Long-chain Surfactants Research Articles

Surface Modification and Assembly of Transparent Indium Tin Oxide Nanocrystals for Enhanced Conductivity

In a solution-phase synthesis of nanocrystals (NCs), organic surfactants play an important role in size and shape control as well as in facilitating the stable dispersion of NCs in solvents. However, in order to use these NCs for electrical applications, the surfactants must be removed effectively. Here we report that monodisperse indium tin oxide (ITO) NCs were synthesized and stabilized with oleate/oleylamine ligands, and these long-chain surfactants were readily substituted with tetrabutylammonium hydroxide (TBAOH), forming a stable methanol dispersion. Uniform assemblies of ITO NCs were made by spin-coating the ITO–TBAOH NC dispersions with an assembly thickness controllable from 68 to 260 nm by the NC solution concentration. An annealing treatment at 120 °C and 300 °C under Ar + 5% H2 for 1 h effectively removed the TBAOH, and the ITO NC assemblies showed high transparency (>88%) and low resistivity (2.6 × 10–3 Ω·cm). Our new approach to surface modification of ITO NCs with a volatile surfactant foll...

Adsorption–desorption behavior of naphthalene onto CDMBA modified bentonite: Contribution of the π–π interaction

To enhance the removal of aromatic hydrophobic contaminants and to explore the π–π interaction between solute and adsorbent, organoclays modified with an aromatic long-chain alkyl surfactant, cetyldimethylbenzylammonium (CDMBA), were synthesized in this study. The adsorption–desorption behavior of naphthalene (NA) onto the resultant CDMBA-Bent (organoclays modified with CDMBA) was studied using batch-adsorption experiments.The structural characteristics of organobentonites were studied using X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR). The interlayer surfactant of CDMBA-Bent adopted similar packing pattern to that of CTMA-Bent (organoclays modified with CTMA), and the alkyl chain packing density of CDMBA-Bent was lower than that of CTMA-Bent under the same surfactant loading. The adsorption coefficients (koc) of CDMBA-Bent towards NA were about 1.6 times higher than those of CTMA-Bent at all surfactant loadings tested. All desorption isotherms of NA from both CDMBA-Bent and CTMA-Bent showed hysteresis. The hysteresis index (calculated as kD/kA) of NA by CDMBA-Bent was much lower than that by CTMA-Bent, indicating a higher extent of irreversibility. A strong electron donor–acceptor interaction was explored between the aromatic rings of CDMBA and NA by 1H-NMR analysis. This specific π–π interaction may account for the high adsorption capacity and irreversibility of NA onto CDMBA-Bent. These results offered new insights of the adsorption mechanism of NA onto organoclay.

Processable 3-nm thick graphene platelets of high electrical conductivity and their epoxy composites

Graphene platelets (GnPs) are a class of novel 2D nanomaterials owing to their very small thickness (∼3 nm), high mechanical strength and electric conductivity (1460 S cm−1), and good compatibility with most polymers as well as cost-effectiveness. In this paper we present a low-cost processing technique for producing modified GnPs and an investigation of the electrical and mechanical properties of the resulting composites. After dispersing GnPs in solvent N-methyl-2-pyrrolidone, a long-chain surfactant (Jeffamine D 2000, denoted J2000) was added to covalently modify GnPs, yielding J2000-GnPs. By adjusting the ratio of GnPs to the solvent, the modified GnPs show different average thickness and thus electrical conductivity ranging from 694 to 1200 S cm−1. To promote the exfoliation and dispersion of J2000-GnPs in a polymeric matrix, they were dispersed in the solvent again and further modified using diglycidyl ether of bisphenol A (DGEBA) producing m-GnPs, which were then compounded with an epoxy resin for the development of epoxy/m-GnP composites. A percolation threshold of electrical volume resistivity for the resulting composites was observed at 0.31 vol%. It was found that epoxy/m-GnP composites demonstrated far better mechanical properties than those of unmodified GnPs of the same volume fraction. For example, m-GnPs at 0.25 vol% increased the fracture energy release rate G1c from 0.204 ± 0.03 to 1.422 ± 0.24 kJ m−2, while the same fraction of unmodified GnPs increased G1c to 1.01 ± 0.24 kJ m−2. The interface modification also enhanced the glass transition temperature of neat epoxy from 58.9 to 73.8 °C.

Transfer hydrogenation of acetophenone in an organic-aqueous biphasic system containing double long-chain surfactants

Transfer hydrogenation of acetophenone catalyzed by a water-soluble ruthenium complex, RuCl2(TPPTS)2 [TPPTS: P(m-C6H4SO3Na)3], in the presence of surfactants, was studied. The results showed that the reaction was obviously accelerated by double long-chain cationic surfactants. This was attributed to the formation of vesicles. The active ruthenium catalyst was enriched at the biphasic interface owing to the static electricity attraction between ruthenium anionic species and the positive electric field of the vesicle hydrophilic interface, at the same time the water insoluble substrate was solubilized in the hydrophobic interior core of vesicles.

Development of polymer composites using modified, high-structural integrity graphene platelets

Abstract Previous studies on polymer/graphene composites have mainly utilized either reduced graphene oxide or graphite nanoplatelets of over 10 nm in thickness. In this study we covalently modified 3-nm thick graphene platelets (GnPs) by the reaction between the GnPs’ epoxide groups and the end-amine groups of a commercial long-chain surfactant ( M w = 2000), compounded the modified GnPs ( m -GnPs) with a model polymer epoxy, and investigated the structure and properties of both m -GnPs and their epoxy composites. A low Raman I D / I G ratio of 0.13 was found for m -GnPs corresponding to high structural integrity. A percolation threshold of electrical conductivity was observed at 0.32 vol% m -GnPs, and the 0.98 vol% m -GnPs improved the Young’s modulus, fracture energy release rate and glass transition temperature of epoxy by 14%, 387% and 13%, respectively. These significantly improved properties are credited to: (i) the low Raman I D / I G ratio of GnPs, maximizing the structural integrity and thus conductivity, stiffness and strength inherited from its sister graphene, (ii) the low thickness of GnPs, minimizing the damaging effect of the poor through-plane mechanical properties and electrical conductivity of graphene, (iii) the high-molecular weight surfactant, leading to uniformly dispersed GnPs in the matrix, and (iv) a covalently bonded interface between m -GnPs and matrix, more effectively transferring load/electron across interface.

Removal of bisphenol A from wastewater by Ca-montmorillonite modified with selected surfactants

Organo Arizona SAz-2 Ca-montmorillonite was prepared with different surfactant (DDTMA and HDTMA) loadings through direct ion exchange. The structural properties of the prepared organoclays were characterized by XRD and BET instruments. Batch experiments were carried out on the adsorption of bisphenol A (BPA) under different experimental conditions of pH and temperature to determine the optimum adsorption conditions. The hydrophobic phase and positively charged surface created by the loaded surfactant molecules are responsible for the adsorption of BPA. The adsorption of BPA onto organoclays is well described by pseudo-second order kinetic model and the Langmuir isotherm. The maximum adsorption capacity of the organoclays for BPA obtained from a Langmuir isotherm was 151.52mg/g at 297K. This value is among the highest values for BPA adsorption compared with other adsorbents. In addition, the adsorption process was spontaneous and exothermic based on the adsorption thermodynamics study. The organoclays intercalated with longer chain surfactant molecules possessed a greater adsorption capacity for BPA even under alkaline conditions. This process provides a pathway for the removal of BPA from contaminated waters.

Intercalation of a Surfactant with a Long Polyfluoroalkyl Chain into a Clay Mineral: Unique Orientation of Polyfluoroalkyl Groups in Clay Layers

Eight novel polyfluorinated surfactants (C(n)F(2n+1)CONH(CH2)2 N(+)(CH3)2C16H33 Br(-); abbreviated as CnF-S, where n = 1, 2, 3, 4, 5, 6, 8, 10) were synthesized and their intercalation into cation-exchangeable clay was investigated. All of the polyfluorinated surfactants intercalated in amounts exceeding the cation exchange capacity (CEC) of the clay. The C4F-S and C5F-S surfactants exhibited intercalation up to 480% of the CEC as a saturated adsorption limit. On the basis of X-ray analysis, CnF-S surfactants intercalated between clay nanosheets to form a bilayer structure in which the surfactant molecules tilt at an angle of ∼60° with respect to the clay surface. The saturated adsorption limits and layer distances differed between surfactants with short (n = 1, 2) and long (n = 3-10) perfluoroalkyl chains. For long-chain surfactants, their saturated adsorption limits were independent of the perfluoroalkyl chain length and the layer distances systematically increased with increasing perfluoroalkyl chain length. These results suggest that the microscopic orientation differed between the short and long chains. X-ray analysis showed that the long-chain surfactants orient the perfluoroalkyl chains at a tilt of 41 ± 5° with respect to the clay layer. This value was in good agreement with polarized IR measurements of 42 ± 2° for this angle.

Thermal stability and hot-stage Raman spectroscopic study of Ca-montmorillonite modified with different surfactants: A comparative study

Three long chain cationic surfactants were intercalated into Ca-montmorillonite through ion exchange and the obtained organoclays were characterized by X-ray diffraction (XRD), high resolution thermogravimetric analysis (TG) and Raman spectroscopy. The intercalation of surfactants not only changes the surface properties of clay from hydrophilic to hydrophobic but also greatly increases the basal spacing of the interlayers based on XRD analysis. The thermal stability of organoclays intercalated with three surfactants (TTAB, DTAB and CTAB) and the different arrangements of the surfactant molecules intercalated into Ca-montmorillonite were determined by TG-DTG analysis. A Raman spectroscopic study on the Ca-montmorillonite modified by three surfactants prepared at different concentrations provided the detailed conformational ordering of different intercalated long-chain surfactants under different conditions. The wavenumber of the antisymmetric stretching mode is more sensitive than that of the symmetric stretching mode to the mobility of the tail of the amine chain. At room temperature, the conformational ordering is more easily affected by the packing density in the lateral model. With the increase of the temperature, the positions of both the antisymmetric and symmetric stretching bands shift to higher wavenumbers, which indicates a decrease of conformational ordering. This study offers new insights into the structure and properties of Ca-montmorillonite modified with different long chain surfactants. Moreover, the experimental results confirm the potential applications of organic Ca-montmorillonites for the removal of organic impurities from aqueous media.

Sorption of short- and long-chain perfluoroalkyl surfactants on sewage sludges

Perfluoroalkyl surfactants (PASs) have attracted increasing concerns in recent years due to their global distribution, persistence, bioaccumulation and potential toxicity. Since sludge was a significant source of PASs to environment, the sorption of short (C2–C6) and long-chain (C7–C15) PASs on different sewage sludge was investigated in this study. The equilibrium data were well represented by the Freundlich isotherm and were generally nonlinear. In order to elucidate the sorption mechanism of PASs to sludge, effect of sludge property, solution chemistry and molecular structure were also investigated in details. The dominant sludge parameter influencing sorption of PASs was protein in extracellular polymeric substances. The sorption of PASs onto sludge increased as solution pH decreased. For all the PASs homologues, enhanced adsorption occurred with increasing calcium concentration in solution. For PASs with C5–C15, sorption on sludge increases with increasing alkyl chain length, while for PASs with C2–C5, the association of sludge decreases when the alkyl chain length increases. The perfluorinated sulfonic acid (PFSA) demonstrated substantially stronger sorption than perfluorinated carboxylic acid (PFCA) analog. Evidence for both hydrophobic and electrostatic interactions was found.

Reversible dispersion–precipitation of single-walled carbon nanotubes by pH change and addition of organic components

Single-walled carbon nanotubes (SWCNTs) were dispersed in an aqueous solution of a long-chain amidoamine surfactant (C18AA) at a high concentration (>0.5 wt%). The SWCNT dispersion was very stable in the pH range from 7.0 to 11.5. Addition of chloroform into the aqueous dispersion at pH 11.5 brought about the precipitation of SWCNTs in water, although there was no effect on the dispersibility of SWCNTs at pH 7. We demonstrated that reversible dispersion–precipitation regulation of SWCNTs in water can be achieved by changing pH and adding the C18AA surfactant in a biphasic system of C18AA–water–chloroform.

Internal Structure and Rheological Properties of Cosmetic and Toiletry Products

It is very important for product engineers in the field of cosmetics and toiletry industry to guarantee consumers to keep the constant quality and feeling of the products during the home use. This study aims at establishing technology for property control of toiletry products containing a long-chain alcohol and surfactants. Internal structure of cosmetic and toiletry products such as a self-assembly comprising cetyltrimethylammonium chloride (C16CA), cetyl alcohol (C16OH) and water was examined by electron microscopy et al. Rheological behaviors of the self-assembly were also observed to clarify the internal structure change during aging. It was confirmed that the self-assembly prepared at higher temperature involves multilamellar vesicles dispersed in continuous phase and also that semi translucent lamella was formed when self-assembly was prepared at room temperature. Phase transition of self-assembly from multilamellar vesicles to lamellae was confirmed on aging. Shear flow tests described showed that self-assembly is shear thinning with a hysteresis at higher shear rate and the maximum apparent viscosity made a steep and linear increase in a few days after preparation, followed by a gradual increase on further aging. Based on the creep test, a mechanical model for self-assembly was presented by 6 elements. The dependence of dynamic modulus (G') and loss modulus (G") on frequency (ω) was obtained. The Cole-Cole plots were combination of 2 arcs, indicating coexistence of 2 different relaxation mechanisms. They are attributed to the formation of the networks of vesicles and of lamellae. The change in the relaxation mechanisms also corresponds to the phase transition in self-assembly. In conclusion, this study unveiled the internal structure of the self-assembly comprising surfactants as a main component and showed its close relation with rheological behaviors.

Solution Properties and Emulsification Properties of Amino Acid-Based Gemini Surfactants Derived from Cysteine

Amino acid-based anionic gemini surfactants (2C(n)diCys, where n represents an alkyl chain with a length of 10, 12, or 14 carbons and "di" and "Cys" indicate adipoyl and cysteine, respectively) were synthesized using the amino acid cysteine. Biodegradability, equilibrium surface tension, and dynamic light scattering were used to characterize the properties of gemini surfactants. Additionally, the effects of alkyl chain length, number of chains, and structure on these properties were evaluated by comparing previously reported gemini surfactants derived from cystine (2C(n)Cys) and monomeric surfactants (C(n)Cys). 2C(n)diCys shows relatively higher biodegradability than does C(n)Cys and previously reported sugar-based gemini surfactants. Both critical micelle concentration (CMC) and surface tension decrease when alkyl chain length is increased from 10 to 12, while a further increase in chain length to 14 results in increased CMC and surface tension. This indicates that long-chain gemini surfactants have a decreased aggregation tendency due to the steric hindrance of the bulky spacer as well as premicelle formation at concentrations below the CMC and are poorly packed at the air/water interface. Formation of micelles (measuring 2 to 5 nm in solution) from 2C(n)diCys shows no dependence on alkyl chain length. Further, shaking the mixtures of aqueous 2C(n)diCys surfactant solutions and squalane results in the formation of oil-in-water type emulsions. The highly stable emulsions are formed using 2C₁₂diCys or 2C₁₄diCys solution and squalane in a 1:1 or 2:1 volume ratio.

Oxidative C–C coupling of 2,6-di-tert-butylphenol in aqueous media via catalytically active molybdate surfactants

Long-chain N-alkyliminodiacetatomolybdate catalytic surfactants can be incorporated within a CTAB micellar solution and have shown catalytic activity for the oxidation of 2,6-di-tert-butylphenol to the corresponding diphenoquinone in aqueous media.

Local mobility of micelles of new cationic surfactants and their interactions with hydrophobically modified polyacrylamides

The local dynamics and organization of micelles of new long-chain cationic surfactants with saturated hydrocarbon fragments (from C16 to C22) are investigated via the EPR spin-probe technique. The local mobility of spin probes in the hydrocarbon core of a micelle changes insignificantly, while the order parameter noticeably increases with lengthening of the hydrocarbon fragment of the surfactant molecule. The specific features of the interaction of the surfactants with network junctions of the gels formed by two types of hydrophobically modified polyacrylamides—either containing charged groups (sodium acrylate) in the backbone or lacking these groups—are studied. In both cases, the local mobility of network junctions of the gel increases after the introduction of the surfactant (C18). Moreover, for surfactant with a long alkyl group (C2), the microscopic viscosity of the gel based on the uncharged polymer decreases, although the local mobility of the network junctions increases. Possible causes of the observed specific features are discussed.

Application of mass spectrometry for study of the adsorption of multicomponent surfactant mixtures at the solid/solution interface

The selective adsorption of the components of a polydisperse gemini surfactant blend (alkylbenzenesulfonate-Jeffamine salt, ABSJ) in aqueous solution onto Berea sandstone, a reference material in enhanced oil recovery (EOR), was investigated. The individual adsorption isotherms of the four, benzene-ring containing ABSJ components with different alkyl chain lengths (ranging from decyl to tridecyl of the alkyl chain length) were simultaneously determined by using a four-channel electrospay ionization mass spectrometer (ESI-MS) for concentration analysis. This analytical device provided selective information (based on the differences in the mass to charge ratio) on the adsorption of each component in the mixed surfactant system. The overall isotherm obtained from the superposition of the individual isotherms determined by ESI-MS agreed well with the isotherm determined by UV spectrometry; the UV equipment is benzene-ring sensitive, irrespective of the alkyl chain length. The S-shaped isotherms reached a plateau at the critical micelle concentration. Longer-chain surfactants adsorbed preferentially over the short chain homologs, independently of solution concentration. This analytical device provided the net adsorption isotherm. Most analytical methods are not component selective, and thus they are not able to measure the individual isotherms in multicomponent solutions. Here, we report on a novel method which describes the selective determination of the individual adsorption isotherms of surfactants in a multicomponent mixture. The theoretical background of the method is described in detail.

Vegetable-Derived Long-Chain Surfactants Synthesized via a “Green” Route

There is no doubt that the surfactant and detergent industry is facing increasing severe environmental impact, and environmentally benign pathways are preferred to prepare these materials. We report herein a green route toward the preparation of vegetable-derived long-chain surfactants. The synthesis process possesses the following characteristics: bioresource-derived erucic acid (leftovers of rapeseed oil) was used as a starting material; no solvent was used and no chemical waste was produced; and high-yield products could be obtained in short reaction time. Compared with traditional surfactants bearing a saturated hydrophobic tail shorter than C18, the erucic acid-derived surfactants are more environmentally friendly because of their lower dosages in practical applications and the presence of the chemical degradable unsaturated bond and amido group in their molecular architecture.

Coarse-graining MARTINI model for molecular-dynamics simulations of the wetting properties of graphitic surfaces with non-ionic, long-chain, and T-shaped surfactants

We report on a molecular dynamics investigation of the wetting properties of graphitic surfaces by various solutions at concentrations 1-8 wt. % of commercially available non-ionic surfactants with long hydrophilic chains, linear or T-shaped. These are surfactants of length up to 160 Å. It turns out that molecular dynamics simulations of such systems ask for a number of solvent particles that can be reached without seriously compromising computational efficiency only by employing a coarse-grained model. The MARTINI force field with polarizable water offers a framework particularly suited for the parameterization of our systems. In general, its advantages over other coarse-grained models are the possibility to explore faster long time scales and the wider range of applicability. Although the accuracy is sometimes put under question, the results for the wetting properties by pure water are in good agreement with those for the corresponding atomistic systems and theoretical predictions. On the other hand, the bulk properties of various aqueous surfactant solutions indicate that the micellar formation process is too strong. For this reason, a typical experimental configuration is better approached by preparing the droplets with the surfactants arranged in the initial state in the vicinity of contact line. Cross-comparisons are possible and illuminating, but equilibrium contact angles as obtained from simulations overestimate the experimental results. Nevertheless, our findings can provide guidelines for the preliminary assessment and screening of surfactants. Most importantly, it is found that the wetting properties mainly depend on the length and apolarity of the hydrophobic tail, for linear surfactants, and the length of the hydrophilic headgroup for T-shaped surfactants. Moreover, the T-shaped topology appears to favor the adsorption of surfactants onto the graphitic surface and faster spreading.

Viscosity of aqueous micellar solutions of surfactants

The viscosity of aqueous micellar solutions of two long-chain surfactants, C24H43N2ClO and C21H38NCl, is studied in a concentration range of 10−4–10−2 mol/L and a temperature range of 20–40°C. It is established that, in the region of critical micelle concentration, the viscosity is a nonmonotonic function of concentration and has minima and maxima.

Effect of Temperature and Added Counter Ions on Micelle Formation of Guanidine Surfactants

Abstract Electrical conductivity was measured for aqueous solutions of long-chain guanidine surfactants (G12 and MG12) at different temperatures and with various added counter ions. The critical micelle concentration (cmc) of these surfactants determined from the specific conductivity (κ) vs. concentration (c) plot is lower than those of the typical cationic surfactants, such as alkyltrimethylammonium chloride with the same hydrocarbon chain length. The electrical conductivity data were analyzed according to the mixed electrolyte model of micelle solution, and the degree of counter ion binding (β) was calculated. The thermodynamic parameters for micelle formation were estimated using the values of cmc and β as a function of temperature. The more negative ΔGmic for MG12 indicates more favored micellization. The contribution of entropy term to the micelle formation is superior to that of enthalpy term in the system under study, which indicates micellization is entropy driven. By comparing the cmc and ΔGmic it is evident that all cmc decreases and the more observed negative ΔGmic in the presence of different added salts. The anion effect on the guanidine surfactants micelle formation with added salts showed the micelle forming efficiency order as: Cl− < Br− < NO3 − < Ac−.

Interactions between ethyl(hydroxyethyl) cellulose and lysine-based surfactants in aqueous media

In this work, the interaction between ethyl(hydroxyethyl) cellulose (EHEC) and three dimeric lysine-based surfactants of distinct chain length (C6, C8 and C10) have been assessed and the system was evaluated in terms of its temperature-dependent gelling capacity. The viscosity profile depends on the specific surfactant, its concentration and temperature. The observed profiles reflected polymer–polymer associations at elevated temperatures and polymer-surfactant interactions, implying the formation of micellar-type associations. The systems induce gelation at higher temperatures. Longer chain-length surfactants induce gelation at lower concentrations due to their stronger tendency to self-assemble. The thermo-responsive gels showed gel strength generally lower than 20Pa.sn and a fractal dimension of 2.3–2.4, respectively, indicating the formation of soft gels comprising a tight and homogeneous network. The weakest gel was produced in the presence of the C6 surfactant. 2D Small-Angle Light Scattering patterns showed a pronounced effect of temperature in terms of the evolution of large hydrophobic clusters, an event precluded when high concentrations of the longer chain surfactants were used.