Ying Zhang,Hongsheng Lu,Baogang Wang,Na Wang,Dongfang Liu
A novel stimulus-responsive non-Pickering emulsion stabilized by nano-SiO2 particles was prepared in our recent study. 4-formylbenzoic acid and hexylamine through a dynamic covalent bond form a surface-active substance, which was confirmed by Fourier transform infrared (FTIR) and 1H NMR. Through optimization experiments, it was proved that a stable emulsion can be formed by low surfactant concentration (below cmc) and low nano-SiO2 particle concentration (0.5 wt %). In this emulsion, nano-SiO2 particles are not located at the interface of oil–water but dispersed in the continuous phase of the emulsion, which is different from the Pickering emulsion. The negatively charged nano-SiO2 particles and anionic surfactants repel each other, thereby synergistically stabilizing the emulsion so that the concentrations of surfactants and nanoparticles required to stabilize the emulsion are reduced. In addition, the system can also control the formation and fracture of dynamic covalent bonds by changing pH, thereby controlling the stability and demulsification of the emulsion. At the same time, this non-Pickering emulsion could be used as a microreactor for chemical synthesis and still had a high yield after three cycles. This study provides a new application direction for this environmentally friendly emulsion.
Nano SiO 2 particles (NPs) combined with organosilane surfactants present a promising avenue for the development of stable fluorine-free firefighting foams. In this study, hydrophilic nano SiO 2 particles, non-ionic organosilane surfactant (SiCare2238), and amphoteric hydrocarbon surfactant (LAMC) were prepared as a mixed dispersion to investigate the interactions between nano particles and surfactants, foaming ability, and foam stability of the mixed dispersion. Results indicated that the surface activity, electrical conductivity, and foaming ability of the mixed dispersion decreased with increasing NPs concentration. The impact of NPs on foam stability depended on the filling and blocking mechanisms within the platform boundary of the formed liquid film. At NPs concentrations below 1.5%, strong electrostatic interactions among surfactant molecules resulted in the adsorption of surfactant molecules on the nano particle surface, preventing the formation of a network structure at the platform boundary, thereby reducing foam stability. At NPs concentrations above 1.5%, a significant number of NPs formed a network structure, filling and blocking the platform boundary, leading to delayed foam drainage, coarsening, and enhanced foam stability. This study provides theoretical guidance for the application of nano particles in fluorine-free.
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