On the relation between the solvent parameters and the physical properties of methyl-4,6-O-benzylidene-α-d-glucopyranoside organogels

This paper reports the mechanisms of gel formation, the thermal properties and the microstructures of the networks of the gels composed of methyl-4,6-O-benzylidene-α-d-glucopyranoside and selected organic solvents: p-xylene, benzene, toluene, diphenyl ether and tetraethoxysilane. The Fourier transform infrared measurements together with simulation spectra, the air bath method and Polarized Optical Microscopy were employed in our studies. The experimental data show that the solvent has an influence on the microstructure of the gel network but there is no predictable influence of the solvent polarity on the shape of the formed gelator aggregates and correspondingly on the fibrous assemblies as revealed by the different microstructure of the gel network. Independently of the solvent polarity, the studied gelator, like other methyl-4,6-O-benzylidene derivatives of monosaccharides, formed gels through the formation of a hydrogen-bond network. The solvent parameters, such as the dielectric constant, Hildebrand solubility parameter, the polarity scale E_T and the Kamlet–Taft parameters were considered to quantify solvent effects on the gelation. The conclusions about the correlations are of interest but only to this particular sugar based gels.     

Preparation of Metal Oxide Nanotubes Using Gelators as Structure-Directing Agents

Summary: Cationic gelators, capable of gelling alcohols, were developed as structure-directing agents for preparing metal oxides. The sol-gel polymerization of metal alkoxides using the gelators as templates afforded metal oxide nanotubes. The unique structure of metal oxides was created by transferring the shape of fibrous aggregates of gelator. The electrostatic interaction between cationic gelator and anionic metal oxide precursor plays an important role for acting as templates.     

Organization of helical mesoporous silica nanotubes

Mesoporous silica nanotubes with coiled pore channels in the walls were prepared using the self-assemblies of a gelator as template previously. The TEM images were simulated using Autodesk 3D studio MAX 9.0 here. These hierarchical nanotubes were organized into μm-size balls by increasing the concentration of gelator and controlling stirring speed. Bimodal pore structure was identified by a N₂ adsorption method.     

Morphological studies of a (self-assembling oil gelator/liquid crystal) composite system

The aggregation structure of a novel (self-assembling oil gelator/liquid crystal) composite was investigated using light scattering studies and morphological observations. The oil gelator forms a self-assembled-networks aggregate in an organic solvent with a low molecular weight liquid crystal (LC). It became apparent from Hv light scattering patterns and polarizing optical microscopy that two types of LC molecular alignments exist in the composite: a random orientation and a spherulite type one in a nematic gel state. Also, optical and atomic force microscopic observations revealed that fibrils which formed bundles in the fibre-like and spherulite-like aggregates, were formed in the composite. The alignment of the liquid crystal molecules was related to the aggregation structure of the self-assembling oil gelator in a liquid crystal gel state.     

Morphological studies of a (self-assembling oil gelator/liquid crystal) composite system

The aggregation structure of a novel (self-assembling oil gelator/liquid crystal) composite was investigated using light scattering studies and morphological observations. The oil gelator forms a self-assembled-networks aggregate in an organic solvent with a low molecular weight liquid crystal (LC). It became apparent from Hv light scattering patterns and polarizing optical microscopy that two types of LC molecular alignments exist in the composite: a random orientation and a spherulite type one in a nematic gel state. Also, optical and atomic force microscopic observations revealed that fibrils which formed bundles in the fibre-like and spherulite-like aggregates, were formed in the composite. The alignment of the liquid crystal molecules was related to the aggregation structure of the self-assembling oil gelator in a liquid crystal gel state.     

Optically Transparent Hydrogels from an Auxin–Amino‐Acid Conjugate Super Hydrogelator and its Interactions with an Entrapped Dye

Low‐molecular‐weight organic hydrogelators (LMHGs) that can rigidify water into soft materials are desirable in various applications. Herein, we report the excellent hydrogelating properties of a simple synthetic auxin–amino‐acid conjugate, naphthalene‐1‐acetamide of L ‐phenylalanine ( 1‐NapF , M_w=333.38 Da), which gelated water even at 0.025 wt %, thereby making it the most‐efficient LMHG known. Optically transparent gels that exhibited negligible scattering in the range 350–900 nm were obtained. A large shift from the theoretical pK_a value of the gelator was observed. The dependence of the minimum gelator concentration (MGC) and the gel‐melting temperatures on the pH value indicated the importance of H‐bonding between the carboxylate groups on adjacent phenylalanine molecules in the gelator assembly. FTIR spectroscopy of the xerogels showed a β‐sheet‐like assembly of the gelator. Variable‐temperature ¹H NMR spectroscopy demonstrated that π stacking of the aromatic residues was also partly involved in the gelator assembly. TEM of the xerogel showed the presence of a dense network of thin, high‐aspect‐ratio fibrillar assemblies with diameters of about 5 nm and lengths that exceeded a few microns. Rheology studies showed the formation of stable gels. The entrapment of water‐soluble dyes afforded extremely fluorescent gels that involved the formation of J‐aggregates by the dye within gel. A strong induced‐CD band established that the RhoB molecules were interacting closely with the chiral gelator aggregates. H‐bonding and electrostatic interactions, rather than intercalation, seemed to be involved in RhoB binding. The addition of chaotropic reagents, as well as increasing the pH value, disassembled the gel and promoted the release of the entrapped dye with zero‐order kinetics.     

Self‐Assembled Fibers Containing Stable Organic Radical Moieties: Alignment and Magnetic Properties in Liquid Crystals

Macroscopically oriented stable organic radicals have been obtained by using a liquid–crystalline (LC) gel composed of an l ‐isoleucine‐based low molecular weight gelator containing a 2,2,6,6‐tetramethylpiperidine 1‐oxyl moiety. The LC gel has allowed magnetic measurements of the oriented organic radical. The gelator has formed fibrous aggregates in liquid crystals via intermolecular hydrogen bonds. The fibrous aggregates of the radical gelator are formed and oriented on cooling by applying a magnetic field to the mixture of liquid crystals and the gelator. Superconducting quantum interference device (SQUID) measurements have revealed that both oriented and nonoriented fibrous aggregates exhibited antiferromagnetic interactions, in which super‐exchange interaction constant J is estimated as ?0.89 cm^?1.     

Small angle X-ray scattering analysis of the effect of cold compaction of Al/MoO3 thermite composites

Nanothermites composed of aluminum and molybdenum trioxide (MoO(3)) have a high energy density and are attractive energetic materials. To enhance the surface contact between the spherical Al nanoparticles and the sheet-like MoO(3) particles, the mixture can be cold-pressed into a pelleted composite. However, it was found that the burn rate of the pellets decreased as the density of the pellets increased, contrary to expectation. Ultra-small angle X-ray scattering (USAXS) data and scanning electron microscopy (SEM) were used to elucidate the internal structure of the Al nanoparticles, and nanoparticle aggregate in the composite. Results from both SEM imaging and USAXS analysis indicate that as the density of the pellet increased, a fraction of the Al nanoparticles are compressed into sintered aggregates. The sintered Al nanoparticles lost contrast after forming the larger aggregates and no longer scattered X-rays as individual particles. The sintered aggregates hinder the burn rate, since the Al nanoparticles that make them up can no longer diffuse freely as individual particles during combustion. Results suggest a qualitative relationship for the probability that nanoparticles will sinter, based on the particle sizes and the initial structure of their respective agglomerates, as characterized by the mass fractal dimension.     

Investigation of a catalyst ink dispersion using both ultra-small-angle X-ray scattering and cryogenic TEM

The dispersion of Nafion ionomer particles and Pt/C catalyst aggregates in liquid media was studied using both ultra-small-angle X-ray scattering (USAXS) and cryogenic TEM. A systematic approach was taken to study first the dispersion of each component (i.e., ionomer particles and Pt/C aggregates), then the combination of the components, and last the catalyst ink. Multiple-level curve fitting was used to extract the particle size, size distribution, and geometry of the Pt/C aggregates and the Nafion particles in liquid media from the scattering data. The results suggest that the particle size, size distribution, and geometry are not uniform throughout the systems but rather vary significantly. It was found that the interaction of each component (i.e., the Nafion ionomer particles and the Pt/C aggregates) occurs in the dispersion. Cryogenic TEM was used to observe the size and geometry of the particles in liquid directly and to validate the scattering results. The TEM results showed excellent agreement.     

Effect of alcohol-water exchange and surface scanning on nanobubbles and the attraction between hydrophobic surfaces

4-(4′-Butoxyphenyl)phenyl-β-O-d-glucoside was synthesized as a low-molecular-mass gelator. It was able to immobilize a variety of aqueous and organic solvents in large amounts through the formation of three-dimensional self-assembled fibrillar networks. The morphologies of the aggregates depended on the nature of solvent where they were formed. Planar ribbons were observed in water, while helical ribbons were dominant in toluene and sheets in CHCl₃. The xerogel from water exhibited a lamellar structure with a d-spacing of 2.45 nm as demonstrated by 1D-WAXD, indicating a bilayer structure interdigitated with butoxy tails, whereas the xerogel from CHCl₃ or toluene yielded a lamellar structure with a d-spacing of 3.05 nm, implying a bilayer structure interdigitated with glycosyl heads. Increasing the content of 1,4-dioxane in water caused a gradual transformation from planar to twisted ribbons and then tubes.     

Hydrophobie effects on photophysical and photochemical processes: VI. Character of aggregates formed by hydrocarbon with long chain in poor solvents

Dodecyl β-naphthoate and 3-octadecyl pyrene were used as fluorescence probes for estimation of microscopic polarity in aggregates formed by long chain hydrocarbon Cn (n-10, 12, 14, 16, 18) in dimethyl sulfoxide-water mixed solvent. The polarity in the aggregates is similar to that in cyclohexane. The average aggregation number (N?) was determined by using time resolved fluorescence technique. N? is dependent on substrate chain length and varies from 15 to 30. The microviscosity was also measured by fluorescence depolarization method. Above phase transition temperature, the microviscosity in aggregates is slightly larger than that in micelle, but below this temperature, the microviscosity in aggregates is as large as that in solid phase.     

The Special “Morse Code” between Solvent Polarity and Morphology Flexibility in a POSS–Dendrimer Supramolecular System

An amazing phenomenon of the relative magnitude of modulus of two liquid-crystal (LC) gels is found inverted under/above their phase transition temperature T_LC-iso, which is further proved to be caused by their diverse morphology flexibility. By testing the polarity of two LCs, gelator POSS-G1-Boc (POSS=polyhedral oligomeric silsesquioxane) was discovered to self-assemble into more flexible structures in a relatively low polar LC, whereas more rigid ones are formed in higher polar LC. Hence, a fitting function to connect morphology flexibility with solvent polarity was established, which can even be generalized to a number of common solvents. Experimental observations and coarse-grained molecular dynamics simulations revealed that solvent polarity mirrors a “Morse code”, with each “code” corresponding to a specific morphology flexibility.     

Investigation of Voids in Polyacrylonitrile Fibers by USAXS and SAXS

The void structure of polyacrylonitrile(PAN) fibers was investigated using ultra-small angle X-ray scattering(USAXS) and small angle X-ray scattering(SAXS). A quantitative method was developed to analyze connected USAXS/SAXS data and thus determine the void parameters of PAN fibers. The results showed that voids affected the mechanical performance of PAN fibers and were present throughout the entire wet-spinning process. When the absolute quantity and size of voids decreased, the tensile strength and modulus of PAN fibers increased. The void parameters were optimized by controlling the production process, and thus the tensile strength and modulus of PAN fibers were increased. The method for analyzing the void structure developed in this study is useful for analyzing voids over with larger size range, as well as the effect of the void structure on the mechanical performance of fibers.     

Influence of solvent on the thermal stability and organization of self-assembling fibrillar networks in methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside gels

Sugar based low-molecular-mass organogelator (LMOG) methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside, is a unique gelator because its small and weakly-interacting molecules can form large supramolecular structures in nonpolar, but also in polar, solvents and cause their gelation. The self-assembling properties of the gelator were studied in selected nonpolar and polar solvents. It was shown that the driving forces for both types of solvent are the intermolecular hydrogen bond interaction. The effect of the nature of the solvent on the thermal stability of the gels and on the three-dimensional network organization was determined. Different solvent parameters, such as dielectric constant, one-component solubility parameter, the polarity parameter and the Kamlet-Taft parameters were considered to quantify solvent effects on the gelation. Some correlation between these parameters and the gel stability, microstructure and the enthalpy of the phase transition were established. The effort to correlate the Kamlet-Taft parameters to the thermal stability and gelation ability is also possible but applies only to the studied gelator.     

2,3-di-n-decyloxy-6,7-dichloroanthracene (Cl2DDOA), a new low-molecular-mass fluorescent organogelator: physical properties and structures

To extend the family of 2,3-didecyloxyanthracene (DDOA, 1), an organogelator having a rodlike shape, a high polarity, and fluorescing properties, the 6,7-dichloro derivative (Cl2DDOA, 2), was designed and prepared. Compound 2 forms gels in alcohols, nitriles, and alkanes. The electronic absorption spectra of the gel show a finer structure than those of the isotropic solutions, pointing to a specific degree of packing of the molecules; such an aggregation mode is also supported by fluorescence data. The gel-to-sol temperatures (Tm) were determined as a function of gelator concentration and the corresponding enthalpies (DeltaHm) were extracted. Scattering experiments have shown that the molecular packing in aggregates of 2 organogels is less reminiscent of the crystalline state than was the situation with DDOA gels. 2 organogels in butanol are made up of 120 A radius fibers much thinner than those observed in DDOA gels (r ca. 300 A) and with rather monodisperse cross sections. In 1-octanol, dodecane, or cyclohexane, the fibrillar organogel networks involve a broader distribution of the related cross sections through anisometric sections of the fibers and/or formation of bundles.     

In situ studies of monosaccharide gelation using the small-angle X-ray scattering time-resolved method

The process of gelation of one of the monosaccharides, alpha-galactose-based gelator, with benzene as a solvent, has been studied. Small-angle X-ray scattering (SAXS) synchrotron time-resolved measurements were performed throughout the gelation process. The obtained SAXS measurements were elaborated using such methods as the fractal analysis, Fourier transform to get distance distribution functions, and simulation of a cluster model. We obtained the picture of the mesostructure development from the sol state to the gel state. Our results indicate that the fractal-type aggregates exist in the sol and the process of gelation is accompanied by the structural transition. This transition causes the aggregates to become smaller and denser, and their shapes differ from those of the sol. The complex method of SAXS data treatment we established seems to be a useful tool also for further studies of monosaccharide gelation.     

Rupture and regeneration of colloidal crystals as studied by two-dimensional ultra-small-angle X-ray scattering

The structure of colloidal crystals of silica particles in water was studied by using the two-dimensional (2D) ultra-small-angle X-ray scattering (USAXS) technique. By violent shaking of the dispersion, large (body-centered cubic, bcc) crystals were broken into microcrystals while the lattice structure and lattice constant were preserved. The 2D-USAXS profiles revealed that the [111] direction of bcc microcrystals was parallel to the capillary axis and their orientational distribution with respect to the capillary axis was random. While a prepeak was observed in the one-dimensional USAXS measurements, no such peak was detected by the 2D-USAXS technique. The prepeak was concluded to be due to {110} being rotated by 54.7 degrees (the angle between [001] and [111]) from the capillary axis. The diffraction from the plane was out of the horizontal plane and was observed at a lower angle as a prepeak by detector scanning in the horizontal direction.     

Hydrogen-bonding A(LS)2-type low-molecular-mass gelator and its thermotropic mesomorphic behavior

A unique cholesterol-based A(LS)₂-type gelator, which is a hydrogen-bonding complex based on an ALS-type non-gelator molecule 3-cholesteryl 4-(trans-2-(4-pyridinyl)vinyl)phenyl succinate and a counterpart 3-cholesteryloxycarbonylpropanoic acid, shows strong gelation ability in alcohol and aromatic solvents. The formed gel has a high T_g at low gelation concentration, and its xerogel shows fibrillar microstructure revealed by scanning electron microscopy (SEM). FTIR confirms the existence of intermolecular hydrogen bond in the gelator, and X-ray diffraction (XRD) analysis reveals that the gelator possesses a folded conformation in gel and self-assembles into the fibrillar structure mainly by van der Waals interaction between cholesteryl moieties of the gelator. Further more, the thermotropic behavior of the xerogel is studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM), which shows typical optical textures of liquid crystals.