Superstable Wet Foams and Lightweight Solid Composites from Nanocellulose and Hydrophobic Particles

Colloids are suitable options to replace surfactants in the formation of multiphase systems while simultaneously achieving performance benefits. We introduce synergetic combination of colloids for the interfacial stabilization of complex fluids that can be converted into lightweight materials. The strong interactions between high aspect ratio and hydrophilic fibrillated cellulose (CNF) with low aspect ratio hydrophobic particles afford superstable Pickering foams. The foams were used as a scaffolding precursor of porous, solid materials. Compared to foams stabilized by the hydrophobic particles alone, the introduction of CNF significantly increased the foamability (by up to 350%) and foam lifetime. These effects are ascribed to the fibrillar network formed by CNF. The CNF solid fraction regulated the interparticle interactions in the wet foam, delaying or preventing drainage, coarsening, and bubble coalescence. Upon drying, such a complex fluid was transformed into lightweight and strong architectures, which displayed properties that depended on the surface energy of the CNF precursor. We show that CNF combined with hydrophobic particles universally forms superstable complex fluids that can be used as a processing route to synthesize strong composites and lightweight structures.

Hierarchically Porous Ceramics via Direct Writing of Binary Colloidal Gel Foams

Hierarchically porous ceramics with a high specific surface area and interconnected porosity may find potential application as particulate filters, catalyst supports, and battery electrodes. We report the design and programmable assembly of cellular ceramic architectures with controlled pore size, volume, and interconnectivity across multiple length scales via direct foam writing. Specifically, binary colloidal gel foams are created that contain entrained bubbles stabilized by the irreversible adsorption of attractive alumina and carbon (porogen) particles at their air-water interfaces. Composition effects on foam ink rheology and printing behavior are investigated. Sintered ceramic foams exhibited specific permeabilities that increased from 2 × 10^-13 to 1 × 10^-12 m² and compressive strengths that decreased from 40 to 1 MPa, respectively, with increasing specific interfacial area. Using direct foam writing, 3D ceramic lattices composed of open-cell foam struts were fabricated with tailored mechanical properties and interconnected porosity across multiple length scales.