Colloidal Solutions: Lyophilic and Lyophobic Colloids

Colloidal Solutions

Lyophilic Colloids

• Also known as hydrophilic colloids
• Particles or molecules are strongly solvated by the dispersion medium (usually water)
• Examples: starch, gelatin, and proteins
• Properties:
  • Reversible sol-gel transition
  • High viscosity
  • High stability due to solvation

Lyophobic Colloids

• Also known as hydrophobic colloids
• Particles or molecules are not solvated by the dispersion medium
• Examples: metal sols, sulfur sols, and clay suspensions
• Properties:
  • Irreversible sol-gel transition
  • Low viscosity
  • Low stability due to lack of solvation
  • Can be stabilized by adding emulsifying agents or surfactants

Gels

• Colloidal system in which the disperse phase has formed a network of particles
• Properties:
  • Non-flowing, semi-rigid structure
  • High viscosity
  • Reversible sol-gel transition
  • Examples: agar agar, gelatin, and silica gel

Tyndall Effect

• Scattering of light by colloidal particles
• Observed when a beam of light passes through a colloidal solution
• Properties:
  • Scattered light is blue or violet due to shorter wavelengths
  • Can be used to distinguish between colloidal solutions and true solutions
  • Named after John Tyndall, who discovered the phenomenon

Emulsions

• Colloidal system in which two or more liquids are mixed
• Properties:
  • One liquid is dispersed in another in the form of droplets
  • Droplets are stabilized by emulsifying agents or surfactants
  • Examples: mayonnaise, milk, and cream
  • Can be classified as:
    • Oil-in-water (O/W) emulsions
    • Water-in-oil (W/O) emulsions

Colloidal Solutions

Lyophilic Colloids

• Strongly solvated by dispersion medium (usually water)
• Examples: starch, gelatin, and proteins
• Reversible sol-gel transition
• High viscosity
• High stability due to solvation

Lyophobic Colloids

• Not solvated by dispersion medium
• Examples: metal sols, sulfur sols, and clay suspensions
• Irreversible sol-gel transition
• Low viscosity
• Low stability due to lack of solvation
• Can be stabilized by emulsifying agents or surfactants

Gels

• Disperse phase forms network of particles
• Non-flowing, semi-rigid structure
• High viscosity
• Reversible sol-gel transition
• Examples: agar agar, gelatin, and silica gel

Tyndall Effect

• Scattering of light by colloidal particles
• Observed when light passes through colloidal solution
• Scattered light is blue or violet due to shorter wavelengths
• Distinguishes colloidal solutions from true solutions
• Named after John Tyndall

Emulsions

• Two or more liquids mixed
• One liquid dispersed in another as droplets
• Droplets stabilized by emulsifying agents or surfactants
• Examples: mayonnaise, milk, and cream
• Classifications:
• Oil-in-water (O/W) emulsions
• Water-in-oil (W/O) emulsions