Self-emulsification surfactants

Self-emulsification The polymer molecules are modified chemically by the introduction of basic (e.g., amino) or acidic (e.g., carboxyl) groups in such concentration and location that the polymer undergoes self-emulsification without surfactant after dispersion in an acidic or basic solution. 

Figure 1. Effect of Binary Mixture Surfactant Concentration and Self-Emulsification Temperature on Emulsion Droplet Size for the Miglyol 812-Tagat TO System as Determined by Laser Diffraction. Bars Represent Standard Errors.

During the studies of phase behaviour two types of liquid crystalline phases were identified. LC material was viscous and exhibited intense "white" birefingence. material was apparently homogeneous but of low viscosity and exhibited "multi-coloured" birefringence. The liquid crystalline phases observed in the equilibrium studies of surfactant concentrations up to 25 are unlikely to take part in the self-emulsification process due to the presence of two-phase regions between L2 and liquid crystalline phases however, LC material may account for the improved stability of emulsions formed by 25 surfactant systems (Table II). Figure 4c indicates that by increasing the surfactant concentration to 30 the... 

The concept of interfacial mesophases promoting spontaneous emulsification (21.22) can be applied to the Tagat TO - Miglyol 812 system, where stable liquid crystalline dispersion phases are adequate to promote the process of self-emulsification. The stability of the resulting emulsion systems can also be accounted for by liquid crystalline interface stabilisation (23.24). Phase separation of material as observed above 55f surfactant, in conjuction with the increased viscosities of such systems, will inhibit the dynamics of the self-emulsification process and hence the quality of self-emulsified systems declines when the surfactant concentration is increased above 55. ... 

Wakerly, M.G., Pouton, C.W., Meakin, . J., and Morton, F.S. (1986). Self-emulsification of vegetable oil-nonionic surfactant mixtures A proposed mechanism of action. A.C.S. Symposium, 311, 242-255. 

Emulsions are two-phase systems formed from oil and water by the dispersion of one liquid (the internal phase) into the other (the external phase) and stabilized by at least one surfactant. Microemulsion, contrary to submicron emulsion (SME) or nanoemulsion, is a term used for a thermodynamically stable system characterized by a droplet size in the low nanorange (generally less than 30 nm). Microemulsions are also two-phase systems prepared from water, oil, and surfactant, but a cosurfactant is usually needed. These systems are prepared by a spontaneous process of self-emulsification with no input of external energy. Microemulsions are better described by the bicontinuous model consisting of a system in which water and oil are separated by an interfacial layer with significantly increased interface area. Consequently, more surfactant is needed for the preparation of microemulsion (around 10% compared with 0.1% for emulsions). Therefore, the nonionic-surfactants are preferred over the more toxic ionic surfactants. Cosurfactants in microemulsions are required to achieve very low interfacial tensions that allow self-emulsification and thermodynamic stability. Moreover, cosurfactants are essential for lowering the rigidity and the viscosity of the interfacial film and are responsible for the optical transparency of microemulsions [136]. 

In some cases under the conditions similar to those corresponding to the formation of lyophilic colloidal systems, a spontaneous formation of emulsions, the so-called self-emulsification, may take place. This is possible e.g. when two substances, each of which is soluble in one of the contacting phases, react at the interface to form a highly surface active compound. The adsorption of the formed substance under such highly non-equilibrium conditions may lead to a sharp decrease in the surface tension and spontaneous dispersion (see, Chapter III, 3), as was shown by A.A. Zhukhovitsky [42,43], After the surface active substance has formed, its adsorption decreases as the system reaches equilibrium conditions. The surface tension may then again rise above the critical value, acr. Similar process of emulsification, which is an effective method for preparation of stable emulsions, may take place if a surfactant soluble in both dispersion medium and dispersed liquid is present. If solution of such a surfactant in the dispersion medium is intensively mixed with pure dispersion medium, the transfer of surfactant across the low surface tension interface occurs (Fig. VIII-10). This causes turbulization of interface... 

Microemulsions are transparent systems of two immiscible fluids, stabilized by an interfacial film of surfactant or a mixture of surfactants, frequently in combination with a cosurfactant. These systems could be classified as water-in-oil, bicontinuous, or oil-in-water type depending on their microstructure, which is influenced by their physicochemical properties and the extent of their ingredients. - SMEDDSs form transparent microemulsions with a droplet size of less than 50 nm. Oil is the most important excipient in SMEDDSs because it can facilitate self-emulsification and increase the fraction of lipophilic drug transported through the intestinal lymphatic system, thereby increasing absorption from the gastrointestinal tract. Long-chain and medium-chain... 

While studying phase formation when surfactants - hydrocarbon oil mixtures (i.e. three component systems) were added to increasing amounts of water (i.e. forming four component systems) it was observed that those systems which initially developed large quantities of liquid crystalline phases later formed better, finer emulsions than those systems that initially consisted of isotropic phases. These observations and their association with the process of self emulsification or easy emulsion formation in the systems investigated are presented in this report. 

While conducting an investigation into the effect of formulation variables on the self emulsification of hydrocarbon oils, it was observed that the order of increasing reduction in yo/w in the presence of the surfactants employed as well as the extent of formation... 

Patlonlc 1001 is a glycerol mono oleate product. It is derived from natural fats and oils, and incorporates a surfactant for aqueous self-emulsification. 

In self-emulsification or direct emulsification methods, a solution of the oil and surfactant in an appropriate solvent (that is also soluble in the continuous aqueous phase) is simply added to water to form oil-in-water (0/W) emulsions in one step, under agitation. Similarly, a solution of water and surfactant in an appropriate solvent (also soluble in the oil phase) is added to the oil to form water-in-oil (W/0) emulsions [19]. It is called direct or self-emulsification because the emulsion is just obtained by a dilution process without any phase inversion. This method uses the chemical energy of dissolution in the continuous phase of the solvent present in the initial system (which is going to constitute the dispersed phase). When the intended continuous phase and dispersed phase are mixed. 

The so-called self-emulsification is referred to those methods in which the nano-emulsion is just obtained by a dilution process without any inversion of phases. It is also called direct emulsification because the initial emulsion type is that of the intended final emulsion [19]. It should be taken into account that the term self-emulsification is frequently used in the Ulerature to describe emulsification mechanisms, in which not only dilution processes but also processes implying changes in the spontaneous curvature of the surfactant film are involved. Therefore, this terminology is often misleading. 

Miller, C.A., Spontaneous emulsification Recent development with emphasios on self-emulsification. In J. Sjblom, (Ed.), Surfactant Science Series 132 Emulsions and Emulsion Stability, 2nd Edition, pp. 107-126. New York Marcel Dekker, 2006. 

Formation of Hposomal vesicles under controlled conditions of emulsification of Hpids with phosphoHpids has achieved prominence in the development of dmgs and cosmetics (42). Such vesicles are formed not only by phosphoHpids but also by certain nonionic emulsifying agents. Formation is further enhanced by use of specialized agitation equipment known as microfluidizers. The almost spontaneous formation of Hposomal vesicles arises from the self-assembly concepts of surfactant molecules (43). Vesicles of this type are unusual sustained-release disperse systems that have been widely promoted in the dmg and cosmetic industries. 

Aqueous molecular assemblies such as micelles and bilayer membranes are formed by the self-assembly of amphiphihc compounds (Figure 11.la, b) [10]. Aqueous micelles have been utihzed for a variety of apphcations in surfactant industry, including emulsification, washing, and extraction processes [11]. BUayer membranes are basic structural components of biomembranes, and their structures are maintained even in dilute aqueous media. This is in contrast to micelles that show dynamic equihbrium between aggregates and monomeric species. Thus bilayers are more stable and sophisticated self-assemblies, and they require suitable molecular design of the constituent amphiphiles. BUayer membranes and vesicles have wide-ranging applications, as exemphfied by drug dehvery [12], sensors [13], and bilayer-templated material synthesis [14]. 

There are a large number of methods (Table 2) to prepare nanoparticulate systems. These depend to a large extent on the material (polymer, protein, metal, ceramic) that will form the basis of the carrier. One can, in essence, consider three approaches to their production (0 by comminution (in the case of solids, milling, and in the case of liquids, high pressure emulsification) (ii) molecular self-assembly, such as that occurs with polymeric surfactants to form polymeric micelles or with dendrons to form dendrimeric aggregates and (iii) precipitation from a good solvent as shown in Figure 6. 

In all of the above formulations, the role of surface chemistry is crucial, both in the formulation of the product and its subsequent application. Even for simple formulations of water-soluble actives, surface-active agents (sometimes referred to as wetters ) are needed to enable the spray solution to adhere to the target surface and spread over a large area. The surface-active agents also play a more subtle role in optimization of biological efficacy. With self-emulsifiable oils (referred to as emulsifiable concentrates (ECs)), surfactants are added in high concentrations to ensure the spontaneity of emulsification on dilution. The adsorption and conformation of the surfactant molecules at the oil/water (OAV) interface is crucial for spontaneous emulsification of the oil... 

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