1D materials from ionic self-assembly in mixtures containing chromonic liquid crystal mesogens.

Ionic self-assembly is a simple yet powerful method to obtain robust nanostructures. Herewith, we use mixtures of oppositely-charged porphyrins that can act as mesogens to form chromonic liquid crystals in water, i.e., molecular stacks with orientational (nematic) or positional (hexagonal) order. Electrostatic locking coupled with π-π interactions between aromatic groups within the stacks, together with inter-stack hydrogen bonding induce formation of all-organic crystalline nanofibers with high aspect ratio (a few tenths of nanometers in width but several tenths of micrometers in length) and that display branching. The nanofibers prepared from metal-free porphyrin units feature interesting optical properties, including an absorption spectrum that is different from the simple sum of the individual spectra of the components, which is attributed to a striking aggregation-induced chromism. When in contact with some polar organic solvents the materials become fluorescent, as a result of disaggregation. In a proof-of-concept, the obtained self-assembled one-dimensional (1D) materials were carbonized (yield ca. 60%) to produce nitrogen-doped carbon nanofibers that can be used as active electrode materials for energy storage applications.

Quick and Sensitive Detection of Water Using Galvanic-Coupled Arrays with a Submicron Gap for the Advanced Prediction of Dew Condensation.

We have demonstrated a highly sensitive moisture sensor that can detect water molecules, in addition to water droplets, and therefore, can predict dew condensation with high accuracy and high speed before the formation of water droplets, showing a better performance than a commercial hygrometer. Additionally, the dependence of the output response from the sensor on factors, such as the cooling rate of the sensor's surface and the vapor pressure in the chamber, that affect the performance of the moisture sensor has been clarified. The output response showed a clear dependence on the variation in cooling rate, as well as the vapor pressure. The higher the cooling rate and vapor pressure, the higher the output response. The output response showed a linear response to the change in the above-mentioned parameters. The higher sensitivity and accuracy of the moisture sensor, as a function of the physical parameters, such as cooling rates, vapor pressure, enables the sensor to perform in advanced detection applications. The sensor can be modified to the actual target regarding the surface nature and the heat capacity of the target object, making it more suitable for wide applications.

Enhancement of Sensitivity and Accuracy of Micro/Nano Water Droplets Detection Using Galvanic-Coupled Arrays.

A moisture sensor has been reported that detects invisibly small water droplets and distinguishes their particle size with high accuracy and high speed. This sensor uses narrow lines of dissimilar metals as electrodes, arranged with gaps of 0.5 to 10 µm. The working principle for this sensor is that it measures the galvanic current generated when a water droplet forms a bridge-like structure between the electrodes. In addition, the surface of the sensor was controlled by using hydrophilic polymer, GL, and hydrophobic polymer, PMMA. The study of the relationship between the contact angle, projected area of water droplets and current response from the sensor with a modified surface showed that in the case of GL, the contact angle was small (wettability increased) and the average value and distribution of the projected water droplet area and the sensor's response increased. This enhanced the sensor's sensitivity. On the other hand, in the case of PMMA, the contact angle was large (wettability decreased), the area of the water droplet and its distribution became small and the accuracy of discriminating the water droplet's diameter by the sensor enhanced. Therefore, by rendering sensor's surface hydrophilic and hydrophobic, the sensitivity and accuracy of the sensor could be enhanced.

Self-Assembled Fullerene Crystals as Excellent Aromatic Vapor Sensors.

Here we report the aromatic vapor sensing performance of bitter melon shaped nanoporous fullerene C60 crystals that are self-assembled at a liquid-liquid interface between isopropyl alcohol and C60 solution in dodecylbenzene at 25 °C. Average length and center diameter of the crystals were ca. 10 µm and ~2 µm, respectively. Powder X-ray diffraction pattern (pXRD) confirmed a face-centered cubic (fcc) structure with cell dimension ca. a = 1.4272 nm, and V = 2.907 nm³, which is similar to that of the pristine fullerene C60. Transmission electron microscopy (TEM) confirmed the presence of a nanoporous structure. Quartz crystal microbalance (QCM) results showed that the bitter melon shaped nanoporous C60 performs as an excellent sensing system, particularly for aromatic vapors, due to their easy diffusion through the porous architecture and strong π⁻π interactions with the sp²-carbon.

Hierarchical heterostructure of Ag-nanoparticle decorated fullerene nanorods (Ag-FNRs) as an effective single particle freestanding SERS substrate.

A hierarchical heterostructure composed of silver nanoparticles (Ag-NPs: average diameter ∼10 nm) on fullerene nanorods (FNRs: average length ∼11 µm and average diameter ∼200 nm) was fabricated using a simple solution route. It was used as an effective single particle freestanding surface enhanced Raman scattering (SERS) substrate for the detection of target molecules (Rhodamine 6G: R6G). FNRs were formed ultra-rapidly (formation process completed in a few seconds) at a liquid-liquid interface of methanol and C60/mesitylene solution then Ag-NPs were grown directly on the surfaces of the FNRs by treatment with a solution of silver nitrate in ethanol. This unique hierarchical heterostructure allows efficient adsorption of target molecules also acting as an effective SERS substrate capable of detecting the adsorbed R6G molecules in the nanomolar concentration range. In this study, SERS spectra are acquired on an isolated single Ag-FNR for the detection of the absorbed molecule rather than from a bulk, large area film composed of silver/gold nanoparticles as used in conventional methods. Thus, this work provides a new approach for the design and fabrication of freestanding SERS substrates for molecular detection applications.

Surfactant-free Fabrication of Fullerene C60 Nanotubules Under Shear.

A method for controlling the self-assembly of fullerene C60 molecules into nanotubules in the fcc phase, devoid of entrapped solvent, has been established in a thin film microfluidic device. The micron length C60 nanotubules, with individual hollow diameters of 100 to 400 nm, are formed under continuous flow processing during high shear micromixing of water and a toluene solution of the fullerene, in the absence of surfactant, and without the need for further down-stream processing. TEM revealed pores on the surface of the nanotubes, and the isolated material has a much higher response to small molecule sensing than that for analogous material formed using multistep batch processing.

Surfactant-Triggered Nanoarchitectonics of Fullerene C60 Crystals at a Liquid-Liquid Interface.

Here, we report the structural and morphological modulation of fullerene C60 crystals induced by nonionic surfactants diglycerol monolaurate (C12G2) and monomyristate (C14G2). C60 crystals synthesized at a liquid-liquid interface comprising isopropyl alcohol (IPA) and a saturated solution of C60 in ethylbenzene (EB) exhibited a one-dimensional (1D) morphology with well-defined faceted structure. Average length and diameter of the faceted rods were ca. 4.8 µm and 747 nm, respectively. Powder X-ray diffraction pattern (pXRD) confirmed a hexagonal-close packed (hcp) structure with cell dimensions ca. a = 2.394 nm and c = 1.388 nm. The 1D rod morphology of C60 crystals was transformed into "Konpeito candy-like" crystals (average diameter ca. 1.2 µm) when the C60 crystals were grown in the presence of C12G2 or C14G2 surfactant (1%) in EB. The pXRD spectra of "Konpeito-like" crystals could be assigned to the face-centered cubic (fcc) phase with cell dimensions ca. a = 1.4309 nm (for C12G2) and a = 1.4318 nm (for C14G2). However, clusters or aggregates of C60 lacking a uniform morphology were observed at lower surfactant concentrations (0.1%), although these crystals exhibited an fcc crystal structure. The self-assembled 1D faceted C60 crystals and "Konpeito-like" C60 crystals exhibited intense photoluminescence (PL) (∼35 times greater than pC60) and a blue-shifted PL intensity maximum (∼15 nm) compared to those of pC60, demonstrating the potential use of this method for the control of the optoelectronic properties of fullerene nanostructures. The "Konpeito-like" crystals were transformed into high surface area nanoporous carbon with a graphitic microstructure upon heat-treatment at 2000 °C. The heat-treated samples showed enhanced electrochemical supercapacitance performance (specific capacitance is ca. 175 F g-1, which is about 20 times greater than pC60) with long cyclic stability demonstrating the potential of the materials in supercapacitor device fabrication.

Nanoporous carbon materials with enhanced supercapacitance performance and non-aromatic chemical sensing with C1/C2 alcohol discrimination.

We have investigated the textural properties, electrochemical supercapacitances and vapor sensing performances of bamboo-derived nanoporous carbon materials (NCM). Bamboo, an abundant natural biomaterial, was chemically activated with phosphoric acid at 400 °C and the effect of impregnation ratio of phosphoric acid on the textural properties and electrochemical performances was systematically investigated. Fourier transform-infrared (FTIR) spectroscopy confirmed the presence of various oxygen-containing surface functional groups (i.e. carboxyl, carboxylate, carbonyl and phenolic groups) in NCM. The prepared NCM are amorphous in nature and contain hierarchical micropores and mesopores. Surface areas and pore volumes were found in the range 218-1431 m2 g-1 and 0.26-1.26 cm3 g-1, respectively, and could be controlled by adjusting the impregnation ratio of phosphoric acid and bamboo cane powder. NCM exhibited electrical double-layer supercapacitor behavior giving a high specific capacitance of c.256 F g-1 at a scan rate of 5 mV s-1 together with high cyclic stability with capacitance retention of about 92.6% after 1000 cycles. Furthermore, NCM exhibited excellent vapor sensing performance with high sensitivity for non-aromatic chemicals such as acetic acid. The system would be useful to discriminate C1 and C2 alcohol (methanol and ethanol).

Low-Band-Gap BODIPY Conjugated Copolymers for Sensing Volatile Organic Compounds.

Conjugated polymers with strong photophysical properties are used in many applications. A homopolymer (P1) and five new low band gap copolymers based on 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) and acceptors 3,6-dithienyldiketopyrrolopyrrole (P2), phthalimide (P3), benzotriazole (P4), 4,7-dithienyl[1,2,3]triazolo[4,5g]quinoxaline (P5), and 2,5-dithienylthieno[3,4-b]pyrazine (P6) were prepared by means of Sonogashira polymerization. The characterization of polymers by using (1) H NMR, absorption, and emission spectroscopy is discussed. All polymers with high molecular weights (Mn ) of 16 000 to 89 000 g mol(-1) showed absorption maxima in the deep-red region (λ=630-760 nm) in solution and exhibited significant redshifts (up to 70 nm) in thin films. Polymers P2, P5, and P6 showed narrow optical band gaps of 1.38, 1.35, and 1.38 eV, respectively, which are significantly lower than that of P1 (1.63 eV). The HOMO and LUMO energy levels of the polymers were calculated by using cyclic voltammetry measurements. The LUMO energy levels of BODIPY-based alternating copolymers were independent of the acceptors; this suggests that the major factor that tunes the LUMO energy levels of the polymers could be the BODIPY core. All polymers showed selective and reproducible detection of volatile organic solvents, such as toluene and benzene, which could be used for developing sensors.

Nonionic amphiphile nanoarchitectonics: self-assembly into micelles and lyotropic liquid crystals.

Amphiphiles, molecules that possess both hydrophilic and hydrophobic moieties, are architecturally simple molecules that can spontaneously self-assemble into complex hierarchical structures from lower to higher dimensions either in the bulk phase or at an interface. Recent developments in multifunctional nanostructure design using the advanced concept of nanoarchitectonics utilize this simple process of assembly. Amphiphilic self-assemblies involving lipids or proteins mimic the structure of biological systems, thus highlighting the necessity of a fundamental physical understanding of amphiphilic self-assembly towards a realization of the complex mechanisms operating in nature. Herein, we describe self-assembled microstructures of biocompatible and biodegradable tetraglycerol lauryl ether (C12G4) nonionic surfactant in an aqueous solvent system. Temperature-composition analyses of equilibrium phases identified by using small-angle x-ray scattering (SAXS) provide strong evidence of various spontaneously self-assembled mesostructures, such as normal micelles (Wm), hexagonal liquid crystal (H1), and reverse micelles (Om). In contrast to conventional poly(oxyethylene) nonionic surfactants, C12G4 did not exhibit the clouding phenomenon at higher temperatures (phase separation was not observed up to 100 °C), demonstrating the greater thermal stability of the self-assembled mesophases. Generalized indirect Fourier transformation (GIFT) evaluation of the SAXS data confirmed the formation of core-shell-type spherical micelles with a maximum dimension ca. 8.7 nm. The shape and size of the C12G4 micelles remained apparently unchanged over a wide range of concentrations (up to 20%), but intermicellar interactions increased and could be described by the Percus-Yevick (PY) theory (after Carnahan and Starling), which provides a very accurate analytical expression for the osmotic pressure of a monodisperse hard sphere.

Nanoporous carbon tubes from fullerene crystals as the π-electron carbon source.

Here we report the thermal conversion of one-dimensional (1D) fullerene (C60) single-crystal nanorods and nanotubes to nanoporous carbon materials with retention of the initial 1D morphology. The 1D C60 crystals are heated directly at very high temperature (up to 2000 °C) in vacuum, yielding a new family of nanoporous carbons having π-electron conjugation within the sp(2)-carbon robust frameworks. These new nanoporous carbon materials show excellent electrochemical capacitance and superior sensing properties for aromatic compounds compared to commercial activated carbons.

In-situ formation of silver nanoparticles using nonionic surfactant reverse micelles as nanoreactors.

In this paper, we report the one-step synthesis of metallic silver nanoparticles (Ag NP) using nonionic surfactant reverse micelle as nanoreactors. Diglycerol monolaurate (C12G2) spontaneously self-assemble into spheroid reverse micelles having size 10-12 nm in cyclohexane under ambient conditions of temperature and pressure. The spheroid C12G2 reverse micelles swell with water. Swollen reverse micelles having size - 20 nm are formed upon incorporation of 1% water. We used C12G2 reverse micelles as nanoreactors for making ordered nanostructure of Ag-NP by replacing water with aqueous silver nitrate solution. The diglycerol moiety of the surfactant reduces silver ions into metallic silver and thereby stabilizes the generated Ag NP. We found that shape and size of the Ag NP is closely related to the structure of nanoreactor. Similar results have been observed in linear chain alkane n-octane. We found bigger Ag NP from the C12G2/octane reverse micelle system as the size of the micelle in this system is bigger than that of the C12G2/cyclohexane system. This simple approach based on in-situ reduction of metal ions (without the need of reducing agent) opens a new possibility for the development of controlled synthesis of nanostructured noble metallic nanoparticles.

Photorheological response of aqueous wormlike micelles with photocleavable surfactant.

Recently, we have reported a new cinnamic acid-type photocleavable surfactant, C4-C-N-PEG9 that experiences a photocleavage through UV-induced cyclization in aqueous solution, yielding a coumarin derivative (7-butoxy-2H-chromen-2-one) and an aminated polyoxyethylene compound. Here, we have studied the effects of C4-C-N-PEG9 on the photorheological behavior of viscoelastic wormlike micelles formed by aqueous mixture of nonionic surfactants, polyoxyethylene phytosterol ether (PhyEO20) and tetraoxyethylene dodecyl ether (C12EO4). The 4.9 wt % PhyEO20/H2O + 2.4 wt % C12EO4 solution forms wormlike micelles, and its viscosity is ~10 Pa·s. We have found that the addition of C4-C-N-PEG9 into this viscous, non-Newtonian fluid system decreases the viscosity. Viscosity decreased in parallel to the C4-C-N-PEG9 concentration reaching ~0.003 Pa·s at 2.5 wt % of C4-C-N-PEG9. However, viscosity of the C4-C-N-PEG9 incorporated system increased significantly (~200 times at 1.5 wt % of C4-C-N-PEG9 system) upon UV irradiation. Small-Angle X-ray scattering studies have shown that addition of C4-C-N-PEG9 favors wormlike-to-sphere type transition in the micellar structure. However, UV irradiation in the C4-C-N-PEG9 incorporated system causes one-dimensional micellar growth. Since C4-C-N-PEG9 has relatively bigger headgroup size compared to the C12EO4, addition of C4-C-N-PEG9 into wormlike micelles reduces the critical packing parameter resulting in the formation of spherical aggregates. UV irradiation induced one-dimensional micellar growth is caused due to photocleavage of the C4-C-N-PEG9 into a less surface-active coumarin derivative and an aminated polyoxyethylene compound, as confirmed by UV-vis spectrometry and HPLC measurements. The hydrophobic coumarin derivative formed after cleavage of C4-C-N-PEG9 goes to the micellar core and is responsible for decreasing the viscosity. However, the hydrophilic aminated polyoxyethylene prefers to reside at the vicinity of headgroup of PhyEO20 reducing the interhead repulsion, increasing the critical packing parameter and the viscosity as well.

Worm-like soft nanostructures in nonionic systems: principles, properties and application as templates.

The principles, occurrence, structure and properties of worm-like micellar solutions in nonionic surfactant systems is reviewed, with focus in certain experimental methods used to characterize such soft nanostructured systems. Formulation plays a critical role in the design of worm-like micellar systems and derived viscoelastic networks. Micellar growth in one dimension, and hence formation of worm-like aggregates, is favoured by an increase in the average surfactant molecular packing parameter. Such an increase can be induced by addition of cosurfactant or amphiphilic oil that tends to penetrate in the surfactant palisade layer and reduce the specific surface area. On the other hand, long and bulky oils prone to be solubilized in the micellar core, cause a rod-sphere transition and therefore a decrease in viscosity. Salts have a small effect on the behaviour of nonionic worm-like micelles, contrary to what is found for ionic surfactant systems. The effect of raising temperature on worm-like micellar solutions is the result of a balance between the dehydration of the surfactant head groups, which favors elongation, the kinetics of micellar disruption and the formation of structures with nearly zero curvature. Therefore, a viscosity maximum as a function of temperature is found in many systems. Reverse worm-like micelles with a hydrophilic core can also be formed in organic solvents, even in the absence of ionic components or water. Worm-like micelles are useful as templates for the formation of ordered mesoporous oxides. The interaction of micelles with silica species results in the formation of silica-surfactant complexes that later precipitate as hexagonal phase via a cooperative mechanism.

Recent Advancements in Novel Sensing Systems through Nanoarchitectonics.

The fabrication of various sensing devices and the ability to harmonize materials for a higher degree of organization is essential for effective sensing systems. Materials with hierarchically micro- and mesopore structures can enhance the sensitivity of sensors. Nanoarchitectonics allows for atomic/molecular level manipulations that create a higher area-to-volume ratio in nanoscale hierarchical structures for use in ideal sensing applications. Nanoarchitectonics also provides ample opportunities to fabricate materials by tuning pore size, increasing surface area, trapping molecules via host-guest interactions, and other mechanisms. Material characteristics and shape significantly enhance sensing capabilities via intramolecular interactions, molecular recognition, and localized surface plasmon resonance (LSPR). This review highlights the latest advancements in nanoarchitectonics approaches to tailor materials for various sensing applications, including biological micro/macro molecules, volatile organic compounds (VOC), microscopic recognition, and the selective discrimination of microparticles. Furthermore, different sensing devices that utilize the nanoarchitectonics concept to achieve atomic-molecular level discrimination are also discussed.

Biomass Nanoarchitectonics for Supercapacitor Applications.

Nanoarchitectonics integrates nanotechnology with numerous scientific disciplines to create innovative and novel functional materials from nano-units (atoms, molecules, and nanomaterials). The objective of nanoarchitectonics concept is to develop functional materials and systems with rationally architected functional units. This paper explores the progress and potential of this field using biomass nanoarchitectonics for supercapacitor applications as examples of energetic materials and devices. Strategic design of nanoporous carbons that exhibit ultra-high surface area and hierarchically pore architectures comprising micro- and mesopore structure and controlled pore size distributions are of great significance in energy-related applications, including in high-performance supercapacitors, lithium-ion batteries, and fuel cells. Agricultural wastes or natural biomass are lignocellulosic materials and are excellent carbon sources for the preparation of hierarchically porous carbons with an ultra-high surface area that are attractive materials in high-performance supercapacitor applications due to high electrical and ion conduction, extreme porosity, and exceptional chemical and thermal stability. In this review, we will focus on the latest advancements in the fabrication of hierarchical porous carbon materials from different biomass by chemical activation method. Particularly, the importance of biomass-derived ultra-high surface area porous carbons, hierarchical architectures with interconnected pores in high-energy storage, and high-performance supercapacitors applications will be discussed. Finally, the current challenges and outlook for the further improvement of carbon materials derived from biomass or agricultural wastes in the advancements of supercapacitor devices will be discussed.

Nanoporous Hollow Carbon Spheres Derived from Fullerene Assembly as Electrode Materials for High-Performance Supercapacitors.

The energy storage performances of supercapacitors are expected to be enhanced by the use of nanostructured hierarchically micro/mesoporous hollow carbon materials based on their ultra-high specific surface areas and rapid diffusion of electrolyte ions through the interconnected channels of their mesoporous structures. In this work, we report the electrochemical supercapacitance properties of hollow carbon spheres prepared by high-temperature carbonization of self-assembled fullerene-ethylenediamine hollow spheres (FE-HS). FE-HS, having an average external diameter of 290 nm, an internal diameter of 65 nm, and a wall thickness of 225 nm, were prepared by using the dynamic liquid-liquid interfacial precipitation (DLLIP) method at ambient conditions of temperature and pressure. High temperature carbonization (at 700, 900, and 1100 °C) of the FE-HS yielded nanoporous (micro/mesoporous) hollow carbon spheres with large surface areas (612 to 1616 m2 g-1) and large pore volumes (0.925 to 1.346 cm3 g-1) dependent on the temperature applied. The sample obtained by carbonization of FE-HS at 900 °C (FE-HS_900) displayed optimum surface area and exhibited remarkable electrochemical electrical double-layer capacitance properties in aq. 1 M sulfuric acid due to its well-developed porosity, interconnected pore structure, and large surface area. For a three-electrode cell setup, a specific capacitance of 293 F g-1 at a 1 A g-1 current density, which is approximately 4 times greater than the specific capacitance of the starting material, FE-HS. The symmetric supercapacitor cell was assembled using FE-HS_900 and attained 164 F g-1 at 1 A g-1 with sustained 50% capacitance at 10 A g-1 accompanied by 96% cycle life and 98% coulombic efficiency after 10,000 consecutive charge/discharge cycles. The results demonstrate the excellent potential of these fullerene assemblies in the fabrication of nanoporous carbon materials with the extensive surface areas required for high-performance energy storage supercapacitor applications.

Wormlike micelle formation by acylglutamic acid with alkylamines.

Rheological properties of alkyl dicarboxylic acid-alkylamine complex systems have been characterized. The complex materials employed in this study consist of an amino acid-based surfactant (dodecanoylglutamic acid, C12Glu) and a tertiary alkylamine (dodecyldimethylamine, C12DMA) or a secondary alkylamine (dodecylmethylamine, C12MA). (1)H NMR and mass spectroscopic data have suggested that C12Glu forms a stoichiometric 1:1 complex with C12DMA and C12MA. Rheological measurements have suggested that the complex systems yield viscoelastic wormlike micellar solutions and the rheological behavior is strongly dependent on the aqueous solution pH. This pH-dependent behavior results from the structural transformation of the wormlike micelles to occur in the narrow pH range 5.5-6.2 (in the case of C12Glu-C12DMA system); i.e., positive curved aggregates such as spherical or rodlike micelles tend to be formed at high pH values. Our current study offers a unique way to obtain viscoelastic wormlike micellar solutions by means of alkyl dicarboxylic acid-alkylamine complex as gemini-like amphiphiles.

Peptide-based gemini amphiphiles: phase behavior and rheology of wormlike micelles.

Aqueous binary phase behavior of a peptide-based gemini amphiphile with glutamic acid and lysine as spacer group, acylglutamyllysilacylglutamate (m-GLG-m where m = 12, 14, and 16), has been reported over a wide range of concentration and temperature. Lauroylglutamyllysillauroylglutamate, 12-GLG-12, self-assembles into spherical micelles above critical micelle concentration (CMC). The micellar region extends up to 32 wt %, and an ordering of spherical micelles into micellar cubic phase, I(1), takes place at 33 wt % at 25 °C. The phase transition, I(1) - hexagonal liquid crystal, (H(1)) - lamellar liquid crystal, (L(α)) has been observed with further increase in concentration; moreover, mixed phases are also observed between the pure liquid crystal domains. Similar phases were observed with 16-GLG-16 above 50 °C (Krafft temperature). The partial ternary phase behavior shows that the micellar solutions of m-GLG-m can solubilize a large amount of cationic amphiphile, alkyltrimethylammonium bromide, C(n)TAB, (where n = 14 (TTAB) and 16 (CTAB)) at 25 °C. An addition of C(n)TAB to the aqueous solutions of 16-GLG-16 in a dilute region forms a transparent solution of viscoelastic wormlike micelles at very low concentration (0.25 wt %) even at ambient condition. A mixture of oppositely charged amphiphiles, m-GLG-m and C(n)TAB, exhibits synergism as a result the amphiphile layer curvature, becomes less positive, and favors the transition from sphere to rod to transient networks (wormlike micelles). The gemini amphiphile, 16-GLG-16, forms wormlike micelles at relatively low concentrations compared to others reported so far. Viscosity increases by six orders of magnitude compared to that of pure solvent. The hydrophobic chain length of m-GLG-m and coamphiphile affects the rheology; the maximum viscosity achieved with 16-GLG-16/H(2)O/CTAB is higher than that of 14-GLG-14/H(2)O/CTAB, 12-GLG-12/H(2)O/CTAB, and 16-GLG-16/H(2)O/TTAB systems. These temperature-sensitive systems exhibited viscoelastic behavior described by the Maxwell mechanical model with a single stress relaxation mode.

Structure and rheology of charge-free reverse micelles in aromatic liquid phenyloctane.

Reverse micelles formulation requires an inclusion of water or other polar molecules in the binary mixture of ionic surfactant and oil and generally exhibit spheroid geometry with a small aggregation number. Here, we report structure and rheology of charge-free (nonionic) reverse micelles in surfactant/oil systems. We have systematically investigated intrinsic parameters for the shape, size, and internal cross section structure control of such micelles using small-angle X-ray scattering (SAXS) and the rheometry. We found that diglycerol monomyristate (C14G2) when added into an aromatic organic liquid phenyloctane, spontaneously self-assembles into spheroid micelles with maximum diameter ca. 6.7 nm. Decrease in surfactant chain length favors globular-to-rod type transition and micellar aggregation number (N(agg)) increases significantly. On the other hand, increase in surfactant weight fraction induces one-dimensional (1-D) micellar growth; N(agg) increases in parallel to the surfactant concentration. Reverse micelles shrink with the rise of temperature, which is close to the rod-to-sphere type transition. However, water causes a significant micellar growth; N(agg) increases drastically, which shows that water not only increase reverse micellar size but also increases the number of surfactant molecules per micelle. All these microstructure transitions could be understood in terms of the modification of the critical packing parameter (cpp). The SAXS results are very well supported by the geometrical model fittings and rheometry.