Particle-stabilized foams as advanced materials for energy management

This thesis develops a scalable, water-based route to renewable, multifunctional foams that integrate steady-state thermal insulation, fire safety, phase-change heat storage, and acoustic damping. The materials are built from cellulose nanofibers and fumed silica nanoparticles; these serve as cooperative stabilizers of wet Pickering foams, which form hierarchical, open-cell solids upon drying. The interfacial energy is tuned (H₂O/EtOH) to promote particle adsorption at the bubbles, while cellulose nanofibers form an entangled network that suppresses drainage and preserves the gas-templated architecture after drying. The resulting foams exhibit a porosity > 98%, a density of ~22–30 kg m⁻³, specific surface areas of ~200 m² g⁻¹, and a multimodal pore system spanning the micro/meso/macro scales. Structure–property relationships reveal a compressive modulus of ~170–320 kPa, attributable to silica-reinforced nanofiber lamellae. The thermal conductivity ranges from 33 to 36 mW m⁻¹ K⁻¹, comparable to conventional polymer foams, despite a sustainable composition. Thermogravimetric and gas evolution analyses indicate the onset of major mass loss near 330–345 °C, significant char yields, and a predominance of CO₂/H₂O evolution. Fire retardancy testing demonstrates selfextinguishing behavior and superior results versus the polyurethane benchmark. To ensure dynamic thermal regulation, polyethylene glycol was incorporated into the Pickering foams as a phase-change material. Capillary confinement and hydrogen bonding prevent leakage up to a polyethylene glycol loading of ~80 wt%, while differential scanning calorimetry demonstrates sharp, repeatable melting/crystallization with latent heat values of ~55–130 J g⁻¹. Infrared thermography under irradiative heating reveals a lower maximum temperature and delayed cooling compared with the Styrofoam benchmark, evidencing coupled insulation and latent heat buffering. The thesis provides a critical mechanistic understanding of stabilizing foams using sustainable nanofibers and nanoparticles and validates the use of these materials for multifunctional energy management applications. The insights provided in this thesis are significant in terms of accelerating the industrial deployment of next-generation, high-performance, and sustainable porous materials.