Alkyltrimethylammonium Surfactants Research Articles

Cationic micelles in deep eutectic solvents: effects of solvent composition.

Deep eutectic solvents (DES) are mixtures of hydrogen bond donors and acceptors that form strongly hydrogen-bonded room temperature liquids. Changing the H-bonding components and their ratios can alter the physicochemical properties of deep eutectic solvents. Recent studies have shown p-toluenesulfonic acid (pTSA) forms room temperature liquids with choline chloride (ChCl) at different molar ratios: 1 : 1, 1 : 2 and 2 : 1 [Rodriguez Rodriguez et al., ACS Sustain. Chem. Eng., 2019, 7(4), 3940]. They also showed that the composition affects the physical properties of these liquids and their ability to dissolve metal oxides. In this work we evaluate the solubility and self-assembly of cationic surfactants alkyltrimethyl ammonium bromides (CnTAB) in these pTSA/ChCl based liquids. CnTABs are insoluble in 1pTSA : 2ChCl, whereas in 1pTSA : 1ChCl and 2pTSA : 1ChCl they form micelles. We characterise CnTAB (n = 12, 14, 16) micelles using small angle neutron scattering and also look at interaction of water with the micelles. These studies help determine the interaction of DES components with the surfactant and the influence of varying pTSA and water ratios on these interactions. This provides potential for controlled surfactant templating and for tuning rheology modification in such systems.

FAIR and scalable management of small-angle X-ray scattering data.

A modular research data management toolbox based on the programming language Python, the widely used computing platform Jupyter Notebook, the standardized data exchange format for analytical data (AnIML) and the generic repository Dataverse has been established and applied to analyze small-angle X-ray scattering (SAXS) data according to the FAIR data principles (findable, accessible, interoperable and reusable). The SAS-tools library is a community-driven effort to develop tools for data acquisition, analysis, visualization and publishing of SAXS data. Metadata from the experiment and the results of data analysis are stored as an AnIML document using the novel Python-native pyAnIML API. The AnIML document, measured raw data and plots resulting from the analysis are combined into an archive in OMEX format and uploaded to Dataverse using the novel easyDataverse API, which makes each data set accessible via a unique DOI and searchable via a structured metadata block. SAS-tools is applied to study the effects of alkyl chain length and counterions on the phase diagrams of alkyltrimethyl-ammonium surfactants in order to demonstrate the feasibility and usefulness of a scalable data management workflow for experiments in physical chemistry.

Photophysical characterization of a sub-micellar triblock copolymer-cationic surfactant aggregate for nanostructure synthesis

Surfactant assemblies are popular media for the synthesis of a variety of nanostructures. However, the use of excessive surfactants in these assemblies is detrimental to biological and medical applications. Herein, we optimized the size and interfacial packing of a sub-micellar aggregate of a triblock copolymer F127 (poly-(ethylene oxide)101 (EO101)−poly(propylene oxide)56 (PPO56)−PEO101), and several cationic alkyl trimethylammonium surfactants at minute concentrations and demonstrated its feasibility in synthesizing gold nano-triangles. We tracked various stages of the sub-micellar aggregate using an ultrasensitive photoacid 8-hydroxypyrene-1,3,6-trisulfonate (HPTS or Pyranine). The emission intensity (protonated/deprotonated) ratio of HPTS follows an intricate pattern against the surfactant concentration displaying three transition points (T1–3). The ratio starts to increase above an initial concentration (T1), attaining a maximum at an intermediate concentration (T2), and after that, decreases again before leveling off at a higher concentration (T3). Fluorescence anisotropy measurements of the methoxy analog 8-methoxypyrene-1,3,6-trisulfonate (MPTS) further revealed that the most organized state is near the critical point T2. Moreover, isothermal titration calorimetry (ITC) showed maximum enthalpy change at the same composition confirming optimum interaction. Finally, we show that the assemblies containing ultralow concentrations of both F127 and cationic surfactant can be a potent medium for synthesizing gold nano-triangles.

Synthesis and Properties of New Cleavable Cationic Surfactants Containing Carbonate Groups

AbstractA novel series of cleavable alkyltrimethylammonium surfactants with different hydrocarbon chain lengths (C8–16) were synthesized. A carbonate break site inserted between the polar head and the hydrocarbon chain makes these compounds hydrolyzable. The reagents used are renewable, (bio)degradable, or reusable. The hydrolysis of these cleavable surfactants will lead to the generation of fatty alcohols and choline, which is an essential biological nutrient. The surface activities in aqueous solution of the synthesized carbonates fulfill the requirement of being good surfactants. In addition, the cleavable compounds containing n‐decyl and n‐dodecyl chains showed similar or higher antimicrobial activities when compared to a non‐cleavable analog.

Alkyltrimethylammonium (ATMA) surfactants as cyanocides - Effects on photosynthesis and growth of cyanobacteria

Cyanobacteria and their toxins present potential hazard to consumers of water from lakes, reservoirs and rivers, thus their removal via water treatment or at the source, is essential. Here, we report that alkyltrimethylammonium (ATMA) surfactants, such as octadecyltrimethylammonium (ODTMA) bromide, act as cyanocides that efficiently inhibit photosynthesis and growth of cyanobacteria. Green algae were found less sensitive than cyanobacteria to ATMA compounds. Fluorescence measurements and microscopic observations demonstrated that cyanobacteria cells (Aphanizomenon or Microcystis) disintegrate and lose their metabolic activity (photosynthesis) upon exposure to ATMA bromides (estimated ED50(1hr) ranged between 1.5 and 7 μM for ODTMA-Br or hexadecyltrimethylammonium (HDTMA) bromide). Other ATMA compounds, such as tetradecyltrimethylammonium (TDTMA) or dodecyltrimethylammonium (DDTMA) bromides had similar inhibitory effect but their toxicity to cyanobacteria (measured as ED50(1hr) for photosynthetic efficiency) decreased, as the length of the alkyl chain decreased. All ATMA compounds used in this study showed lower toxicity to green algae than to cyanobacteria. A toxicity mechanism for ATMA cations is proposed, based on real time fluorescence signals and on alteration of cell ultra-structure revealed by electron microscopy. The present study sheds light on the toxic effect of ATMA surfactants on cyanobacteria and its potential application for controlling the occurrence of cyanobacterial bloom in lakes, reservoirs or rivers to secure the safety of drinking water and to mitigate and manage bloom events.

The electrokinetic properties of cationic surfactants adsorbed on a hydrophobic substrate: effect of chain length and concentration

Electrokinetic (EK) properties, such as the electro-osmotic flow (EOF), are influenced by surfactant adsorption at the solid–liquid interface. With the growing popularity of poly(methyl methacrylate) (PMMA) as the substrate for polymeric-based microfluidics, it is important to understand the effect of surfactants on EOF in these devices. Here, we investigate the effect of surfactant chain length and concentration on the electro-osmotic (EO) mobility induced by three cationic surfactants cetyl trimethylammonium bromide (CTAB), trimethylammonium bromide (TTAB), dodecyl trimethylammonium bromide (DTAB) in PMMA microcapillaries. The EO mobility curve as a function of concentration shows three regimes. First, at very low concentrations below 0.002 mM, the mobility is constant and approximately equal to the value obtained with the surfactant-free electrolyte (1 mM KCl). Next, the EOF reverses and mobility increases linearly with surfactant concentration. Finally, the mobility reaches a plateau at a concentration well below surfactant CMC (0.2-mM CTAB, 0.5-mM TTAB and 2-mM DTAB) and decreases at the vicinity of CMC. Our results show that the rate of change in mobility with respect to concentration is a linear function of chain length and increases with longer-chain surfactants. In addition, we deduce the magnitude of Van der Waals or cohesive energy between the adsorbed alkyl chains from the EO mobility values. For the alkyl trimethylammonium surfactants adsorbed on the hydrophobic surface of PMMA, this energy was found to be 0.114 kT smaller than the reported value for ionic surfactants adsorbed on a hydrophilic surface.

Phase Behavior Controlled by the Addition of Long-Chain n-Alcohols in Systems of Cationic Surfactant/Anionic Polyion Complex Salts and Water.

Phase behavior of surfactants in water may be affected by the addition of a third component, and the present study discusses how long-chain n-alcohols affect phase transitions of systems formed by the surfactant hexadecyltrimethylammonium bromide, C16TAB, or its complex salts formed with polyacrylate, C16TAPA30, as well as other previously reported complex salts/water/alcohol systems. Structural characterization by X-ray diffraction patterns at small and wide angles and different temperatures was performed for samples containing n-decanol, n-dodecanol, or n-tetradecanol. Differential scanning calorimetry (DSC) was also used to study the phase transition. The results allowed us to observe and understand the coexistence of lamellar gel (Lβ) and lamellar liquid-crystal (Lα) phases, elucidating the structure of a previously reported mesophase, proposing an alternative assignment. Whereas the chain-melting transition is well-known to be sharp for lipids, we have found that it is broader for C16TAB and C16TAPA in the presence of these n-alcohols. We have investigated the effects of their composition and chain length on the temperature and enthalpy of transition. This elucidates why the addition of n-alcohols with chains slightly shorter than that of the surfactants leads to the formation of an ordered gel-like lamellar phase (Lβ). n-Alcohols act as neutral cosurfactants, leading to more packing, and all of the factors converge to a limit situation, associated with a common critical area occupied by each alkyl chain. We compared our results with other mesophase systems from the literature, demonstrating that the same trends of phase behavior occur for complex salts of other polyelectrolytes with alkyltrimethylammonium surfactants.

Use of dye complexation dynamics to determine α‐cyclodextrin host:guest stability constants

AbstractDynamics of host:dye complexation have been used, as an alternative to displacement assays, for determination of additional host:guest stability constants. Requirement of this new methodology is host:guest complexation being much faster than host:dye in order to guaranty that host:guest system is in equilibrium at each time during dye inclusion into the host cavity. Methodology was tested by studying α‐CD:surfactant complexation using alkyltrimethylammonium surfactants with different alkyl chain length. Experimental results confirm the formation of 1:1 α‐CD:surfactant complexes with binding constants strongly dependent on the surfactant hydrophobicity.

Effect of cationic surfactant cetyltrimethylammonium bromide on the enzymatic hydrolysis of cellulose

Effect of cationic surfactants alkyltrimethylammonium bromide (CnTAB) with varied alkyl chain lengths on the enzymatic hydrolysis of Avicel and the surface charge of cellulase was investigated. Enzymatic hydrolysis of Avicel increased linearly from 42.1 to 61.4 % with the increase of the concentration of cetyltrimethylammonium bromide (C16TAB) logarithmically from 0.0001 to 0.01 mM, and reached a maximum value at the concentration of 0.01–0.03 mM. When the concentration was increased further, the cellulase solution became positively charged and the enzymatic hydrolysis of Avicel decreased rapidly. With the increasing alkyl chain length, CnTAB provided more proton and neutralized the negative charge of cellulase more obviously. Therefore, the required concentration of CnTAB could be less to enhance the enzymatic hydrolysis of Avicel. In addition, C16TAB could enhance enzymatic hydrolysis efficiency of corncob at high solid content from 35.0 to 56.3 %; C16TAB could reduce about 60 % of the cellulase loading in the enzymatic hydrolysis of corncob to obtain the same glucose yield. Effect of C16TAB on the enzymatic hydrolysis of typical pretreated softwood and hardwood was also investigated. This study laid the foundation for using CnTAB to recover cellulase, and provided the design direction for cellulase with higher activity and better stability by adjusting its hydrophilicity and chargeability.

Rod-shaped silica particles derivatized with elongated silver nanoparticles immobilized within mesopores

Silver-derivatized silica particles possessing a non-spherical morphology and surface plasmon resonance properties have been achieved. Nanometer-sized silica rods with uniformly sized mesopore channels were prepared first making use of alkyltrimethyl ammonium surfactants as porogens and the 1:0.10 tetraethyl orthosilicate (TEOS) : 3-aminopropyltriethoxysilane (APTES) mixture as a silicon source. Silica rods were subsequently functionalized by introducing elongated silver nanoparticles within the intra-particle mesopores thanks to the AgNO3 reduction procedure based on the action of hemiaminal groups previously located on the mesopore walls. The textural and structural features of the samples were inferred from the combined characterization studies including SEM and TEM microscopy, nitrogen adsorption-desorption at 77K, powder XRD in the small- and wide-angle region, as well as UV–visible spectroscopy. 129Xe NMR spectroscopy appeared particularly useful to obtain a correct information about the porous structure of rod-shaped silica particles and the silver incorporation within their intra-particle mesopores.

Water-Insoluble Surface Coatings of Polyion-Surfactant Ion Complex Salts Respond to Additives in a Surrounding Aqueous Solution.

Hydrated, but water-insoluble, "complex salts" (CS) composed of alkyltrimethylammonium surfactant ions with polyacrylate counterions are known to exhibit a rich phase behavior in bulk mixtures with water and have recently been shown to act as water-responsive surface coatings. Here it is shown, by SAXS measurements, that surface coatings of CS also respond to various added solutes in a surrounding aqueous solution, by altering their liquid crystalline structure. The obtained results provide new information on the phase behavior of CS in contact with water and aqueous solutions. Solutes such as acids, salts, excess ionic surfactant, or water-soluble polymers act on the CS by altering the polyion charge density, screening the electrostatic interaction, changing the curvature of the surfactant aggregate, or increasing the osmotic pressuring in the surrounding solution, all of which may result in a phase transition in the film. In water, all studied CS surface coatings had a micellar cubic structure, which could change to 2D hexagonal, HCP, or disordered micellar structure, depending on the identity of the CS and the identity and concentration of the added solute. For some systems, even dissolved CO2 from the ambient air was sufficient to induce a structural change in the film. Especially the films containing the long polyions remained intact even for large concentrations of solutes in the contacting solutions, and extensive washing in water resulted, in most cases, in films with the "original" structure found in water.

Water-responsive internally structured polymer-surfactant films on solid surfaces.

Water-insoluble films of oppositely charged polyion-surfactant ion "complex salts" (CS) are readily cast on solid surfaces from ethanolic solutions. The methodology introduces new possibilities to study and utilize more or less hydrated CS. Direct SAXS measurements show that the surface films are water-responsive and change their liquid crystalline structure in response to changes in the water activity of the environment. In addition to the classical micellar cubic and hexagonal phases, a rectangular ribbon phase and a hexagonal close-packed structure have now been detected for CS composed of cationic alkyltrimethylammonium surfactants with polyacrylate counterions. Added cosurfactants, decanol or the nonionic surfactant C12E5, yield additional lamellar and bicontinuous cubic structures. Images of the surfaces by optical and atomic force microscopy show that the films cover the surfaces well but have a more or less irregular surface topology, including "craters" of sizes ranging from a few to hundreds of micrometers. The results indicate possibilities to create a wealth of water-responsive structured CS films on solid surfaces.

Silver nanoparticle-containing submicron-in-size mesoporous silica-based systems for iodine entrapment and immobilization from gas phase

Submicron-in-size silica particles with controllable morphology, particle size and mesoporosity, have been prepared under basic conditions making use of cationic alkyltrimethylammonium surfactants (CnTAB, n=12,16,18) as porogens. Gaseous nitrogen adsorption, XRD and TEM experiments revealed quasi-spherical homodispersed objects possessing regular mesopores of the MCM-41 type; lengthening of the hydrophobic tail of the template resulted in smaller particles with greater intraparticle pores. The aggregation and sintering of individual silica particles during the calcination step led to the formation of particle clusters comprising interparticle voids, as evidenced by the 129Xe NMR and TEM studies. The calcined particles were subsequently loaded with metallic silver. The measurements of iodine adsorption onto Ag-functionalized materials from the gas phase were supplemented by XRD, SEM/EDX, and TGA/DTA studies. It was demonstrated that the functionalized silica retained much gaseous iodine in an irreversible manner, mainly as an ‘interfacial’ AgI. The best compromise between the textural parameters and the post-synthesis functionalization was obtained for the large-pore silica templated with C18TAB. Indications about the presence of silver metal nanoparticles, displaying certain heterogeneity in size and shape, within the pores of this sample were given based on the analysis of 129Xe NMR spectra supplemented by UV–Visible absorption spectra and powder XRD patterns in the wide-angle region. The material can be recommended for the entrapment and immobilization of radioactive iodine in the nuclear industry since it guarantees that the adsorbed pollutant is primarily localized within the material pores and is thermally stable up to 800K in air.

Cubic Pm3n supermicroporous silicas and aluminosilicates templated by short-chain alkyltrimethylammonium surfactants

Highly ordered cubic Pm3n silicas and aluminosilicates were prepared using alkyltrimethylammonium bromide with C10 and C12 carbon chains as templates.

Hexagonal closest-packed spheres liquid crystalline phases stabilised by strongly hydrated counterions

The sequence and structure of lyotropic liquid crystals formed in C12-C16 alkyltrimethylammonium surfactants with hydrolysable and multivalent phosphate (PO4(3-), HPO4(2-) and H2PO4(-)), oxalate (HC2O4(-) and C2O4(2-)), and carbonate (HCO3(-)/CO3(2-)) counterions were determined using a concentration gradient method coupled with polarising optical microscopy and small angle X-ray scattering. In addition to the discrete cubic (I1, space group Pm3n) and hexagonal (H1, p6m) phases, almost all of these surfactants also formed the (previously) rare hexagonally closest-packed spheres (HCPS, P63/mmc) phase at compositions between the Pm3n cubic and L1 micellar phases. This structure has not been previously observed in cationic surfactants, but is readily achieved by using strongly hydrated counterions to stabilise spherical micelles at high concentrations.

Interaction of the model alkyltrimethylammonium ions with alkali halide salts: an explicit water molecular dynamics study

We present an explicit water molecular dynamics simulation of dilute solutions of model alkyltrimethylammonium surfactant ions (number of methylene groups in the tail is 3, 5, 8, 10, and 12) in mixture with NaF, NaCl, NaBr, and NaI salts, respectively. The SPC/E model is used to describe water molecules. Results of the simulation at 298 K are presented in the form of radial distribution functions between nitrogen and carbon atoms of CH$_2$ groups on the alkyltrimethylammonium ion, and the counterion species in the solution. The running coordination numbers between carbon atoms of surfactants and counterions are also calculated. We show that I$^-$ counterion exhibits the highest, and F$^-$ the lowest affinity to "bind" to the model surfactants. The results are discussed in view of the available experimental and simulation data for this and similar solutions.

Competition between surfactant micellization and complexation by cyclodextrin

Supramolecular property systems composed of alkyltrimethylammonium surfactants and β-cyclodextrin were studied by means of a chemical probe. Solvolysis of 4-methoxybenzenesulfonyl chloride (MBSC) was used in the mixed systems with the aim of being able to determine the concentration of uncomplexed cyclodextrin in equilibrium with the micellar system. The surfactants used enabled us to vary the length of the hydrocarbon chain between 6 and 18 carbon atoms. In all cases the existence of a significant concentration of uncomplexed CD was observable in equilibrium with the micellar system. The percentage of uncomplexed cyclodextrin increases both on increasing and decreasing the surfactant alkyl chain length, being minimal for alkyl chains between 10-12 carbon atoms. This behavior is a consequence of two simultaneous processes: complexation of surfactant monomers by the cyclodextrin and surfactant self-assembly to form micellar aggregates. By using Gibbs free energies for micellization and surfactant complexation by β-CD, we can quantitatively explain the observed behavior.

Comb-like ionic complexes of hyaluronic acid with alkyltrimethylammonium surfactants

Stoichiometric complexes of hyaluronic acid with alkyltrimethylammonium surfactants bearing octadecyl, eicosyl and docosyl groups were prepared by ionic coupling in aqueous solution. The complexes were non soluble in water but soluble in organic solvents. In the solid state they self-assembled in a biphasic layered structure with the alkyl side chains forming a separate phase that melted in the 50–60°C range. They were stable to heating up to above 200°C.

Nanocomposites of comb-like ionic complexes of bacterial poly(glutamic acid) with nanoclays

Nanocomposites made from stoichiometric complexes of bacterial polyglutamic acid with alkyltrimethyl ammonium surfactants and Cloisite 30B were prepared for a wide range of compositions spanning from 3% to 90% of inorganic contents. The TGA analysis ascertained the compositions of the nanocomposites and revealed that their thermal decomposition proceeded through a mechanism similar to that of the complexes. Their structure and nanomorphology were examined by DSC, XRD and TEM which evidenced an exfoliated structure for low contents in Cloisite (less than 10%). Nanocomposites with high Cloisite compositions consisted of mixtures of isolated clay lamellae with stacks of intercalated polyacid-Cloisite layers heterogeneously dispersed in a disordered complex matrix. Both thermal and mechanical properties of the surfactant complexes changed steadily with the increasing amount of added nanoclay. An exceptional mechanical tensile behavior was however observed for the composite containing 3% of Cloisite, which was associated to the occurrence of a fully exfoliated structure.

Resiliently Spherical Micelles of Alkyltrimethylammonium Surfactants with Multivalent, Hydrolyzable Counterions

A series of C(12)-C(16) alkyltrimethylammonium surfactants with hydrolyzable phosphate (PO(4)(3-), HPO(4)(2-), and H(2)PO(4)(-)), oxalate (HC(2)O(4)(-) and C(2)O(4)(2-)), and carbonate (HCO(3)(-) and CO(3)(2-)) counterions have been prepared, and their micellar solution behavior has been characterized. Critical micelle concentrations were measured using electrical conductivity and were found to depend on both the counterion and its hydrolysis state. All monovalent counterions bind less strongly to the micelle surface than does bromide or chloride, whereas multivalent species bind more strongly. Small-angle neutron scattering reveals that, unlike alkyltrimethylammonium bromides and chlorides, micelles are small and spherical in the presence of hydrolyzable counterions of all valences and remain spherical even in the presence of added electrolyte. This is consistent with the strong solvation of even strongly bound hydrolyzable counterions, which prevents the screening of repulsions between adjacent headgroups necessary for sphere-cylinder transformations. Salts of multivalent hydrolyzable counterions could thus be used to control the micelle structure in novel ways.