What does plastic/interfacial film theory state?

• A. Emulsifier surrounds droplets as thin film that prevents contact and coalescence
• B. Emulsifier dissolves completely in oil
• C. Emulsifier forms micelles in water to solubilize oil
• D. Emulsifier increases interfacial tension

Answer: (A)

Plastic/interfacial film theory says that the emulsifier adsorbs at the oil–water interface to form a thin, viscoelastic (plastic) film around each dispersed droplet. This interfacial film acts as a mechanical barrier that prevents droplets from touching and coalescing, so stability arises from the film’s ability to resist rupture and keep droplets separated. Coalescence occurs mainly when the film ruptures or becomes too thin under stress, not because the emulsifier simply dissolves in oil, forms micelles in water, or increases interfacial tension.