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How to Make Colloidal Silica

Colloidal silica consists of silica spheres only a few hundred nanometers in diameter. Since the size of these spheres is comparable to the wavelength of most visible light, they interact strongly with light when bound in a regular series of bands and gaps known as a periodic array. In nature, the gemstone opal is an example of such an array. Most chemistry labs can easily synthesize colloidal silica.

Things You'll Need

Graduated pipette
Ammonia
Distilled water
Ethanol
100-milliliter plastic bottle with cap
Magnetic stirring rod
Magnetic stirrer
Tetraethyl orthosilicate (TEOS)
Syringe

Instructions

- 1
  Use the graduated pipette to measure 6 milliliters of ammonia, 7 milliliters of distilled water and 35 milliliters of ethanol into a clean plastic bottle.
- 2
  Place a magnetic stirring rod into the solution, and place the bottle atop a magnetic stirrer. Turn on the stirrer. Adjust the stirring speed until the solution is being stirred vigorously without splashing.
- 3
  Fill a syringe with 2 milliliters of TEOS. Inject the TEOS into the bottle as quickly as possible (i.e., within 10 seconds), without stopping the magnetic stirrer.
- 4
  Cap the bottle, and allow the magnetic stirrer to continue stirring the solution for two to three hours.

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