Emulsions in Chemistry

Emulsions

• Biphasic heterogeneous systems containing two immiscible liquids
• One phase (dispersed) is finely subdivided and distributed as droplets within the other (dispersion medium)
• Dispersed phase: internal or discontinuous
• Dispersion medium: external or continuous
• Emulsifying agents stabilize emulsions by:
  • Preventing particle coalescence
  • Maintaining individual droplet integrity
  • Decreasing interfacial tension between liquids

Types of Emulsions

• Oil in water (O/W): Oil is the dispersed phase, water is the dispersion medium
• Water in oil (W/O): Water is the dispersed phase, oil is the dispersion medium

Purposes & Advantages of Emulsions

• Stable and homogeneous mixtures: of immiscible liquids
• Aqueous phase is easily flavored
• Oil taste can be masked
• Faster absorption compared to solid dosage forms
• Oral O/W emulsions:
  • Mask oil taste (liquid paraffin)
  • Improve oil absorption
• Semisolid emulsions:
  • O/W (vanishing creams)
  • W/O (cold creams)
  • O/W preferred for ease of application and removal
• Smaller particle size: makes oils more digestible and absorbable (e.g., mineral oil as cathartic)

Uses of Emulsions

• Internal Use (oral or IV injection)
• External Use (skin or mucous membrane)

Ideal Emulsifying Agent Characteristics

• Compatible with other ingredients
• Stable and non-deteriorating
• Nontoxic with respect to intended use and dosage
• Minimal odor, taste, and color
• Promotes emulsification and maintains emulsion stability

Types of Emulsifying Agents

• Carbohydrate materials: acacia, tragacanth, agar, pectin (hydrophilic colloids, O/W emulsions).
• Protein substances: gelatin, egg yolk (O/W emulsions).
• High molecular weight alcohols: stearyl alcohol, cetyl alcohol, glyceryl monostearate (thickening agents and stabilizers for O/W emulsions).
• Wetting agents:
  • Anionic, cationic, or non-ionic
  • Non-ionic: effective pH 3-10
  • Cationic: effective pH 3-7
  • Anionic: require pH greater than 8
• Finely divided solids: bentonite, magnesium hydroxide, aluminum hydroxide (O/W or W/O depending on mixing order)

Mixed Emulsifiers

• Blends of emulsifiers are more efficient for stable emulsions.
• Benefits:
  • Provide proper hydrophilic-lipophilic balance
  • Establish stable interfacial film
  • Desired consistency to product
  • Tragacanth or agar are frequently combined with acacia in O/W emulsions to increase viscosity and slow creaming.

Emulsion Preparation Methods

• Dry Gum Method
  • Emulsifying agent (e.g., acacia) mixed with oil before adding water
  • Also known as the 4:2:1 method (oil:water:emulsifier)
• Wet Gum Method
  • Emulsifier dispersed in water before adding oil
• Bottle Method
  • Emulsion formed by shaking ingredients in a closed bottle
• In Situ (Nascent) Soap Method
  • Soap formed in situ as the emulsifier

Steps in Emulsion Preparation

• Primary emulsion: thick, creamy, and stable emulsion (oil, acacia, water)
• Dilution: addition of other substances

Methods of Emulsification

• Continental or Dry Gum Method (4:2:1):
  • External phase (water) added to internal phase (oil mixed with emulsifier)

Explore the fascinating world of emulsions, which are biphasic heterogeneous systems containing immiscible liquids. This quiz covers the types of emulsions, their stabilization methods, and the purposes and advantages they offer in various applications. Test your knowledge on oil in water and water in oil mixtures!