Cationic Surfactant Headgroups Research Articles

Effect of head-group of cationic surfactants and structure of ionic groups of anionic polyelectrolyte in oppositely charged polymer-surfactant complexes

In this study, a detailed assessment of interactional conduct between different head-groups of cationic surfactants and different monomer fragments of anionic polyelectrolyte of aqueous media is reported. Tensiometry, conductometry, viscosimetry, dynamic light scattering have been employed to get insight into interactions among cationic surfactant and polyelectrolyte in interfacial region critical aggregation and micellization concentration, surface excess concentration, surface pressure at interface, minimum area occupied with the aid of one molecule of cationic surfactant at air-solvent interface, adsorption efficiency, surface tension at critical micelle concentration and the positive degree of counterion binding had been calculated. Thermodynamic parameters, i.e., standard Gibbs free energy of micellization and adsorption processes had been evaluated. Polyelectrolyte-surfactant interaction used to be studied in dependence on nature of head-group of cationic surfactant and polyelectrolyte chain and their influence on colloidal-chemical parameters of polyelectrolyte-surfactant complexes has been compared. Petrocollecting ability of these complexes in the waters of various mineralization degree was investigated.

Nitroxyl spin probe in ionic micelles: A molecular dynamics study

The compounds containing nitroxyl radical (NO˙) are actively used as spin probes to examine colloid systems, including lipid membranes and micelles. Their electron paramagnetic resonance spectrum provides information about the composition of the medium, in particular, the content of water there. Yet, the proper treatment of the measurement results demands understanding the microscopic characteristics of the molecular probe. In the present paper, we extend our previous studies on the microscopic state of acid-base and solvatochromic probes in surfactant micelles to the field of spin probes. We report the results of molecular dynamics simulation of a common spin probe, methyl-5-doxylstearate, in micelles of anionic (sodium n-dodecyl sulfate, SDS) and cationic (n-dodecyltrimethylammonium bromide, DTAB) surfactants. The localization of the molecule within the micelles, its shape, composition of the local environment, hydration were quantified and compared with the available relevant experimental data. No significant dissimilarity was found in the characteristics of the probe molecule in both kinds of micelles. However, the characteristics of the O˙ atom carrying the unpaired electron are pronouncedly different, namely, in DTAB micelles it is less hydrated and forms less hydrogen bonds with water. Similar situation was observed for the COO group. The main reason was found to be the interactions with cationic surfactant headgroups, which screen the O˙ atom and COO group from water. These findings allowed revisit the point of view that the surface layer of DTAB micelles as a whole is less hydrated in comparison to that of the SDS ones.

Nanoconfinement and Mass Transport in Silica Mesopores: the Role of Charge at the Single Molecule and Single Pore Levels

Polarization-dependent single molecule tracking was employed to simultaneously probe the translational and orientational diffusion of four perylene diimide (PDI) dyes, having different lengths and charges, within the one-dimensional (1D) nanoscale pores of surfactant-templated mesoporous silica films. The wide-field fluorescence videos acquired reveal that a significant fraction of the molecules follow 1D pathways and exhibit highly polarized fluorescence, consistent with their orientational confinement. Single-frame step size distributions prepared from these data were fit to a new model that accurately describes the distribution for 1D Fickian diffusion in the presence of finite localization precision. Average diffusion coefficients obtained from mean square displacement (DMSD) data were 20-100% larger for the two uncharged PDIs compared to the charged PDIs, reflecting electrostatic interactions of the latter with oppositely charged sites on the cationic surfactant headgroups and deprotonated silanol sites on the pore walls. Polarization-dependent tracking data show that the longest uncharged PDI was most strongly confined, while the three shorter dyes were less confined. The cationic PDI produced a wobbling angle distribution that was broader than the others, suggesting it explores more of the pore diameter. The results provide new knowledge on the mechanisms by which the dye molecules interact with the pore-filling medium and the pore surfaces, helping to elucidate the factors controlling the rate of mass transport.

Deciphering the role of the head group of cationic surfactants in their binding interactions with heme protein and their release by β-cyclodextrin

We decipher the mode of binding of surfactants with hemoglobin and their release by β-cyclodextrin.

Silver Nanoparticles Synthesized Using Caesalpinia sappan Extract as Potential Novel Nanoantibiotics Against Methicillin-Resistant Staphylococcus aureus.

Silver nanoparticles (AgNPs) have been shown to be effective antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA). In this study, AgNPs were synthesized using Caesalpinia sappan extract as a reducing agent to convert Ag+ to AgNPs. Seven stabilizers (surfactants and polymers) were added during the reduction step to increase the colloidal stability and to enhance the antibacterial activity of the AgNPs. Spherical and amorphous particles were primarily observed, with estimated diameters ranging from 30.2 to 47.5 nm. X-ray diffraction confirmed the face centered cubic structures of the AgNPs. Among the employed stabilizers, the cationic surfactant cetyltrimethylammonium bromide (CTAB) exhibited the highest antibacterial activity against 19 strains of MRSA, followed by polyvinylpyrrolidone (PVP, average molecular weight of 10,000). In contrast, the anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (NaDDBS) did not exhibit any significant antibacterial activity, suggesting that the cationic surfactant head group contributed to the higher antibacterial activity of the AgNPs against MRSA.

In situ growth of ZnO nanoparticles in precursor-insensitive water-in-oil microemulsion as soft nanoreactors.

Zinc oxide (ZnO) nanostructures of uniform shapes and sizes (spherical, needle-like, and acicular) were directly synthesized using a relatively precursor-insensitive water-in-n-heptane microemulsion system stabilized by a mixture of cationic and non-ionic surfactants. With this colloidal system, the synthesized ZnO possesses the highest reported surface area (76 m2 g−1) among the published reports utilizing other microemulsion systems. Such precursor insensitivity allowed studying the effect of Zn precursor:precipitating agent molar ratio (as high as 1:8) on the particle size, specific surface area, porosity, and morphology of the synthesized nanoparticles. The interaction of the cationic surfactant head groups and their Br− counter ions with Zn2+ and OH− ions is believed to play a major role in controlling the ZnO characteristics. Due to such interactions, it is believed that the nucleation processes are retarded while the growth is more dominating if compared with other microemulsion systems.

NMR Investigation of Exchange Dynamics and Binding of Phenol and Phenolate in DODAC Vesicular Dispersions

The interaction between phenol molecules, both in their undissociated and dissociated states, and cationic dioctadecyl dimethylammonium chloride (DODAC) vesicles were thoroughly investigated using NMR techniques. In particular, diffusion and relaxation measurements, combined with the two sites Kärger model, were used to evaluate the exchange dynamics and the binding of the aromatic molecules to the vesicles. The results reveal that, besides concentration and vesicle preparation method, pH conditions have the biggest impact on the phenol sorption behavior. Although the dissociated form of phenol formed at high pH is more hydrophilic, the results indicated that phenol-DODAC interactions were largely favored in basic conditions as a consequence of the strong electrostatic interaction between the phenolate anions and the cationic surfactant headgroup.

NMR study of the influence of pH on phenol sorption in cationic CTAB micellar solutions

Interactions between phenol and cationic cetyltrimethylammonium bromide (CTAB) micelles have been investigated by means of nuclear magnetic resonance spectroscopy. The combined use of 1H and NOESY techniques revealed that phenol has different preferred locations of interaction depending on the pH. At neutral pH (6.70) conditions, phenol molecules are preferentially located in the outer micelle region, at the micelle–water interface, while at more basic pH (9.94), the deprotonated phenol molecules (C 6H 5O −) are immersed into the palisade layer of the micelle. In addition, quantitative estimates of the solubilized fraction of phenol were obtained by using PFG-NMR. The results indicate that the phenol–CTAB interactions, although already present in neutral pH conditions, are largely favored in basic conditions as a consequence of the strong electrostatic interaction between the negatively charged phenolate ions and the positive charge of the cationic surfactant head group.

Effect of Cationic Surfactant Head Groups on Synthesis, Growth and Agglomeration Behavior of ZnS Nanoparticles

Colloidal nanodispersions of ZnS have been prepared using aqueous micellar solution of two cationic surfactants of trimethylammonium/pyridinium series with different head groups i.e., cetyltrimethylammonium chloride (CTAC) and cetyltrimethylpyridinium chloride (CPyC). The role of these surfactants in controlling size, agglomeration behavior and photophysical properties of ZnS nanoparticles has been discussed. UV–visible spectroscopy has been carried out for determination of optical band gap and size of ZnS nanoparticles. Transmission electron microscopy and dynamic light scattering were used to measure sizes and size distribution of ZnS nanoparticles. Powder X-ray analysis (Powder XRD) reveals the cubic structure of nanocrystallite in powdered sample. The photoluminescence emission band exhibits red shift for ZnS nanoparticles in CTAC compared to those in CPyC. The aggregation behavior in two surfactants has been compared using turbidity measurements after redispersing the nanoparticles in water. In situ evolution and growth of ZnS nanoparticles in two different surfactants have been compared through time-dependent absorption behavior and UV irradiation studies. Electrical conductivity measurements reveal that CPyC micelles better stabilize the nanoparticles than that of CTAC.

Sulfate and Surfactants as Boosters of Kraft Lignin Precipitation

In the spirit of the biorefinery concept, an increasing interest in further utilization of technical lignins outside the pulp mills has arisen. In this context optimization of the precipitation process to increase the yield of the lignin recovered is of great importance. The objectives of this investigation have been to study how specific salts and surfactants affect kraft lignin yield during precipitation and washing. From the results it was seen that additions of sodium sulfate increased the yield of precipitation at elevated temperatures at much lower concentrations than sodium chloride. Earlier studies of the effect of monovalent salts on kraft lignin stability have shown that specific ions either increase or decrease the formation of precipitates during kraft lignin aggregation. Thus, the presented results in this study further strengthen this dependency concerning divalent anions. Regarding the role of surfactants as precipitation enhancers, cationic surfactants gave rise to fast aggregation and relatively high yields. This was found mainly due to attractive electrostatic interactions between the cationic surfactant headgroup and the oppositely charged groups on the kraft lignin macromolecules, introducing an increased degree of hydrophobicity of the lignin and thus a decreased stability. The nonionic surfactants tested affected the system very differently. In some cases the aggregation was fast and the aggregates became relatively large before settling, whereas some surfactants induced the formation of relatively dense precipitates that settled rapidly. Concerning kraft lignin precipitate washing, calcium chloride at concentrations in the millimolar region decreased the lignin losses dramatically.

Effects of head group of cationic surfactants on the hydrolysis of p‐nitrophenyl acetate catalyzed by α‐chymotrypsin

AbstractThe kinetics of hydrolysis of p‐nitrophenyl acetate catalyzed by α‐chymotrypsin (α‐CT) has been studied in the presence of several cationic surfactants having different head groups maintaining the dodecyl hydrophobic residue and bromide counterion. The enzyme activity was tested in the presence of dodecyl trimethylammonium bromide (DTAB), dodecylpyridinium bromide (DPB), dodecyldimethylethanolammonium bromide (DDMEAB), dodecyldiethylethanolammonium bromide (DDEEAB), benzyldimethyldodecylammonium bromide (BDDAB), and dodecyltriphenylphosphonium bromide (DTPB) surfactants. The extent of superactivity depends upon head groups of surfactants. The activity of α‐CT depends on the surfactant concentration and it varies with the surfactant head group dimensions (DTPB > DDEEAB > DTAB > BDDAB > DDMEAB > DPB). For all surfactants, DTPB exhibits highest superactivity. The effects of surfactants on the apparent kinetic parameters like Michaelis constant Km and the catalytic constant kcat have been determined. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 377–381, 2009

Effect of surfactant on reductive dechlorination of trichloroethylene by zero-valent iron

Trichloroethylene (TCE) is a representative dense nonaqueous phase liquid (DNAPL) in groundwater. TCE as a form of free fluid has been treated by surfactant-enhanced aquifer remediation (SEAR). After application of SEAR, groundwater contains little amount of residual TCE and surfactant. Residual TCE could be treated by zero-valent iron (ZVI). However, surfactant might modify the surface property of ZVI. As a result, the reduction of TCE on the surface of ZVI might be affected by the presence of surfactant. In this study, the effect of surfactant types on reductive dechlorination of TCE was investigated using zero-valent iron. Cationic surfactant enhanced the dechlorination rate of TCE at a concentration below the critical micelle concentration (CMC) compared to pure ZVI. Electrostatic interaction between electronegative chloride group of TCE and positive head group of cationic surfactant was increased sorption of TCE on the surface of ZVI. However, anionic and nonionic surfactants inhibited the reductive dechlorination of TCE because of the decrease of TCE sorption on the surface of ZVI. The reduction rate of TCE in the presence of nonionic surfactant is dependent on the length of hydrophobic carbon chain in nonionic surfactant. Little amount of cationic surfactant could enhanced the reductive dechlorination rate of TCE. As a result, the time to treat TCE in groundwater will be shortened.

Interactions of a Hydrophobically Modified Polymer with Oppositely Charged Surfactants

The interaction of a hydrophobically modified anionic polymer (PMAOVE) with a cationic surfactant (DTAB) was studied using a multi-technique approach: turbidity, surface tension, and viscosity measurements, as well as EPR (5-doxyl stearic acid) and fluorescence (pyrene) probe techniques were used. In the investigated pH range (4-10), the cationic surfactant headgroups interact with the anionic carboxylic groups of the polymer backbone. In addition, nonpolar interactions of the surfactant chains with the n-octyl chains of PMAOVE stabilize the PMAOVE-DTAB complexes. Charge neutralization of the anionic polymer by the cationic surfactant leads to precipitation of the PMAOVE-DTAB complex at a certain DTAB concentration range. Further addition of DTAB causes a charge reversal of the complex and, subsequently, resolubilization of the precipitate. At an acidic pH (pH = 4), a second precipitation was observed, which is probably caused by conformational changes in the PMAOVE-DTAB complex. This second precipitate can be resolubilized by further addition of surfactant. At a neutral and basic pH, this second precipitation is absent. EPR analysis indicates that the surfactants form an ordered structure at the extended polymer chain at a neutral and basic pH, whereas at an acidic pH, a less ordered surfactant layer is formed on the coiled polymer with more hydrophobic microdomains.

Postsynthesis of Hexagonally Packed Porous Zirconium Phosphate through a Novel Anion Exchange between Zirconium Oxide Mesophase and Phosphoric Acid

Porous zirconium phosphates having ordered hexagonal pore system and high surface area have been prepared by post-treating surfactant-assisted zirconium oxide mesophase with phosphoric acid solution. The zirconium phosphates with P/Zr atomic ratios of 0.08−1.67 and maintaining totally the hexagonal structure were obtained by varying the phosphoric acid concentration (0.01−1 M), varying the treatment time (0.08−5 h), and repeating the treatment (1−6 times). Zirconium phosphates with P/Zr atomic ratios over 1.0 withstood the calcination up to 873 K and showed the BET specific surface area of 456−547 m2 g-1. The porous zirconium phosphates were characteristic of micropores with the pore size of 1.30−1.66 nm due to partial condensation of the mesopores during the calcination. The formation mechanism of the hexagonal zirconium phosphates was clarified to be essentially an anion exchange of HPO42- ions for SO42- ions which mediated the cationic zirconium species and the cationic surfactant headgroups within the as-synthesized zirconium oxide mesophase through electrostatic interactions, together with a reaction between the phosphoric acid and the Zr−OH groups. The anion exchange was confirmed to yield the phosphorus species showing two 31P MAS NMR bands at ca. −3.0 and −9.2 ppm, while the reaction of phosphoric acid with the Zr−OH groups was suggested to form the phosphorus species corresponding to a band at −19.4 ppm.

Binding of Dodecyltrimethylammonium Bromide to pH-Responsive Nanocolloids Containing Cross-Linked Methacrylic Acid−Ethyl Acrylate Copolymers

The binding of dodecyltrimethylammonium bromide (DoTab) to cross-linked methacrylic acid-ethyl acrylate (MAA-EA) copolymers with various MAA/EA molar ratios at different degrees of neutralization (alpha) was quantitatively studied using isothermal titration calorimetry, dynamic light scattering, surfactant selective electrode, and electrophoresis techniques. The surfactant binds to the polymers at all degrees of neutralization, but via different mechanisms. When alpha is sufficiently high, the binding is primarily electrostatic interaction between the surfactant and ionized polymer chains, which is reinforced by the micellization of electrostatically bound surfactant molecules. The saturation takes place at charge ratio ([DoTa(+)]/[ approximately COO(-)]) close to 1, indicating that the binding is a one-to-one charge neutralization between the cationic surfactant headgroups and anionic carboxylate sites of the polymers. When alpha is low, the binding of DoTab to the unneutralized polymers is driven by the hydrophobic interaction. The onset of hydrophobic binding takes place at DoTab concentration as low as 0.01 mM in 0.05 wt % polymer solution, where the saturation occurs at C(DoTab) approximately 0.19 mM and the amount of bound surfactant is approximately 0.09 mmol of DoTab/(g of polymer) at saturation concentration. The binding results in the formation of the polymer-surfactant complex. For the polymer with low MAA/EA molar ratio, the complex coagulates at a higher DoTab concentration that leads to phase separation; however, for polymers with high MAA/EA molar ratio, the complex remains dispersed and the mixture is stable even at high DoTab concentration.

Molecularly ordered inorganic frameworks in layered silicate surfactant mesophases.

Self-assembled lamellar silica-surfactant mesophase composites have been prepared with crystal-like ordering in the silica frameworks using a variety of cationic surfactant species under hydrothermal conditions. These materials represent the first mesoscopically ordered composites that have been directly synthesized with structure-directing surfactants yielding highly ordered inorganic frameworks. One-dimensional solid-state 29Si NMR spectra, X-ray diffraction patterns, and infrared spectra show the progression of molecular organization in the self-assembled mesophases from structures with initially amorphous silica networks into sheets with very high degrees of molecular order. The silicate sheets appear to be two-dimensional crystals, whose structures and rates of formation depend strongly on the charge density of the cationic surfactant headgroups. Two-dimensional solid-state heteronuclear and homonuclear NMR measurements show the molecular proximities of the silica framework sites to the structure-directing surfactant molecules and establish local Si-O-Si bonding connectivities in these materials.

Influence of Surfactant-based Microheterogeneous Fluids on Aggregation of Copper Phthalocyanine Tetrasulfonate

Electronic absorption spectroscopy was used to measure the molecular association of copper phthalocyanine tetrasulfonate in micellar solutions, a microemulsion made with cationic surfactant, and homogeneous solvents. Analysis of absorbance versus concentration data using a multiple-aggregation model and non-linear regression analysis gave values of association constants, molar absorptivities and estimates of average aggregation number. Microemulsions and aqueous micellar solutions made with alkylammonium surfactants inhibited aggregation, probably because of interactions between the phthalocyanine sulfonate groups and the cationic surfactant head groups at interfacial surfaces. Similar aggregation behavior was observed previously in multiple-bilayer films of cationic surfactants. Water and aqueous solutions containing tetraethylammonium bromide or anionic SDS micelles provide environments facilitating extensive aggregation of Cu II PcTS 4−. The major species are dimers in water and acetonitrile/water, but the formation of higher aggregates is promoted by addition of SDS or TEAB. Aprotic organic solvents provide environments intermediate between these two extremes, giving relatively large aggregation numbers (i.e. five to seven) but smaller association constants than aqueous media not containing cationic surfactants.

Dielectric Relaxation of Surfactant Micellar Solutions

Dielectric relaxation behavior of spherical micelles of cationic surfactants, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and cetyltrimethylammonium bromide, in aqueous solution was examined in the frequency range from 106 to 109 Hz. Each surfactant solution shows pronounced dielectric dispersions with two distinct relaxation times above the critical micelle concentrations. A slow relaxation mode with a relaxation time τs ∼ 5 ns reduced its magnitude with increasing the concentration of surfactants (CD). On the other hand, the magnitude of a fast relaxation mechanism with the relaxation time τf ∼ 0.5 ns was proportional to CD. The slow relaxation mode was attributed to the fluctuation of a counterion distribution around the spherical micelle or that of a distribution of dissociated cationic surfactant headgroups on the micellar surface. The fast relaxation mode was assigned to the rotational motion of ionic pairs consisting of surfactant cations and counteranions in the spherical micelle.

Fluorescence Investigation of Multiple Partitioning Sites in Aqueous and Reverse Micelles

Our investigations seek to illustrate the use of fluorescence spectral deconvolution to characterize multiple partitioning sites for aromatic chromophores within aqueous and reverse micelles. The spatial distribution of solutes within micellar systems is dictated by a variety of noncovalent interactions. To probe for multiple partitioning microenvironments, we use the aromatic fluorophore Prodan with its extensive solubility in a range of media and its appreciable spectral sensitivity to the polarity of its surroundings. We conduct a systematic study of the partitioning of Prodan in aqueous micellar systems with anionic, cationic, zwitterionic, and nonionic surfactant headgroups and in reverse micellar systems with both anionic and cationic surfactant headgroups. By deconvoluting the overall Prodan fluorescence emission spectrum into a sum of overlapping Gaussian functions, the principal microenvironments of the Prodan molecules may be ascertained. Fluorescence data are consistent with the location of Pro...

Formation and coexistence of the micelles and vesicles in mixed solution of cationic and anionic surfactant

In the aqueous mixtures of sodium alkylcarboxylate and alkyltrimethylammonium bromide, large unilamelar vesicles can be formed spontaneously or by sonication as the total carbon number in the HC chains is 19 (or larger). Vesicle formation can be influenced by changes of pH, molar ratio of the two surfactant components, and the polar head group of cationic surfactant. Micelles may coexist with the vesicles in these mixed systems. The larger hydrodynamic radius (∼200 nm) and aggregation number (∼800) illustrate that the shape of the micelle in 1:1 C9H19COONa−C10H21N(CH3)3Br is rod-like. In some mixed systems, the micelles can be transformed into stable vesicles by sonication — a phenomenon revealed for the first time. The surface-chemical properties of these catanionic surfactant solutions and the stabilities of vesicle have been studied systematically.