Lecithin Organogels in a Hydrocarbon Oil

We demonstrated the existence of lecithin organogel at 20°C in a system containing the following components: phospholipid mixture with 40 wt % of phosphatidylcholine, hydrocarbon (vaseline) oil, and water, at phosphatidylcholine concentrations above 1.2 wt % and in the range of W = [H₂O]/[lec] values varying from 3.25 to 7.0. The dependences of the viscosity of lecithin organogels in a hydrocarbon oil on water and lecithin concentrations, as well as on temperature were established.     

Lecithin Organogels Containing Poly(ethylene glycol) Monolaurate

The effect of added poly(ethylene glycol) monolaurate (PEGML) on the formation and properties of lecithin organogels composed of polymer-like micelles was studied by the methods of dynamic rheology and the Fourier transform IR spectroscopy. It was established that the addition of even small amounts of PEGML causes a significant decrease in viscosity, whereas the elastic properties of organogels remained almost unchanged. The analysis of the scaling dependences indicated that the formation mechanism of polymer-like lecithin micelles remained also unchanged. Spectral studies revealed that the PEGML molecules affect intermolecular hydrogen bonding during their incorporation into micelles, thus stabilizing micellar structure. This effect is caused by the partial dehydration of the lecithin polar region. This leads to a decrease in the number of hydrogen bonds or their weakening and, as a result, to the disintegration of polymer-like lecithin micelles into shorter micellar aggregates.     

Tillandsia-Inspired Hygroscopic Photothermal Organogels for Efficient Atmospheric Water Harvesting

Tillandsia species with degenerated roots have evolved into hygroscopic leaves that absorb moisture from air. This interesting biological adaptability has inspired us to develop an integrated hygroscopic photothermal organogel (POG) to achieve a solar-powered atmospheric water harvesting (AWH). The well-designed hydrophilic co-polymeric skeleton is fabricated to accommodate hygroscopic glycerin medium, which enables the POG self-contained property, mechanically flexibility and synergistic enhancement of moisture sorption. The integration of interpenetrated photothermal component of poly-pyrrole-dopamine (P-Py-DA) can endow the POG an efficient solar-to-thermal property for controllable solar-driven interfacial water releasing. The integrated POG has an equilibrium moisture sorption of 16.01 kg m⁻² at the RH of 90 %, and daily water production as high as 2.43 kg m⁻² day⁻¹ is achieved in actual outdoor experiments.     

Effects of Additives on Lipase Immobilization in Microemulsion-Based Organogels

An inexpensive, facile, and environmentally benign method was developed to improve the activity and stability of Candida rugosa lipase (triacylglycerol acylhydrolase) immobilized on microemulsion-based organogels (CRL MBGs) via the addition of additives during immobilization. The additives used were polyethylene glycol (PEG) or polysaccharides. This study is the first report on the effect of additives in CRL MBGs. Among the tested additives, PEG produced the most improvement in the immobilized CRL, enhancing its stability in organic solvents (specifically polar solvents). The results of circular dichroism and fluorescence spectra experiments indicated that exposure of the acidic CRL to electronegative additives in the buffer, such as polyethylenimine and the electropositive surfactant cetyltrimethylammonium bromide, may change the lipase secondary structure, ultimately causing enzyme inactivation. However, sodium bis(2-ethylhexyl)sulfosuccinate and PEG 2000 had minimal effects on the secondary structure of CRL. The CRL MBGs containing PEG 2000 demonstrated remarkable retention of their catalytic activity during the recycling test. No significant changes in enzymatic activity were observed, even after nine runs, and 90 % of the original yield was maintained after 15 cycles.     

Phase Diagram of Gelatin Plasticized by Water and Glycerol

Summary: Gelatin is widely used in capsules manufacturing. Most of the capsules in pharmaceutical applications are hard capsules made out of concentrated solutions of gelatin, where water has been progressively removed during the drying process. More recently soft capsules found an increasing interest in pharmaceutical and cosmetic applications where they are filled and sealed with a liquid substance. In order to keep the shells of capsules flexible after drying at room temperature, plasticizer is added to the gelatin aqueous solutions. We present in this paper a systematic investigation of gelatin films, equilibrated under a range of relative humidity (RH). The films contain glycerol as plasticizer P or only water and gelatin, (G). In order to analyze the role of the plasticizer, we fixed various P/G ratios and measured the water retention versus RH. Films were characterized by DSC (Mettler Toledo DSC823). Glass transition temperature T_g, melting temperature T_m and enthalpy associated with helix-coil transition were determined. The role of water and glycerol was examined in relation with the large variations of these transition temperatures with film composition. Non equilibrium effects are also discussed, in particular concerning the glass transition temperature, the relaxation effects and the water repartition between amorphous coils and helical structure. In conclusion, we propose a unique phase diagram of the gelatin films with any proportion of water and glycerol.     

甘油-水-氯化钠三元溶液中甘油浓度对甘油自扩散系数的影响

利用分子动力学模拟方法研究了浓度对甘油-水-氯化钠三元溶液中甘油自扩散系数的影响. 随着甘油浓度的增大, 甘油的自扩散系数逐渐减小. 氢键分析表明, 甘油自扩散系数的减小来源于其参与的甘油-水氢键数目的减少和甘油-甘油氢键数目的增加.     

Reversibly Thermosecreting Organogels with Switchable Lubrication and Anti-Icing Performance

Synthetic gels with switchable interfacial properties have great potential in smart devices and controllable transport. Herein, we design an organogel by incorporating a binary liquid mixture with an upper critical solution temperature (UCST) into a polymer network, resulting in reversible modulation of lubrication and adhesion properties. As the temperature changes, the lubricating mechanism changes reversibly from boundary lubrication to hydrodynamic lubrication due to phase separation within the binary solution permeating the gel (friction coefficient 0.4–0.03). Droplets appear on the gel surface at low temperature and disappear with temperature higher than the critical phase separation temperature (T_ps) of the organogel. The organogel possesses a relatively low ice adhesive strength (less than 1 kPa). This material has potential applications in anti-icing and smart devices, and we believe that this design strategy can be expanded to other systems such as aqueous solutions and hydrogels.     

Volumetic Properties of Glycerol with N,N-Dimethylformamide and with Water at 25 and 35°C

Densities of glycerol + N,N-Dimethylformamide (DMF) and glycerol + water mixtures have been measured over the full range of compositions at 25 and 35°C. Excess molar volumes and excess partial molar volumes, of each system have been calculated. All mixtures show negative values of the excess molar volume due to increased interactions between unlike molecules.     

Determination of Glycerol and Serum Triglycerides with Collagen-Immobilized Glycerol Dehydrogenase and Amperometric Detection

Abstract

An amperometric procedure is described for the determination of glycerol and triglycerides in aqueous samples and in serum using glycerol dehydrogenase immobilized on a collagen membrane. Glycerol is determined by measurement of the steady-state oxidation currents generated at a platinum electrode by NADH produced in the enzyme-catalyzed reaction. The triglycerides were first hydrolyzed by the enzyme lipase in solution and the resulting glycerol determined similarly. Olive oil, determined to contain 78 % triolein, was used as the source of triglycerides in this study. For both glycerol and triglycerides the calibration plots are linear in the range from 0 to 12 μM, with detection limits of 0.2 and 0.7 μM, respectively. The immobilized glycerol dehydrogenase retained high operational activity for a period longer than 30 days.     

Lecithin organogels with n-alkyl-D- glucosides and n-alkly-D-lactobionamide

 Jelly-like phases formed by mixtures of soybean lecithin with pure n-dodecyl-β-D-glucopyranoside (DDPG), commercial alkylpoly-glucoside (APG) or n-dodecyl-β-D-lactobionamide (DLBA) in decane in the presence of small amounts of water were studied by oscillating rheology and FT-IR-spectroscopy. It was established that the sugar derivatives can modify the rheological properties of lecithin organogels in different ways. The viscosities, the structural relaxation times and the shear moduli decrease with increasing content of DDPG, while the same parameters increase for DLBA. For APG the modulus is increasing while the viscosity and the structural relaxation time are decreasing. By means of FT-IR spectroscopy and examination of the Cole–Cole-plots of the loss modulus vs. the storage modulus it was shown that the sugar derivatives influence both the strength of the hydrogen bonds between the molecules in the polymer-like micelles and the micellar dynamics. Received: 10 November 1997 Accepted: 11 December 1997     

电流变液体的研究进展

电流变液体自从20世纪40年代首次发现以来,由于其广泛的工程应用前景以及潜在的巨大经济和社会效益,已经成为众多研究领域的一个热点.本文综述了电流变液体的组成、电流变材料的研究进展、影响电流变效应的主要因素以及电流变液体研究的应用进展.     

高岭土／羧甲基淀粉复合颗粒的制备及其协同电流变效应

通过二次插层取代法，以二甲基亚砜为前驱体，羧甲基淀粉二次插层取代制备 了高岭土/羧甲基淀粉纳米复合材料。结合XRD，FTIR，SEM和EDS等测试手段对复合 材料的结构进行了表征。研究结果发现，羧甲基淀粉经过二次插层取代引起了高岭 土片层之间的剥离，形成剥离型纳米复合材料。该复合材料制备成电流变液出现了 较大的协同效应，具有很好的电流变行为，并发现电流变性能与复合物中羧甲基淀 粉的含量有密切关系。     

Organogels from liquid and gaseous hydrocarbons

It is shown that n-butane, condensed in autoclave, can readily dissolve the anionic surfactant AOT (bis-2-ethylhexylsodium sulphosuccinate) and that this solution solubilizes water up tow ₀=molar ratio/water-AOT).The microemulsion can be transformed into a gel by solubilizing gelatin in the water microphase. These microemulsion gels are characterized by a very high viscosity (several hundred poise). However, the partial vapour pressure of the n-butane component in the gel is as high as in the liquid state. Infrared studies show that part of the water in the gel is still free.Stability diagrams of this system and¹H-NMR studies to assess the state of water are presented. Analogously to reverse micelles from liquid hydrocarbons, the chemical shift of water protons is shifted to higher fields with respect to bulk water. This effect increases with decreasing temperature andw ₀. At loww ₀ values (< 10), a part of the water in the micelles does not freeze even at –35°C.Due to the rapid evaporation of n-butane from the gel, gelatin films can be prepared simply by casting. Differential scanning calorimetry studies of the gels (from n-butane as well as from isooctane and other hydrocarbons) show that the films have a thermal stability comparable with, and sometimes higher than, gelatin films prepared by conventional methods. Preliminary permeability studies of these films with solutions of amino acid derivatives and with gas such as nitrogen and helium are presented.     

Electrorheological effect in hybrid fluids with liquid crystalline additives

Conventional electrorheological (ER) fluids consist of electrically polarizable particles dispersed in an inert insulating liquid. They are characterized by a development of a yield stress upon application of an external electric field. They resemble Bingham fluids with yield stress value depending on electric field. A viscosity increase in the presence of an electric field has been also found in homogeneous solutions of liquid crystalline polymers with no yield stress observed. In this study these two types of fluids and combined dispersions of the solid particles in the liquid crystalline matrix were investigated. A lyotropic liquid crystalline polymer—poly(n‐hexyl isocyanate) (PHIC)—dissolved in xylene was chosen as the active matrix. The dispersed solid phase was comprised of two kinds of polymers: pyrolyzed polyacrylonitryle (PAN) showing electron conductivity, and PAN doped with two salts (KSCN, NaSCN), resulting in ionic conductivity. The rheological measurements under an electric field were performed. The pristine xylene solution of PHIC was characterized first as well as the 15% m/m dispersions of PAN powders in silicone oil. Then the dispersions in the liquid crystalline matrix were investigated showing a strong ER effect whose magnitude was considerably enhanced in comparison to both ER active components measured separately. Copyright © 2006 John Wiley & Sons, Ltd.     

Supramolecular Organogels Based on Dendrons and Dendrimers

Dendrons and dendrimers have well‐defined, discrete structures that can be precisely controlled at the molecular lever. Owing to their unique architectures and multiple functionalities, dendritic molecules have shown intensive self‐assembly behavior and functional performance. In particular, they have been shown to be promising candidates for applications in the assembly of gel‐phase materials. Furthermore, the introduction of suitable functional moieties into the core, the branches, and/or the periphery of the dendritic gelators enables the construction of smart and functional supramolecular gel materials. Over the past decade, a number of dendritic organogelators that are based on poly(amino acid), poly(amide), and poly(aryl ether) dendrons, or together with multiple alkyl chains on the periphery, have been reported. This review describes the important developments in dendritic organogelators, with an emphasis on new strategies for the molecular design of dendritic gelators, understanding of driving forces for gel formation, and their evolution for potential applications in smart soft materials.     

Reversibly Thermosecreting Organogels with Switchable Lubrication and Anti‐Icing Performance

Synthetic gels with switchable interfacial properties have great potential in smart devices and controllable transport. Herein, we design an organogel by incorporating a binary liquid mixture with an upper critical solution temperature (UCST) into a polymer network, resulting in reversible modulation of lubrication and adhesion properties. As the temperature changes, the lubricating mechanism changes reversibly from boundary lubrication to hydrodynamic lubrication due to phase separation within the binary solution permeating the gel (friction coefficient 0.4–0.03). Droplets appear on the gel surface at low temperature and disappear with temperature higher than the critical phase separation temperature (T_ps) of the organogel. The organogel possesses a relatively low ice adhesive strength (less than 1 kPa). This material has potential applications in anti‐icing and smart devices, and we believe that this design strategy can be expanded to other systems such as aqueous solutions and hydrogels.     

Gelation Behavior of N-Decane Organogels with Gelators C28 and C40

Organogel formation during paraffin crystallization is one of the causes of oilfield problems. We investigated the formation of n-alkane organogels having C₁₀ as liquid phase and n-octacosane (C₂₈) and n-tetracontane (C₄₀) as solid gelators. It was seen that C₁₀/C₂₈ and C₁₀/C₄₀ form organogels with onset gelation temperatures of 33°C and 48°C respectively, while C₁₀/C₂₈/C₄₀, gelify at 52°C. Replacement of C₂₈ by n-heneicosane (C₂₁) reduced the crystallization rate of C₄₀. This result indicates that the onset temperatures and crystallization rates of organogels with gelators in the range of C₂₈ to C₄₀ could be modulated through the introduction of shorter chain n-alkanes.     

Evaluation of Mechanical Properties and Water Vapor Permeability in Chitosan Biofilms Using Sorbitol and Glycerol

Summary: Chitosan biofilms were prepared with and without plasticizer (glycerol and sorbitol). The physical and mechanical properties of chitosan biofilms with and without plasticizer were evaluated. Chitosan was obtained from shrimp wastes and characterized. The film forming solution (FFS) was obtained through chitosan dissolution and drying. The solution had its pH adjusted to 6.0 and oven dried (40 °C, 24 h) with forced air circulation. Chitosan biofilms without plasticizer showed a tensile strength about 36% higher than biofilms produced with plasticizer. On the other hand, biofilms with plasticizer presented superior values of elongation. The permeability of the water vapor and color presented significant difference (p < 0.05) between all biofilms. Chitosan/plasticizer biofilms showed higher values of water vapor permeability in relation to chitosan biofilms without plasticizer.