Ammonium Head Group Research Articles

Wormlike Micellar Glycerol Solutions Formed from a Double-Tailed Surfactant with Two Quaternary Ammonium Head Groups.

Herein, a quaternary ammonium surfactant with dual heads and tails, N1,N1,N1,N3,N3-pentamethyl-N3-(3-(2-tetradecylhexadecanamido)propyl)propane-1,3-diaminium dibromide, abbreviated as Di-C14-N2, was synthesized. For the first time, clear observation of aggregate structures formed by surfactants in pure glycerol systems was achieved using cryogenic transmission electron microscopy (cryo-TEM). The system's rheological properties were analyzed using both steady-state shear and oscillatory rheological measurements. The lubricating efficiency of the Di-C14-N2 glycerol solution was assessed for its tribological properties using a tribological wear tester, white light interferometer, and scanning electron microscope. In glycerol, Di-C14-N2 formed long wormlike micelles, which resulted in a glycerol solution with the zero-shear viscosity of 1013 Pa·s at 90 mM, which is the most viscous glycerol system up to now. The system displayed distinct rheological properties from the aqueous system, as evidenced by two intersections in the loss and storage moduli. The formed wormlike micelles in glycerol lead to a significant alteration in the viscoelasticity of the system, thus endowing the Di-C14-N2 glycerol solution with potential as an eco-friendly lubricant. The friction coefficient of the system was found to be 23% lower and the wear rate was 83% lower than that of pure glycerol after the addition of Di-C14-N2. This demonstrates that the addition of Di-C14-N2 greatly improves the frictional properties of pure glycerol. This study offers the possibility of directly observing the aggregate structures formed by surfactants in pure glycerol systems. It contributes to the exploration of the self-assembly behavior of surfactants in nonaqueous polar media, thereby aiding in a deeper understanding of the correlation between molecular structure, mesoscale structure, and macroscopic properties.

Effect of strong and weak polyelectrolytes on the properties of cationic surfactant with triallyl ammonium head group: Self-assembly and biological assessment

Comprehensive assessment of polymer-colloid systems based on cationic surfactant with triallyl ammonium head group (TAS-16) in the presence of synthetic polyelectrolytes (polyacrylic acid (PAA), sodium polyacrylate (SPA), and sodium polystyrene sulfonate (PSS)) has been carried out. The addition of weak polyelectrolyte PAA significantly reduces the critical micelle concentration of the amphiphile up to 50 times. In conrtrast, strong polyelectrolytes such as PSS and SPA have a much smaller effect on the aggregation threshold of the surfactant. Spherical aggregates with a diameter of 80-230 nm were observed in the surfactant-PAA system using transmission electron microscopy. The mixed compositions exhibited high antitumor activity against the human duodenal adenocarcinoma HuTu 80 cell line (IC50=0.6 μM). The pure polymers do not cause hemolysis and hemagglutination, while TAS-16 exhibits hemolytic activity in both pure and mixed systems. The polymer-colloid complexes containing strong polyelectrolyte SPA were more effective as nanocontainers to enhance the solubility of the hydrophobic antibiotic Amphotericin B.

New long tail gemini surfactant in aqueous solution: Self-assembly, rheological properties and responsiveness to hydrocarbon

Gemini surfactants are promising to replace conventional monomeric surfactants in various applications. In this paper, a new gemini surfactant with long unsaturated oleyl tails and bis(hydroxyethyl) ammonium head groups linked by butyl spacer was synthesized. Its critical micelle concentration in salt-free water (12 µM) is much lower than for its monomeric analog (220 µM). Without any additives this surfactant can form viscoelastic solutions with the viscosity of up to 1 kPa·s and elastic modulus of 15 Pa at the conditions, when the viscosity of the single-chained monomeric analog is close to that of pure water. These are one of the highest values reported so far for C18-tailed gemini surfactants without additives. The structure of the gemini surfactant solutions was studied by cryo-TEM and SAXS. Cryo-TEM revealed the presence of closed-looped micelles coexisting with linear wormlike micelles as well as the regular spacing between the micelles arising from strong electrostatic repulsion between them. The SAXS curves were well-fitted by a form-factor of core–shell cylinder, which yielded the radius of the core and the thickness of the shell equal to 1.4 nm each. Addition of n-decane induced the drop of viscosity by 6 orders of magnitude accompanied by the transformation of wormlike micelles into microemulsion droplets with 4.4 nm radius. Such gemini surfactants providing high viscoelasticity to aqueous solution that is responsive to added hydrocarbon are promising for the application in oil recovery as thickeners of fracturing fluids that can be cleaned up without any breakers at the backflow of oil.

Toroidal micelles formed in viscoelastic aqueous solutions of a double-tailed surfactant with two quaternary ammonium head groups.

Innovation in surfactant structures is an effective way to prepare new soft materials with novel applications. In this study, we synthesized a double-tailed surfactant containing two quaternary ammonium head groups (Di-C12-N2). The Di-C12-N2 solution behavior was investigated by surface tension, fluorescence, rheology, and cryo-TEM methods. Although Di-C12-N2 contained a large double-tailed hydrophobic group, the solubility of Di-C12-N2 was ∼90 mmol L-1 at 25 °C with a Krafft temperature of ∼1 °C. The increase in Di-C12-N2 concentration in the solutions led to the formation of various aggregates, including spherical micelles, worm-like micelles, multi-layered vesicles, and a rare type of small toroidal micelles. The two quaternary ammonium head groups in Di-C12-N2 led to strong electrostatic interactions between molecules, which was critical for the formation of toroidal micelles. Moreover, with an added NaCl concentration of 40 mmol L-1, the viscosity of the 5 mmol L-1Di-C12-N2 solution increased by ∼1000 times compared to the pure 5 mmol L-1Di-C12-N2 solution, revealing the high sensitivity of the unique head groups to ionic strength. This study enriches the research on the self-assembly principles of surfactants and brings new potential applications for new soft materials.

Wormlike micellar solutions formed by an anionic surfactant and a cationic surfactant with two head groups.

Innovation in the molecular structure of surfactants is important for the preparation of soft materials with novel properties. In this study, we synthesized a cationic surfactant, N1,N1,N1,N1,N3,N3,N3-pentamethyl-N3-(3-stearamidopropyl)propane-1,3-diammonium bromide, hereafter referred to as C18-DQA. Unlike conventional cationic surfactants, C18-DQA contains two quaternary ammonium head groups and a long-saturated alkyl chain equal to a chain length of 21 carbon atoms. C18-DQA exhibits a low Krafft point of ∼0 °C and a water solubility >1000 mM at 25 °C. The critical micelle concentration (cmc) of C18-DQA was determined to be 0.59 mM using the Nile red method. C18-DQA was mixed with sodium laurate (SL) at different molar ratios to produce transparent solutions with excellent viscoelasticity over a wide concentration range. The 1 : 1.5 molar ratio C18-DQA/SL mixed solutions exhibited gel-like behavior for a total surfactant concentration of 2.88 wt% (75 mM). The solution with a total surfactant concentration of 300 mM (120 mM C18-DQA and 180 mM SL) achieved a maximum zero-shear viscosity (η0) of 4224 Pa s. Cryogenic transmission electron microscopy analysis revealed the formation of extremely long wormlike micelles, with a cross-sectional diameter of 5 nm and contour length >3 μm, in the mixed solutions. C18-DQA and SL molecules were drawn close by electrostatic attractions, leading to a suitable molecular geometry for the extensive growth of wormlike micelles. This work will act as an important reference for the future preparation of highly viscoelastic solutions by mixing cationic and anionic surfactants. The proposed system is also expected to have potential applications in cosmetic formulations, home care products, and oilfield fracturing fluids.

Effect of Hydration on the Intermolecular Interaction of Various Quaternary Ammonium Based Head Groups with Hydroxide Ion of Anion Exchange Membrane Studied at the Molecular Level

Currently, the main limitation of Anion Exchange Membrane Fuel Cells is related to their low chemical stability under alkaline conditions due to the degradation of quaternary ammonium-based head groups, which lowers the transportation of hydroxide ions as well. The knowledge of the intermolecular interaction of various quaternary ammonium head groups with hydroxide ions is the key to improving hydroxide ion’s diffusivity and chemical stability of various quaternary ammonium-based head groups. Consequently, the intermolecular interaction of hydroxide ions with different quaternary ammonium head groups of anion exchange membranes is investigated at the different hydration levels via classical all-atom Molecular Dynamics and molecular well-tempered MetaDynamics simulation methods in this work. Several quaternary ammonium head groups (a) pyridinium, (b) 1,4-diazabicyclo [2.2.2] octane, (c) benzyltrimethylammonium, (d) n-methyl piperidinium, (e) guanidium, and (f) trimethylhexylammonium were investigated in detail. Classical all-atom molecular dynamic simulations illustrate that the results of radial distribution function between the nitrogen atoms of six different quaternary ammonium head groups and hydroxide ion are as follows: (a) > (c) ≥ (f) > (d) > (e) > (b). In addition, from the diffusion coefficient values it was found that the mobility of hydroxide ion by quaternary ammonium head group (f) was lower than (c) at the different hydration levels.

Key Role of Choline Head Groups in Large Unilamellar Phospholipid Vesicles for the Interaction with and Rupture by Silica Nanoparticles.

For highly abundant silica nanomaterials, detrimental effects on proteins and phospholipids are postulated as critical molecular initiating events that involve hydrogen-bonding, hydrophobic, and/or hydrophilic interactions. Here, large unilamellar vesicles with various well-defined phospholipid compositions are used as biomimetic models to recapitulate membranolysis, a process known to be induced by silica nanoparticles in human cells. Differential analysis of the dominant phospholipids determined in membranes of alveolar lung epithelial cells demonstrates that the quaternary ammonium head groups of phosphatidylcholine and sphingomyelin play a critical and dose-dependent role in vesicle binding and rupture by amorphous colloidal silica nanoparticles. Surface modification by either protein adsorption or by covalent coupling of carboxyl groups suppresses the disintegration of these lipid vesicles, as well as membranolysis in human A549 lung epithelial cells by the silica nanoparticles. Furthermore, molecular modeling suggests a preferential affinity of silanol groups for choline head groups, which is also modulated by the pH value. Biomimetic lipid vesicles can thus be used to better understand specific phospholipid-nanoparticle interactions at the molecular level to support the rational design of safe advanced materials.

New Class of Tunable Choline Bromide-Based Hydrophobic Deep Eutectic Solvents for the Extraction of Bioactive Compounds of Varying Polarity from a Plant Matrix.

Deep eutectic solvents (DESs) are a class of sustainable solvents that have found numerous applications in different fields. One of their main attributes is the possibility of easily modifying their physicochemical properties by varying the type of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) that comprise them. Choline chloride ([Ch+][Cl-])-based hydrophilic DESs were among the first studied and the most used because of their capacity to easily create a hydrogen bonding network that lies in its unique chemical structure, characterized by a hydroxyl substituent within the ammonium headgroup. In this study, a new class of hydrophobic [Ch+][Br-]-modified salts were synthesized to produce HBAs with similar properties to choline for the preparation of hydrophobic DESs. Six different [Ch+][Br-]-based HDESs were prepared and characterized in terms of hydrophobicity, viscosity, and solvation properties (hydrogen bonding, dispersion, dipolarity/polarizability, n-π, and π-π interactions). They were employed as solvents in a microextraction method for the determination of phytochemicals in Cannabis sativa L. plant. The extraction performance of the [Ch+][Br-]-based HDESs was compared to eutectic mixtures based on conventional hydrophobic HBAs, and the results revealed that the unique properties of [Ch+][Br-]-modified salts allowed for the extraction of both hydrophilic (i.e., flavonoids) and hydrophobic compounds (i.e., cannabinoids).

Highly Conductive and Ultra Alkaline Stable Anion Exchange Membranes by Superacid-Promoted Polycondensation for Fuel Cells

A series of anion exchange membranes (4-QPPAF-TMA) were prepared by a metal-free, superacid-promoted polymerization reaction. The polymers were obtained with high molecular weight (Mn = 9.5–19.6 kDa, Mw = 44.9–622.5 kDa). 4-QPPAF-TMA membranes exhibited high hydroxide ion conductivity (up to 115 mS cm–1) at 80 °C, reasonable water absorbability (45% water uptake at 30 °C for 1.7 meq g–1), low to moderate dimensional swelling (5–15% at 30–80 °C for 1.7 meq g–1), and mechanical robustness (12.8 MPa maximum stress and 32% elongation at break for 1.7 meq g–1). Furthermore, 4-QPPAF-TMA membranes exhibited excellent alkaline stability in 8 M KOH at 80 °C for 1000 h, maintaining high conductivity (105 mS cm–1, 97% remaining). density functional theory (DFT) calculations suggested that the unique molecular configuration of the pendant ammonium head groups was responsible for high resistivity to the hydroxide ion attack. A fuel cell was operated with the 4-QPPAF-TMA membrane and an ionomer using a non-PGM cathode catalyst (Fe–N–C) to achieve a peak power density of 215 mW cm–2 accountable for 860 mW mg–1 Pt at a 590 mA cm–2 current density and 0.40 V (Pt–C cathode achieved 370 mW cm–1 at 810 mA cm–2 and 0.50 V). The fuel cell was operated at constant current density (15 mA cm–2) for 240 h with −0.79 mV h–1 average cell voltage decay. The postdurability analyses revealed that the membrane did not deteriorate while the degradation of the cathode catalysts/ionomer caused the performance loss.

DOTAP: Structure, hydration, and the counterion effect

The cationic lipid 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) is one of the original synthetic cationic lipids used for the liposomal transfection of oligonucleotides in gene therapy. The key structural element of DOTAP is its quaternary ammonium headgroup that is responsible for interactions with both nucleic acids and target cell membranes. Because these interactions are fundamental to the design of a major class of transfection lipids, it is important to understand the structure of DOTAP and how it interacts with halide counterions. Here, we use x-ray and neutron diffraction techniques to examine the structure of DOTAP and how chloride (Cl−) and iodide (I−) counterions alter the hydration properties of the DOTAP headgroup. A problem of particular interest is the poor solubility of DOTAP/I− in water solutions. Our results show that the poor solubility results from very tight binding of the I− counterion to the headgroup and the consequent expulsion of water. The structural principles we report here are important for assessing the suitability of DOTAP and its quaternary ammonium derivatives for transfection.

The correlation between the micelle morphology of surface-active ionic liquids with self-assembly and thermodynamic characteristics: coarse-grained MD simulation and experiment.

Surface-active ionic liquids (SAILs) show great promise as novel green solvents due to their low vapor pressure, high thermal stability, high electrical conductivity, and bio-friendly nature to replace traditional volatile organic solvents in industrial processes. In the present work, the combination of coarse-grained (CG) molecular dynamics (MD) simulations with conductivity measurements was employed to explain the correlation between the micelle morphology and physicochemical and thermodynamic properties of self-assembly. A homologous series of SAIL molecules, 1-n-alkyl-3-methylimidazolium bromide [Cnmim][Br] (n = 4, 6, 8, 10, and 12), were chosen at various concentrations to shed light on this issue. Simultaneously two factors of concentration and alkyl chain length affected the morphology to control the physical and thermodynamic features. Moreover, the nature of the headgroup for two SAILs with the longest alkyl chain was assessed by shifting from imidazolium into ammonium. First, the critical micelle concentration (CMC), the degree of counterion dissociation of micelles, and the standard Gibbs energy of micellization of SAILs were determined using conductivity data. The micelle morphology such as the aggregation number, micelle radius, and moment of inertia was computed before, around, and after the CMC by MD simulation. Simulated results in accordance with the experimental measurements provide a quantitative understanding of the micellar properties. Increasing the alkyl chain length was associated with a non-spherical bigger micelle while the ammonium-based surfactant with a lower repulsion between neighboring monomers in micelles induced bigger and more spherical aggregates. Raising the SAIL concentration did not considerably influence the sphericity of the micelle except for the SAIL with the longest tail. The umbrella sampling method calculated the potential of mean force (PMF) for pulling a monomer of SAIL from a pre-assembled micelle into the solution. The dissociation energy of a SAIL monomer from a micelle increased with the tail length or with shifting into the ammonium head group and was substantially influenced by micelle morphology. Comparison between a sphere micelle with an oval one demonstrated that the dissociation of a SAIL monomer from a non-spherical shape needed a higher amount of energy. An improved understanding of how the shape of the SAIL micelles controls the physicochemical properties and stability helps to extend their application to different chemical processes.

Research Progress on the Synthesis of Different Types of Gemini Surfactants with a Functionalized Hydrophobic Moiety and Spacer

AbstractGemini surfactants are advantageous over conventional surfactants as they find applications as antimicrobial agents, corrosion inhibitors, enhanced oil recovery, capping agents for nanoparticle synthesis, drug delivery agents, etc. This article provides a detailed overview of synthetic procedures for various types of geminis and the fundamental physicochemical parameters of these systems. This includes a discussion on the cationic geminis based on various groups such as biphenyl, amide (with/without alkane tail), binol, quaternary ammonium (with/without hydroxyl group as a spacer), morpholinium, pyridinium, amide (with/without alkane tail), ester quaternary ammonium, and imidazolium (spacer with/without hydroxyl group and thioether/ester) types. Further, it is focused on anionic geminis with carboxylate, borate, and sulfonate head groups. Zwitterionic geminis such as betaine surfactants, cocogem surfactants based on dodecylisopropylol amine and dicarboxylic acid, diester type, sulphobetaine gemini based on S‐triazine, zwitterionic hetero gemini containing ammonium and carboxylate head groups, zwitterionic gemini containing quaternary ammonium and a sulfate group, gemini containing phosphodiester anion and quaternary ammonium salt are also reviewed. Lastly, synthesis of nonionic geminis from sunflower oil, amide‐based nonionic, sulfonamide nonionic, N,N’‐diethylaminedialkyldiamide nonionic gemini, sugar‐based gemini, and nonionic gemini with sulfonate spacer have been discussed.

On the structure and stability of novel cationic DPPC liposomes doped with gemini surfactants

A novel formulation of cationic liposomes was studied by mixing dipalmitoylphosphatidylcholine (DPPC) with tetradecyltrimethylammonium bromide gemini surfactants with different alkane spacer groups lengths attached to their ammonium head-groups. The physicochemical characterization of the cationic liposomes was obtained by combining experimental results from differential scanning microcalorimetry (DSC) with molecular dynamic simulations, in order to understand their structural configuration. An adapted Ising model was used to interpret the results in terms of cooperativity of the phase transitions.The gemini surfactants partition into the lipid bilayer of DPPC liposomes, and the induced changes in colloidal stability and phase transition were analyzed in detail. The DPPC liposomes became positively charged upon gemini surfactant partition, showing increased colloidal stability. Our results show significant differences in structural configuration between gemini surfactants with short and long spacer lengths. While gemini with shorter spacers allocate within the lipid bilayer with both headgroups in the same layer, geminis with longer spacers unexpectedly intercalate in the lipid membrane in a particular zig-zag configuration, with each headgroup located at a different side of the bilayer, altering the coupling degree parameters of the membrane’s phase transition.The extraordinary increase of colloidal stability of DPPC liposomes with gemini surfactants at very low molar ratio and the possibility to tune the physicochemical properties of the membrane by control de spacer length of the geminis opens new possibilities for cationic liposomal formulations with potential applications in vaccines, drug/gene delivery or biosensing.

Binding and Degradation Reaction of Hydroxide Ions with Several Quaternary Ammonium Head Groups of Anion Exchange Membranes Investigated by the DFT Method.

Commercialization of anion exchange membrane fuel cells (AEMFCs) has been limited due to the chemical degradation of various quaternary ammonium (QA) head groups, which affects the transportation of hydroxide () ions in AEMs. Understanding how various QA head groups bind and interact with hydroxide ions at the molecular level is of fundamental importance to developing high-performance AEMs. In this work, the binding and degradation reaction of hydroxide ions with several QA head groups—(a) pyridinium, (b) 1,4-diazabicyclo [2.2.2] octane (DABCO), (c) benzyltrimethylammonium (BTMA), (d) n-methyl piperidinium, (e) guanidium, and (f) trimethylhexylammonium (TMHA)—are investigated using the density functional theory (DFT) method. Results of binding energies (“∆” EBinding) show the following order of the binding strength of hydroxide ions with the six QA head groups: (a) > (c) > (f) > (d) > (e) > (b), suggesting that the group (b) has a high transportation rate of hydroxide ions via QA head groups of the AEM. This trend is in good agreement with the trend of ion exchange capacity from experimental data. Further analysis of the absolute values of the LUMO energies for the six QA head groups suggests the following order for chemical stability: (a) < (b)~(c) < (d) < (e) < (f). Considering the comprehensive studies of the nucleophilic substitution (SN2) degradation reactions for QA head groups (c) and (f), the chemical stability of QA (f) is found to be higher than that of QA (c), because the activation energy (“∆” EA) of QA (c) is lower than that of QA (f), while the reaction energies (“∆” ER) for QA (c) and QA (f) are similar at the different hydration levels (HLs). These results are also in line with the trends of LUMO energies and available chemical stability data found through experiments.

Correlating Broadband Photoluminescence with Structural Dynamics in Layered Hybrid Halide Perovskites.

The emission of white light from a single material is atypical and is of interest for solid-state lighting applications. Broadband light emission has been observed in some layered perovskite derivatives, A2PbBr4 (A = R-NH3+), and correlates with static structural distortions corresponding to out-of-plane tilting of the lead bromide octahedra. While materials with different organic cations can yield distinct out-of-plane tilts, the underlying origin of the octahedral tilting remains poorly understood. Using high energy resolution (e.g., quasi-elastic) neutron scattering, this contribution details the rotational dynamics of the organic cations in A2PbBr4 materials where A = n-butylammonium (nBA), 1,8-diaminooctammonium (ODA), and 4-aminobutyric acid (GABA). The organic cation dynamics differentiate (nBA)2PbBr4 from (ODA)PbBr4 or (GABA)2PbBr4 in that the larger spatial extent of dynamics of nBA yields a larger effective cation radius. The larger effective volume of the nBA cation in (nBA)2PbBr4 yields a closer to ideal A-site geometry, preventing the out-of-plane tilt and broadband luminescence. In all three compounds, we observe hydrogen dynamics attributed to rotation of the ammonium headgroup and at a time scale faster than the white light photoluminescence studied by time-correlated single photon counting spectroscopy. This supports a previous assignment of the broadband emission as resulting from a single ensemble, such that the emissive excited state experiences many local structures faster than the emissive decay. The findings presented here highlight the role of the organic cation and its dynamics in hybrid organic-inorganic perovskites and white light emission.

Single-walled zeolitic nanotubes.

We report the synthesis and structure of single-walled aluminosilicate nanotubes with microporous zeolitic walls. This quasi-one-dimensional zeolite is assembled by a bolaform structure-directing agent (SDA) containing a central biphenyl group connected by C10 alkyl chains to quinuclidinium end groups. High-resolution electron microscopy and diffraction, along with other supporting methods, revealed a unique wall structure that is a hybrid of characteristic building layers from two zeolite structure types, beta and MFI. This hybrid structure arises from minimization of strain energy during the formation of a curved nanotube wall. Nanotube formation involves the early appearance of a mesostructure due to self-assembly of the SDA molecules. The biphenyl core groups of the SDA molecules show evidence of π stacking, whereas the peripheral quinuclidinium groups direct the microporous wall structure.

Highly conductive and alkaline stable partially fluorinated anion exchange membranes for alkaline fuel cells: Effect of ammonium head groups

The effect of ammonium structure on partially fluorinated anion exchange membranes was investigated for alkaline fuel cell applications. Precursor copolymers tethered with bromopropyl side chains (PAF-C3-Br) were successfully synthesized and quaternized quantitatively with amines to obtain a series of QPAF-C3-XY membranes containing various ammonium head groups. The head groups (XY) included dimethylbutyl (DMB), dimethylhexyl (DMH), dibutylmethyl (DB), and heterocyclic N-methylpiperidinium (Pip). All of the membranes exhibited well-developed phase-separated morphology regardless of the size of the head groups as confirmed by TEM images. DFT calculations suggested that the hydrophilic domain sizes (determined from TEM images) were dependent on the polar surface area (PSA) rather than the molecular volume of the head groups. Among the membranes, QPAF-C3-Pip possessed the most balanced properties of high conductivity, low water absorbability, reasonable mechanical strength, and alkaline stability. QPAF-C3-Pip membrane (IEC = 1.26 meq/g) achieved 232 mW/m2 of the maximum power density in alkaline fuel cell, which was slightly higher than that of our previous QPAF-C3-TMA with typical trimethyl ammonium head groups (224 mW/cm2). In the durability test for 240 h, the voltage decreased from 0.74 V to 0.43 V with average decay of 1.29 mV/h. The post-durability NMR analysis revealed that the majority of the voltage loss was related to the catalyst layers.

Optimization of Ammonium Head Groups in Partially Fluorinated Anion Exchange Membranes for Alkaline Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) have gained attention due to their possible use of non-precious metal electrocatalysts compared to proton exchange membrane fuel cells.1 However, the chemical/physical instability of anion exchange membranes under operating fuel cell conditions remains an issue.1, 2 We developed previously anion exchange membranes containing perfluoroalkyl and phenylene rings in the main chain (e.g., QPAF-C3-TMA (trimethylammonium)). The polymer main chains were alkaline stable because of the absence of oxygen ether bonds in the main chain, however, the ammonium groups suffered from alkaline degradation.3 In this work, the impact of varying head group structure was investigated through utilizing cyclic piperidine (-Pip), dimethylbutylamine (-DMB), dimethylhexylamine (-DMH), and dibutylmethyl amine (-DB) (Figure 1). All of the membranes showed phase-separated morphology as confirmed from TEM images. The DFT calculations revealed that hydrophilic domain sizes were dependent on polar surface area rather than the molecular size of the head groups. The compact piperidinium-based membrane (QPAF-C3-Pip) exhibited the most balanced properties of low water absorbability, high ionic conductivity, alkaline and mechanical stability. An H2/O2 fuel cell using QPAF-C3-Pip membrane achieved maximum power density of 232 mW/cm2, slightly higher than that of TMA-based membrane (224 mW/cm2). Furthermore, QPAF-C3-Pip membrane showed reasonable durability for 240 h in operating fuel cell at a constant current density of 100 mA/cm2 in which the cell voltage decreased from 0.75V to 0.43V with average voltage decay of 1.24 mV/h, that was more durable than the TMA-based membrane (average decay of 4.8 mV/h at 50 mA/cm2). Other membranes properties will be also discussed.Figure 1. Structure and fuel cell performance of QPAF-C3-Pip membranes

Unfolding of Tryptophanoctyl Ester and Elastic Deformation of Host Micelles via RR'3 N+ ⋅⋅⋅π Interaction: Conceivable Relevance to Wrapping Process of Receptor Mediated Endocytosis.

The interfacial properties of the mixed amphiphiles are modified by a stronger cation-π interaction between the quaternary ammonium head group of CTAB and the π-face of TROE, compared to the tyrosine analogue (TYOE). This eventually triggers a morphology transition through elastic deformation of the spherical micelles of CTAB to cylindrical/wormlike micelles. The unfolding of TROE and the molecular interactions in the nanoenvironment have been recognized by NMR spectroscopy and the physical characteristics of the entangled wormlike micelles are investigated by high resolution transmission electron microscopy (HRTEM), whereas the complex fluidic feature is examined by dynamic rheological measurements. Morphology tuning of the soft nanoaggregates of zwitterionic dodecylphosphocholine by the tryptophan analogue via choline-π interaction has unique biological consequences and we consider the significance of such interactions in facilitating endocytosis of a virion/nano particle(NP) in terms of a quantitative model. The implication in future research on drug development strategies is discussed.

Influence of hydrotrope on micellization behaviour of zwitterionic dimeric surfactants carrying ammonium and phosphodiester headgroups at different temperatures in aqueous medium

Analogous novel zwitterionic dimeric surfactants in the sequence of 2-dodecylphosphate,1-(N,N-dimethyl,N-dodecylammonium)ethane abbreviated as C12(-)–2–C12(+); 2-dodecylphosphate,1-(N,N-dimethyl,N-tetradecylammonium)ethane abbreviated as C12(-)–2–C14(+); and 2-dodecylphosphate,1-(N,N-dimethyl,N-hexadecylammonium)ethane abbreviated as C12(-)–2–C16(+); with phosphodiester anion and quaternary ammonium salt as hydrophilic and the methylene chains as hydrophobic groups, two methylene groups separate the two headgroups, were prepared, and the effect of aromatic hydrotropes aniline hydrochloride (AHC) and sodium salicylate (NaSal) on the mode of micellization at four unlike temperatures with a difference of 5 K in aqueous medium by the method of conductivity were studied. The decrease in cmc of zwitterionic surfactants with the addition/increase in bulk mole fraction of NaSal and AHC is almost linear. But anionic NaSal is more productive as compared to the cationic hydrotrope AHC in reducing the critical micelle concentration (cmc). Negative values of interaction parameter (βm) were found to decline with extension in one of the hydrophobic chain lengths keeping the other hydrophobic chain length identical. Symmetrical zwitterionic surfactants interact more strongly via headgroups and hydrocarbon tails with aromatic hydrotropes and decrease the cmc effectively by concealing of headgroups and hydrophobic forces operating mutually thus promotes micellar shape transition by alteration of micelle surface curvature. The enthalpy of micellization ΔmicH° suggest an endothermic process and the negative value of free energy of micellization ΔmicG° due to encouraging augmentation in entropy of micellization ΔmicS°. The doping of surfactants with organic salts or hydrotropes amplifies the solubilizing power, viscosity and subdue the cmc value. Such systems promise to improve the performance used in separation methods, drug permeation, and delivery as these surfactants are less toxic and less sensitive to changes in pH and ionic strength.