Surfactant systems types

Although spray-dryiag accommodates relatively high content of surfactants, certain types, such as the alkanolamides and some nonionic surfactants are best added to the product after spray-dryiag. Post additioa aot only protects the surfactant from the heat of the tower but also prevents the formation of aerosols ia the exit gas. Aerosols are more difficult to trap ia the scmbbiag system than soHd fines. They are formed by unsulfonated matter from the manufacture of LAS and nonionic surfactants with short ethylene oxide chains (120). 

When the variation of any colligative property of a surfactant in aqueous solution is examined, two types of behavior are apparent. At low concentrations, properties approximate those to be expected from ideal behavior. However, at a concentration value that is characteristic for a given surfactant system (critical micelle concentration, CMC), an abrupt deviation from such behavior is observed. At concentrations above the CMC, molecular aggregates called micelles are formed. By increasing the concentration of the surfactant, depending on the chemical and physical nature of the molecule, structural changes to a more... 

Furthermore, Oda et al. pointed out that there are two topologically distinct types of chiral bilayers, as shown in Figure 5.46.165 Helical ribbons (helix A) have cylindrical curvature with an inner face and an outer face and are the precursors of tubules. These are, for example, the same structures that are observed in the diacetylenic lipid systems discussed in Section 4.1. By contrast, twisted ribbons (helix B) have Gaussian saddlelike curvature, with two equally curved faces and a C2 symmetry axis. They are similar to the aldonamide and peptide ribbons discussed in Sections 2 and 3, respectively. The twisted ribbons in the tartrate-gemini surfactant system were found to be stable in water for alkyl chains with 14-16 carbons. Only micelles form... 

Thus, with nonionic surfactants, both types of micremulsions can be formed depending on the conditions. As shown above, with such systems temperature is the most crucial factor since the solubility of the surfactant in water or in oil depends on the temperature. One should remember that in aqueous solutions, the solubility of nonionic ethoxylated surfactants decreases with increase of temperature, whereas the reverse is true with oil solutions. 

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... 

Surfactants are employed in nanoparticle suspensions. Chen et al. (2002) evaluated the pre paration of amorphous nanoparticle suspensions containing cyclosporine A using the evaporative precipitation into aqueous solution (ERAS) system. The effect of particle size was studied varying the drug surfactant ratios, type of surfactants, temperature, drug load, and solvent. Acceptable particle sizes suitable for both oral and parenteral administration were also studied. Additional articles in the nanoparticle delivery of poorly water-soluble drugs include Kipp (2004), Perkins et al. (2000), Young et al. (2000), and Tyner et al. (2004). 

Previous work has shown that binary surfactant systems containing Dowfax 8390 and the branched hydrophobic surfactant AOT can form Winsor III systems with both PCE and decane whereas DOWFAX 8390 by itself cannot (Wu et. al. 1999). This binary surfactant system was used in conjunction with hydrophobic octanoic acid to help with phase behavior and lessen the required concentration of CaCl2. Since this formulation is rather complicated, questions about field robustness arise. Thus, for the phase behavior studies presented here, we used the simple binary system of the nonionic TWEEN 80 and the branched hydrophobic AOT, and we optimized the NaCl concentration to give the Winsor Type III system. The lesser electrolyte concentration requirement for the binary TWEEN 80/ AOT system helps to decrease the potential for undesirable phase behavior such as surfactant precipitation, thereby increasing surfactant system robustness. 

Figure 5. Phase Diagram for hexadeeane (EACN=16) at 22°C for 2% AOT, 2% Tween 80, and NaCl. The open circles are data. The closed squares represent the phase diagram for a surfactant system which progresses through types ]4=>IIle II with neither phase separation nor precipitation.

The more hydrophobic surfactant system, AOT/TWEEN 80, exhibited the classical Winsor type I <=>III<=>II phase progression for diesel (Figure 4). This surfactant system also formed a middle phase containing equal volumes of hexadecane and water. At present it has not been determined if the classical Winsor Type I-III-II progression occurs for commercial motor oil (EACN = 22.3) with the AOT/Tween 80 system. 

The surfactant system AOT/TWEEN 80 removed 99.4% of residual hexadecane from glass beads in 4.7 pore volumes with a total of 49.6% recovered as free phase, 31.1% recovered as micellarly solubilized, and 18.7% recovered as microemulsified in the middle phase. These results demonstrate the potential efficiency of supersolubilization (i.e., enhanced solubilization as the type I-III boundary is approached), and mobilization (even if just into the type III system but not yet optimal) in expediting extraction of hydrophobic NAPLs. 

The many remarkable physico-chemical properties of aqueous surfactant systems, as well as their numerous practical applications, can be referred to the tendency of the nonpolar groups to avoid contact with water at the same time as the polar part tends to be strongly hydrated. The adsorption of surfactants at interfaces between aqueous solutions and air, another liquid phase or a solid is one consequence of this, the extensive aggregation into various types of large aggregates termed micelles — from lat. micella meaning small bit — and liquid crystalline phases is another. 

The lung comprises about 40 different cell types, amongst which type I and type II alveolar epithelial cells are the major types targeted by pulmonary drug delivery systems. Type I cells play an important role in the absorption process of proteins, while type II cells produce surfactant, regulate the immune response, and serve... 

Emulsions are a class of disperse systems consisting of two immiscible liquids, one constituting the droplets (the disperse phase) and the second the dispersion medium. The most common class of emulsions is those whereby the droplets constitute the oil phase and the medium is an aqueous solution (referred to as O/W emulsions) or where the droplets constitute the disperse phase, with the oil being the continuous phase (W/O emulsions). To disperse a liquid into another immiscible liquid requires a third component, referred to as the emulsifier, which in most cases is a surfactant. Several types of emulsifiers may be used to prepare the system, ranging from anionic, cationic, zwitterionic, and nonioinic surfactants to more specialized emulsifiers of the polymeric type, referred to as polymeric... 

Marosi, G., Marton, A., Csontos, I., Matko, S., Szep, A., Anna, P., Bertalan, G., and Kiss, E. 2004. Reactive surfactants—New type of additive for multicomponent polymer systems. From Colloids to Nanotechnology 125 189-93. 

Vitamin B6 enzyme models that can catalyze five types of reactions - transamination, racemization, decarboxylation, P-elimination and replacement, and aldolase-type reactions - have been reviewed. There are also five approaches to construct the vitamin B6 enzyme models (i) vitamin B6 augmented with basic or chiral auxiliary functional groups (ii) vitamin B6 having an artificial binding site (iii) vitamin B6-surfactant systems (iv) vitamin B6-polypeptide systems (v) polymeric and dendrimeric vitamin B6 systems. These model systems show rate enhancement and some selectivity in vitamin B6-dependent reactions, but they are still primitive compared with the real enzymes. We expect to see improved reaction rates and selectivities in future generations of vitamin B6 enzyme models. An additional goal, which has not received ade-... 

For a successful incorporation of a pigment into the latex particles, both type and amount of surfactant systems have to be adjusted to yield monomer particles, which have the appropriate size and chemistry to incorporate the pigment by its lateral dimension and surface chemistry. For the preparation of the miniemulsions, two steps have to be controlled (see Fig. 14). First, the already hydrophobic or hydrophobized particulate pigment with a size up to 100 nm has to be dispersed in the monomer phase. Hydrophilic pigments require a hydro-phobic surface to be dispersed into the hydrophobic monomer phase, which is usually promoted by a surfactant system 1 with low HLB value. Then, this common mixture is miniemulsified in the water phase employing a surfactant system 2 with high HLB, which has a higher tendency to stabilize the monomer (polymer)/water interface. 

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