Ether Carboxylate Research Articles

Adsorption, Aggregation, and Application Properties of Green Pluronic Aliphatic Alcohol Ether Carboxylic Acids and Nonionic/Amphoteric Surfactants in Water.

In the realm of colloid and interface science, new types of green surfactants, including anionic Pluronic alcohol ether carboxylate (AEC), branched alkyl glucoside (IG), and zwitterionic coconut oil amide propyl betaine (CAB), have been identified and merit further exploration. AEC, characterized by its inclusion of 5 EO and 3.5 PO units, was synthesized, and its behavior in aqueous solutions with IG and CAB was meticulously examined. Their performance in applications such as foam generation, wetting, and the dispersion and stabilization of graphene was also evaluated. At αAE5P3C = 0.5, AE5P3C/CAB exhibited superior surface and interfacial properties compared to AE5P3C/IG. In these hybrid systems, the self-assembly of micelles is predominantly influenced by hydrogen bonding, electrostatic interactions, and hydrophobic forces. Kinetic analysis further confirmed that the driving force for micelle formation in these hybrid systems is enthalpy, with the adsorption process involving a mixed diffusion-kinetic adsorption mechanism. AE5P3C/CAB demonstrated enhanced foaming ability, foam stability, and wetting properties compared to AE5P3C/IG. Intriguingly, the optimal dispersion and stabilization of graphene were achieved with AE5P3C/IG at αAE5P3C = 0.2, providing a foundational basis for its potential application in graphene-based systems. A thorough examination of the synergistic mechanisms and application potential of these three distinct surfactants in aqueous solutions was presented, taking into account various charged ions and the specific hydrophilic and hydrophobic groups of EO and PO. This study not only provides fundamental insights into their intrinsic properties but also offers a fresh perspective for the ongoing exploration of green surfactants.

Application Properties of Gemini Quaternary Ammonium Salt with Quadra‐cationic Sites and Sodium Fatty Alcohol Polyoxyethylene Ether Carboxylate Mixed Systems

AbstractThe application properties such as foam property, electrolyte tolerance, antibacterial activity and antistatic performance of the mixed systems of a novel Gemini quaternary ammonium salt with quadra‐cationic sites (TC‐GS) and sodium fatty alcohol polyoxyethylene ether carboxylate (AE9CNa) at various molar fraction of TC‐GS (αTC‐GS), were investigated systematically. Results show that TC‐GS/AE9CNa mixed systems with different ratios form a homogeneous and transparent solution, which exhibits excellent foam stability and antibacterial activity. The foam volume of the mixed system remains nearly constant from 400 s to 1000 s, and even when TC‐GS is 10 mg/L in the mixed systems, the antibacterial rates against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) for 2 min. are all exceeded 99 %. The mixed systems of TC‐GS/AE9CNa at various αTC‐GS also demonstrate the superior electrolyte tolerance, their maximum tolerance of NaCl, CaCl2 and MgCl2 is severally beyond 270 g/L, 180 g/L and 180 g/L. In addition, both TC‐GS solution and the mixed systems have good antistatic properties, which can reduce the surface resistance of polyester fabric to ≤1010 Ω.

Qualitative analysis of hydrophilic headgroup water molecular space dependence and wetting effects of solution systems on polluting coal dust

The hydrophilic head groups of the surfactants affect the interfacial tension of surfactant solutions and the internal micelle structure of the bulk surfactants. Because of this, investigating the effect of the hydrophilic head groups on the adsorption performance of surfactants is helpful in terms of revealing the wetting mechanism of surfactants on coal at the molecular level. In this work we combine molecular dynamics simulations and quantum chemistry calculations with a collection of experiments to analyze the interaction patterns between sodium dodecyl sulfonate (SDSO), sodium dodecyl sulfate (SDS), sodium fatty alcohol polyoxyethylene ether carboxylate (SSN), and sodium lauryl phosphate (LSN) with coal. The radial distribution results show that SDSO formed the closest first peak of the hydrated layer at 1.31 Å, with a probability peak of 3.92, which exhibited strong hydrogen bonding interactions that are consistent with the relative concentration and average azimuthal shift trends obtained from molecular trajectory simulations. The priority interaction types between four surfactants and water molecules were determined using the energy difference of molecular orbitals in quantum mechanics. The weak interaction between hydrophilic head groups and water molecules was qualitatively and quantitatively analyzed using the Independent Gradient Model (IGMH), and the fundamental reasons affecting the wetting of long flame coal were obtained.

Self-assembly mechanism and application performance in aqueous solutions mediated by ethylene oxide chains in alcohol ether carboxylates and cocamidopropyl betaine

Zwitterionic Cocoamidopropyl Betaine (CAB) and anionic alcohol ether carboxylates have garnered significant attention within the realms of green and colloid chemistry owing to their inherent biocompatibility, multi-responsiveness, and diverse applications. Systematic inquiry into the physicochemical properties, self-assembly mechanisms, and application efficacy of complex systems comprising alcohol ether carboxylate salts with varying ethylene oxide (EO) units (AECnH, n = 5, 7, 9) and CAB-35 in aqueous solutions was undertaken. It was discerned that the optimum physicochemical attributes of the complex system are attained at a molar ratio of AEC of 0.5 (αAEC = 0.5). Incremental augmentation in the number of EO units facilitated the formation of rod-like micelles, exhibiting relatively unstable characteristics, while a reduction in the number of EO units led to the generation of comparatively stable spherical micelles. The self-assembly of micelles in these hybrid systems predominantly hinges upon hydrogen bonding, electrostatic interactions, and hydrophobic forces. Furthermore, kinetic analysis validated that the genesis of micelles in all three hybrid systems is propelled by enthalpy, with the adsorption process entailing a mechanism characterized by mixed diffusion-kinetic adsorption. The optimal wetting performance of the complex system was observed at αAEC = 0.5, while the foam performance demonstrated a diminishing trend with escalating αAEC. This comprehensive discourse delineates the synergistic mechanisms and application efficacy of two distinct classes of green surfactants with disparate charges in aqueous solutions, while contemplating the influence of varying numbers of ethylene oxide chains. Not only does it furnish fundamental insights into their properties, but it also proffers a novel standpoint for the exploration of green surfactants.

Preparation and performance evaluation of a novel temperature-resistant anionic/nonionic surfactant

Aiming at oil extraction from a tight reservoir, the Jilin oil field was selected as the research object of this study. Based on the molecular structures of conventional long-chain alkyl anionic surfactants, a new temperature-resistant anionic/nonionic surfactant (C8P10E5C) was prepared by introducing polyoxyethylene and polyoxypropylene units into double-chain alcohols. The resulting structures were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (1H-NMR), and electrospray ionization mass spectrometry (ESI–MS). Then, based on surface tension, interfacial tension, adsorption resistance, wettability, and emulsification performance tests, the performance of C8P10E5C was evaluated. The FT-IR, ESI–MS, and NMR spectra confirmed that C8P10E5C was successfully prepared. The critical micelle concentration (CMC) of C8P10E5C in water was 2.9510 × 10−4 mol/L (the corresponding mass concentration is 0.26%), and the surface tension of the aqueous C8P10E5C solution at this concentration was 30.5728 mN/m. At 0.3% concentration, the contact angle of the C8P10E5C solution was 31.4°, which is 60.75% lower than the initial contact angle. Under high-temperature conditions, C8P10E5C can still reduce the oil–water interfacial tension to 10−2 mN/m, exhibiting good temperature resistance. At 110 °C, upon adsorption to oil sand, the C8P10E5C solution could reduce the oil–water interfacial tension to 0.0276 mN/m, and the interfacial tension can still reach the order of 10−2 mN/m, indicating that C8P10E5C has strong anti-adsorption capability. Additionally, it has good emulsifying performance; upon forming an emulsion with crude oil, the highest drainage rate was only 50%. The forced imbibition oil recovery of C8P10E5C is 65.8%, which is 38.54, 24.22, and 27.25% higher than those of sodium dodecyl benzene sulfonate, alkyl polyoxyethylene ether carboxylate, and alkyl ether carboxylate, respectively.

Tailoring electrochemically exfoliated graphene electroactive pathways in cementitious composites for structural health monitoring of constructions.

Manipulating and exerting a nanoscale control over the structure of multicomponent materials represents a powerful strategy for tailoring multifunctional composites for structural health monitoring applications. The use of self-sensing, electroactive cementitious composites in large-scale applications is severely hindered by the absence of clear directives and a thorough understanding of the electrical conduction mechanisms taking place within the cement matrix. Here we report on a nanoscale approach towards this goal which is accomplished via the development of a novel, multifunctional cementitious composite incorporating electrochemically exfoliated graphene (EEG). The use of commercially available poly(carboxylate ether)-based superplasticizer allowed us to embed in the cement mortar up to 0.8 wt% of EEG which is fully dispersed in the matrix. The multiscale investigation made it possible to assess the effect of such high dosages of EEG on the mechanical performance and hydration degree of cementitious composites. We used electrochemical impedance spectroscopy to monitor the formation of electroactive EEG-based percolation paths for charge transfer within cement mortar, the latter displaying resistivities of 2.67 kΩ cm as well as EEG-cement-EEG capacitive paths with capacitance of 2.20 × 10-10 F cm-1 for composites incorporating 0.6 wt% of EEG. Noteworthy, we have proposed here for the first time an electrical equivalent circuit for the impedance spectroscopy analysis of cementitious composites with high loadings of graphene, exceeding the percolation threshold. These findings underscore the potential of nanoscale structures for civil engineering applications and more specifically may open new avenues for the technological application of graphene-based cementitious composites in self-sensing structures.

Quaternary ammonium-based and imidazolium-based gemini surfactants: A comparison study

Gemini surfactants have aroused significant attention since their discovery due to their unique properties that arise from the particular molecular structure. However, the effect of a CC double bond in the spacer has seldom been considered, and common quaternary ammonium-based gemini surfactants have seldom been compared with imidazolium-based ones. In this work, four gemini surfactants, denoted as 12–4-12, 12–4u-12, C12im-4-C12im, and C12im-4u-C12im were synthesized and characterized, and the effects of CC double bond in the spacer and hydrophilic headgroup on the fundamental properties were investigated. The results showed that imidazolium-based gemini surfactants (C12im-4-C12im and C12im-4u-C12im) have lower critical micelle concentration (cmc), greater efficiency and effectiveness in reducing surface tension, and superior ability to generate micelles compared to the corresponding quaternary ammonium-based ones, but showed comparatively lower salt resistance, foaming, and antibacterial activity. The introduction of CC in the spacer further decreased the cmc and the Gibbs free energy of micellization, and enhanced the antibacterial activity, but barely affected interfacial adsorption, the efficiency in reducing surface tension, micelle size, or foaming. None of the four gemini surfactants alone was capable of decreasing the interfacial tension to an ultra-low value. The incorporation of sodium cetanol polyoxyethylene ether carboxylate not only significantly decreased the interfacial tension (<10−2 mN·m−1), but also remarkably enhanced the salt resistance capacity up to 80,000 mg·L−1. This information may be helpful for designing new gemini surfactants tailored for different potential applications.

Comparison of mechanical properties of concrete incorporated with Multiwalled Carbon nanotube and partial replacement of cement with flyash

Concrete incorporated with Carbon Nanotubes is an evolving research area. The major reason for this research is due to the significant properties of the Multiwalled Carbon Nanotubes (MWCNT). This research article explained the comparison of the mechanical properties of the concrete. The cement is replaced with fly ash at 20% in its volume. The concrete mechanical properties such as compressive strength, Flexural and Split Tensile strength of the concrete were done. In this research three different levels of incorporations of MWCNTs were done. They are 0.025%, 0.050% and 0.075% in weight of cement were done. In this research three test specimens were casted in each mixes. Totally five mixes were done. They are Conventional Concrete (CC), Fly ash replaced concrete (CF), Fly ash replaced concrete and 0.025% of MWCNT (CNT 1), Fly ash replaced concrete and 0.050% of MWCNT (CNT 2) and flyash replaced concrete and 0.075% of MWCNT (CNT 3). Totally, 84 specimens were 42 cubes, 21 cylinder and 21 prisms were casted in this research. The magnetic stirring method was used for surface decoration or dispersion in Poly Carboxylate Ether for MWCNT.

Comprehensive Assessment of Exposure Pathways for Perfluoroalkyl Ether Carboxylic Acids (PFECAs) in Residents Near a Fluorochemical Industrial Park: The Unanticipated Role of Cereal Consumption.

With the replacement of perfluorooctanoic acid (PFOA) with perfluorinated ether carboxylic acids (PFECAs), residents living near fluorochemical industrial parks (FIPs) are exposed to various novel PFECAs. Despite expectations of low accumulation, short-chain PFECAs, such as perfluoro-2-methoxyacetic acid (PFMOAA), previously displayed a considerably high body burden, although the main exposure routes and health risks remain uncertain. Here, we explored the distribution of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in diverse environmental media surrounding a FIP in Shandong Province, China. PFECAs were found at elevated concentrations in all tested matrices, including vegetables, cereals, air, and dust. Among residents, 99.3% of the ∑36PFAS exposure, with a 43.9% contribution from PFECAs, was due to gastrointestinal uptake. Dermal and respiratory exposures were negligible at 0.1 and 0.6%, respectively. The estimated daily intake (EDI) of PFMOAA reached 114.0 ng/kg body weight (bw)/day, ranking first among all detected PFECAs. Cereals emerged as the dominant contributor to PFMOAA body burden, representing over 80% of the overall EDI. The median EDI of hexafluoropropylene oxide dimer acid (HFPO-DA) was 17.9 ng/kg bw/day, markedly higher than the USEPA reference doses (3.0 ng/kg bw/day). The absence of established threshold values for other PFECAs constrains a comprehensive risk assessment.

Controlling the Formation of Electroactive Graphene-Based Cementitious Composites: Towards Structural Health Monitoring of Civil Structures.

The development of composites combining multiple components each one imparting a specific function to the ensemble is highly sought after for disruptive applications in chemistry and materials science, with a particular importance for the realization of smart structures. Here, we report on the development of an unprecedented multifunctional cementitious composite incorporating reduced graphene oxide (rGO). By design, this material features significantly enhanced electrical properties while retaining the excellent cement's hydration and microstructure. The multiscale investigation on the chemical and physical properties of the dispersion made it possible to establish an efficient preparation protocol for rGO aqueous dispersion as well as rGO-based cementitious composites using a commercial poly(carboxylate ether)-based superplasticizer. The conduction mechanisms within the matrix of rGO containing mortars were unraveled by electrochemical impedance spectroscopy revealing conductive paths originating from bulk cement matrix and rGO nanosheets in composites with rGO loadings as low as 0.075 wt. %. For this rGO loading, we observed the reduction of the resistivity of bulk cement mortar layers from 18.3 MΩ cm to 2.8 MΩ cm. Moreover, the addition of 0.2 wt. % of rGO resulted in the formation of rGO conductive paths with the resistivity of 51.1 kΩ cm. These findings represent a major step forward towards the practical application of graphene-based materials in structural health monitoring of concrete structures.

Cellulose-based polypropoxy ether carboxylates as highly compatible, effective, and migration-resistant plasticizers for poly (lactic acid)

The utilization of cellulose for enhancing the strength, the PLA has received significant attention, however, poor interfacial compatibility of solid cellulose with PLA matrix still hinders their broader application. Herein, highly compatible cellulose-based polypropoxy ether carboxylates (CPPEC) were firstly manufactured via propoxylation of cellulose and following esterification with acetic acid, butyric acid, as well as oleic acid, respectively. Liquid CPPEC delivered excellent performances to PLA, especially, the values of elongation at break and low-temperature resistance of PLA blended with cellulose-based polypropoxy ether acetate (PLA/CPPEA) were respectively increased by 630.9 % and 146.3 % compared with those of neat PLA due to the synergistic effect of propyl and methyl groups in CPPEC with PLA matrix. Additionally, migration resistance of PLA/CPPEA increased 14.3 and 11.2 times, respectively, compared with those of PLA specimens blended with epoxidized soybean oil and dioctyl phthalate. All findings suggest that the CPPEC is suitable for large-scale application in the PLA industry.

Competition between hydrogen bonding and electrostatic repulsion in pH-switchable emulsions

Electrostatic interactions and hydrogen bonding play important roles in the stabilization of self-assembled systems. However, the competition between hydrogen bonding and electrostatic repulsion in emulsions hasn’t been reported. Herein, we report on electrostatic repulsion overcoming hydrogen bonding in oil-in-water (O/W) emulsions prepared by the mixture of escin and hydrophilic silica nanoparticles triggered by pH, in which the location of the nanoparticles is reversibly transformed from being adsorbed at the oil–water interface to being dispersed in the continuous phase. Escin adsorbs on silica particles in alkaline solution by its hydroxyl groups to endow the particles with surface activity, yielding a stable Pickering emulsion. However, such adsorption via hydrogen bonding is reversed by electrostatic repulsion between carboxylate ions and negatively charged silica particles after escin was converted to sodium aescinate. Demulsification occurred after silica particles reverted to being hydrophilic, which could further co-stabilize the oil-in-dispersion (OID) emulsions with sodium aescinate through electrostatic repulsion after re-homogenization. Pickering or OID emulsions with high internal phase volume fraction could also be obtained. This strategy is universal for O/W emulsions stabilized by nanoparticles and similarly charged surfactants with a polar headgroup near the nonionic functional group, e.g. silica plus polyoxyethylene lauryl ether carboxylate. This work aids in understanding the role of electrostatic repulsion and hydrogen bonding in stabilizing emulsions and sheds light on the design of smart surfactants for practical applications.

“The Exploration of a Double and Ternary Composite of Self-Compacting Concrete with Metakaolin and GGBS’’

Self-Compacting Concrete (SCC) is a modern form of concrete that does not involve vibration it during laying or compaction operations. The use of fine materials such as Metakaolin (MK) and GGBS can ensure the required concrete property. One possibility for minimising the cost of self-compacting concrete is to employ mineral admixtures such as Metakaolin and GGBS. It also lowers the heat of hydration. This study adopted (OPC 53) and M30 grade of concrete. In the first trail, MK was kept constant at 5% while GGBS was varied starting at 30% with increments of 5% (30%, 35%, and 40%). In the second trail, MK was kept constant at 10% while GGBS was varied starting at 30% with increments of 5% (30%, 35%, and 40%) replacement by the weight of Portland cement, and performance is assessed and compared to conventional concrete mix. The effect of mineral admixtures on self-compacting concrete workability, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity, With a water cement ratio of 0.47 and manufacturing sand as fine aggregates and 12.5 mm coarse aggregates, a powder content of 520 kg/m3 (as per IS code10262-2019) is chosen as the binder material (Fine aggregate and cement) To improve the flow of the concrete, the superplasticizer poly carboxylate ether was used. As a result, self-compacting concrete's flow and filling capacities have significantly improved. MK5 (double blended mix) and MK5 + GGBS35 (triple blended mix) have higher 28-day strength than other mixes, while MK5 + GGBS35 has a higher modulus of elasticity than other mixes.

Degradation of emerging per- and polyfluoroalkyl substances (PFAS) using an electrochemical plug flow reactor

In recent years, shorter-chain fluorinated compounds have been manufactured as alternatives to legacy per- and polyfluoroalkyl substances (PFAS) after a global ban on some long-chain PFAS. This study is the first to investigate the degradability of emerging PFAS by an electrochemical plug flow reactor (EPFR). Ten different emerging PFAS, representing classes of fluorotelomer alcohol, perfluoroalkyl ether carboxylate, polyfluoroalkyl ethersulfonic acids, perfluoroalkyl ether/polyether carboxylates, perfluoroether sulfonate, N-alkyl perfluoroalkylsulfonamido carboxylate, fluoroalkyl phosphonic acid, and perfluoro alkane sulfonamide were investigated. The process kinetics was performed. The degradation of parent compounds increased with increasing retention time (RT). At 45.2 min of RT, the degradation of parent compounds ranged between 68%−100% with a current density of 17.2 mA/cm2. A linear increase in pseudo-first order rate constants was observed for all PFAS with increasing current density from 5.7 to 28.7 mA/cm2 (R2 > 0.91). The effect of pH, natural organic matter, and bicarbonate on the degradation, defluorination, and fluorine mass balance are reported. Alkaline pH (11) caused a decrease in degradation for all PFAS. While the presence of natural organic matter (NOM) significantly decreased the degradation and defluorination processes, the presence of bicarbonate at all studied concentrations (25, 50, and 100 mg/L) did not affect the process efficiency. The defluorination reduced to 34% from 81% with 15 mg/L NOM. The unknown/undetected fluorine fraction also increased in the presence of 15 mg/L NOM indicating the formation of NOM-PFAS complexes. Additionally, C2-C8 perfluoro carboxylic acids (PFCAs), one perfluoro sulfonic acid (PFSA), two H-PFCAs, and 4:2 fluorotelomer sulfonate (FTS) were identified as degradation byproducts in suspect screening. The electrical energy per order for PFAS ranged between 1.8 and 19.4 kWh/m3. This study demonstrates that emerging types of PFAS can potentially be degraded using an EPFR with relatively low electrical energy requirements.

Sodium fatty alcohol polyoxyethylene ether carboxylate/cationic surfactant binary system for high‐salt oil reservoir

AbstractHigh salinity has been a major challenge in oil recovery. Here, two binary systems composed of sodium fatty alcohol polyoxyethylene ether carboxylate (AECM) and cationic surfactants, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPyCl) were developed. Their fundamental properties; namely, oil/water interfacial tension, wettability, emulsification, adsorption, and oil‐washing were investigated and compared. The results showed that both AECM–CTAB (4:6–7:3, m/m) and AECM–CPyCl (5:5–6:4, m/m) could decrease oil/water interfacial tension below 10−2 mN/m. Even the total salinity was close to 200,000 mg/L after 7 days of quartz sand adsorption, showing a good interfacial activity and excellent anti‐adsorption properties. All these compound drives could effectively change the wettability of the glass surface, which reduced the contact angle to a minimum of 54.76°. In addition, the emulsification time could reach up to 24 h at 85°C, with excellent emulsification performance at high temperatures. The oil washing efficiency could reach 74.68% after 48 h. According to our comprehensive analysis, the best formulation was obtained at AECM/CTAB ratio of 5:5.

Dilution and packing of anionic liquid surfactant in presence of divalent and trivalent counter-ions

Alkyl ether carboxylates are part of a new class of ionic liquids based on the Concept of Melting Point Lowering due to Ethoxylation (COMPLET) and possess unique aggregation behaviour due to the simultaneous anionic and non-ionic nature of the surfactant anion. Previous publications on H[C8E8c] (Polyoxyethylene(8) octyl ether carboxylic acid) and its monovalent salts have shown a variety of phases in aqueous systems with a transition from small spherical micelles at high water contents towards a phase of interdigitated head groups at low water contents. In the present paper, we examine the shorter homologue H[C8E5c] (Polyoxyethylene(5) octyl ether carboxylic acid) and its di- and trivalent transition and rare earth metal salts using X-ray scattering methods in the small- and wide-angle range (SWAXS). These measurements confirm the presence of spherical micelles in diluted aqueous systems which aggregate and whose head groups interdigitate at higher concentrations of the isotropic, non-birefringent ionic liquid. Swelling experiments yield two-dimensional swelling of the microstructure, and combined with the scattering pattern, the data infer prolate spheroidal direct (o/w) micelles with interdigitated head groups, which align to form short linear chains. These chains are offset to form a localised hexagonal close-like packing of the micelles. Most interesting, within this packing, the metal cations are confined into channels between the micelles in linear chains with ion-ion distances of 0.4–1.1 nm. In particular, in the water-free ionic liquid, this confinement may be responsible for some of the unique properties of these systems. It is suggested that the confinement of the cations leads to strong ion-ion aggregation that could be at the origin of the very peculiar magnetic properties of these simple one-component liquids, which contrasts with classical ferrofluids, in which magnetic nanoparticles are dispersed in another liquid.

Mechanistic Investigations of Thermal Decomposition of Perfluoroalkyl Ether Carboxylic Acids and Short-Chain Perfluoroalkyl Carboxylic Acids.

In this study, we investigated the thermal decomposition mechanisms of perfluoroalkyl ether carboxylic acids (PFECAs) and short-chain perfluoroalkyl carboxylic acids (PFCAs) that have been manufactured as replacements for phased-out per- and polyfluoroalkyl substances (PFAS). C-C, C-F, C-O, O-H, and C═C bond dissociation energies were calculated at the M06-2X/Def2-TZVP level of theory. The α-C and carboxyl-C bond dissociation energy of PFECAs declines with increasing chain length and the attachment of an electron-withdrawing trifluoromethyl (-CF3) group to the α-C. Experimental and computational results show that the thermal transformation of hexafluoropropylene oxide dimer acid to trifluoroacetic acid (TFA) occurs due to the preferential cleavage of the C-O ether bond close to the carboxyl group. This pathway produces precursors of perfluoropropionic acid (PFPeA) and TFA and is supplemented by a minor pathway (CF3CF2CF2OCFCF3COOH → CF3CF2CF2· + ·OCFCF3COOH) through which perfluorobutanoic acid (PFBA) is formed. The weakest C-C bond in PFPeA and PFBA is the one connecting the α-C and the β-C. The results support (1) the C-C scission in the perfluorinated backbone as an effective PFCA thermal decomposition mechanism and (2) the thermal recombination of radicals through which intermediates are formed. Additionally, we detected a few novel thermal decomposition products of studied PFAS.

Effect of oxyethylene and oxypropylene groups on the interfacial structure and property of extended surfactants: Molecular simulation and experimental study

Extended surfactants including oxyethylene (EO) and oxypropylene (PO) groups have great potential applications in the fields of oil recovery, separation and extraction, fabric washing, medicine and cosmetics vehicles. In this work, the interfacial structure and dynamic property of six alkyl polyoxypropylene polyoxyethylene ether carboxylates (C12POmEOnC, m = 5 and 15, n = 5, 10 and 15) at the water/oil interface were investigated with interfacial tension (IFT) experiments and molecular dynamics (MD) simulations. C12PO15EO5C was found to reduce the experimental IFT value to the order of 10-3 mN/m. Further, the interfacial thickness, stretch degree, hydrogen bond number and radial distribution function were calculated and analyzed in detailed simulations. The simulation results demonstrated that long PO chain curled in a helical shape to wrap hydrophilic oxygen atoms in the oil phase and reached a compact arrangement on the interface but short PO chain could not; long EO chain partially laid flat on the interface (about 5 EO units) and partially extended into the aqueous phase bringing the hydrophilic oxygen atoms close to water molecules while forming vacancies on the water side. Therefore, C12PO15EO5C had the tightest interfacial arrangement. Theoretical and experimental results are in fairly good agreement and they will provide enlightening insights into the design and synthesis of more effective extended surfactants.

Synergistic effects of Gemini cationic surfactants with multiple quaternary ammonium groups and anionic surfactants with long EO chains in the mixed systems

In this study, two different anionic surfactants containing long polyoxyethylene chains involving sodium fatty alcohol ether carboxylates (AE9C) as well as isomeric sodium fatty alcohol ether sulfates (iso-AE9S) are mixed with a new Gemini cationic surfactant bearing four quaternary ammonium groups (TC-GS). Then, the surface properties and aggregation behavior of the two mixed systems were investigated. The effect of the long polyoxyethylene chains on the conformation and hydration of the hydrophilic head group of AE9C and iso-AE9S weakened their negative charge density, thus hindering their excessive electrostatic adsorption with TC-GS and improving the stability of the mixed systems. The positive synergistic effects of TC-GS/AE9C and TC-GS/iso-AE9S exhibited significantly lower critical micelle concentration, faster diffusion rates, and superior wetting capability compared to single surfactants. The micellization process of both mixed systems is spontaneously enthalpy-driven, and the diffusion-adsorption process is consistent with the mixed diffusion-kinetic mechanism. Finally, both mixed systems are capable of forming complex and interesting aggregate morphologies, with TC-GS/AE9C can form multilayer spherical vesicles and TC-GS/iso-AE9S can form multicompartment concentric spherical vesicles.

Rock–Fluid Interactions of Alkyl Ether Carboxylate Surfactants with Carbonates: Wettability Alteration, ζ-Potential, and Adsorption

This work evaluated the rock–fluid interactions of two linear alkyl ether carboxylate (AEC) surfactants C11E11A and C12E7A in carbonates: wetting ability, ζ-potential, and adsorption capacity. Contact angle measurements showed that the ability of AECs to hydrophilize the surface is strongly affected by the ethylene oxide (EO) chain length and the presence of electrolytes. An AEC with a shorter EO chain C12E7A demonstrated a better wetting ability and decreased the contact angle value on the limestone surface from 113 to 27 ± 11° in deionized (DI) water and until 17 ± 5° in 5 wt % NaCl. The mechanism of surfactant action was assessed through thermodesorbed hydrocarbon analysis and organic matter characterization with the help of the Rock-Eval (RE) pyrolysis technique for the first time. The analysis results revealed that all surfactant compositions partially removed free oil and heavy oil components from limestone samples. Also, the presence of C12E7A molecules was detected in the samples after surfactant treatment that indicates that a better wetting ability is achieved by the combination of washing hydrocarbons and adsorption of surfactants on clean sites. The combination of ζ-potential measurements and static adsorption test on crushed limestone demonstrated that the adsorption of AECs in deionized water is not governed by electrostatic interactions and mainly occurs due to hydrogen bonding. Salinity has a significant effect on the adsorption behavior of AECs and leads to the partial destruction of hydrogen bonds and the shift from monomolecular adsorption in DI water to polymolecular adsorption in brines. The adsorption of C11E11A achieved ∼9 mg/g-rock and was higher than that of C12E7A, showing a maximum value of ∼4 mg/g-rock. This work provides a set of experiments that characterize the behavior of AECs during interactions with carbonate rock and describes a novel approach of the wettability shift mechanism assessment through RE pyrolysis.