Section 7: Colloidal Dispersions & Applications

Colloidal Dispersion Particle Size

Features an internal dispersed phase particle diameter ranging strictly between 1 nanometer and 500 nanometers.

Colloid Optical Visibility

Cannot be resolved using an ordinary light microscope; requires visualization via an electron microscope.

Colloid Structural Passability

Capable of passing cleanly through standard filter paper but blocked by semipermeable membranes.

Colloid Kinetic Passability

Diffuse exceptionally slowly through media; common examples include Milk of Magnesia, Al Hydroxide, Silver Protein, and ophthalmic gels.

Faraday-Tyndall Effect

The optical scattering of a light beam by colloidal particles; widely leveraged to calculate colloid molecular weight.

Electron Microscope Colloid Use

Deployed with high resolution to directly observe the physical size, geometric shape, and structure of colloidal particles.

Brownian Movement Definition

The continuous, random zigzag movement of colloidal particles; velocity increases as particle size decreases.

Colloid Diffusion Principle

Spontaneous particle movement from high to low concentration until uniform; a direct result of Brownian motion described by Fick's First Law.

Colloid Osmotic Pressure Law

Described and calculated mathematically via the van't Hoff equations: π = cRT or π = iCRT.

Colloid Sedimentation Accelerators

Settle faster when particle size is larger, particle density exceeds the liquid, or solvent viscosity is low.

Colloid Viscosity Geometry Effects

Resistance to flow under stress; spherical colloids are less viscous, while linear, elongated colloids are highly viscous.

Zeta / Electrokinetic Potential

The electrical potential measured between the shear plane of tightly bound particle layers and the electroneutral region.

Zeta Potential Stability Rule

High zeta potential triggers strong particle repulsion (deflocculation), while weak potential leads to weak repulsion and aggregation.

Nernst / Electrothermodynamic Potential

The electrical potential measured between the actual particle surface and the electroneutral region; key in biological/electrochemical cells.

Colloid Charge Stability Rule

Particles carrying identical electrical charges repel each other; more charge equals more repulsion and higher colloid stability.

Lyophobic Sol Stabilization

Accomplished by adding a tiny, precise amount of electrolyte to provide enough surface charge to drive repulsion.

Protective Solvent Layer

Prevents hydrophobic particles from sticking together by coating them with a protective hydrophilic colloid solvent sheath.

Colloid Protection Example

Adding hydrophilic gelatin or acacia polymers to a hydrophobic colloid system to boost stability.

Gold Number Definition

The absolute weight in milligrams of a protective hydrophilic colloid required to prevent the coagulation of a standard gold sol.

Gold Number Efficiency Rule

A lower gold number signifies a much better, highly powerful protective ability.

Gelatin vs Acacia Gold Number

Gelatin (G.N. = 0.01) is vastly more effective as a protective colloid than acacia (G.N. = 0.2).

Dialysis Purification Method

Separates colloidal particles from impurities using a semipermeable membrane made of collodion or cellophane.

Ultrafiltration Purification Method

Filters out small impurities by conducting filtration under negative pressure or suction.

Electrodialysis Purification Method

Speeds up purification by applying a strong electrical potential across the semipermeable membrane.

Lyophilic Colloids Profile

Solvent-loving large organic molecules with high affinity for the dispersion medium; exceptionally stable against electrolytes (e.g., gelatin/water, acacia/water, insulin).

Lyophobic Colloids Profile

Solvent-hating inorganic particles with little attraction to the medium; require ultrasonication or a colloid mill to disperse (e.g., Au, Ag, S).

Association / Amphiphilic Colloids

Formed by surfactants whose individual molecules carry two distinct regions of opposing solution affinities, aggregating into micelles.

Hydrogels Application

Colloidal gels with water as the dispersion medium, used for wound healing, tissue engineering scaffolds, and sustained drug release.

Microparticles Application

Tiny polymer microspheres (0.2–5 μm) that serve as targeted carriers for vaccines and anticancer drugs.

Liposomes Application

Phospholipid vesicles with a lipid bilayer and liquid core; carries lipophilic drugs in the membrane and hydrophilic drugs in the core.

Micelles Application

Surfactant aggregates featuring a tight hydrophobic core, used to solubilize poorly water-soluble pharmaceuticals.