Thermo‐mechanical properties of candelilla wax and dotriacontane organogels in safflower oil

The thermo‐mechanical properties of organogels developed by a complex mixture of n‐alkanes present in candelilla wax (CW) were investigated and compared with the ones of organogels developed by a pure n‐alkane, dotriacontane (C₃₂). In both cases, the liquid phase used was safflower oil high in triolein (SFO) and the variables studied were two levels of gelator concentration (1 and 3%), cooling rates of 1 and 10 °C/min, and two gel setting temperatures, 5 and 25 °C (T_set). Based on comparisons of the organogels made with C₃₂, the presence of minor molecular components in CW had a profound effect on the crystal habit of the n‐alkanes in CW‐based organogels, and therefore on their physical properties. Thus, independent of the cooling rate and T_set, C₃₂ showed a higher solubility and higher self‐assembly capability in the SFO than CW. Nevertheless, for the same gelator concentration and time‐temperature conditions, C₃₂ organogels had lower G' profiles than CW organogels. Additionally, independent of the type of gelator, more stable organogel structures were developed at T_set = 5 °C and using the lower cooling rate. The rheological behavior of the organogels was explained considering the formation of a rotator phase by the n‐alkanes, its solid‐solid transition, and their dependence as a function of the cooling rate and T_set. The results here obtained showed that it is possible to gelate SFO through organogelation with CW and without the use of trans fats.     

The influence of the type of oil phase on the self‐assembly process of γ‐oryzanol + β‐sitosterol tubules in organogel systems

Mixtures of γ‐oryzanol and β‐sitosterol were used to structure different oils (decane, limonene, sunflower oil, castor oil, and eugenol). The γ‐oryzanol and β‐sitosterol mixtures self‐assemble into double‐walled hollow tubules (～10 nm in diameter) in the oil phase, which aggregate to form a network resulting in firm organogels. The self‐assembly of the sterol molecules into tubules was studied using light scattering and rheology. By using different oils, the influence of the polarity of the oil on the self‐assembly was studied. The effects of temperature and structurant concentration on the tubuler formation process were determined and the thermodynamic theory of self‐assembly was applied to calculate the change in Gibbs free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰) resulting from the aggregation of the structurants was determined. The self‐assembly was found to be enthalpy‐driven as characterized by a negative ΔH⁰ and ΔS⁰. A decreasing polarity of the oil promotes the self‐assembly leading to formation of tubules at higher temperatures and lower structurant concentrations.     

Structure and Physical Properties of Organogels Developed by Sitosterol and Lecithin with Sunflower Oil

High linoleic acid sunflower oil (HLSO) with various sitosterol (Sit) to lecithin (Lec) mass ratios (i.e., 0:100–100:0) were used to develop organogels at two storage temperatures (T_s: 5 and 25 °C). The results showed that, at 25 °C, the hardness value of organogels obtained from HLSO with both Sit and Lec was higher than that of organogels developed from HLSO with only Sit or Lec. Microscopy revealed that the shapes of the crystals in the organogels varied significantly with the composition of the structurant and the T_s. At both T_s used, the Sit:Lec (80:20) system had a lower degree of supersaturation compared with the (100:0) system. X‐ray diffraction (XRD) revealed that Sit:Lec mass ratio of 70:30, 80:20 and 100:0 had similar short spacings, and the presence of Lec might be adverse to the formation of Sit crystal in oil. Small‐angel X‐ray scattering (SAXS) showed that the layer thickness of Sit/Lec/HLSO organogel was larger than that of Sit/HLSO organogel. It was found that the presence of Lec induced the change of self‐assembly structure of Sit in HLSO and caused the changes of physical properties of organogels obtained.     

Stabilization of meat suspensions by organogelation: A rheological approach

The stabilization of suspensions is a relevant issue in several industrial applications and particularly in the food area. Water‐based systems are widely studied and they are commonly stabilized by the addition of hydrocolloids (such as polysaccharides or proteins) whereas for oil‐based products less information is available. In this paper, oil‐based meat suspensions are investigated, and the addition of organogelators is proposed as a potential solution to the stability problems currently observed in some practical applications. Investigated suspensions are obtained by grinding a meat phase with vegetable oil blends, thus yielding products typically used in the traditional southern Italian diet as spreadable spicy sauces or as oil‐based dressings for pizzas. The effects of proposed additives were investigated by destabilizing the modified suspensions (by centrifugation) and comparing their rheological characteristics and oil loss to those of the unmodified systems (i.e., without addition of stabilizers). It was observed that both additives exert a stabilizing action, even if one of them (monoglycerides of fatty acids) is more effective than the other, even at a very low concentration. The adopted rheological approach has proved very useful to determine the type and amount of the proper organogelator to be used as an oil suspension stabilizer.     

Self-Assembly of Saturated and Unsaturated Phosphatidylcholine in Mineral and Vegetable Oils

We studied the molecular self-assembly of commercial and pure-saturated and pure-unsaturated phosphatidylcholine (PtdCho) in vegetable (VO) and mineral (MO) oils. The PtdCho self-assembly was monitored through rheology, differential scanning calorimtery (DSC), and polarized light microscopy. The results showed that in the presence of just the constituent water, the PtdCho self-assembly occurred through the formation of a “liquid structure” stabilized by electrostatic interactions. The DSC measurements did not evidence the development of the “liquid structure.” However, the phase shift angle (δ) measured by rheology closely followed the PtdCho self-assembly in both oils. The kinetics of the PtdCho self-assembly and the crystal habit developed depended on the PtdCho solubility in the oil, the PtdCho purity, and the extent of unsaturation. Thus, the saturated PtdCho crystallized in the VO developing an organization of intertwined crystals that resulted in organogels with a true-gel behavior (G′ of 12.2 × 10⁵ to 16 × 10⁵ Pa). In the MO, the saturated PtdCho crystallized in smaller microstructures developing organogels with higher G′, particularly with the commercial PtdCho (i.e., G′ of 32 × 10⁵ Pa). With the unsaturated PtdCho, the presence of cis unsaturations favored the formation of inverted micelles in the VO and MO organogels. Thus, in contrast to the saturated PtdCho organogels, the unsaturated PtdCho organogels had lower G′ (30 × 10² to 45 × 10² Pa) with a gel-like behavior.     

Crystalline stability of self-assembled fibrillar networks of 12-hydroxystearic acid in edible oils

The stability of organogels differs based on the organogelator concentration, storage temperature, and solvent type. Organogel post-crystallization annealing was monitored at 5 °C, 15 °C, 20 °C or 30 °C for up to 1 month. Gels, stored at 5 °C, had highly immobilized oil, as judged from large T₂ relaxation peaks at 50–70 ms determined by pulsed nuclear magnetic resonance (pNMR) and visual observations. When the gels were stored at 30 °C, the 50–70 ms T₂ relaxation peak shifted to longer relaxation times, indicating that the oil was more mobile than at 5 °C. Along with the increase in syneresis at 30 °C, the 12HSA network’s crystallinity was also greater, having fewer inclusions of liquid oil, as determined by pNMR. The highly branched network observed at 5 °C changed more in time with regards to crystallinity although it entrained the oil to a much greater extent than the gels stored at 30 °C.     

Light‐Triggered Self‐Assembly of a Spiropyran‐Functionalized Dendron into Nano‐/Micrometer‐Sized Particles and Photoresponsive Organogel with Switchable Fluorescence

The synthesis, self‐assembly, and spectroscopic investigations of spiropyran (SP)‐functionalized dendron 1 are reported. Under UV light irradiation, assembly of 1 into nano‐/microparticles occurs due to the transformation of the closed form of SP into the open merocyanine (MC) form. The formation of these nano‐/microparticles is confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) experiments in addition to the confocal laser scanning microscopy (CLSM) measurements. These nano‐/microparticles exhibit relatively strong red emission. It is interesting to note that the direct cooling of the toluene/benzene solution of 1 to 0 °C leads to gel formation. Multivalent π–π interactions due to the dendron in 1 may be the driving‐force for the gelation. The UV light irradiation cannot destroy the gel phase, and in fact, the gel–gel transition is successfully realized. The purple‐blue gel exhibits relatively strong red fluorescence; moreover, the fluorescence can be reversibly switched by alternating UV and visible light irradiation. The results clearly indicate that the MC form after aggregation becomes more stable and fluorescent.     

长链烷氧基芳香醇凝胶因子的合成及性能

为了研究有机凝胶的溶剂效应,合成了单链烷氧基芳香醇系列化合物S-C12、S-C14、S-C16及三链化合物T-C14。测试了它们的凝胶性能并分析了侧链的影响。阴离子测试结果表明,该系列凝胶化合物可以对氟离子刺激作出响应。运用扫描电子显微镜观察并分析了凝胶的微观形貌,并通过核磁共振光谱及红外光谱研究了系列化合物的成胶驱动力。红外光谱中,溶液状态下游离态羟基吸收波数(3 673 cm~(-1))较凝胶状态下(3 651cm~(-1))发生了蓝移,由此证明氢键是凝胶形成的重要驱动力。计算了凝胶因子S-C14及14种有机溶剂的梯氏参数并绘制了梯氏图,获得S-C14在有机溶剂中形成凝胶的预测区域,并对该预测区域的有效性进行了验证。采用Kamlet-Taft参数法分析并明确了溶剂得失氢键能力以及溶剂极性对所合成化合物凝胶性能的影响,并利用文献报道的系列凝胶因子对所得结论的一致性进行了验证。     

Cyclic voltammetry investigation of diffusion of ferrocene within propylene carbonate organogel formed by gelator

Propylene carbonate organogel containing LiClO₄ was formed in the presence of gelator bis-(4-stearoylaminophenyl) methane (BSAPM). The electrochemical behavior and diffusion of ferrocene (Fc) and ferricenium (Fc⁺) entrapped within the organogel was investigated by cyclic voltammetry. The Fc molecules still show redox activity within the organogels in comparison with corresponding solutions of propylene carbonate containing LiClO₄. The shape of the cyclic voltammograms of the Fc electrooxidation in organogel was similar to that in corresponding solutions. The results indicated that redox reactions of Fc/Fc⁺ were a quasi-reversible process of diffusion-controlled single electron transfer in organogels. The diffusion coefficients of Fc and Fc⁺ in organogels decreased with an increase of the concentration of gelator BSAPM, but increased with an increase of temperature. The temperature dependence of the diffusion coefficient in organogels followed classical Arrhenius equation. The activation energy in organogels was found of no difference from that in corresponding solutions.     

Structure and dynamics of hydrogels and organogels: An NMR spectroscopy approach

Hydrogels and organogels are semi-solid systems, in which a liquid phase is immobilized by a three-dimensional network composed of self-assembled, intertwined polymer/gelator fibers. Investigations pertaining to these systems have only picked up speed in the last few decades. Consequently, many burning questions regarding these systems, such as the specific molecular requirements guaranteeing gelation, still await definite answers. Nonetheless, the application of different hydrogels and organogels to various areas of interest, i.e., as drug delivery devices, has been quick to follow their discoveries.The use of NMR spectroscopy for the characterization of polymer hydrogels and organogels has recently seen enormous growth. The NMR measurements involving magic angle spinning (MAS) in the solid-state NMR, spin relaxation times, nuclear Overhauser enhancements (NOE), or multiple-quantum (MQ) spectroscopy, the pulse field gradient (PFG) technique and magnetic resonance imaging (MRI) allow obtaining the detailed information on morphology, molecular organization, specific interactions and internal mobility of constituents.This review aims at providing a global view and capabilities all of these NMR methods in comprehensive studies of hydrogels and organogels, with special emphasis on the interplay between the morphology and molecular mobility of constituents and the intermolecular interactions.