OIA1008 DISPERSE SYSTEMS - COLLOIDS

Colloidal System

A dispersion where particles (1 nm – 1 µm) are distributed in a continuous medium.

Dispersed Phase

The substance in small particles within the dispersion medium.

Dispersion Medium

The continuous phase in which colloidal particles are distributed.

Faraday-Tyndall Effect

Light scattering by colloidal particles creates a visible cone.

Turbidity Measurement

T = 1/L ln (I₀/Iₜ)

T: Turbidity

L: Sample path length

I₀: Incident light intensity

Iₜ: Transmitted light intensity.

Spectrophotometry & Nephelometry

Used to measure colloid turbidity and molecular weight.

Hydrophilic vs. Lyophobic Colloids

Hydrophilic colloids scatter light less than lyophobic colloids.

Brownian Motion

Random zig-zag motion of colloidal particles due to collisions with dispersion medium molecules.

Diffusion

Particles move from high to low concentration due to Brownian motion.

Osmotic Pressure (van’t Hoff Equation)

π = cRT

π: Osmotic pressure

c: Solute concentration

R: Gas constant

T: Temperature.

Osmotic Pressure in Colloids

π/cg = RT(1/M + Bcg)

Used to determine colloid molecular weight.

Sedimentation (Stokes’ Law)

V = 2r²(ρ - ρ₀)g / 9η₀

V: Sedimentation velocity

r: Particle radius

ρ - ρ₀: Density difference

η₀: Medium viscosity

g: Gravity.

Ultracentrifugation

Uses high-speed rotation to sediment colloidal particles.

Viscosity & Einstein’s Equation

η = η₀ (1 + 2.5ϕ)

η: Dispersion viscosity

η₀: Medium viscosity

ϕ: Volume fraction of colloidal particles.

Colloidal Particles Acquire Charge via:

Ion dissolution (e.g., AgI with Ag⁺ or I⁻).

Ionization of surface groups (e.g., proteins).

Ion adsorption (selective adsorption of ions).

Electrical Double Layer (EDL)

Inner Layer (Stern layer): Strongly bound counter-ions.

Diffuse Layer: Loosely bound ions distributed in medium.

Zeta Potential (ζ-Potential)

Governs colloidal stability; low ζ leads to flocculation.

Debye-Hückel Length (1/κ)

Distance where potential decays exponentially.

Donnan Membrane Equilibrium

Charged macromolecules influence ion diffusion across membranes.

Stable Colloidal Systems

Particles remain dispersed due to Brownian motion and repulsion.

Flocculation vs. Coagulation

Flocculation: Loose aggregates, easily redispersed.

Coagulation: Permanent aggregation.

DLVO Theory

Total energy of interaction: VT = VA + VR

VA: Attractive Van der Waals forces.

VR: Repulsive electrostatic forces.

Controlled Flocculation in Suspensions

Adding electrolytes compresses the electric double layer, promoting controlled flocculation.

Steric Stabilization

Macromolecules adsorbed onto particles prevent aggregation.

Lyophilic Colloid is stabilized by:

Electrical double layer.

Solvation (hydration shell around particles).

Salting Out Effect

High salt concentrations remove hydration shells, leading to precipitation.

Coacervation

Separation of colloid-rich layers due to electrolyte/nonsolvent addition.

Microencapsulation

Encapsulation of solid particles by coacervate layers.

DLVO Theory of Stability

Stability depends on balance between attraction (VA) and repulsion (VR).

Electrolyte Effect on Stability

High electrolyte concentration compresses the EDL, leading to flocculation.

Steric Stabilization Mechanism

Non-ionic polymers (e.g., methylcellulose) adsorbed onto colloids prevent aggregation.

Colloidal Silver (Ag)

Antimicrobial agent.

Colloidal Gold (Au)

Used in diagnostics (e.g., lateral flow tests).

Proteins as Natural Colloids

Essential for muscle, bone, and enzymatic activity.

Synthetic Polymers in Drug Formulation

Used in coatings, controlled-release drug delivery.

Nanoparticle-Based Drug Delivery

Colloidal carriers enhance bioavailability of poorly soluble drugs.

Liposomes

Phospholipid-based vesicles for targeted drug delivery.

Emulsions & Suspensions in Pharmacy

Colloidal suspensions improve solubility and drug stability.