Emulsifying agents with relatively strong hydrophobic groups produce O/W or W/O emulsions?

• A. O/W
• B. Both
• C. Neither
• D. W/O

Answer: (D)

Emulsifiers work by sitting at the oil–water interface with a lipophilic tail and a hydrophilic head, and the balance between these tendencies (the HLB value) determines which phase will be continuous. When an emulsifier has relatively strong hydrophobic groups, it is more lipophilic and has a low HLB. Such a surfactant stabilizes water droplets that are dispersed in oil (water-in-oil) because its lipophilic tail loves the oil phase, while its hydrophilic head can contact the water inside the droplets, forming a protective film around the droplets. This makes water-in-oil emulsions the favored type with these more lipophilic emulsifiers. In contrast, emulsifiers with higher HLB (more hydrophilic) tend to stabilize oil droplets in water (oil-in-water). For reference, low HLB values (roughly 3–6) favor W/O, while high HLB values (roughly 8–12 or higher) favor O/W. Span 80 is a classic low-HLB example that forms W/O, while Tween 80 is a high-HLB example that forms O/W.