Interfacial polymeric surfactants

Because almost any diacid can be leaddy converted to the acid chloride, this reaction is quite versatile and several variations have been developed. In the interfacial polymerization method the reaction occurs at the boundary of two phases one contains a solution of the acid chloride in a water-immiscible solvent and the other is a solution of the diamine in water with an inorganic base and a surfactant (48). In the solution method, only one phase is present, which contains a solution of the diamine and diacid chloride. An organic base is added as an acceptor for the hydrogen chloride produced in the reaction (49). Following any of these methods of preparation, the polymer is exposed to water and the acid chloride end is converted to a carboxyhc acid end. However, it is very difficult to remove all traces of chloride from the polymer, even with repeated washings with a strong base. 

The stability of various niosomal formulations depends on factors such as preparation methods, storage temperature, the encapsulated drug, the surfactants, and additive mixture [41,52,64,65], It may be possible to stabilize niosomes by a variety of methods such as the use of membrane-spanning lipids, the interfacial polymerization of surfactant monomers in situ, addition of polymerized surfactants, cholesterol, steric and electrostatic stabilizers to the formulation [41,52]. In general, vesicle aggregation may be prevented by inclusion of... 

The emulsifying properties of these polymeric surfactants demonstrate that the chemical structure influences the kinetic behaviour of interfacial tension reduction. An increase of sulfopropyl moieties reduces the interfacial tension slower while an increase in 2-hydroxy-3-phenoxy propyl moieties reduces the interfacial tension faster. The ionic strength of the emulsion appears to increase the rate of tension reduction. The average droplet size of oil-in-water emulsions in presence of previously dissolved 2-hydroxy-3-phenoxy propyl sulfopropyl dextran is around 180 nm immediately after preparation and increases with time. The presence of ionic moieties appeared to facilitate emulsification at low polymer concentrations due to electrostatic repulsions between the oil droplets [229]. 

Swelling of polystyrene latex particles with styrene. The swelling ratios and the corresponding interfacial tensions for the different-size latexes with added anionic surfactants Aerosol MA and sodium dodecyl sulfate are listed in Table II. Those values obtained with added nonionic surfactant Triton X-100 and polymeric surfactant polyvinyl pyrrolidone are listed in Table III. Figure 1 compares theoretical curves from Model I with all of the experimental data. It is found that a curve corresponding to Xmp = 0.35 fits the data best. Therefore, a semi-empirical... 

Encapsulation. Immobilization of enzymes by encapsulation within semipermeable structures dates back to the 1970s. There are three fundamental variations of this approach. In coacervation, aqueous microdroplets containing the enzyme are suspended in a water-immiscible solvent containing a polymer, such as cellulose nitrate, polyvinylacetate, or polyethylene. A solid film of polymer can be induced to form at the interface between the two phases, thereby producing a microcapsule containing the enzyme. A second approach involves interfacial polymerization in which an aqueous solution of the enzyme and a monomer are dispersed in an immiscible solvent with the aid of a surfactant. A second (hydrophobic) monomer is then added to the solvent and condensation polymerization is allowed to proceed. This approach has been used extensively with nylons, but is also applicable to polyurethanes, other polyesters, and polyureas. 

Harrison KL, daRocha SRP, Yates MZ, Johnston KP, Canelas D, DeSimone JM. Interfacial activity of polymeric surfactants at the polystyrene-carbon dioxide interface. Langmuir 1998 14 6855-6863. 

During emulsification an increase in the interfacial area A takes place and this causes a reduction in T. The equilibrium is restored by the adsorption of surfactant from the bulk, but this takes time (shorter times occur at higher surfactant activity). Thus, e is small whether a is small or large. Because of the lack or slowness of equilibrium with polymeric surfactants, e will not be the same for expansion and compression of the interface. 

Another important use of the PHS-PEO-PHS block copolymer is the formation of a viscoelastic film around water droplets [11, 12] this results from the dense packing of the molecule at the W/O interface, which leads to an appreciable interfacial viscosity. The viscoelastic film prevents transport of water from the internal water droplets in the multiple emulsion drop to the external aqueous medium, and this ensures the long-term physical stability of the multiple emulsion when using polymeric surfactants. The viscoelastic film can also reduce the transport of any a.i. in the internal water droplets to the external phase. This is desirable in many cases when protection of the ingredient in the internal aqueous droplets is required and release is provided on application of the multiple emulsion. 

It should be emphasised that polymeric surfactants prevent the coalescence of water droplets in the multiple emulsion drops, as well as coalescence of the latter drops themselves. This is due to the interfacial rheology of the polymeric surfactant films. As a result of the strong lateral repulsion between the stabilising chains at the interface (PHS chains at the W/O interface and PEO chains at the O/W interface), these films resist deformation under shear and hence produce a viscoelastic film. On approach of the two droplets, this film prevents deformation of the interface so as to prevent coalescence. 

Law TK, Florence AT, Whateley TL. Stabilization of emulsions by interfacial polymerization of poloxamer surfactant derivatives. Colloid Polym Sci 1986 264 167-170. 

Polymeric surfactants are generally (far) more surface active, but they give lower surface pressures than most amphiphiles. At the plateau value of the surface excess they are not very tightly packed (most amphiphiles are), but they extend fairly far into the solution. The exchange between solution and interface may be very slow, and the Gibbs equation does not seem to hold. Most amphiphiles can displace polymers from the interface, if present in sufficient concentration, since they give a lower interfacial tension. Mixed surface layers can also be formed. 

---