Role of Pickering stabilization and bulk gelation for the preparation and properties of solid silica foams

Abstract

Foaming of particulate suspensions, followed by foam drying, is developed as an efficient method for production of highly porous materials with various applications. A key factor for success is the appropriate choice of surfactants which both modify the particle surface and stabilize the foam. Here we compare the efficiency of this method for silica suspensions containing two surfactants which lead to very different types of foam stabilization. Cationic TTAB leads to particle-stabilized foams (Pickering stabilization) whereas zwitterionic CAPB - to surfactant-stabilized foams. Thus we determined the general (common) features shared between the various surfactant systems: (1) The foaminess is controlled exclusively by the suspension viscosity under shearing conditions which mimic precisely the foaming process; (2) The foam stability to drainage and coarsening is controlled exclusively by the suspension yield stress; (3) The surfactant adsorption on the particle surface should occur in the time scale of seconds to minutes, thus ensuring appropriate rheological properties of the foaming suspension. Similar kinetic effects could be of high interest to other colloid systems and processes, e.g. for kinetic control of the internal structure and properties of aerogels produced from sheared suspensions, and for control of the transient rheological properties and non-Newtonian flow of particulate gels.

A Novel Approach to Fabricate Foam Ceramics from Steel Slag

“…With the increase of steel slag solid loading, the porosity of foam ceramics decreases from 85.6% to 68.4% and the compressive strength increases from 1.74 MPa to 2.93 MPa ( Figure 5). Low solid loading leads to low viscosity of suspension, which is conducive to the incorporation of more air into the ceramic slurry during agitation [34,35]. erefore, as the solid content of the steel slag increases, the porosity of foam ceramics decreases and the compressive strength increases, which can be explained by the model of Gibson and Ashby [36].…”

Generation and stability of cement soap films

“…incorporate air in, a cement paste. This first step is not as simple Unfortunately, highly viscous suspensions show lower foamabilities 9 and the complex rheology (in particular the yield stress) also modifies the stability of the foamed structure 9,10 . Secondly, the paste is also a suspension of particles, typically 1 to 100 microns in size, hence comparable to the typical thickness of fresh soap films [11][12][13] .…”

“…A first consequence is that the paste rheology is modified 14 . But this also renders the particles hydrophobic and surface-active, enabling the formation of so-called particle-stabilised foams 9,[15][16][17] . This favors the formation of particle-laden films which may ultimately solidify as cement films 18 and form closed cell foams with a low thermal conductivity 19 .…”

Combination of egg white protein and microgels to stabilize foams: Impact of processing treatments

“…Besides protein monolayers, there is burgeoning interest in using Pickering stabilization, i.e. stabilization of bubbles by solid particles (Lesov et al, 2017;Li et al, 2019b). Adsorbed particles can enhance the stability of foams against disproportionation and coalescence for longer periods by virtue of the ultra-high desorption energies of the particles once adsorbed (Binks et al, 2017).…”