Surfactant Chain Length Research Articles

Influence of sugar surfactant structure on the encapsulation of oil droplets in an amorphous sugar matrix during freeze-drying

The encapsulation of O/W emulsion droplets in a freeze-dried amorphous sugar matrix was investigated, focusing on the impact of the molecular structure of the emulsifying surfactant. O/W emulsions, containing various surfactants, were freeze-dried in the presence of a sugar. Thirty types of surfactants, including eighteen different sugar surfactants and ten types of commercially available sugar ester mixtures, were used. Linoleic acid methyl ester and trehalose were used as the oil phase and sugar. The amounts of oil droplets encapsulated in freeze-dried amorphous sugar matrix were analyzed by Fourier transform Infrared spectroscopy. Sugar surfactants were generally superior to the other classes of surfactants for oil droplet encapsulation during freeze-drying, and there was the optimum alkyl chain length of the sugar surfactant. Sugar esters generally exhibited greater oil encapsulation than sugar ethers. Larger sugar head group appeared to result in better encapsulation in the case of sugar esters, but the opposite tendency was found for sugar ethers. A limited combination of sugar surfactants (15% sucrose mono- and 85% di-stearate) resulted in the maximum oil droplet encapsulation efficiency although these surfactants are individually quite poor in the encapsulation and other tested combinations did not improve the encapsulation efficiency relative to their individual effectiveness.

Spontaneous Vesicle Based Excipient Formation in Mixtures of Sodium N-(n-Alkanoyl)-L-alaninate and N-Cetylpyridinium Chloride: Effect of Hydrocarbon Chain Length

The hydrocarbon chain length effects of sodium N-alkanoyl-L-alaninate and N-cetylpyridinium chloride surfactants have been studied at various mixing ratios and concentrations. Both cationic and anionic surfactants form micellar solution in water, whereas by mixing the two surfactants in different compositions and concentrations, stable unilamellar vesicles are formed spontaneously. The variation of the chain length of the anionic surfactant produces a large effect on the stability of mixed surfactant systems. The vesicles formed by the mixtures are found to be thermodynamically stable in different composition and concentration in aqueous media. These vesicles formed by surfactant mixtures are stable for more than one month both for anionic- and cationic-rich side in very dilute solutions. The stability of the vesicle was examined by measuring the turbidity, which remains unchanged for a long time. Dynamic light scattering as well as transmission electron microscopic experiments were performed to investiga...

Spectrophotometric investigation of the interactions between cationic porphyrazine and different anionic surfactants

Interactions between tetrakis(N, N � ,N �� ,N ��� -tetramethyl tetra-2,3-pridino)porphyrazine copper(II) (Cu(tmtppa)) with anionic surfactants: sodium dodecyl sulfate (SDS), sodium tetradecyl sulfonate (STS) and sodium hexadecyl sulfonate (SHS) were investigated in aqueous submicellar solutions using spectrophotometric method at 298.15, 303.15, 313.15, 318.15 and 323.15 K. Binding constants between the submicellar solutions of surfactants and Cu(tmtppa) system were calculated from the changes in absorbance values at different temperatures. The results showed that increasing alkyl chain length of surfactants caused a stronger interaction indicating the importance of hydrophobic forces. It was found that the values of binding constant increased with increasing temperature. Thermodynamic parameters (ΔG ◦ , ΔH ◦ and ΔS ◦ ) were determined for the binding processes of porphyrazine-surfactant system. It was concluded from ΔG ◦ and ΔH ◦ values that the binding process occurred

Surfactant chain length controls photoinduced electron transfer in surfactant bilayer protected carbon nanoparticles

Negatively charged fluorescent carbon nanoparticles (CNPs) were synthesized from amino acids with bilayer of cationic surfactants of varying chain lengths on the surface. Degree of photoinduced electron transfer (PET) between an electron donor in the bilayer and the CNP core can be efficiently controlled depending on the thickness of the bilayer.

Molecular mechanism of micellar catalysis of cross aldol reaction: Effect of surfactant chain length and surfactant concentration

The importance of alkyl chain length and concentration of quaternary ammonium surfactants (QAS) in the micellar catalysis of cross aldol reaction was investigated. The NaOH-micellar system catalyzed aldol reaction of benzaldehyde and cyclohexanone to α,α′-dibenzylidene cyclohexanone (di condensation/desired product) over mono condensation product was used as model reaction for this study. The C16QAS micellar system (QAS with n-hexadecyl group) gave highest cyclohexanone conversion (90%) to desired product (82%) showing that C16QAS micellar system possesses optimum properties and/or microenvironment for this reaction. Furthermore, the micellar system with high surfactant concentration (C16QAS; >150mM) made the reaction faster giving >99% conversion to selectively desired product (>99%) within 30min The large interface created by C16QAS micelles in the aqueous medium at high surfactant concentration makes the reaction faster by facilitating the interaction of hydrophobic reactants and water soluble catalyst (OH− ions). The activation of benzaldehyde molecules, their localization preferably near the interface and stabilization of enolate ions (reactive intermediates) by micellar system at high surfactant concentration were observed to be promoting the cross reaction selectively to the desired product.

High-Resolution Ultrasonic Spectroscopy Study of Interactions between Hyaluronan and Cationic Surfactants

Interactions in a cationic surfactant-hyaluronan system in water and in sodium chloride solution were investigated by high-resolution ultrasonic spectroscopy at 25 °C. Two alkyltrimethylammonium bromide surfactants of different chain lengths (tetradecyl and hexadecyl) were used; hyaluronan molecular weight ranged from 10 to 1750 kDa. Two main parameters-ultrasonic velocity and attenuation-were measured in the titration regime. Up to six different regions could be identified in the velocity titration profiles in water in a narrow interval of surfactant concentration. These regions differed primarily in the compressibility of structures formed in the system. The number of detected transitions was higher for the tetradecyl surfactant; therefore, the increased length of the hydrophobic chain simplified the details of the structure-forming behavior. The measurement of attenuation was much less sensitive and detected only the formation of microheterogeneous structures or visible phase separates. The richness of the titration profiles was depressed in salt solution, where essentially only two principal regions were observed. On the other hand, the effect of hyaluronan molecular weight on the positions of boundaries between regions was more significant in the presence of salt. Besides electrostatic interactions, hydrophobic interactions are also relevant for determining the behavior of hyaluronan-surfactant systems and the properties of formed complexes (aggregates).

Size control of surfactant vesicles made by a mixture of cationic surfactants and organic derivatives.

Spontaneous size-controllable vesicles that are prepared by a mixture of surfactants with different alkyl chain lengths (n-alkyltrimethylammonium bromide, C(n)TAB) and an organic derivative (5-methyl salicylic acid, 5mS) in aqueous solution have been investigated. When the organic derivative 5mS is mixed with the C(n)TAB surfactants in aqueous solution, the surfactant vesicles are spontaneously formed above a certain 5mS concentration. Small angle neutron scattering reveals that the core radius of surfactant vesicles is clearly increased from ca. 31 nm to ca. 97 nm with the alkyl chain length of surfactants while the bilayer thickness of the vesicles is nearly constant. The structure of surfactant vesicles maintains against temperature change ranging from 30 degrees C to 45 degrees C, showing no structural change. These results can provide thermally stable surfactant vesicles with various sizes and constant bilayer thickness that may possess a different permeability and may allow the surfactant vesicle to be used in gene or drug delivery for a variety of goods.

Loading capacity and interaction of DNA binding on catanionic vesicles with different cationic surfactants.

Cationic and anionic (catanionic) vesicles were constructed from the mixtures of sodium laurate (SL) and alkyltrimethylammonium bromide (CnTAB, n = 12, 14, and 16) and were used to control the loading capacity of DNA. The binding saturation point (BSP) of DNA to catanionic vesicles increases with the chain length of cationic surfactants, which is at 1.0, 1.3 and 1.5 for CnTAB with n = 12, 14, and 16, respectively. Our measurements showed that the loading capacity and affinity of DNA can be controlled by catanionic vesicles. It increases with the chain length of cationic surfactants. Because of a large reduction in surface charge density, catanionic vesicles are prone to undergo re-aggregation or fusion with the addition of DNA. DNA molecules can still maintain original coil state during the interaction with catanionic CnTAL vesicles. (1)H NMR data reveals that the obvious dissociation of anionic ions, L(-), from catanionic C14TAL vesicles is due to the interaction with DNA; however, this phenomenon cannot be observed in C12TAB-SL vesicles. Agarose gel electrophoresis (AGE) results demonstrate that the electrostatic interaction between the two oppositely charged cationic and anionic surfactants is stronger than that between DNA and cationic surfactant, CnTAB (n = 12, 14, and 16). Not only is the dissociation of L(-) simply determined by the charge competition, but it also depends largely on the variations in the surface charge density as well as the cationic and anionic surfactant competing ability in geometry configuration of catanionic vesicles. The complicated interaction between DNA and catanionic vesicles induces the deformation of cationic vesicles. Our results should provide clear guidance for choosing more proper vectors for DNA delivery and gene therapy in cell experiments.

Preparation of Cationic Surfactant Intercalated Graphene Oxide and Quantitative Determination of the Interlamellar Spacing

Graphene Oxide (GO) was prepared from natural graphite and treated with different types and various amounts of cationic surfactants to form the intercalation nanocomposites. The resulting specimens were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XRD), and Thermogravimetric analysis (TGA). X-ray diffraction patterns revealed that the interlamellar spacing strongly depended on the mole mass ratios between GO to cationic surfactants and the alkyl chain length of surfactants. In addition, a model was proposed to illustrate the procedure of cetyltrimethylammonium chloride (CTAC)-GO intercalation, and the angles of inclination between the alkyl chains and GO planes were calculated based on the model.

Alkyl chain length asymmetry effects of mixed n-acyl sarcosinate and N-cetylpyridinium chloride surfactants: Spontaneous formation of stable nanovesicles as excipient

The effect of hydrocarbon chain length of sodium-n-acyl sarcosinate (SNAS) and N-cetylpyridinium chloride (CPC) surfactants has been studied at various mixing ratios and concentrations. The variation of the chain length of the anionic surfactant produces a significant effect on the stability of mixed surfactant systems. The unilamellar vesicles formed by the mixtures are shown to be thermodynamically stable in different ratios and concentration in aqueous media. These vesicles formed by surfactant mixtures are stable for a long period of time such as several years both for anionic-rich and cationic-rich side in very dilute solutions. The stability of the vesicles was validated by UV absorbance spectra which remain unchanged for a long time. Both cationic and anionic surfactants are soluble in water forming micellar solutions individually, but mixing of two surfactants in different mole ratios and concentration forms stable vesicles. Dynamic light scattering (DLS) as well as transmission electron microscopic (TEM) experiments was performed to investigate the structural properties of the different types of aggregates and the formation of nano-vesicular structures as well. The effect of salt, pH, temperature, and cholesterol on the microviscosity of the domains was evaluated by using steady-state fluorescence depolarization method. Fluorescence microscopic images technique and conductivity measurements have corroborates the formation of hollow spherical structure of the vesicles. The surface chemical properties of the mixed surfactant systems and the stability of vesicles have been studied systematically keeping in view the primary aim of the study.

Rheological response and small-angle neutron-scattering study of diester-bonded cationic biodegradable gemini surfactants in presence of different additives

Morphological changes and internal packing arrangements of planar dicationic-ester-bonded biodegradable gemini surfactants ethane-1, 2-diyl-bis(N,N-dimethyl-N-alkylammonium acetoxy) dichlorides (m-E2-m) have been explored by exploiting small-angle neutron-scattering (SANS) measurements. The data have been analyzed on the basis of Hayter and Penfold model for macroion solutions to obtain information about the aggregation behavior at the molecular level. The extent of micellar growth and structural changes of the micelles formed by these surfactants have been found to depend on the number of methylene units in their tail length. The growth and variation of micellar shape are more pronounced for the surfactant with longer tail length (m = 16), whereas the surfactants with shorter tail length showed less variation of these properties in aqueous solution. Semi-major axes of the micelles show flexibility while varying the concentration and temperature of the systems; however, semi-minor axes remain rigid. Changes in the structural parameters of the micelles with addition of different salts were also inferred from SANS measurements. The intensity of scattered neutrons at the low Q region was found to increase while varying the nature of salt from monovalent to trivalent. On the basis of rheological responses, the rich aggregation behavior resulting from the addition of sodium salicylate (NaSal) is attributed to the special molecular structure of the gemini surfactant and the appropriate interaction between the surfactant and NaSal. This is inferred on the basis of behavior observed by varying the chain length (m) of the gemini surfactant that resulted in the formation of different types of microstructures.

Mixed micellization of gemini and conventional surfactant in aqueous solution: A lattice Monte Carlo simulation

In the current study, we have investigated the micellization of pure gemini surfactants and a mixture of gemini and conventional surfactants using a 3D lattice Monte Carlo simulation method. For the pure gemini surfactant system, the effects of tail length on CMC and aggregation number were studied, and the simulation results were found to be in excellent agreement with the experimental results. For a mixture of gemini and conventional surfactants, variations in the mixed CMC, interaction parameter β, and excess Gibbs free energy GE with composition revealed synergism in micelle formation. Simulation results were compared to estimations made using regular solution theory to determine the applicability of this theory for non-ideal mixed surfactant systems. A large discrepancy was observed between the behavior of parameters such as the activity coefficients fi and the excess Gibbs free energy GE and the expected behavior of these parameters as predicted by regular solution theory. Therefore, we have used the modified version of regular solution theory. This three parameter model contains two parameters in addition to the interaction parameters: the size parameter, ρ, which reflects differences in the size of components, and the packing parameter, P*, which reflects nonrandom mixing in mixed micelles. The proposed model provides a good description of the behavior of gemini and conventional surfactant mixtures. The results indicated that as the chain length of gemini surfactants in mixture is increased, the size parameter remains constant while the interaction and packing parameters increase.

Unique influence of cholesterol on modifying the aggregation behavior of surfactant assemblies: investigation of photophysical and dynamical properties of 2,2'-bipyridine-3,3'-diol, BP(OH)2 in surfactant micelles, and surfactant/cholesterol forming vesicles.

The binding and rotational properties of an excited-state intramolecular proton transfer (ESIPT) fluorophore, 2,2'-bipyridine-3,3'-diol, BP(OH)2 has been investigated in alkyltrimethylammonium bromide containing (CnTAB, n = 12, 14, and 16) micelles and alkyltrimethylammonium bromide/cholesterol (CnTAB (n = 14 and 16)/cholesterol) forming vesicles using fluorescence-based spectroscopy techniques. The formation of thermodynamically stable unilamellar self-assemblies of alkyltrimethylammonium bromide/cholesterol are characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. Individually, aqueous solutions of all these alkyltrimethylammonium bromide form micelles after certain surfactant concentration (critical micelle concentration, cmc) of surfactant, whereas cholesterol molecules are insoluble in water. But with the variation of the cholesterol-to-surfactant molar ratio (Q = [cholesterol]/[surfactant]), uniform distribution of vesicular aggregates in aqueous solution can be obtained. The micelle-to-vesicle transition of surfactant solution upon addition of cholesterol also influences the steady state emission profile, fluorescence lifetime, and rotational dynamics of BP(OH)2 molecule. The diketo tautomer of BP(OH)2 molecule gets stabilized as the concentration of surfactant increases in aqueous solution. Fluorescence lifetime and rotational time constant of the BP(OH)2 molecule are also influenced by the variation of alkyl chain length of surfactant molecule. The emission quantum yield (Φ) is also found to be sensitive with surfactant concentration, variation in chain length of surfactants, and it saturates after the cmc of surfactants. The rigid and restricted microenvironment of vesicle bilayer enhance the lifetime and also rotational relaxation of BP(OH)2 significantly. The rotational behavior of BP(OH)2 in surfactant/cholesterol self-assemblies is also explained by using analytical parameters related to time-resolved anisotropy following two-step process and wobbling in a cone models.

Controlling the swelling and rheological properties of hydrophobically modified polyacrylic acid nanoparticles: Role of pH, anionic surfactant and electrolyte

Nanosized particles of poly(acrylic acid), which is chemically cross-linked and hydrophobically modified, was investigated with the swelling behavior as triggered by ionization and surfactant binding. It was found that the viscosity, elasticity and transmittance of the solutions are dramatically affected when the pH increases above 6.5; viscosity changes can amount to more than 7 orders of magnitude. At low pH, where the polymer is weakly charged and the interaction with the solvent is poor, and the solution is liquid-like (G″>G′) and turbid. At pHs above 6.5, the solution becomes a transparent gel with solid-like behavior (G′>G″). Additionally, at low pH, the addition of anionic surfactant promotes the swelling of the polymer with consequent gelation leading to a solution behavior with essentially identical properties as when the polymer has a high charge density. Thus addition of moderate amounts of surfactant can increase the viscosity by 7 orders of magnitude. Moreover, an increase in the surfactant chain length is found to strengthen the surfactant binding to the polymer. The results are discussed in terms of the delicate balance between the osmotic swelling (counterion entropy effect) and restoring forces due to the hydrophobic interactions.

Soluble aggregates in aqueous solutions of polyion-surfactant ion complex salts and a nonionic surfactant.

Water-soluble aggregates based on two polyion-surfactant ion "complex salts", consisting of hexadecyltrimethylammonium (C16TA(+)) and polyacrylate (PA(-)) with either 25 or 6000 repeating units, with added nonionic surfactant octaethylene glycol monododecyl ether (C12E8) have been investigated. A previous phase study has shown that added C12E5 or C12E8 can solubilize complex salts in aqueous systems, and that increasing the poly(ethylene oxide) chain length of the nonionic surfactant and/or decreasing the polyion length favors dissolution. In this work we report on dynamic light scattering, NMR diffusometry, small-angle X-ray scattering, and isothermal titration calorimetry measurements performed to characterize the solubilized composite aggregates in dilute aqueous solution in terms of size and stoichiometry. It was found that mixed aggregates of polyacrylate, C16TA(+) ions, and C12E8, with almost constant stoichiometry, coexist with free micelles of C12E8 at all investigated mixing ratios. The length of the polyion only weakly affects the stoichiometry of the mixed aggregates while strongly affecting their size and water solubility.

Study of the interactions in dicationic gemini–anionic conventional mixed surfactant systems in the viewpoint of regular solution theory

In the present study, the influence of the hydrocarbon chain length of gemini surfactants on the process of micellization in mixed surfactant systems was investigated. Experiments were carried out with alkyldiyl-α, ω-bis(tetradecyldimethylammonium bromide) (m-4-m) dicationic gemini (m=14, 16)/anionic sodium dodecylbenzene sulfonate (SDBS) mixed surfactant systems in different ratios. The critical micelle concentration (cmc) values of binary mixtures of surfactants were evaluated using surface tension measurements. Results showed that mixtures of the SDBS with gemini surfactants possessed significant deviations from ideal behavior (attractive interactions). The application of the regular solution theory (RST) to experimental data yielded the interaction parameter at mixed micelles (β) and air–water interface (βσ), indicating an attractive interaction and reflecting the synergistic behavior in both the systems. The experimental mole fraction (X1) was found to be lower than the ideal mole fraction (X1ideal), the mole fractions of SDBS for both systems, provided that mixed micelles were more occupied by SDBS. In addition, the micelle aggregation number (Nagg) increased with an increase in the length of the hydrophobic tail. The micropolarity and binding constant (Ksv) values of various combinations were determined from the ratio of intensity (I1/I3) of peaks of pyrene fluorescence emission spectrum and its quenching.

Effect of Hydrophobicity and Temperature on the Interactions in the Mixed Micelles of Triblock Polymers [(EO76PO29EO76) and (EO19PO69EO19)] with Monomeric and Gemini Surfactants

AbstractThe interactions in the mixed micelles of two triblock polymers, F68 (EO76PO29EO76) and P123 (EO19PO69EO19), with a series of monomeric (dodecyltrimethyl ammonium bromide, tetradecyltrimethyl ammonium bromide and cetyltrimethyl ammonium bromide) and gemini {dimethylene bis(alkyldimethyl ammonium bromide), m‐2‐m, where m = 10, 12 and 14} cationic surfactants were studied by surface tension and viscosity measurements in aqueous solutions at different temperatures. The mixed micellar and interfacial properties of the binary mixtures were analyzed using Clint, Rubingh, Rosen and Maeda approaches. Both F68 and P123 show weak interactions with the studied cationic surfactants at 298.15 K which become favorable (synergistic) at higher temperatures. Further, the synergistic interactions are more in mixtures of P123 than F68 at higher temperatures. A comparison of the effects of number of EO and PO blocks in triblock polymers on various physicochemical parameters of the mixed micelles has also been made. The unfavorable enthalpy changes are compensated by favorable entropy changes as a result of the hydrophobic effect. The relative viscosity (ηr) studies show that the size of the micelles formed by pure P123 is smaller than those of F68. The values of ηr for the mixed micelles of F68 show significant variation with chain length of gemini surfactants whereas no such effect is seen in mixtures with P123.

Parameterization of a mesoscopic model for the self-assembly of linear sodium alkyl sulfates.

A systematic approach to develop mesoscopic models for a series of linear anionic surfactants (CH3(CH2)n - 1OSO3Na, n = 6, 9, 12, 15) by dissipative particle dynamics (DPD) simulations is presented in this work. The four surfactants are represented by coarse-grained models composed of the same head group and different numbers of identical tail beads. The transferability of the DPD model over different surfactant systems is carefully checked by adjusting the repulsive interaction parameters and the rigidity of surfactant molecules, in order to reproduce key equilibrium properties of the aqueous micellar solutions observed experimentally, including critical micelle concentration (CMC) and average micelle aggregation number (Nag). We find that the chain length is a good index to optimize the parameters and evaluate the transferability of the DPD model. Our models qualitatively reproduce the essential properties of these surfactant analogues with a set of best-fit parameters. It is observed that the logarithm of the CMC value decreases linearly with the surfactant chain length, in agreement with Klevens' rule. With the best-fit and transferable set of parameters, we have been able to calculate the free energy contribution to micelle formation per methylene unit of -1.7 kJ/mol, very close to the experimentally reported value.

Removal of Humic Acid by Organo-Montmorillonites: Influence of Surfactant Loading and Chain Length of Alkylammonium Cations

In this study, the characterization and adsorption properties of montmorillonite (MMT) and organomontmorillonites with different surfactant/cationic exchange capacity (CEC) ratios (1 and 2) of tetradecyl trimethylammonium (TDTMA+) and hexadecyl trimethylammonium (HDTMA+) cations were evaluated. The particle apparent diameter, determined by laser and scanning electron microscopy showed aggregate formation, which varied with loading and cation length of the surfactant used. X-ray diffraction analysis revealed the formation of a pseudotrilayer arrangement of both surfactants in the interlayer space, FTIR showed the characteristic bands of the surfactants and micelle formations, and zeta potential determinations indicated neutral or negative surface charge values, except for sample obtained with one CEC concentration exchanged with HDTMA+ (HDTMA1-MMT) where a charge reversal to positive was found. Higher adsorption amounts of humic acid (HA) were found for HDTMA1-MMT and TDTMA1-MMT samples than for MMT sample, while the increase in the loading of both surfactants decreased the amounts of HA adsorbed could be assigned to a higher micelle formation and different packing density of alkyl chain, in the external surface. The correlation found between the total surface area and negative zeta potential values and the HA adsorption rate, within each surfactant, indicated the strong influence that these properties have on HA adsorption.

Effect of pH, salt concentration and chain length of surfactants on the MO removal from water by pyridinium-based gemini surfactant

Dye stuffs are an environmental problem, and their presence in drinking water and bio ecosystems such as rivers and water ways have long been recognized as deleterious. Current methods for their removal largely rely on adsorption techniques which are costly and produce another waste to be disposed off, whereas the concept of reverse micelles acting to encapsulate the dye in aqueous micro pool in solvent environment provides a useful chemistry. The removal of methyl orange from aqueous phase in amyl alcohol solvent using cationic surfactants was studied. Experiments were conducted by mixing a known quantity of dye in aqueous phase and solvent-containing surfactants in a simple mixer. The separation of solvent phase, containing encapsulated dye in reverse micelles, from aqueous phase due to gravity results in the separation of dye from water. The effects of dye and surfactant concentration, pH, salts like KCl and MgCl2 were studied. The percentage removal of the dye depends upon the size of the reverse micelle of the surfactant. The solvent used for the dye removal can be recovered by distillation method and can be reused.