Understanding the factors that affect bubble dissolution under pressure is crucial for the pneumatic transport of dispersions. This study probes the kinetics of air dissolution, the air solubility at a given pressure, and the gas diffusion due to bubble dissolution to elucidate the molecular mechanisms of gas transport in liquid dispersions with varied structures and viscosities. We achieve our aims by using water-glycerol mixtures, silicone oils with different viscosities, surfactant solutions containing worm-like micelles and having different macroscopic viscosities, particle suspensions, and surfactant solutions capable of forming a condensed adsorption layer on the bubble surfaces at ambient conditions. The results show that the dissolution rate does not depend on the macroscopic viscosity for silicone oils and solutions containing worm-like micelles, indicating that gas diffusion occurs faster than the movement of big polymeric molecules and worm-like micelles. We could predict the experimentally determined diffusion coefficients by accounting for free volume in these media and using the equation for Knudsen diffusion. We show that one way to decrease the rate of bubble dissolution under pressure is to add surfactants, which can decrease the permeability of the adsorption layer formed on the bubble surface by forming a condensed adsorption layer.

Emulsification experiments with four silicone oils, having viscosities ranging from 0.01 to 30 Pa.s, were conducted in two types of media: nearly Newtonian polyvinyl alcohol (PVA) solutions and non-Newtonian mixtures induced by worm-like micelles in solutions of sodium laureth sulfate and cocoamidopropyl betaine (BS) with NaCl. The increased viscosity of BS solutions upon the addition of NaCl did not significantly affect the drop size in the formed emulsions. In contrast, the increased viscosity of solutions with higher PVA concentrations significantly reduced the drop sizes for all silicone oils. A theoretical expression predicting the maximum drop size in both types of media (nearly Newtonian and non-Newtonian) was derived and validated against experimental data. The expression accounts for shear-thinning behavior in both the aqueous and oil phases. Interfacial stress dominates the breakage of less viscous oils, while viscous stress inside the breaking drop plays a leading role for more viscous oils. The formation of emulsions with similar sizes in non-Newtonian solutions of BS with different NaCl concentrations was explained by their strongly shear-thinning behavior, which leads to nearly similar viscosity at high shear rates, despite their zero-shear viscosities differing by more than two orders of magnitude.

Preparation of particle-loaded foams, followed by drying, sintering and/or cross-linking are widely explored routes for developing lightweight ceramics with high mechanical strength. The non-sintered dry ceramic foams are less studied due to their intricate production and the assumed poor mechanical strength of the obtained “green” materials. Here we produce lightweight ceramics from foamed particle suspensions containing spherical silica particles with radii varied between 4.5 nm and 7 µm. The wet foams are prepared in the presence of cationic surfactant and were dried at ambient conditions to obtain porous materials with mass densities between 100 and 700 kg/m3. The materials containing smaller particles exhibited much higher strength (by up to 2000 times), approaching that of the sintered materials. A new theoretical expression for predicting the mechanical strength of such materials is derived and is used to explain the measured strengths of the produced materials through the van der Waals attraction between the particles in the final dry materials.

Lipid nanoemulsions and nanosuspensions are used as flavor carriers and bubble stabilizers in soft drinks and foods, as well as delivery vehicles for lipophilic drugs in pharmaceutics. Common techniques for their formation are the high-pressure and ultrasonic homogenizers. These techniques dissipate most of the input energy, which results in excessive heating and generation of free radicals that might modify sensitive ingredients. Low energy methods are also used in some applications, but they have specific limitations restricting their universal use. In the current study, we propose an alternative approach – a flow reactor with a variable temperature, which utilizes the lipids’ polymorphic transitions to induce spontaneous fragmentation of the lipid microparticles into nanoparticles. The reactor allows us to obtain emulsions or suspensions with particle diameters tunable between 20 and 800 nm when appropriate surfactants, temperature profiles, and flow rates are applied. The fragmentation is comparable to that in a high-pressure homogenizer at ca. 500 bars or higher, without creating emulsion overheating or cavitation typical for the conventional methods. The flow reactor can be scaled up to industrial applications using simple scaling rules.