Researchers in France have developed photosensitive polyurethane formulations that allow the solidification of liquid foams to be triggered and controlled using ultraviolet light.
The approach uses a photobase generator as a latent catalyst. When the formulation is exposed to UV radiation, the generator releases a base that accelerates the polyurethane reaction, allowing researchers to choose when the foam begins to solidify.
Guillaume Cotte-Carluer and colleagues at the Institut Charles Sadron in Strasbourg said the method could provide greater control over foam morphology without requiring a separate formulation for each cellular structure.
Foam properties are strongly influenced by bubble size, liquid content and the length of time for which the liquid foam is allowed to drain before curing. In conventional PU processes, bubble formation, drainage and polymerization occur simultaneously, making it difficult to adjust one of these parameters independently.
The researchers combined the UV-sensitive polyurethane formulations with a millifluidic system capable of mixing viscous components and generating foams with a uniform bubble-size distribution.
By changing the point at which the foam was irradiated, the team could control how long it drained before solidification. This made it possible to alter the final cellular morphology while retaining the same underlying formulation.
The researchers also combined the photobase generator with a conventional catalyst. They said this hybrid approach provided a still wider range of solidification behavior by combining gradual background curing with the acceleration produced by UV exposure.
The system is currently a laboratory-scale method intended primarily for the production and study of model foams. However, externally triggered curing could eventually prove useful in applications requiring precisely controlled porous structures, including insulation, filtration, lightweight components and tissue-engineering scaffolds.
The researchers said the principal innovation was the ability to obtain foams with customizable morphologies from a single formulation, rather than reformulating the chemistry to produce each structure.