This practical involves making a colloid mixture of cornflour and vegetable oil. This mixture can be picked up with a spoon and brought toward an electrostatic source such as a Van De Graff generator or polycarbonate strip whereupon it becomes attracted towards it. When the electrostatic source nears the colloid, it causes the cornflour particles to line up which blocks the flow of the oil. Removing the source allows the mixture to behave like a liquid once again.
Equipment typically required (per set):
The oil and cornflour is mixed in a beaker to form the colloid, stirred gently until it forms a slimy liquid consistency. The polystyrene block or polycarbonate strip is charged using a duster or the Van De Graff generator is switched on. A spoonful of the mixture is brought close to the electrostatic source and poured. If the mixture becomes charged it should stop flowing and become rigid, some parts may even snap off. As soon as the mixture is taken away from the source it should return to a liquid state once again.
- Electrostatic source (Van De Graff generator/polystyrene block/polycarbonate strip)
- 250ml Vegetable oil
- 50g of cornflour
- 400ml beaker
- Stirring rod
The word Colloid means glue-like and originates from Greek. It describes materials that are mainly liquid but also have other properties, These properties arise from the presence of macromolecules dissolved in liquid or by mixing two or more solid, liquid or gas phases.