Multifold curdlan gel formation by dialysis into aqueous solutions of metal salts

We have found that the dialysis of curdlan dissolved in alkaline solution into aqueous solutions of metal salts yielded multifold gel structures. Aqueous sodium chloride and potassium chloride as well as pure water induced isotropic gels. Aqueous calcium salts induced liquid crystalline gel with refractive index gradient/amorphous gel alternative structure. Aqueous salts of trivalent aluminum and ferric cations induced a rigid liquid crystalline gel, which shrank above a threshold concentration of each salt. On the other hand, Liesegang ring-like pattern was observed with aqueous solutions of mixed salts of calcium chloride and magnesium chloride. The patterns have been classified to discuss the mechanism of forming the variety of structures.     

Influence of kappa-carrageenan gel structures on the diffusion of probe molecules determined by transmission electron microscopy and NMR diffusometry

The influence of the microstructures of different kappa-carrageenan gels on the self-diffusion behavior of poly(ethylene glycol) (PEG) has been determined by nuclear magnetic resonance (NMR) diffusometry and transmission electron microscopy (TEM). It was found that the diffusion behavior was determined mainly by the void size, which in turn was defined by the state of aggregation of the kappa-carrageenan. The kappa-carrageenan concentration was held constant at 1 w/w%, and the aggregation was controlled by the amount of potassium and/or sodium chloride and, for samples containing potassium, also by the cooling rate. Gels containing potassium formed microstructures where kappa-carrageenan strands are rather evenly distributed over the image size, while sodium gels formed dense biopolymer clusters interspersed with large openings. In a gel with small void sizes, relatively slow diffusion was found for all PEG sizes investigated. Extended studies of the self-diffusion behavior of the 634 g mol(-)(1) PEG showed that there is a strong time dependence in the measured PEG diffusion. An asymptotic lower time limit of the diffusion coefficient was found in all gels when the diffusion observation time was increased. According to the ratio, D/D(0), where D(0) is the diffusion coefficient in D(2)O and D is the diffusion coefficient in the gels, the gels could be divided into three classes: small, medium, and large voids. For quenched kappa-carrageenan solutions with salt concentrations of 20 mM K(+), 100 mM K(+), or 20 mM K(+)/200 mM Na(+) as well as slowly cooled solutions with only 20 mM K(+), D/D(0) ratios between 0.18 and 0.29 were obtained. By quenching a kappa-carrageenan solution with 100 mM K(+), the D/D(0) was 0.5, while D/D(0) ratios between 0.9 and 1 were obtained in a quenched solution with 250 mM Na(+) and slowly cooled samples with 20 mM K(+)/200 mM Na(+) or 250 mM Na(+).     

Liquid crystalline gel with refractive index gradient of curdlan

Curdlan dissolved in aqueous sodium hydroxide was dialyzed to aqueous calcium chloride to form a gel. Transparent and turbid concentric layers observed in the gel cross section perpendicular to the long axis of the dialysis tube were identified as liquid crystalline gels with refractive index gradient and amorphous gels, respectively. The thickness of each layer was proportional to the diameter of the dialysis tube, and the gelation proceeded in proportion to the root of time. The unique pattern formation was attributed to the change of curdlan conformation and calcium-induced cross-linking resulting from a diffusion of calcium cations and hydroxide anions through the dialysis tube. It is suggested that the orderedness of the curdlan molecules decreases by the increase of the curvature of the concentric liquid crystal layers as the layer comes toward the center of the dialysis tube.     

Liquid crystalline gel beads of curdlan

Curdlan beads consisting of liquid crystalline gel (LCG) and amorphous gel (AG) in alternating layers in a wide range of diameters were newly prepared by interfacial insolubilization reactions using calcium chloride as the setting reagent. The thickness of the liquid crystalline layer was proportional to the diameter of the gel bead, and the proportional constant agreed with that determined for the cylindrical gel prepared by a dialysis method. The proportional constant initially increased with increasing calcium concentration of the dispersing medium and saturated at a high concentration limit. These results suggest that the mechanisms for forming the alternating LCG/AG structures prepared with different boundary conditions are the same. The LCG/AG structure could be controlled by calcium concentration.     

Dynamics in dialysis process for liquid crystalline gel formation

The processes of gelation and liquid crystalline formation in the dialysis of Curdlan solution have been observed under crossed nicols, and the calcium concentration and pH of the inner solution were traced. The results showed that the gelation and the liquid crystalline formation occurred simultaneously to form liquid crystalline gel (LCG), but the birefringence of the LCG increased even after the gelation, suggesting further ordering of the Curdlan molecules. On the basis of the calcium ion diffusion, a simple theory for the time development of the thickness of the LCG layer was developed. The experimental and theoretical results agree very well until an amorphous gel (AG) ring appears. The whole process was expressed by a master curve by reducing time and distance data for different radius dialysis tubes by those at the final state; a scaling behavior with respect to the dialysis tube radius was found. The experimental analysis for the calcium concentrations and the pH indicates that forming Curdlan LCG with high ordering of Curdlan molecules consists of two steps: the diffusion of calcium ions inducing the ordering of Curdlan molecules and yielding cross-links simultaneously, and the local relaxation of the Curdlan molecules increasing the ordering degree further.     

Reaktion von Kaolinit mit Kaliumhydroxid

The reaction of kaolinite with potassium hydroxide (1 to 9N) was investigated between 70 and 90°C. During a first period of the reaction the content of Si and Al in solution increased and reached a maximum in 100 to 240 minutes, depending on KOH concentration and temperature; then an amorphous aluminosilicate gel formed. After an induction period, again depending on KOH concentration and temperature, the concentrations of Si and Al decreased rapidly, due to the formation of a crystalline potassium aluminosilicate.     

Hydration of NaCl on glassy, supercooled-liquid, and crystalline water

Interactions of sodium chloride with amorphous and crystalline water films, leading to the possible formation of a dilute NaCl solution, were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature. A monolayer of NaCl tends to remain on the surface or in subsurface sites of thick amorphous solid water films (200 monolayers); the Na+ ion is hydrated preferentially, whereas the Cl- ion is segregated at the surface. The hydration structure of NaCl is fundamentally unchanged for viscous liquid water that appears at temperatures higher than 136 K. The solubility of NaCl increases abruptly at 160 K because of the evolution of supercooled liquid water, which can hydrate the Cl- ion efficiently. However, the diffusion of the ions toward the bulk of supercooled liquid water is interrupted by crystallization; therefore, the dilute NaCl solution that is characterized by completely separated Na+-Cl- pairs may not be formed. When NaCl is deposited on the crystalline ice film, hydration of NaCl is enhanced above 160 K as well, indicating that a liquidlike phase coexists with crystals.     

Associative and segregative phase separations of gelatin/kappa-carrageenan aqueous mixtures

The effects of ionic strength, temperature, and pH on the phase separation behavior of type B pigskin gelatin/sodium-type kappa-carrageenan aqueous mixtures were investigated. Depending on the different combinations of temperature and sodium chloride (NaCl) concentration, the mixtures showed compatible, associative, and segregative phase separation behaviors. Additionally, a coexistence of associative and segregative (associative-co-segregative) phase separations was expected at low temperature and low NaCl concentration. These different phase separation events were observed using confocal scanning laser microscopy. Moreover, it was found that the segregative phase separation when alone is induced by the ordering of kappa-carrageenan chains, while that in the coexistence region is induced by the ordering of gelatin chains. pH had a significant effect on the associative phase separation, resulting in morphologies changing from compatible solution to liquid coacervate and further to solid precipitate with decreasing pH. These were attributed to the dramatic changes of the charge density of amphoteric gelatin during the pH decrease.     

Diffusion of sodium dodecyl sulfate micelles in agarose gels

The gradient diffusion of ionic sodium dodecyl sulfate micelles in agarose gel was investigated at moderate concentrations above the CMC. Of particular interest were the effects of micelle, gel, and sodium chloride concentration on the micelle diffusivity. Holographic interferometry was used to measure the gradient diffusion coefficient at three sodium chloride concentrations (0, 0.03, 0.10 M), three gel concentrations (0, 1, 2 wt%), and several surfactant concentrations. Time-resolved fluorescence quenching was used to measure aggregation numbers both in solution and gel. The micelle diffusivity increased linearly with surfactant concentration at the two larger sodium chloride concentrations and all gel concentrations. In general, the strength of this effect increased with decreasing sodium chloride concentration and increased with gel concentration. This behavior is evidence of decreasing micelle-micelle electrostatic interactions with increasing sodium chloride concentrations, and increasing excluded volume effects and hydrodynamic screening with increasing gel concentration, respectively. The only exception was at 0.1M sodium chloride and 2 wt% agarose, which showed a slight reduction in the slope compared to 1 wt% agarose. It was found that the concentration effect is quite strong for charged solutes: at a NaCl concentration of 0.03 M in a 2% agarose gel, in a solution with 3% SDS micelles by volume, the micelle diffusion coefficient is doubled relative to its value in the same gel at infinite dilution. The extrapolated, infinite-dilution diffusion coefficients and the rate at which the micelle diffusivity increased with surfactant concentration were compared with predictions of previously published theories in which the micelles are treated as charged, colloidal spheres and the gel as a Brinkman medium. The experimental data and theoretical predictions were in good agreement.     

Phase equilibria and phase structure in the ternary systems sodium or potassium octanoate-octanoic acid-water

Two isotropic solution regions and several liquid crystalline regions occur in the ternary system sodium octanoate-octanoic acid-water at 20°C The solution regions are an aqueous solution and a solution of sodium octanoate and water in liquid octanoic acid. A region displaying one-dimensional lamellar structure is located in the center of the phase diagram. A region along the soap-water axis has a two-dimensional normal hexagonal structure. Another region at high octanoic acid content has a reversed hexagonal structure. Along the soap-fatty acid axis the acid-soap 2NaC₈:1HC₈ in crystalline state is found.X-ray and density findings for the various phases are presented, and structural parameters for the different liquid crystalline phases are estimated.The phase behavior of the potassium soap system is similar to that of the sodium system.The isothermal ternary phase diagram of a soap, the corresponding fatty acid and water provides information about the ionization state of the system, from the unionized fatty acid to the fully ionized soap.     

Effects of magnetite nanoparticles on the thermorheological properties of carrageenan hydrogels

The influence of magnetite (Fe(3)O(4)) nanoparticles on the rheological properties of kappa-, iota- and lambda-carrageenan gels has been investigated. Small amplitude oscillatory shear measurements were performed to study the effect of the presence of Fe(3)O(4) nanoparticles with particle sizes of ca. 10 nm on the gel properties, as a function of carrageenan type, carrageenan concentration and magnetite load. The formation of Fe(3)O(4) nanoparticles on the presence of biopolymer was observed to promote the gelation process and lead to stronger gels as indicated by an increase in the gel viscoelastic moduli and of the gelation temperature. This effect was more marked for kappa-carrageenan than for iota- and lambda-carrageenan and has been proposed to depend not only on Fe(3)O(4) concentration but also on the concentration of potassium ions. A mechanism based on the combined effect of Fe(3)O(4) nanoparticles and potassium ions was suggested, involving the adsorption of potassium ions on the negatively charged surface of the Fe(3)O(4) nanoparticles, thus leading to an increase of the potassium ion concentration within the "carrageenan cages" containing the magnetite. This would, therefore, promote more extensive biopolymer helical aggregation, thus resulting in the formation of a stronger kappa-carrageenan gel in the presence of Fe(3)O(4), as observed. Since iota- and lambda-carrageenan gels are known to be less sensitive to potassium ions concentration, the effect of precipitating Fe(3)O(4) within these biopolymers is reduced.     

Coupling between polysaccharide gelation and micro-phase separation of globular protein clusters

The effect of gelation of the polysaccharide phase on the phase separation was investigated for mixtures of anionic polysaccharide (kappa-carrageenan) and globular protein (beta-lactoglobulin) clusters at pH 7 well above the iso-electric point. Gelation of kappa-carrageenan was induced by cooling in the presence of KCl. In the liquid state the protein clusters phase-separate into relatively dense micro-domains. When the polysaccharide phase gelled during cooling, the turbidity of the systems decreased dramatically. Light scattering experiments showed that the density of the micro-domains decreased, while microscopy showed that the number and size was not strongly modified. It is concluded that smaller protein clusters leave the micro-domains when kappa-carrageenan gels. The effect could be reversed by reheating the samples and thus melting the gel and was observed for repeated heating and cooling cycles. The effect of gelation on phase separation decreases with increasing polysaccharide concentration and with ageing of the liquid mixture. The latter is caused by the formation of bonds between the protein clusters in the micro-domains that slowly reinforce with time.     

A thermoreversible double gel: characterization of a methylcellulose and kappa-carrageenan mixed system in water by SAXS, DSC and rheology

Sol-gel and gel-sol thermal transition of methylcellulose/water, kappa-carrageenan/water and methylcellulose/kappa-carrageenan/water mixtures was investigated utilizing small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) and oscillatory rheological experiments in temperature regime from 20 to 80 degrees C. Methylcellulose (E461) and kappa-carrageenan (E407) are well-known additives used for gelation in various nutrition and other products. The formulation and characterization of a mixed thermoreversible methylcellulose/kappa-carrageenan/water gel with very interesting double thermal transition gel-sol-gel upon heating was possible. This specific thermal behavior provides a liquid state of the system between the low-temperature and high-temperature gel-state and at the same time allows for the easy temperature tuning of the system's state. As such this system is suggested to be further tested as potential carrier for various functional colloidal systems.     

Deposition and aggregation of aspirin molecules on a phospholipid bilayer pattern

Aspirin and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) are deposited from their alcoholic mixed solution onto highly oriented pyrolytic graphite (HOPG) by spin coating. The film structure and morphology are characterized by atomic force microscopy (AFM). The barely soluble DMPE forms a highly oriented stripe phase as a result of its one-dimensional epitaxy with the HOPG lattice. The bilayer stripe pattern exposes the cross section of the lipid bilayer lamellae and enables the direct visualization of the molecular interactions of drug or biological molecules with either the hydrophobic or the hydrophilic part of the phospholipid bilayer. The bilayer pattern affects the aspirin molecular deposition and aggregation. AFM shows that the aspirin molecules prefer to deposit and aggregate along the aliphatic interior part of the bilayer pattern, giving rise to parallel dimer rods in registry with the underlying pattern. The nonpolar interactions between aspirin and the phospholipid bilayer are consistent with the lipophilic nature of aspirin. The bilayer pattern not only stabilizes the rodlike aggregate structure of aspirin at low aspirin concentration but also inhibits crystallization of aspirin at high aspirin concentration. Molecular models show that the width of the DMPE aliphatic chain interior can accommodate no more than two aspirin dimers. The bilayer confinement may prevent aspirin from reaching its critical nucleus size. This study illustrates a general method to induce a metastable or amorphous form of an active pharmaceutical ingredient (API) by chemical confinement under high undercooling conditions. Metastable and amorphous solids often display better solubility and bioavailability than the stable crystalline form of the API.     

Molecular Filtration of Hydrocarbon Isomers Through Polymer/[Liquid Crystal] Composite Membranes

Ultrathin membranes of a polymer/(liquid crystal) mixture were prepared by spreading a single drop of a casting solution on the water surface. The thickness and the aggregation state of the water-cast membrane can be controlled by the kind of solvent and the concentration of the solution. In the case of a liquid crystalline state above the crystal-nematic phase transition temperature, T _KN, the polymer (liquid crystal) composite membrane follows Henry's law for the sorption isotherm of hydrocarbon gases and, also, Fickian sorption for the sorption-desorption kinetics. These results indicate that hydrocarbon gases permeate through a homogeneous medium composed of liquid crystalline molecules. Therefore, the permeability coefficients of hydrocarbon gases can be controlled by the dimensions of the channels through which the gas molecules diffuse. The channel for diffusion is generated by thermal or fluctuating molecular motion which opens up the intermolecular distance between liquid crystalline molecules. In the case of a self-supported liquid crystalline membrane, the channel dimension can be controlled in the range of several Å by both the intermolecular distance and the degree of thermal molecular motion of the liquid crystalline molecules. Separation of hydrocarbon isomers was investigated by use of composite membranes composed of a polymer matrix and self-supported liquid crystalline molecules.     

Interface characteristics of a Zr‐based BMG/copper laminated composite

Diffusion bonding of metallic glasses and crystalline metals utilizing excellent superplasticity of monolithic bulk metallic glasses (BMGs) within supercooled liquid region has been found to be an efficient method to improve the room temperature plasticity and fracture toughness of metallic glass. A Zr‐based BMG/copper laminated composite was fabricated by copressing method, and the interface bonding status was characterized by scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy. No void or crack is detected, and the interface is a metallurgical bonding of atomistic level. Although the BMG retains amorphous state after copressing at 390 °C, the region of the amorphous‐crystalline mixture structure with the width of 30–40 nm occurred within the diffusion zone. Copyright © 2013 John Wiley & Sons, Ltd.     

Liquid Metals and Liquid Semiconductors

Numerous liquid systems have electrical properties which resemble those of crystalline and amorphous semiconductors. The existence of “semiconducting” behavior in these liquids is mostly related to a continuous transition from a metallic to a “semiconducting” state when a thermodynamic variable such as temperature, density or concentration is changed. Changes in the nature of the chemical interaction and the associated changes in the structure of the liquid are of fundamental importance for the transition to a “semiconducting” state. This will be demonstrated for the ionic liquid CsAu, for covalent liquid selenium, and for expanded liquid metals.     

Thin La2Zr2O7 films made from a water-based solution

Thin films of La₂Zr₂O₇ (LZO) are highly regarded as possible buffer layers in the coated conductor configuration. This report describes a new synthesis for thin crystalline LZO films, based on a largely water-based solution, mainly containing metal acetates, acetic acid and an organic amine-base: triethanolamine. Initially, a thin layer of amorphous material is deposited on the textured Ni-5 at%W substrate by means of dip-coating. Only by careful control of the thermal treatment can the layer be transformed into a crystalline layer. Important parameters in this respect are the heating rate and the dwell time. The amorphous gel is analysed by HR-TGA/DTA and HR-TEM. The textured layers are analysed by XRD, pole figures, RHEED, AFM and SEM.     

Formation of supercooled liquid solutions from nanoscale amorphous solid films of methanol and ethanol

Molecular beam techniques are used to create layered nanoscale composite films of amorphous methanol and ethanol at 20 K. The films are then heated, and temperature programed desorption and infrared spectroscopy are used to observe the mixing, desorption, and crystallization behavior from the initially unmixed amorphous layers. We find that the initially unmixed amorphous layers completely intermix to form a deeply supercooled liquid solution after heating above T(g). Modeling of the desorption kinetics shows that the supercooled liquid films behave as ideal solutions. The desorption rates from the supercooled and crystalline phases are then used to derive the binary solid-liquid phase diagram. Deviations from ideal solution desorption behavior are observed when the metastable supercooled solution remains for longer times in regions of the phase diagram when thermodynamically favored crystallization occurs. In those cases, the finite lifetime of the metastable solutions results in the precipitation of crystalline solids. Finally, in very thick films at temperatures and compositions where a stable liquid should exist, we unexpectedly observe deviations from ideal solution behavior. Visual inspection of the sample indicates that these apparent departures from ideality arise from dewetting of the liquid film from the substrate. We conclude that compositionally tailored nanoscale amorphous films provide a useful means for preparing and examining deeply supercooled solutions in metastable regions of the phase diagram.     

十一种壳聚糖衍生物的紫外吸收特性

十一种壳聚糖衍生物的紫外吸收特性;壳聚糖;胆甾液晶;紫外光吸收剂;化妆品