Colorful Cocktails

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Science  26 Jul 2002:
Vol. 297, Issue 5581, pp. 479
DOI: 10.1126/science.297.5581.479b

Working with a cocktail of methyl methacrylate (MMA), divinyl benzene, octane, and glycerol, Wormuth et al. created a set of brightly colored emulsions. When illuminated with white light, a “standard” emulsion can be prepared that transmits red light but appears to be blue when viewed at higher angles. The aesthetically pleasing colors are caused by a matching of the refractive index of the droplets with that of the continuous phase for a narrow range of wavelengths, so that the rest of the spectrum is scattered. For example, raising the temperature of the standard emulsion shifts the light absorbance minima to shorter wavelengths, so that the transmitted light is a green-blue color and the scattered light is violet. The colorful emissions are only observed for a limited range of compositions and temperature (for example, at higher concentrations methyl acrylic acid can be substituted for MMA), and often the net effect is an overall turbidity of the emulsion (which happens if ethylene glycol is substituted for the glycerol). Parallel studies by the same authors have also shown that these cocktails can be polymerized to form a porous latex material. — MSL

Langmuir 10.1021/la0157566 (2002).

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