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Encapsulation of Bioactive Compounds
Published in Munmaya K. Mishra, Applications of Encapsulation and Controlled Release, 2019
Francesco Donsì, Mariarenata Sessa, Giovanna Ferrari
Liposomes are spherical bilayers made of amphiphilic molecules, such as phospholipids, which are characterized by an inner hydrophilic water domain physically separated from the bulk of water. Due to their structure, liposomes may enclose bioactive molecules of hydrophilic nature in the inner hydrophilic domain as well as molecules of lipophilic nature in the bilayer. Liposome fabrication is based on the spontaneous association of amphiphilic molecules in a lamellar phase, induced by the proper selection of solvent, concentration, and temperature conditions, followed by its dispersion by intense mechanical disruption or the use of solvent evaporation techniques. Liposomes can be structured in (1) single bilayers, forming unilamellar vesicles, (2) several concentric bilayers, forming multilamellar vesicles, or (3) non-concentric bilayers, forming multivesicular vesicles.143 The use of liposomes in the food industry is limited by the high cost of pure lecithins, which are the most suitable food-grade amphiphilic molecules, the low encapsulation efficiency, and the complicated and costly fabrication process.
Aggregation Behavior in One-Phase (Winsor IV) Microemulsion Systems
Published in Promod Kumar, K. L. Mittal, Handbook of Microemulsion Science and Technology, 2018
Shmaryahu Ezrahi, Abraham Aserin, Nissim Garti
The lamellar phase (designated Lα) consists of alternating stacks of infinite planar bilayers (also designated as membranes) separated by intervening layers of solvent, usually water, and arranged parallel to one another [85,111]. The surfactants in the bilayers are organized in such a way that the hydrophobic tails of the surfactant molecules are at the center of the lamellae and the hydrophilic portions of the molecules are in contact with the solvent layer [112]. This phase exhibits quasi-long-range positional solid-like order (even at high dilution [108]) along the direction perpendicular to the layers. In the two other in-plane directions the system is liquidlike, i.e., the solvent and surfactant molecules are free to move in this plane [111] (Fig. 9). Stable lamellar phases are almost ubiquitous in the concentrated region of the phase diagrams of binary and multicomponent systems. However, their existence in very dilute solutions has only recently been observed and studied systematically
Emulsions and Microemulsions
Published in K.S. Birdi, Surface Chemistry and Geochemistry of Hydraulic Fracturing, 2016
Near the surfactant region, one finds the crystalline or lamellar phase. This is the region in which one finds hand soaps. Ordinary hand soap is mainly salts of fatty acid (coconut oil, fatty acids, or mixtures) (85%) plus water (15%) and some salts and so on. X-ray analyses have shown that the crystalline structure consists of a series of a layer of soap separated by a water layer (with salts). The hand soap is produced by extruding under high pressure. This process aligns the lamellar crystalline structure lengthwise. It is further found that complex structures are present in the other regions in the phases (Figure 8.2). The diagram is strongly dependent on temperature.
Detergents in the coacervate form with plant extracts obtained under supercritical carbon dioxide conditions as examples of sustainable products
Published in Journal of Dispersion Science and Technology, 2020
Artur Seweryn, Tomasz Wasilewski
In the case of applications hydrophobic phase (extract) in compositions, intramicellar solubilization occurs. The micelles transform into aggregates containing a hydrophobic substance, and an adsorptive surfactant layer forms on their surface. The addition of consecutive portions of sodium chloride to the starting formulations led to changes in the viscosity of the systems, which can be attributed to transformations in the structure of the bulk phase of the surfactant solution. In the case of the analyzed washing agents, it is a multi-component system containing both ionic and nonionic surfactants. The effects observed in washing agents include both the disappearance of the zeta potential of ionic surfactants and the dehydration of polyoxyethylene chains of nonionic surfactants in mixed micelles arising from both types of compounds. After the addition of salt mixed micelles are transformed into cylindrical micelles. A consequence of this structure of the solution is its relatively high viscosity. At the electrolyte concentration characteristic of the product cylindrical micelles are transformed into flat micelles which as referred to as lamellae. The bulk phase of the solution reveals a liquid crystalline lamellar phase (so-called Lα phase). Further transformations occur at the next electrolyte portions. The flat micelles of the lamellar phase start forming clusters arranged in onion-like layers, creating lamellar droplets (vesicles) which, after achieving an appropriate size, may separate from the solution. Where this happens, a biphasic system arises, with one phase built of lamellar droplets and containing a high concentration of surfactants, but with low solvent and salt contents. The phase is referred to as the coacervate.[30–32,46–48] The salt concentrations necessary for the coacervation process to occur in the starting formulations of the detergents, together with the percentage proportions of the phases isolated in the process, are listed in Table 2.
Phase behaviour of alkynyl-terminated bicyclo[3.3.0]octa-1,4-diene ligands: a serendipitous discovery of novel calamitic liquid crystals
Published in Liquid Crystals, 2021
Finn Schulz, Max Deimling, Sabine Laschat
In order to gain further understanding of the mesophase, XRD measurements were performed. Wide-angle X-ray scattering (WAXS) of diene 1a with alkyl chain and 1c with alkyne chain revealed a sharp signal at 2Θ = 3.2° for 1a and 3.3° for 1c and a broad reflex in the wide-angle range with the maximum at 20.2° in both cases (Figures 4(a) and S3). These results matched very well with the proposed lamellar phase. The sharp reflexes can be assigned to the lamellar layers of a smectic phase (001), while the broad signal represents the molten alkyl chains (halo). The XRD data of 1a and 1c are summarised in Table 2. Due to trigonometric reasons, the layer spacing d of 1a is about 1 Å larger than d of alkyne derivative 1c. The linear geometry of the alkyne unit in 1a leads to a longer sidechain despite the shorter bond length. However, in both cases d is about 1 Å smaller than the calculated molecular length [17]. This might be due to random tilts of the molecules and indicates a monolayer. Temperature-dependent SAXS measurements revealed a slight increase of the smectic layer spacing of ca. 0.8% throughout the mesophase (Figure 4(b,c)) contradicting the expected SmA phase. In most cases, orthogonal mesophases decrease their layer spacing upon heating. With higher temperatures, the smectic order partner decreases, and the molecules possess a larger tilt. However, on average, the molecules are still orthogonally aligned with respect to the layer direction. In our case, there must be an antagonistic effect to the diffuse cone model [18]. This phenomenon might be caused by the particular nature of the core. The bicyclo[3.3.0]octadiene unit is rigid, but not planar and behaves like an open book scaffold. The angle between the two five-membered rings might change depending on the temperature. This would have a big impact on the overall molecular geometry and therefore counterbalance the expected layer shrinkage caused by a reduced smectic order parameter.