyophilic Colloids

  • Strong affinity for dispersion medium.

  • Reversible colloids.

  • Influenced by pH, not salts.

  • Increase viscosity.

  • Examples: Cellulose derivatives, gelatin gum, starch.

Lyophobic Colloids

  • Low affinity for dispersion medium.

  • Irreversible colloids.

  • Stabilized by surfactants/protectors.

  • Influenced by electrolytes.

  • Examples: Metals, oxides, sulfides, waxes.

4. Methods of Colloid Preparation

Dispersion Methods

  • Mechanical methods: colloidal mills, ultrasound generators, electric arc.

Condensation Methods

  • Chemical reactions: reduction, oxidation, hydrolysis, double exchange.

  • Precipitation via non-solvent addition.

  • Controlled concentration for nucleation and growth.

5. Colloid Stability and Properties

  • Dialysis: Separation of colloidal particles from impurities.

  • Electrodialysis: Removal of ions using an electric field.

  • Ultrafiltration: Selective filtration of colloidal particles.

6. Brownian Motion and Diffusion

  • Brownian Motion: Random, zigzag motion of colloidal particles.

  • Diffusion: Movement of particles from high to low concentration.

    • Fick’s First Law:

    • Einstein’s Diffusion Law:

7. Sedimentation (Stokes’ Law)

  • Sedimentation Rate:

    • = particle diameter.

    • = densities of dispersed and dispersing phases.

    • = viscosity.

    • = gravitational acceleration.

8. Optical Properties (Tyndall Effect)

  • Scattering of light by colloidal particles.

  • Used for estimating particle size and interactions.

9. Electrophoresis & Zeta Potential

  • Electrophoresis: Movement of colloidal particles under electric potential.

  • Charge Influences:

    • Ion adsorption.

    • Water dissociation.

    • Ionization of particle groups.

  • Electric Double Layer:

    • Nernst Potential: Surface to neutral region.

    • Stern Potential: Stern plane to neutral region.

    • Zeta Potential: Sliding plane to neutral region.

  • Zeta Potential Measurement:

    • Measured via electrophoretic mobility.

    • High zeta potential = greater colloidal stability.

10. Stability and Aggregation

  • Stable System: Particles remain separate.

  • Coagulation: Particles permanently join.

  • Flocculation: Particles form soft aggregates.

  • Forces Involved:

    • Electrostatic repulsion.

    • Van der Waals attraction.

    • Steric stabilization (polyelectrolytes, polymers).

  • Factors Affecting Stability:

    • Electrolytes.

    • Coacervation (phase separation).