Thin coatings for fire protection: An overview of the existing strategies, with an emphasis on layer-by-layer surface treatments and promising new solutions

Catastrophes due to fires cause a lot of material damages and the loss of many human lives. They have been rising in number and severity over the years because of the extensive use of flammable materials such as polymers, which is why it is necessary to design strategies to limit their flammability. Most commercial solutions rely on adding molecules called fire retardant in the bulk of the polymers. On the other hand, concerns regarding the health and environmental hazards of this type of treatments have been growing among both the scientific community and the general public, and regulations were strengthened in response. In this context, fire retardant surface treatments have attracted a lot of the attention recently as they allow to concentrate the fire retardant effect at the interface between the material and the flame, that is, where the combustion process appears. Coatings with thicknesses ranging from the dozens of nanometers to a few micrometers are favored as they limit the amount of material used and limit the impact on the functional properties of the material. This review aims at giving an overview of the different strategies for developing thin coatings for fire protection, with a special emphasis on layer-by-layer surface treatments, which is one of the most promising solutions being developed. One pot strategies as well as several opportunities for new designs are also proposed in order to give some perspectives and new ideas on the development of novel systems.