Cetyltrimethylammonium Tosylate Research Articles

Origin of steady state stress fluctuations in a shear-thinning worm-like micellar system

Large, irregular stress fluctuations under a constant applied shear rate are observed during the flow of dilute worm-like micellar solutions even at low Reynolds numbers. Statistical properties of such fluctuations showing signatures of chaos and elastic turbulence have been studied extensively. Although the mechanisms like boundary slippage, dynamics of shear band interface, time-dependent secondary flows, and inertio-elastic effects are conceived as the possible factors for such striking flow properties, their contributions in different non-linear flow regimes remain poorly understood. Here, we study the Taylor–Couette flow of a well-characterized aqueous worm-like micellar system formed by 2 wt. % cetyltrimethylammonium tosylate and 100 mM sodium chloride (2 wt. % CTAT + 100 mM NaCl). For a fixed applied shear-rate just beyond the onset of shear-thinning, high-speed optical imaging in the flow-gradient plane reveals spatiotemporally varying velocity gradients in the system. In this regime, the magnitude of stress fluctuations remains insignificant. However, the fluctuation becomes substantial beyond a critical shear rate deep inside the non-linear regime of the flow curve when significant free-surface undulations, sustained stick-slip, and elastic recoil events are observed. Imaging in the flow-vorticity and the gradient-vorticity plane indicates that such dynamics are primarily driven by the elasticity-induced turbulent flows in the system. Furthermore, in this regime, we find that the characteristic persistent time of stress fluctuations matches well with the time scales of the stick-slip events, as well as the micellar breaking time, indicating a possible connection between the striking stress dynamics and the micellar kinetics.

Evaluating methods to create protein functionalized catanionic vesicles.

Catanionic surfactant vesicles (SVs) composed of sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium tosylate (CTAT) have potential applications as targeted drug delivery systems, vaccine platforms, and diagnostic tools. To facilitate these applications, we evaluated various methods to attach proteins to the surface of SDBS/CTAT vesicles. Acid phosphatase from wheat germ was used as a model protein. Acid phosphatase was successfully conjugated to vesicles enriched with a Triton-X 100 derivative containing an unsaturated ester. Enzymatic activity of acid phosphatase attached to vesicles was assessed using an acid phosphatase assay. Results from the acid phosphatase assay indicated that 15 ± 3% of the attached protein remained functional but the presence of vesicles interferes with the assay. DLS and zeta potential results correlated with the protein functionalization studies. Acid phosphatase functionalized vesicles had an average diameter of 175 ± 85 nm and an average zeta potential of -61 ± 5 mV in PBS. As a control, vesicles enriched with Triton-X 100 were prepared and analyzed by DLS and zeta potential measurements. Triton X-100 enriched vesicles had an average diameter of 140 ± 67 nm and an average zeta potential of -49 ± 2 mV in PBS. Functionalizing the surface of SVs with proteins may be a key step in developing vesicle-based technologies. For drug delivery, antibodies could be used as targeting molecules; for vaccine formulation, functionalizing the surface with spike proteins may produce novel vaccine platforms.

Osmotic-pressure-induced phase transition of a surfactant-DNA complex.

We have studied the effect of osmotic pressure on complexes formed by DNA with the cationic surfactant cetyltrimethylammonium tosylate using small-angle x-ray scattering. Earlier studies have shown that these complexes exhibit three different phases depending on the DNA and surfactant concentrations in the solution. The hexagonal superlattice phase (H_{I,s}^{c}) is found to be corralled into the hexagonal phase (H_{I}^{c}) above a threshold osmotic pressure. We have also estimated the DNA to surfactant micelle stoichiometry of the complexes in the three phases using elemental analysis. Our results provide further support for the structures of these complexes proposed earlier based on small-angle x-ray scattering data.

Contrasting effect of 1-butanol and 1,4-butanediol on the triggered micellar self-assemblies of C16-type cationic surfactants.

The self-assembly in aqueous solutions of three quaternary salt-based C16-type cationic surfactants with different polar head groups and identical carbon alkyl chain viz., cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number (Nagg) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the three cationic surfactants, the molecular dynamics (MD) simulation was performed for CPB micelles in an aqueous solution of alcohols that highlighted the micelle solvation and structural transition, which is further complemented in terms of critical packing parameter (PP) for the examined systems.

Extraction of Membrane Components from Neisseria gonorrhoeae Using Catanionic Surfactant Vesicles: A New Approach for the Study of Bacterial Surface Molecules.

Identification of antigens is important for vaccine production. We tested extraction protocols using cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS) to formulate surfactant vesicles (SVs) containing components from Neisseria gonorrhoeae. Carbohydrate and protein assays demonstrated that protein and carbohydrates were incorporated into the vesicle leaflet. Depending on the extraction protocol utilized, 100–400 µg of protein/mL of SVs solution was obtained. Gel electrophoresis followed by silver staining demonstrated that SV extracts contained lipooligosaccharide and a subset of bacterial proteins and lipoproteins. Western blotting and mass spectral analysis indicated that the majority of the proteins were derived from the outer membrane. Mass spectrometric and bioinformatics analysis of SVs identified 29 membrane proteins, including porin and opacity-associated protein. Proteins embedded in the SVs leaflet could be degraded by the addition of trypsin or proteinase K. Our data showed that the incorporation of CTAT and SDBS into vesicles eliminated their toxicity as measured by a THP-1 killing assay. Incorporation of gonococcal cell surface components into SVs reduced toxicity as compared to the whole cell extracts, as measured by cytokine induction, while retaining the immunogenicity. This process constitutes a general method for extracting bacterial surface components and identification of antigens that might be included in vaccines.

Nanostructured hybrid fluids of amphiphilic diblock copolymers and surfactant worm-like micelles complexes

This paper reports the synthesis and characterization of two poly(methyl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers and their synergistic interaction with cetyltrimethylammonium tosylate (CTAT) worm-like micelles (WLMs) in aqueous solutions. The rheological behavior of the mixtures of the copolymers and CTAT was compared with the water soluble homopolymer, poly(2-(dimethylamino)ethyl methacrylate). The polymers were synthesized via ATRP, and were characterized using GPC, FTIR and 1H NMR. The rheological behavior of CTAT WLMs was explored under continuous shear flow, varying the (co)polymer concentration, adding salt to the (co)polymer/CTAT systems and changing the pH and the temperature. The effect of the copolymer on CTAT pseudoplasticity reveals the synergy between both compounds, leading to mixed worm like micelles. Based on our rheological results, spherical mixed micelles are not formed for the systems studied since shear induced structures (SIS) were formed even at high (co)polymer concentration. These SIS are characteristic of CTAT worm-like micelles and demonstrate that the surfactant keeps its micellar configuration in water, albeit modified by the co-micellization with the (co)polymer molecules. We demonstrate that shear produces a more pronounced effect in the viscosity of CTAT/polymer mixed worm-like micelles for systems containing interacting diblock copolymers than those containing homopolymers. The novel copolymer/surfactant fluids prepared here exhibit viscosities that can be tuned from 10 to 10,000 times the viscosity of water by selecting molecular weights, solution concentrations, ionic environment, temperature and shear rates.

The effect of glycols and their ethers on micellar behavior of cetyltrimethylammonium tosylate

The effect of glycols viz., ethylene glycol (EG), diethylene glycol (DEG) propylene glycol (PG), dipropylene glycol (DPG) and their monoalkyl ethers on the morphological features of cetyltrimethylammonium tosylate (CTAT) micelle was examined from viscosity and small angle neutron scattering (SANS) measurements. EG and DEG, and their short chain ethers showed an initial increase in viscosity followed by a decrease while long chain PG, DPG and their ethers showed a monotonous decrease in viscosity. SANS results support the viscosity behavior. These trends are explained on the basis of hydrophobicity of the additives that determines its location in the micelle exerting an effect on micelle morphology. The critical micelle concentrations (CMCs) of CTAT determined tensiometrically for selected systems are also reported. This study helps in fine tuning of rheology of micellar systems in the presence of gycols and their ethers often used with surfactant systems.

A facile route for wettability regulation by modifying the submicron/nanoscale physical topography of porous films

Porous anatase TiO2 films with disparate submicron/nanoscale topographies were fabricated in this study. The wettability of the films could be regulated from super-hydrophilicity to hydrophobicity using a facile soft template route. The surface morphologies of the prepared films were investigated by FESEM and AFM, with the porous structures characterized via BET. The wetting property of the films with micro level morphology was studied by contact angle (CA) measurements. On the above basis, the macroporous surfaces (templated by triblock copolymer P123 or cetyltrimethylammonium tosylate (CTATos)) with superhydrophilicity (CA=0°) and the mesoporous surface (templated by cetyltrimethyl ammonium bromide (CTAB)) with hydrophobic characteristic (CA=96°) were detected. It is interesting to find that even though the chemical composition is hydrophilic, the hydrophobic surface could still be formed by the mesoporous topography with a possible wetting mechanism based on the Cassie model. Moreover, the morphology dominant hydrophobicity was well maintained after heating at 500°C for 2h (CA=91°), bringing the material greater potential under harsh conditions.

Shear-induced structural and thermodynamic phase transitions in micellar systems.

In this contribution a methodology to compute and classify shear-induced structural and phase transitions in surfactant/water mixtures from rheological measurements is presented. Non-linear rheological experiments, considering variations in surfactant concentration and temperature, are analyzed. In particular, the parameters of the BMP (Bautista-Manero-Puig) model, obtained from the fitting of the shear stress versus shear rate data, which are functions of surfactant concentration and temperature, allow classifying structural and phase transition boundaries. To test this methodology, we consider the analysis of the shear-induced structural and phase transitions of two micellar systems, cetyltrimethylammonium tosylate (CTAT)/water as a function of CTAT concentrations and Pluronics P103/water as a function of temperature. We found that the CTAT/water system presents a first-order phase transition at 30 ° C, and around 31 to 32 wt.% from isotropic to nematic phases, whereas a 20 wt.% Pluronics P103 aqueous micellar solution has two second-order (structural) phase transitions, one from spherical to cylindrical micelles at 33.1 ° C, and another one from cylindrical micelles to a nematic phase at 35.8 ° C and one first-order phase transition around 37.9 ° C at high shear rates near to the cloud point previously reported. The proposed methodology is also able to identify the instability regions where the wormlike micelles are broken, producing the typical shear banding behavior.

Microstructure and transitions in mixed micelles of cetyltrimethylammonium tosylate and bile salts

The effect of bile salts viz. sodium cholate (NaC) and sodium deoxycholate (NaDC) on the size and transition of cetyltrimethylammonium tosylate (CTAT) micelles is examined by viscosity, cryogenic transmission electron microscopy (Cryo-TEM), small angle neutron scattering (SANS), nuclear Overhauser enhancement spectroscopy (NOESY) and 1H NMR. The viscosity of worm-like micelles of CTAT solution strongly decreases as the temperature increases favoring the transformation to spheroidal micelles. At low NaC concentration (5–10mM), viscosity of 20mM CTAT solutions decreases, reaching a constant value close to that of water. However, for NaDC, a peak in viscosity is seen followed by a drop around 3mM concentration. The microstructure of CTAT micelles gets altered by bile salts as revealed by cryo-TEM. As manifested by SANS results, NaC transforms worm-like CTAT micelles into small spherical/ellipsoidal mixed micelles. However, there was no difference in SANS plot of worm-like CTAT micelles in D2O and in presence of NaDC; these clearly suggest the presence of worm-like micelles. NaDC behaves differently, showing a maximum in viscosity for 20mM CTAT at ∼3mM concentration and phase separation at equimolar ratio. The results are discussed in terms of location of bile salt in mixed micelles determined by NOESY and 1H NMR experiments.

Effect of polymers on worm-like micelles of cetyltrimethylammonium tosylate

Abstract Aqueous solution behaviour of worm-like micelles of cetyltrimethylammonium tosylate (CTAT) was examined in the presence of some water soluble nonionic polymers viz. poly(ethylene oxide) 4000 (PEO 4K), poly(propylene oxide) 1000 (PPO 1K), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) and poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) type linear triblock copolymers and nonlinear octablock copolymers by an array of techniques. CTAT forms worm-like micelles at very low concentrations. Very hydrophilic PEO 4K molecules surround micelle surface leading to viscosity increase while PPO 1K and linear triblock copolymers demonstrates distinct interaction with worm-like CTAT micelles. They form smaller mixed micelles strongly depending on their structure and hydrophobicity. Structurally different PEO-PPO-PEO type nonlinear block copolymer display dissimilar effect on morphology of CTAT micelles. Small angle neutron scattering (SANS) measurements provide clear idea about structural transitions from worm-like to spherical/ellipsoidal micelles with different dimensions. The different behaviour shown by the polymers is explained on the basis of their interaction with different interiors of CTAT micelles. 1 H NMR and nuclear overhauser enhancement spectroscopy (NOESY) experiments provide idea about location of these additives and site of interaction. The present study validates how the size of worm-like micelles can easily be tuned up by different polymers.

The influence of concentration and pH on the structure and rheology of cationic surfactant/hydrotrope structured fluids

Abstract In this paper, we show how to tailor the structure and rheology of aqueous solutions of the cationic surfactant cetyltrimethylammonium tosylate, CTAT, by adding a hydrotrope (potassium phthalic acid, PPA) or changing pH. Aqueous solutions of neat CTAT and CTAT/PPA binary mixtures were evaluated under different hydrotrope concentrations and compared with solutions of an analogous surfactant, cetyltrimethylammonium chloride (CTAC). PPA content promotes substantial increases in micellar flexibility and inter-micellar entanglements, resulting in a higher degree of structure in the fluid. Increasing the pH in neat CTAT leads to significant increases in low shear rate viscosities in comparison with CTAT at its original pH, because the OH ions favor surfactant aggregation as well as the growth of worm-like micelles. Nevertheless, increasing the pH in CTAT/PPA mixtures produced a progressive decrease in the low shear rate viscosities. This result is due to the nature of the interactions between CTAT and PPA, as well as to the ionization degree of the functional groups present in PPA. Cryo-TEM and 1 H NMR measurements evidenced, respectively, the microstructural and chemical environmental changes of CTAT upon PPA addition and explain the rheological properties of the CTAT/PPA mixtures as a function of the fluid structure.

One-pot pseudomorphic crystallization of mesoporous porous silica to hierarchical porous zeolites

Hierarchically porous silica with mesopore and zeolitic micropore was synthesized via pseudomorphic crystallization under high-temperature hydrothermal treatment in the presence of cetyltrimethylammonium tosylate and tetrapropylammonium ions. A combined characterization using small-angle X-ray diffraction (XRD), nitrogen adsorption, high-resolution transmission electron microscopy (TEM), thermogravimetric analysis (TG), and elemental analysis showed that dual templates, CTA+ and TPA+ molecules, can work in a cooperative manner to synthesize mesoporous zeolite in a one-pot system by precisely tuning the reaction conditions, such as reaction time and temperature, and type and amount of heterometal atoms. It is found that the presence of Ti precursor is critical to the successful synthesis of such nanostructure. It not only retards the nucleation and growth of crystalline MFI domains, but also acts as nano-binder or nano-glue to favor the assembly of zeolite nanoblocks.

Directed assembly of vesicle-templated polymer nanocapsules under near-physiological conditions.

This work addresses the challenge of creating hollow polymer capsules with wall thickness in the single-nanometer range under mild conditions. We present a simple and scalable method for the synthesis of hollow polymer nanocapsules in the bilayers of spontaneously assembled surfactant vesicles. Polymerization is initiated thermally with the help of a peroxide initiator and an amine activator codissolved with monomers and cross-linkers in the hydrophobic interior of the surfactant bilayer. To avoid premature polymerization, the initiator and the activator were added separately to the mixtures of cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS) containing monomers and cross-linkers. Upon hydration and mixing of the aqueous solutions, equilibrium monomer-loaded vesicles formed spontaneously after a brief incubation. The removal of oxygen and further incubation at slightly elevated temperatures (35-40 °C) for 1 to 2 h has led to the formation of hollow polymer nanocapsules. Structural and permeability characterization supported the high yield of nanocapsules with no pinhole defects.

1-Hexanol triggered structural characterization of the worm-like micelle to vesicle transitions in cetyltrimethylammonium tosylate solutions

Incorporation of 1-hexanol close to the palisade layer of CTAT micelles favors transition of worm-like micelles to vesicular structuresviaformation of elongated worm-like micelles.

One-step synthesis of mesoporous ZSM-11 composites through a dual-template method

Hierarchical porous ZSM-11 composites were hydrothermally synthesized through a one-step route using binary templates of cetyltrimethylammonium tosylate (CTATos) and tetrabutylammonium hydroxide (TBAOH). Influences of aluminum content and crystallization temperature on the morphology and structure were investigated. Powder X-ray diffraction (XRD) and N2 physisorption results show that the mesoporous ZSM-11 composites possess both a considerable mesoporous structure and zeolitic MEL-structure. Moreover, a large amount of aluminum in the gel composition slows the rate of zeolite crystallization, while a high SiO2/Al2O3 ratio is beneficial for the synthesis of mesoporous ZSM-11 without any phase separation. Mesoporous ZSM-11 aluminosilicates were compared to pure ordered mesoporous materials, zeolites and a mechanical mixture of meso and microphases for their catalytic activity in low-density polyethylene (LDPE) pyrolysis. The results suggest that all mesoporous ZSM-11 composites show higher catalytic performance for LDPE cracking.

Interaction between Cetyltrimetylammonium Tosylate and Two Poly(oxyethylene)–Poly(oxypropylene)–Poly(oxyethylene) Block Copolymers Studied by Cyclic Voltammetry

Mixtures of hexadecyltrimetylammonium tosylate (hexadecyltrimethylammonium p-toluene sulfonate or cetyltrimethylammonium tosylate, CTAT) with two Pluronic block copolymers, F127 and F68, were studied using cyclic voltammetry. The hydrodynamic radii of aggregates were analyzed in light of the aggregate composition. It was confirmed that the mixtures CTAT-F127 and CTAT-F68 have different behaviors. This corroborates that the interaction between different Pluronics and the same conventional surfactant depends on the kind of copolymer surfactant and also that differences in the size of the hydrophobic and the hydrophilic parts of the molecule may cause different behaviors. The penetration of CTAT into the micelle core may be more or less hindered by the size and structure of the hydrophilic shell. However, once the conventional surfactant has penetrated the corona and reached the polyoxypropylene core in a cooperative manner, the aggregates tend to disappear, thus being replaced by smaller structures, which are probably complexes having a finite number of CTAT molecules per copolymer molecule.

Preparation of High‐Quality MCM‐48 Mesoporous Silica and the Mode of Action of the Template

AbstractUltrastable MCM‐48 silica with Ia3d cubic structure was synthesized by using only the surfactant cetyltrimethylammonium tosylate (CTATos) as template at extremely low surfactant concentration (CTATos/SiO2 = 0.068). Characterization by small‐angle X‐ray diffraction (XRD), nitrogen adsorption, and high‐resolution transmission electron microscopy (HRTEM) clearly shows that the obtained MCM‐48 silica has a highly ordered structure and large surface area (ca. 1281 m2/g) and pore volume (ca. 1.07 cm3/g). The regular cubic arrays were well retained even after this material was calcined at a high temperature of 900 °C for 3 h or heated at reflux in boiling water for 12 h. The Fourier transform infrared (FTIR) spectrum, thermogravimetric analysis (TG), and chemical analysis provide strong evidence that the formation of MCM‐48 is attributed to the retention of tosylate (Tos–) counteranions of the surfactant in the interface between surfactant and silicate. The current synthetic strategy is suitable for routine and large‐scale preparations of mesoporous silica with different topological structures.

Phase behavior of the cetyltrimethylammonium tosylate (CTAT)–water system

A partial phase diagram of the cetyltrimethylammonium tosylate (CTAT)–water system has been constructed from polarizing optical microscopy and small-angle x-ray scattering studies. This system is found to exhibit a nematic phase over a wide range of CTAT concentration, from about 32 to 45wt.%, which is very unusual for aqueous solutions of pure surfactants. At higher CTAT concentrations a hexagonal phase occurs which is stable up to at least 90°C. Detailed analysis of the diffraction data confirms that the hexagonal phase consists of long cylindrical micelles arranged on a two-dimensional hexagonal lattice.

Cerium(IV) oxide: Synthesis in alkaline and acidic media, characterization and adsorption properties

Cerium(IV) oxide or ceria materials were synthesized in alkaline and acidic media, using cerium(IV) sulfate as ceria precursor and cetyltrimethylammonium tosylate as template, in order to evaluate the effect of pH on the morphology and texture of synthesized materials. The results show that the surface area, the pore size and volume, and the surface charge can be tuned by changing the pH. Both ceria materials are formed by nanoparticles although in the material synthesized in acidic media (CeO2(B)) the particles tend to form an ordered mesoporous structure with a narrower porous size distribution, mainly due to the formation of voids between them. CeO2 material synthesized in alkaline media (CeO2(A)), on the contrary, shows an irregular distribution of the pores with different sizes, which were probably formed by the stacking of ceria particles. These differences seem to be also attributed to the interaction between CTAT and ceria nanoparticles during the synthesis at both experimental conditions. The grain size, the surface area, the porous volume, and the isoelectric point of the synthesized materials were 8.5nm, 33.52m2g−1, 0.06cm3g−1, and 4 for CeO2(A), respectively; and 13.4nm, 21.98m2g−1, 0.05cm3g−1, and 7.4 for CeO2(B), respectively. Adsorption studies of synthesized materials toward tetracycline and minocycline antibiotics were performed and discussed.