Type Of Ionic Surfactant Research Articles

Molecular dynamics simulation of surfactant induced wettability alteration of shale reservoirs

Shale oil has recently received considerable attention as a promising energy source due to its substantial reserves. However, the recovery of shale oil presents numerous challenges due to the low-porosity and low-permeability characteristics of shale reservoirs. To tackle this challenge, the introduction of surfactants capable of modifying wettability has been employed to enhance shale oil recovery. In this study, we perform molecular dynamics simulations to investigate the influence of surfactants on the alteration of wettability in shale reservoirs. Firstly, surfaces of kaolinite, graphene, and kerogen are constructed to represent the inorganic and organic constituents of shale reservoirs. The impact and underlying mechanisms of two types of ionic surfactants, namely, the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) and cationic surfactant dodecyltrimethylammonium bromide (DTAB), on the wettability between oil droplets and surfaces are investigated. The wettability are analyzed from different aspects, including contact angle, centroid ordinates, and self-diffusion coefficient. Simulation results show that the presence of surfactants can modify the wetting characteristics of crude oil within shale reservoirs. Notably, a reversal of wettability has been observed for oil-wet kaolinite surfaces. As for kerogen surfaces, it is found that an optimal surfactant concentration exists, beyond which the further addition of surfactant may not enhance the efficiency of wettability alteration.

A critical assessment of the role of ionic surfactants in the exfoliation and stabilization of 2D nanosheets: The case of the transition metal dichalcogenides MoS2, WS2 and MoSe2

Transition metal dichalcogenides (TMDs), like other two-dimensional layered materials beyond graphene, have gained enormous interest in recent years owing to their distinct electronic and optical properties, and potential applicability in areas such as sensing, nanoelectronics and catalysis. Surfactant-assisted exfoliation is commonly used to prepare aqueous dispersions of TMD nanosheets, but a clear picture of the TMD and surfactant features that influence the dispersion process is still lacking. In this work, we present a systematic study of the dispersibility of MoS2, WS2 and MoSe2 in aqueous medium using a cationic (cetyltrimethylammonium bromide, CTAB) and an anionic (sodium cholate, SC) dispersant, in a wide concentration range (seven orders of magnitude) and resorting to a carefully controlled sonication-centrifugation procedure. We present detailed, high precision dispersibility curves (concentration of dispersed TMD versus concentration of surfactant used), together with zeta potential and pH measurements, allowing insight into the influence of the type of metal and chalcogen, surfactant charge and surfactant concentration, on the effectiveness of the exfoliation and stabilization. The metal (Mo vs. W) influences the dispersibility at low surfactant concentrations, while the chalcogen (S vs. Se) plays a more significant role as the surfactant concentration is increased, alongside the surfactant charge. Structural characterization by scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM) shows that the methodology applied yields well-exfoliated nanosheets with controlled mean lateral dimension (≈ 100 nm) and thickness (≤5 layers). Finally, the type of ionic surfactant (cationic vs. anionic) and its concentration play a pivotal role in the profile of the dispersibility curves, leading us to propose two types of master curves with distinct regions of phase behavior.

Novel Structural Increments for Estimating the Krafft Temperature of Ionic Surfactants in Aqueous Solutions

AbstractIn this work, we report results of our investigation on the relationship between the Krafft temperature of ionic surfactants in aqueous solutions and their chemical structure. We tested empirical values of the Krafft temperature available in literature for aqueous solutions of 234 ionic surfactants and correlated them to the surfactant chemical structure. In this work, we propose a novel set of 67 group contributions for calculation of the Krafft temperature of ionic surfactants in aqueous solutions. Using them, the Krafft temperature values in aqueous solutions for 174 anionic, 43 cationic, and 17 zwitterionic surfactants were calculated and the estimated values obtained in this way were compared with experimental values. We have demonstrated that the newly developed set of numerical values structural group contributions of the surfactants allows correct estimation of the Krafft temperature value for the tested set of data with the maximum error 7.6°C and the mean square error 3.7°C for various types of ionic surfactants in aqueous solutions.

Enhancement of thermal conductivity of polymethyl methacrylate-coated graphene/epoxy composites using admicellar polymerization with different ionic surfactants

In this study, thermally conductive graphene/epoxy composites were prepared from graphene and coated with polymethyl methacrylate (PMMA) using admicellar polymerization. In this process, the surfactant plays a key role, and two types of ionic surfactants [sodium dodecyl sulfate (SDS) and, cetyltrimethylammonium bromide (CTAB)] were used. PMMA-functionalized graphenes using SDS (S-PfRG) and CTAB (C-PfRG) were prepared as fillers, and PMMA was coated on the graphene in different forms). Both S-PfRG and C-PfRG were fabricated into epoxy composites showing different thermal conductivities. In the S-PfRG/epoxy composites, S-PfRG improved the interfacial adhesion between the filler and matrix, but because of the coating of PMMA, graphene was presented in an aggregated form. However, the C-PfRG/epoxy composite exhibited not only good interfacial adhesion but also well-dispersed graphene in the matrix. As a result, the thermal conductivity was increased to 0.670 W/mK, which was a 403% increase when compared to that of the untreated graphene/epoxy composite.

A sensing mechanism for the detection of carbon nanotubes using selective photoluminescent probes based on ionic complexes with organic dyes.

The multifunctional properties of carbon nanotubes (CNTs) make them a powerful platform for unprecedented innovations in a variety of practical applications. As a result of the surging growth of nanotechnology, nanotubes present a potential problem as an environmental pollutant, and as such, an efficient method for their rapid detection must be established. Here, we propose a novel type of ionic sensor complex for detecting CNTs – an organic dye that responds sensitively and selectively to CNTs with a photoluminescent signal. The complexes are formed through Coulomb attractions between dye molecules with uncompensated charges and CNTs covered with an ionic surfactant in water. We demonstrate that the photoluminescent excitation of the dye can be transferred to the nanotubes, resulting in selective and strong amplification (up to a factor of 6) of the light emission from the excitonic levels of CNTs in the near-infrared spectral range, as experimentally observed via excitation-emission photoluminescence (PL) mapping. The chirality of the nanotubes and the type of ionic surfactant used to disperse the nanotubes both strongly affect the amplification; thus, the complexation provides sensing selectivity towards specific CNTs. Additionally, neither similar uncharged dyes nor CNTs covered with neutral surfactant form such complexes. As model organic molecules, we use a family of polymethine dyes with an easily tailorable molecular structure and, consequently, tunable absorbance and PL characteristics. This provides us with a versatile tool for the controllable photonic and electronic engineering of an efficient probe for CNT detection.

Is there a ‘matrix suppression effect’ under fast‐atom bombardment liquid secondary ion mass spectrometry of ionic surfactants in glycerol?

AbstractSome features of a ‘matrix suppression effect’ caused by ionic surface‐active compounds under fast‐atom bombardment (FAB) liquid secondary ion mass spectrometry (LSIMS) are being revised. It is shown that abundant transfer of the glycerol matrix molecules to the gas phase does occur under FAB‐LSIMS of ionic surfactants, contrary to popular belief. This process can be obscure because of the dependence of the charge state of the glycerol‐containing cluster ions on the type of ionic surfactant. It is revealed that, while glycerol matrix signals are really completely suppressed in the positive ion mass spectra of cationic surfactants (decamethoxinum, aethonium), abundant deprotonated glycerol and glycerol‐anion clusters are recorded in the negative ion mode. In the case of an anionic surfactant (sodium dodecyl sulfate), on the contrary, glycerol is completely suppressed in the negative ion mode, but is present in the protonated and cationized forms in the positive ion mass spectra. It is suggested that such patterns of positive and negative ion FAB‐LSIMS spectra of ionic surfactants solutions reflect the structure and composition of the electric double layer formed at the vacuum‐liquid interface by organic cations or anions and their counterions. Processes leading to the formation of the glycerol‐containing ions preferentially of positive or negative charge are discussed. The most obvious of them is efficient binding of glycerol to inorganic counterions of the salts Cl− or Na+, which is confirmed by data from quantum chemical calculations. The high content of the counterions and relatively small content of glycerol in the sputtered zone may be responsible for the charge‐selective suppression of neat glycerol clusters of opposite charge to the counterions. In the case of a mixture of cationic and anionic surfactants the substitution of inorganic counterions by organic ones was observed. The dependence of the exchange rate in the surface layer is not a linear function of the bulk solution concentration, and an effect of abrupt recharging of the surface can be registered. No both positively or negatively charged pure glycerol and glycerol‐inorganic counterion clusters are recorded for the mixture. Correlations between the mass spectrometric observations and some phenomena of surface and colloid chemistry and physics are discussed. Copyright © 2007 John Wiley & Sons, Ltd.

Electrokinetic behavior and colloidal stability of polystyrene latex coated with ionic surfactants

This work is focused on analyzing the electrokinetic behavior and colloidal stability of latex dispersions having different amounts of adsorbed ionic surfactants. The effects of the surface charge sign and value, and the type of ionic surfactant were examined. The analysis of the electrophoretic mobility ( μ e ) versus the electrolyte concentration up to really high amounts of salt, much higher than in usual studies, supports the colloidal stability results. In addition, useful information to understand the adsorption isotherms was obtained by studying μ e versus the amount of the adsorbed surfactant. Aggregation studies were carried out using a low-angle light scattering technique. The critical coagulation concentrations (ccc) of the particles were obtained for different surfactant coverage. For latex particles covered by ionic surfactants, the electrostatic repulsion was, in general, the main contribution to the colloidal stability of the system; however, steric effects played an important role in some cases. For latices with not very high colloidal stability, the adsorption of ionic surfactants always improved the colloidal stability of the dispersion above certain coverage, independently of the sign of both, latex and surfactant charge. This was in agreement with higher mobility values. Several theoretical models have been applied to the electrophoretic mobility data in order to obtain different interfacial properties of the complexes (i.e., zeta potential and density charge of the surface charged layer).

The effect of surfactant type on protein displacement from the air–water interface

Displacement of the proteins (β-lactoglobulin and β-casein) from air–water interfaces by non-ionic surfactants (Tween 20 and Tween 60) and ionic surfactants (Sodium Dodecyl Sulphate (SDS), Cetyl-Trimethyl-Ammonium Bromide (CTAB) and Lyso-Phosphatidyl-Choline-Lauroyl (LPC-L)) was studied. Interfacial structure was sampled using Langmuir–Blodgett deposition onto mica for imaging by atomic force microscopy. In all cases protein displacement was found to occur through an orogenic mechanism. For the non-ionic surfactants displacement involved nucleation and growth of surfactant domains, leading to failure of the protein network, and subsequent loss of protein into the bulk phase. The surface pressure dependences of surfactant domain growth, and the failure of the network, were found to be the same for Tween 20 and Tween 60. This suggests that protein network breakdown was dominated by the mechanical properties of the network, and unaffected by any protein–surfactant binding. Displacement of protein by ionic surfactants was found to be dominated by nucleation of surfactant domains, with little domain growth prior to failure of the network. The size of the domains formed by the ionic surfactants was found to be determined by the level of the intermolecular repulsive forces. Electrostatic screening of these charges led to an increase in the size of the domains. The surface pressure at which the networks failed was found to be dependent on the type of ionic surfactant and, in all cases, to occur at higher surface pressures than that required for non-ionic surfactants. This has been attributed to surfactant-protein binding that strengthens the protein network.

Critical Micellization Concentration of Surfactants in Aqueous Solution and Free Energy of Micellization

The relationship between the critical micellization concentration (cmc) of a surfactant in solution and its free energy of micellization is probably the most widely used one in surfactant science. Until recently, most surfactants discussed in the literature were made up of one polar head group, nonionic or ionic, bonded to a single hydrophobic moiety. Recently, studies have been initiated on new types of ionic surfactants: bolaforms, surfactants with divalent counterions, gemini, or dimeric surfactants, etc. This paper first derives the relationship between the cmc and for a very general type of ionic surfactant, made up of a surfactant ion containing i polar groups of valency zs bonded to j alkyl chains, with counterions of valency zc. The form of this relationship is examined for several types of ionic surfactants. It is shown that many reported studies did not use the correct relationship to evaluate the free energy of micellization from the value of the cmc. In particular, the counterion contribution was often neglected, which resulted in large errors. The use of the correct equations is shown to yield values for the free energy of transfer of a methylene group from water to the micellar pseudophase which are largely independent of the surfactant chemical structure, as it is to be expected.

Binding characteristics of ionic surfactants with human hair

Binding isotherms of two types of ionic surfactants, CmH2m +1SO4Na (m = 8,10,12) and CnH2n + 1N+(CH3)3C1 (n=10, 12), to human hair in aqueous solutions were examined to clarify effects of hydrophobic and electrostatic interaction of ionic surfactants with hair. The binding isotherms of anionic surfactants showed cooperativity with discontinuously increasing shapes, while the binding isotherms of cationic surfactants showed a Langmuir-type, regardless of the difference of a hair condition.

From Micellar Solutions to Liquid Crystalline Phases

AbstractThe types of micelles and their sizes which exist in surfactant solutions in the isotropic concentration range in between the critical micelle concentration (Ccmc) and the concentration for liquid crystal formation (Cl.c.) are discussed. Four different types of ionic surfactants are treated: single chain surfactants with a cubic phase as the first l.c. phase single chain surfactants with a hexagonal phase as the first l.c. phase double chain surfactants with a lamellar phase as the first l.c. phase perfluoro‐surfactants.

Studies on spermicidal activity of surfactants. I. Correlation between spermicidal effect and physicochemical properties of p-menthanylphenyl polyoxyethylene (8.8) ether and related surfactants.

The spermicidal activities of seven nonionic surfactants against human spermatozoa were objectively determined by a statistical method, and two types of ionic surfactants were also studied for purposes of comparison. The nonionic surfactants, p-menthanylphenyl polyoxethylene adducts used in this work were synthesized from turpentine oil. These surfactants were used in the experiment after a careful confirmation of their chemical composition and molecular weight distribution. The spermicidal activities of the surfactants in terms of minimum concentrations to accomplish irreversible immobilization of all sperms in zero time was, in decreasing order, nonionic, cationic and anionic. When the most commonly used nonionics alone were considered, the sequence of decreasing spermicidal potency was isononylphenyl polyoxyethylene (9.0) ether (nonoxynol-9), p-menthanylphenyl polyoxyethylene (8.8) ether (menfegol), isooctylphenyl polyoxyethylene (9.0) ether (octoxynol-9). The surface tension and wetting time of these surfactants were determined with a view to finding physico-chemical measures of their spermicidal activity. In the statistical analysis regarding all the nine surfactants, there was a significant correlation (p less than 0.05) between spermicidal potency and critical micelle concentration (cmc) whereas there was no significant relationship between spermicidal potency and cmc regarding the seven nonionics. There was again no significant correlation between spermicidal potency and wetting time in all but nonionics with a common hydrophobic structure. As neither surface tension nor wetting time appeared to be a valid factor, general measure of spermicidal potency of nonionic surfactants, the partition ratios between n-octanol or n-hexane and water was determined. As a result, it was revealed that there was a significant correlation (p less than 0.05) between spermicidal potency and partition coefficient, when four types of nonionic surfactants with different hydrophobic group, which were chosen from among the seven nonionics, were tested with n-hexane. The close relationship between spermical activity and partition coefficient suggests that the spermicidal activities of these surfactants are associated with their structural affinity to the lipids of spermatozoal cell membrane.