OIA1008 DISPERSE SYSTEMS - COLLOIDS

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38 Terms

1

Colloidal System

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

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2

Dispersed Phase

The substance in small particles within the dispersion medium.

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3

Dispersion Medium

The continuous phase in which colloidal particles are distributed.

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4

Faraday-Tyndall Effect

Light scattering by colloidal particles creates a visible cone.

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5

Turbidity Measurement

T = 1/L ln (I₀/Iₜ)

T: Turbidity

L: Sample path length

I₀: Incident light intensity

Iₜ: Transmitted light intensity.

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6

Spectrophotometry & Nephelometry

Used to measure colloid turbidity and molecular weight.

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7

Hydrophilic vs. Lyophobic Colloids

Hydrophilic colloids scatter light less than lyophobic colloids.

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8

Brownian Motion

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

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9

Diffusion

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

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10

Osmotic Pressure (van’t Hoff Equation)

π = cRT

π: Osmotic pressure

c: Solute concentration

R: Gas constant

T: Temperature.

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11

Osmotic Pressure in Colloids

π/cg = RT(1/M + Bcg)

Used to determine colloid molecular weight.

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12

Sedimentation (Stokes’ Law)

V = 2r²(ρ - ρ₀)g / 9η₀

V: Sedimentation velocity

r: Particle radius

ρ - ρ₀: Density difference

η₀: Medium viscosity

g: Gravity.

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13

Ultracentrifugation

Uses high-speed rotation to sediment colloidal particles.

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14

Viscosity & Einstein’s Equation

η = η₀ (1 + 2.5ϕ)

η: Dispersion viscosity

η₀: Medium viscosity

ϕ: Volume fraction of colloidal particles.

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15

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).

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16

Electrical Double Layer (EDL)

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

Diffuse Layer: Loosely bound ions distributed in medium.

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17

Zeta Potential (ζ-Potential)

Governs colloidal stability; low ζ leads to flocculation.

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18

Debye-Hückel Length (1/κ)

Distance where potential decays exponentially.

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19

Donnan Membrane Equilibrium

Charged macromolecules influence ion diffusion across membranes.

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20

Stable Colloidal Systems

Particles remain dispersed due to Brownian motion and repulsion.

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21

Flocculation vs. Coagulation

Flocculation: Loose aggregates, easily redispersed.

Coagulation: Permanent aggregation.

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22

DLVO Theory

Total energy of interaction: VT = VA + VR

VA: Attractive Van der Waals forces.

VR: Repulsive electrostatic forces.

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23

Controlled Flocculation in Suspensions

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

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24

Steric Stabilization

Macromolecules adsorbed onto particles prevent aggregation.

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25

Lyophilic Colloid is stabilized by:

Electrical double layer.

Solvation (hydration shell around particles).

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26

Salting Out Effect

High salt concentrations remove hydration shells, leading to precipitation.

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27

Coacervation

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

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28

Microencapsulation

Encapsulation of solid particles by coacervate layers.

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29

DLVO Theory of Stability

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

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30

Electrolyte Effect on Stability

High electrolyte concentration compresses the EDL, leading to flocculation.

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31

Steric Stabilization Mechanism

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

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32

Colloidal Silver (Ag)

Antimicrobial agent.

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33

Colloidal Gold (Au)

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

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34

Proteins as Natural Colloids

Essential for muscle, bone, and enzymatic activity.

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35

Synthetic Polymers in Drug Formulation

Used in coatings, controlled-release drug delivery.

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36

Nanoparticle-Based Drug Delivery

Colloidal carriers enhance bioavailability of poorly soluble drugs.

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37

Liposomes

Phospholipid-based vesicles for targeted drug delivery.

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38

Emulsions & Suspensions in Pharmacy

Colloidal suspensions improve solubility and drug stability.

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