Tuning stability, rheology, and fire-extinguishing performance of advanced firefighting foam material by inorganic nanoparticle flame retardants.

HYPOTHESIS: Nanoparticle-stabilized foams are extremely stable, and flame retardant inorganic nanoparticles should be able to add sealing capacity of firefighting foams on flammable liquid fuels, and hence enhance fire extinguishment performance on liquid fuel fire. In practice, how do flame retardant nanoparticles resist the destructive effect of oil molecules on foam and tune foam properties? EXPERIMENTS: We have prepared a nanoparticle-enhanced foam comprising of hydrocarbon surfactant, short-chain fluorocarbon surfactant, and nanoparticles. The interactions among nanoparticles and surfactant molecules were characterized by using dynamic surface tension and conductivity. Stability, rheology, and oil resistivity on liquid fuel of the nanoparticle-enhanced foam were evaluated systematically. Fire suppression effectiveness of the foams was verified based on a standard experiment. FINDINGS: Foam stability and oil resistivity were enhanced due to self-assembled network structures formed by jammed aggregates composed by nanoparticles and surfactants in Plateau borders and bubble films, providing structural recoverability and enhanced viscoelasticity within foam. Foams containing nano-SiO2, nano-CaCO3, nano-Al(OH)3, and nano-Mg(OH)2 show difference in fire extinguishment due to different ability to enhance foam properties. Foam containing nano-Al(OH)3 shows the strongest adaptation and could shorten fire extinguishing time by 2 times and prolong burn-back time by 2.3 times compared with commercial product.

An Eco-Friendly Quaternary Ammonium Salt as a Corrosion Inhibitor for Carbon Steel in 5 M HCl Solution: Theoretical and Experimental Investigation.

The corrosion of industrial material is a costly problem associated with global economic losses reaching trillions of US dollars in the repair of failures. Injecting corrosion inhibitors is the most practically promising method for decelerating corrosion reactions and protecting surfaces. Recent investigations have focused on surfactants as corrosion inhibitors due to their amphiphilic nature, low cost, and simple chemical preparation procedures. This study aims to investigate the performance of an environment-friendly Quaternium-22 (Q-22) surfactant which is widely used in cosmetics for C-steel corrosion inhibition in a 5 M HCl medium. Weight loss experiments were performed at different concentrations and immersion times, presenting a maximum efficiency at 2.22 mmol·L-1. The influence of Q-22 on the corrosion behavior of C-steel was elucidated using non-destructive electrochemical measurements. The overall results revealed that adding varied concentrations of Q-22 significantly decreases the corrosion rate of C-steel. The results revealed the physisorption nature of Q-22 onto the C-steel surface, with adsorption following the Freundlich isotherm (∆Hads= -16.40 kJ·mol-1). The relative inhibition performance of Q-22 was also evaluated by SEM and AFM analyses. Lastly, quantum chemical calculations based on density functional theory (DFT) demonstrated that Q-22 has promising molecular features concerning the anticorrosive mechanism.

Physical stability of N,N-dimethyldecanamide/α-pinene-in-water emulsions as influenced by surfactant concentration.

In recent years, interest in submicron emulsions has increased due to their high stability and potential applications in the encapsulation and release of active ingredients in many industrial fields, such as the food industry, pharmaceuticals or agrochemicals. Furthermore, the social demand for eco-friendly solutions to replace hazardous solvents in many dispersion formulations has steadily risen. In this study, the influence of surfactant concentration on the formation and physical stability of submicron oil-in-water emulsions using a high-pressure dual-channel homogenizer (microfluidizer) has been investigated. The formulation involved the use of a blend of two green solvents (N,N-dimethyldecanamide and α-pinene) as dispersed phase and a nonionic polyoxyethylene glycerol ester derived from coconut oil as emulsifier (Levenol® C-201), which enjoys a European eco-label. Therefore, these emulsions may find applications as matrices for agrochemicals. Physical stability and rheological properties of the emulsions studied showed an important dependence on the eco-friendly surfactant concentration. The lowest surfactant concentration (1wt%) yielded the onset of a creaming process after a short aging time and was not enough to avoid recoalescence during emulsification. On the other hand, the higher surfactant concentrations (4-5wt%) resulted in depletion flocculation, which in turn triggered emulsion destabilization by coalescence. The optimum physical stability was exhibited by emulsions containing intermediate surfactant concentrations (2-3wt%) since coalescence was hardly significant and the onset of a weak creaming destabilization process was substantially delayed.

Rheological behavior of aqueous dispersions containing blends of rhamsan and welan polysaccharides with an eco-friendly surfactant.

Small amplitude oscillatory shear and steady shear flow properties of rhamsan gum and welan gum dispersions containing an eco-friendly surfactant (a polyoxyethylene glycerol ester) formulated to mimic the continuous phase of O/W emulsions were studied using the surface response methodology. A second order polynomial equation fitted the influence of surfactant concentration, rhamsan/welan mass ratio and total concentration of polysaccharides. Systems containing blends of rhamsan and welan did not show synergism but thermodynamic incompatibility and made it possible to adjust the linear viscoelastic and low shear rate flow properties to achieve values in between those of systems containing either rhamsan or welan as the only polysaccharide. All the systems studied exhibited weak gel rheological properties as the mechanical spectra displayed the plateau or rubber-like relaxation zone, the linear viscoelastic range was rather narrow and flow curves presented shear thinning behavior, which fitted the power-law equation. While mechanical spectra of the systems studied demonstrated that they did not control the linear viscoelastic properties of the corresponding emulsions, the blend of rhamsan and welan gums was able to control the steady shear flow properties.

Development and rheological properties of ecological emulsions formulated with a biosolvent and two microbial polysaccharides.

The influence of gum concentration and rhamsan/welan gum ratio on rheological properties, droplet size distribution and physical stability of eco-friendly O/W emulsions stabilized by an ecological surfactant were studied in the present work. The emulsions were prepared with 30wt% α-pinene, a terpenic solvent and an ecological alternative for current volatile organic compounds. Rheological properties of emulsions showed an important dependence on the two studied variables. Flow curves were fitted to the Cross model and no synergistic effect between rhamsan and welan gums was demonstrated. Emulsions with submicron mean diameters were obtained regardless of the gum concentration or the rhamsan/welan ratio used. Multiple light scattering illustrated that creaming was practically eliminated by the incorporation of polysaccharides. The use of rhamsan and welan gums as stabilizers lead to apparent enhancements in emulsion rheology and physical stability.

Adsorption at the biocompatible α-pinene-water interface and emulsifying properties of two eco-friendly surfactants.

In this contribution, we provide an accurate characterization at the α-pinene/water interface of two commercial polyoxytheylene glycerol ester surfactants which differ in the number of ethylene oxide (EO) groups, comprising a systematic analysis of interfacial pressure isotherms, dynamic curves, interfacial rheology and emulsifying properties. Polyoxyethylene glycerol esters derived from cocoa oil are non-ionic surfactants obtained from a renewable source which fulfill the environmental and toxicological requirements to be used as eco-friendly emulsifying agents. α-Pinene is a renewable biosolvent completely insoluble in water, which could find numerous applications. Interfacial rheology and equilibrium interfacial pressure data fitted a rigorous reorientation model that assumes that the surfactant molecules, when adsorbed at the interface, can acquire two orientations. The surfactant with the highest number of EO groups (Levenol C201) turned out to be more surface active at the α-pinene/water interface. In addition, the surfactant with the lowest number of EO groups (Levenol H&B) is solubilized into the adjacent oil phase. Slightly concentrated α-pinene emulsions were obtained using both surfactants. Nevertheless, more stable α-pinene emulsions with smaller droplet sizes and lower polidispersity were obtained when Levenol C201 was used as emulsifier instead of Levenol H&B. The systematic characterization presented in this work provides important new findings on the interfacial and emulsifying properties of polyoxytheylene glycerol ester surfactants, which can be applied in the rational development of new biocompatible products.