Surface activity, foam properties and aggregation behavior of mixtures of short-chain fluorocarbon and hydrocarbon surfactants

Fluoroether Double-Chain Phosphate Surfactants: An Exploration of Alternatives to Fluorotelomer Surfactants

While legacy fluorosurfactants have already been categorized as persistent organic pollutants, there appeared to be many strategies to develop alternatives. In this work, fluoroether double-chain phosphate surfactants (C72 diPAP-Na and C72 diPAP-NH4) were designed and synthesized with the initial intention of exploring the creation of new fluorosurfactants containing oxygen heteroatoms in the fluorocarbon chain segments to provide an alternative to the legacy long-chain fluorosurfactants. Furthermore, it was expected that they would even exceed the existing 6:2 fluorotelomer surfactants (6:2 diPAP-Na and 6:2 diPAP-NH4). Compared with characterizations of surface activity, foam performance, and wettability, the results showed that each of them has its own distinctive performance. Although the C72 series as new fluoroether surfactants cannot fully replace the 6:2 series of fluorosurfactants in terms of performance, there is a possibility of substitution in some aspects, which is of positive significance for further exploration to improve alternatives to legacy fluorosurfactants.

Rheological Properties of Gel Foam Co-Stabilized with Nanoparticles, Xanthan Gum, and Multiple Surfactants

Gel foam has the advantages of gel and foam and shows good prospects for applications in the fields of fire prevention and extinguishing. Rheology has a significant impact on the application of gel foam, but there is little related research. In the present study, hydrophilic silica nanoparticles (NPs) and water-soluble polymer xanthan gum (XG) were combined with fluorocarbon surfactant (FS-50) and hydrocarbon surfactant (APG0810) to create gel foam. The foaming ability and foam drainage were evaluated. The gel foam's rheology, including its flow behavior and viscoelasticity, was systematically investigated. The results show that the foaming of the FS-50/APG0810 mixture decreases but the foam drainage increases in the presence of NPs and/or XG. All of the foams belong to the category of non-Newtonian fluids with shear thinning behavior. The flow curves of the foams are consistent with the Cross model. The presence of XG/NPs enhanced the foam viscoelasticity of the FS-50/APG0810 mixture. The silica NPs showed a better ability to enhance foam viscoelasticity but a worse ability to stabilize the foam compared to XG. This research can offer theoretical support for the industrial usage of gel foam.

Synthesis of Carboxyl Modified Polyether Polysiloxane Surfactant for the Biodegradable Foam Fire Extinguishing Agents

It is necessary to develop novel and efficient alternatives to fluorocarbon surfactant and prepare fluorine-free environmentally-friendly fire extinguishing agent. The carboxyl modified polyether polysiloxane surfactant (CMPS) with high surface activity was synthesized via the esterification reaction using hydroxyl-containing polyether modified polysiloxane (HPMS) and maleic anhydride (MA) as raw materials. The process conditions of the esterification reaction were optimized by orthogonal tests, and the optimum process parameters were determined as follows: reaction temperature of 85 °C, reaction time of 4.5 h, isopropyl alcohol content of 20% and the molar ratio of HPMS/MA of 1/1. The chemical structure, surface activity, aggregation behavior, foam properties, wetting properties and electron distribution were systematically investigated. It was found that the carboxyl group was successfully grafted into silicone molecule, and the conjugated system was formed, which changed the interaction force between the molecules and would affect the surface activity of the aqueous solution. The CMPS exhibited excellent surface activity and could effectively reduce the water's surface tension to 18.46 mN/m. The CMPS formed spherical aggregates in aqueous solution, and the contact angle value of CMPS is 15.56°, illustrating that CMPS had excellent hydrophilicity and wetting performance. The CMPS can enhance the foam property and has good stability. The electron distribution results indicate that the introduced carboxyl groups are more inclined towards the negative charge band, which would be conducive to weak the interaction between molecules and improve the surface activity of the solution. Consequently, new foam fire extinguishing agents were prepared by using CMPS as a key component and they exhibited excellent fire-fighting performance. The prepared CMPS would be the optimal alternative to fluorocarbon surfactant and could be applied in foam extinguishing agents.

Study on the effect of nanoparticles combined with silicone surfactant and cationic surfactant on foam and fire extinguishing performance

Aqueous film-forming foam (AFFF) in firefighting foam can effectively extinguish oil fire. However, AFFF will be phased out due to the presence of persistent organic pollutants such as perfluorooctane sulfonates. It is necessary to explore environment-friendly foam extinguishing agent. Silicone surfactant is a kind of environmentally friendly surfactants with high surface activity, which can be used as a substitute for fluorocarbon surfactant. In this study, silicone surfactant and cationic surfactant were combined to adsorb nanosilica particles to form a multiphase system. The foaming property and foam stability of the multiphase system were tested by stirring method. The foam suppression effect on fuel vapor, fire extinguishing, and burn-back performance was tested by self-designed foam suppression device and foam generating device of porous glass with recyclable liquid supply. The experimental results show that foam stability is enhanced and the foaming property is slightly decreased after the addition of nanoparticles. When the component of three-phase foam reaches the optimum, its suppression effect on fuel vapor is better than that of two-phase foam. The results of fire extinguishing and burn-back performance test showed that the fire extinguishing effect of three-phase foam was slightly worse than that of AFFF, but it has extremely strong burn-back performance.

Application of Nanotechnology in Extinguishing Agents

Extinguishing agents are a very important tool in the field of security, both in terms of private and social aspects. Depending on the type of burning substance and place of fire, appropriately prepared and developed solutions should be used. We can distinguish, among others, materials, powders or foaming agents. Modifications introduced into them, including ones based on the achievements in the field of nanotechnology, can improve their safety of use and extend their service life. Such amendments also reduce the costs of production and neutralization of the area after a fire, and increase the fire extinguishing effectiveness. The introduction of nanoparticles allows, e.g., shortening of the fire extinguishing time, reduction of the risk of smoke emission and the toxic substances contained in it, and an increase in the specific surface of particles and thus increasing the sorption of pollutants. The elaborations use metal nanoparticles, e.g., NP-Ag, metal oxides such as NP-SiO₂, as well as particles of substances already present in extinguishing agents but treated and reduced to nanosize. It should be noted, however, that all changes must lead to obtaining a tool that meets the relevant legal requirements and has appropriate approvals.

Effect of silicones and polymers on the wetting and foaming properties of anionic and nonionic hydrocarbon surfactants

To better understand the effects of nonionic silicones and polymers on the wetting and foaming properties of anionic and nonionic hydrocarbon surfactants and different forces between molecules, nonionic silicone surfactant (GT-248), polymer (HPMC), anionic surfactant (AES), and nonionic surfactants (APG0810) were selected. The CMC ratio is used as a reference to determine the concentration ratio of the APG0810/GT-248 and AES/GT-248 compound solutions, after which HPMC was added to form a compound solution to test the wetting and foaming properties of the compound solution. The results showed that GT-248 obtained a high density of methyl groups on the surface of the solution due to its excellent spreadability and good flexibility of the siloxane chain, effectively reduces the surface tension and wetting time of AES and APG0810 solutions. But in terms of foam performance, after adding GT-248 to solution, the foam stability of AES solution is enhanced, the foam height of AES solution was reduced by 33.7%, the foam stability of APG0810 solution is weakened a lot, and the foam height of APG0810 solution was reduced by 85.4%. Mainly because of the difference in electronegativity between the AES and APG0810 head groups, the strong electronegativity between the AES head groups resulted in a smaller number of GT-248 insertions in the liquid film, which weakened the defoaming effect of GT-248. The weak interaction between the head groups of APG0810 resulted in a higher amount of GT-248 in the liquid film, and thus, the foam performance was greatly reduced. After the AES/GT-248 compound solution was preferred, by comparing the viscosity, surface tension, and the half-life of the foam, it was found that the addition of low concentration of polymer effectively improved the half-life of the foam without affecting the foaming properties, and the final choice of 4:1(AES/GT-248) + 1mgHPMC and 2:1(AES/GT-248) + 1mgHPMC composite solutions can be used as a superior dust suppression material.

Study on Thermal Stability of Gel Foam Co-Stabilized by Hydrophilic Silica Nanoparticles and Surfactants

The combination of nanoparticles (NP) and surfactant has been intensively studied to improve the thermal stability and optimize the performance of foams. This study focuses on the influence of silica NPs with different concentration on the thermal stability of gel foams based on a mixture of fluorocarbon (FS-50) and hydrocarbon (APG0810) surfactants. The surface activity, conductivity, viscosity, and foaming ability of the APG0810/FS-50/NPs dispersions are characterized. The effects of NP concentration on coarsening, drainage, and decay, as well as of the gel foams under thermal action, are systematically studied. Results show that NP concentration has a significant effect on the molecular interactions of the APG0810/FS-50/NP dispersions. The surface tension and conductivity of the dispersions decrease but the viscosity increases with the increase in NP concentration. The foaming ability of APG0810/FS-50 solution is reduced by the addition of NPs and decreases with the increase in NP concentration. The coarsening, drainage, and decay of the gel foams under thermal action slow down significantly with increasing NP concentration. The thermal stability of the gel foams increases with the addition of NPs and further increases with the increase in NP concentration. This study provides a theoretical guidance for the application for gel foams containing NPs and surfactants in fire-extinguishing agents.

Effects of additive dosage and coagulation bath pH on amphoteric fluorocarbon special surfactant (FS-50) blend PVDF membranes

Amphiphilic copolymers containing hydrophilic and hydrophobic blocks represented by surfactants have proven to be more effective for modifying membranes than hydrophilic copolymers. However, studies on the effects of additive and coagulation bath pH on the morphology and properties of surfactant-modified membranes have rarely been reported. Hence, this study aims to investigate the effects of the additive dosage and the coagulation bath pH on the mechanisms of phase inversion and performance improvement of amphoteric fluorocarbon special surfactant (FS-50) blended PVDF membranes. It was observed that the pure water flux increased from 114.68 LMH/bar of the original membrane M0 to 205.02 LMH/bar of the blend membrane M1, and then to 615.88 LMH/bar of the coagulation-bath-regulated membrane MPH9 with a high BSA rejection rate of 90.86%, showing a two-stage jump. The addition of FS-50 promoted the instantaneous phase inversion of the membrane, allowing the blend membrane to exhibit a higher proportion of pore characteristics and stronger permeability. After that, the mechanisms of the membrane phase inversion process affected by the coagulation bath pH were interpreted according to the pH-response characteristics of FS-50 in terms of charge repulsion effect and compressed double-electron layer effect. Furthermore, the cross-sectional morphology and the surface structure of the membrane prepared in acidic and alkaline coagulation baths were significantly affected by the pH of the coagulation bath, exhibiting different features. For one, the porosity of the membranes gradually decreased as the acidity and alkalinity of the coagulation bath increased, and the membrane MPH9 exhibited both maximum surface and overall porosity. For another, the coagulation bath pH did not negatively affect the contact angle, surface roughness and tensile strength of the membranes. Overall, adjusting the dosage of FS-50 and the pH of the coagulation bath is a promising approach to greatly enhance membrane performance.

Thermal Stability of Gel Foams Stabilized by Xanthan Gum, Silica Nanoparticles and Surfactants

The foams stabilized by nanoparticles (NPs), water-soluble polymers, and surfactants have potential application prospects in the development of new, environmentally friendly firefighting foams. In the present study, a gel foam containing a water-soluble polymer (xanthan gum, XG), hydrophilic silica NPs, hydrocarbon surfactant (SDS), and fluorocarbon surfactant (FS-50) were prepared. The surface activity, conductivity, viscosity, and foaming ability of foam dispersions were characterized. The gel foam stability under a radiation heat source and temperature distribution in the vertical foam layer were evaluated systematically. The results show that the addition of NPs and XG has a significant effect on the foaming ability, viscosity and foam thermal stability, but has a very subtle effect on the conductivity and surface activity. The foaming ability of the FS-50/SDS solution was enhanced by the addition of NPs, but decreased with increasing the XG concentration. The thermal stability of the foams stabilized by SDS/FS-50/NPs/XG increased with the addition of NPs and increasing XG concentration. Foam drainage and coarsening were significantly decelerated by the addition of NPs and XG. The slower foam drainage and coarsening are the main reason for the intensified foam thermal stability. The results obtained from this study can provide guidance for developing new firefighting foams.

Strong synergistic effect of cationic hydrocarbon surfactant and novel nonionic tri-block short-chain fluorocarbon surfactant mixtures on surface activity, wettability and solubilization

Abstract

Mixing hydrocarbon surfactants with fluorocarbon surfactants is still an important strategy to improve the economic benefits and performances of fluorocarbon surfactants and expand their range of application. Herein, we prepared a novel kind of hydrocarbon-fluorocarbon surfactant mixtures via mixing a cationic surfactant, cetyltrimethylammonium bromide (CTAB), with a tri-block nonionic short-chain fluorocarbon surfactant (F9EG13F9) in aqueous solution. The results showed that adding a small CTAB amount to F9EG13F9 (the molar fraction of CTAB in the mixture (x1) was 0.2) could greatly reduce its critical micelle concentrations (cmc) from 0.408 mmol/L to 0.191 mmol/L. At this x1, the contact angle of the mixture was the minimum (57.7 °) at 100 s on polytetrafluoroethylene film, which was even lower than that of F9EG13F9. Besides, CTAB/F9EG13F9 mixtures possessed better colloidal stability and solubilization ability toward hydrophobic dye (Sudan І) than F9EG13F9. The outstanding performances of binary surfactant mixtures benefited from the non-ideal mixing and strong synergistic effect evidence that CTAB/F9EG13F9 surfactant mixtures could be used in practical applications instead of individual F9EG13F9, thereby reducing the used cost of F9EG13F9.

Graphical abstract

Synergistic Effect of Binary Surfactant Mixtures in Two-Phase and Three-Phase Systems

Cationic alkyltrimethylammonium bromides (C_nTAB, with n = 8, 12, 16, 18) and their mixtures with n-octanol as a nonionic surfactant were chosen as a model system to study the synergistic effect on foamability (two-phase system) and floatability (three-phase system) of quartz in the presence of binary mixtures of ionic/nonionic surfactants. The foam height of one-component solutions and binary mixtures and floatability of quartz particles were characterized as a function of the surfactant concentration and the number of carbons (n) in the alkyl chain of C_nTAB. The experimental results of foamability and floatability measurements in one-component and mixed solutions revealed the synergistic effect, causing a significant enhancement in the foam height and recovery of quartz. In the presence of n-octanol, the height of foam increased remarkably for all C_nTAB solutions studied, and this effect, whose magnitude depended on the C_nTAB hydrophobic tail length, could not be justified by a simple increase in total surfactant concentration. A similar picture was obtained in the case of flotation response. The mechanism of synergistic effect observed in mixed C_nTAB/n-octanol solutions was proposed. The discussion was supported by molecular dynamics simulations, and the probable mechanism responsible for synergism was discussed. In addition, an analysis allowing accurate determination of the concentration regimes, where the synergistic effect can be expected, was given. It was shown that for the two-phase system, the n-octanol molecule preadsorption at the liquid/gas interface causes an increase in C_nTAB adsorption coverage over the level expected from its equilibrium value in the one-component solution. In the case of the three-phase system, the synergistic effect was related to the ionic surfactants serving as an anchor layer for n-octanol, which, in water/n-octanol solution (one-component system), do not adsorb on the surface of quartz.

Synthesis and Properties of Octadecyl Trimethyl Ammonium Polyacrylic Surfactants

In order to expand the application range of surfactants, octadecyl trimethyl ammonium chloride (OTAC) and polyacrylic acid (PAA) were used as raw materials to synthesize octadecyl trimethyl ammonium polyacrylic (OTAP). The molar ratios of OTAC to polyacrylic acid monomer were 1:1, 1:2 and 1:3. The synthesized compounds were named as OTAP-1, OTAP-2, OTAP-3. The obtained research results show that the best foaming ability was achieved with OTAP-1, and the best foam stability with OTAP-2. When the concentration was 2.0 g/L, the order of the emulsifying ability was: OTAP-1 > OTAP-2 > OTAP-3; when the concentration was 4.0 g/L, the emulsifying ability order was OTAP-2 > OTAP-3 > OTAP-1. OTAP-1 had a corrosion inhibition capacity of up to 85.11 %, and OTAP-2 and OTAP-3 had a sustained release rate of 81.06 % and 72.82 %, respectively. OTAP-3 had a good effect on scale inhibition, and the scale inhibition rate was 65.01 %.

Different strategies of foam stabilization in the use of foam as a fracturing fluid

An attractive alternative to mitigate the adverse effects of conventional water-based fluids on the efficiency of hydraulic fracturing is to inject foam-based fracking fluids into reservoirs. The efficiency of foaming fluids in subsurface applications largely depends on the stability and transportation of foam bubbles in harsh environments with high temperature, pressure and salinity, all of which inevitably lead to poor foam properties and thus limit fracturing efficiency. The aim of this paper is to elaborate popular strategies of foam stabilization under reservoir conditions. Specifically, this review first discusses three major mechanisms governing foam decay and summarizes recent progress in research on these phenomena. Since surfactants, polymers, nanoparticles and their composites are popular options for foam stabilization, their stabilizing effects, especially the synergies in composites, are also reviewed. In addition to reporting experimental results, the paper also reports recent advances in interfacial properties via molecular dynamical simulation, which provide new insights into gas/liquid interfacial properties under the influence of surfactants at molecular scale. The results of both experiments and simulations indicate that foam additives play an essential role in foam stability and the synergic effects of surfactants and nanoparticles exhibit more favorable performance.