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"Smart" capsules
To deliver a content, silica media are often used. Propagation then takes place via the pores of silica or by dissolving the latter, but there is no or very little control over this process.
To overcome this major drawback, scientists from Bordeaux came up with the idea of dispersing oil, which would contain a specific agent, into water. This emulsion consists of liquid oil at production temperature (between 35 and 65°C) which becomes solid at room temperature. A silica shell is then polymerised around the cooled drops, thus leading to capsules that are stable in storage. It is then possible to cause the release of the content of the capsules by heating them beyond the oil’s melting temperature. The transition from solid to liquid state results in a volume expansion of the oil contained, which is sufficient to break the silica shell. Another parameter is adjustable : the mode of release of the content, which can be either via droplet trains (by adding surfactant molecules in the water) or all at once, which allows the speed of release of the content to be controlled.
The principle, patented, is very simple, inexpensive, and has many application areas. This technique could for example be used as a food preservation indicator, enable the release of a perfume in the air, on a fabric or on the skin, or release pesticides or bactericides beyond a certain temperature.
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