In Situ Assembly of Nanostructured Polyelectrolyte Coatings by Aqueous Phase Separation toward Outstanding Thermal Insulation and Fire Resistance

Flame-retardant surface treatments effectively reduce the fire hazard of polymeric foams but are plagued by high coating thickness and deterioration of inherent thermal insulation. Constructing a nanostructure can significantly enhance the thermal insulation of coatings, but current methods usually rely on toxic solvents and harsh conditions. Herein, we present a facile and eco-friendly strategy employing a Cu2+-assisted aqueous phase separation (APS) strategy for the assembly of nanostructured polyelectrolyte coatings in situ. Exploiting the multiple cross-linking interactions between Cu2+ and the polyelectrolyte complex (PEC), the unique nanosheet (∼200 nm) structure was assembled in the PEC coating. When coated on rigid polyurethane foam (RPUF), the thermal conductivity was reduced to 28.1 from 30.0 mW/m·K. Moreover, the coated RPUF manifests a limiting oxygen index of 36% and reduces heat/smoke release (>60%). This work provides a facile and eco-friendly strategy to cast flame-retardant nanostructured coatings for materials with excellent integrated performances.