Polyelectrolytes surfactant systems

The early stages of the process are very similar to those occurring in corresponding systems of mixtures of oppositely charged organic polyelectrolyte and surfactant. Organic polyelectrolyte-surfactant systems are much easier to investigate, however, because of the absence of further polymerization reactions, which enables studies to be carried out under equilibrium conditions. It... 

Particles or macroscopic solid surfaces are present in most of the applications mentioned above. Hence it is important to know how polyelectrolytes and surfactants interact with each other at solid-liquid interfaces. Due to the slow equilibration in many polyelectrolyte-surfactant systems, particularly at interfaces, it is fruitful to distinguish between two situations. In the first case the polyelectrolyte is initially adsorbed at the solid-liquid interface and then the polyelectrolyte is removed from the solution before the surfactant is added. This mimics the situation in many cleaning applications. Most of the studies concerned with polyelectrolyte-surfactant interactions at solid-liquid interfaces belong to this category. 

In this review we focus on polyelectrolyte-surfactant interactions at solid-liquid interfaces as studied with surface force measuring techniques. The last years have seen much progress in this area, and it is timely to recapitulate some main findings. It is, however, clear that in order to understand interfacial properties of polyelectrolyte-surfactant systems one needs to understand bulk association. Further, a multitude of experimental techniques needs to be applied. Recent advances have been made using ellipsometry [34,35], reflectometry [36,37], neutron reflectivity [38], and surface sensitive spectroscopic techniques [39,40], It is also our belief that the... 

Because the main driving force for surfactant self-association in polymer-surfactant mixed systems is the hydrophobic effect, the binding of surfactants to polyelectrolytes exhibits a similar dependence on the length of the alkyl chain as known for free micellization. Surfactants with longer hydrocarbon chains bind more strongly to polyions than those with shorter chains, and the binding starts a lower surfactant concentrations. In this context, a convenient parameter to characterize polyelectrolyte-surfactant systems is the critical aggregation concentration, cac, which is a counterpart of the well-known critical micellization concentration, cmc, but applies to solutions of surfactants in the presence of a polymer. It is defined as the... 

POLYELECTROLYTE-SURFACTANT SYSTEMS SHOW A COMPLEX BEHAVIOUR... 

Lamellar structures of polymer/surfactant systems were studied for polyelectrolyte/surfactant systems [37] as well as for coordination complexes [38]. 

Li, D., M. S. KeUcar, and N. J. Wagner (2012). Phase behavior and molecular thermodynamics of coacervation in oppositely charged polyelectrolyte/surfactant systems A cationic polymer JR 400 and anionic surfactant SDS mixture. Langmuir 28(28) 10348-10362. 

The polyelectrolyte coated surface is uncharged, or in the case of AM-MAPTAC-30 weakly positively charged, before SDS is added. When SDS associates with an uncharged polyelectrolyte layer it will result in a recharging of the interface which results in the development of an electrostatic double layer and a less favorable polyelectrolyte-surface interaction. Thus, the polyelectrolyte-surfactant association at the mica surface is counteracted by electrostatic forces. Instead, it is driven by the hydrophobic interaction between the surfactant tails. This is confirmed by the cooperative nature of the association process observed for all polyelectrolyte-surfactant systems studied in this report. It is well known that hydrophobic interactions are very important also for the association between polyelectrolytes and surfactants in bulk solutions as demonstrated by the cooperativity of this process [16]. The... 

However, contrary to other polyelectrolyte-surfactant systems [39-42], the precipitate does not redissolve with an excess of surfactant, at least in the examined, very broad, interval of concentrations. The difficulty of the redissolution of complexes composed of very highly charged polymers has also been observed in some other studies [41, 43, 44]. 

Interpolymer, polymer-surfactant, and coordination complexes of polybetaines are less developed. The cascade -type complexation observed for the polybetaine-polyelectrolyte system is similar to the layer-by-layer deposition found for oppositely charged polyelectrolytes. The behavior of the polybetaine-surfactant system differs from that of polyelectrolyte-surfactant and polyampholyte-surfactant complexes, leading to inter- or intramolecular comicellization or converting the whole macromolecule to either a polycation or polyanion. 

The most common emulsions used in dermatological therapy are creams. These are two-phase preparations in which one phase (the dispersed or internal phase) is finely dispersed in the other (the continuous or external phase). The dispersed phase can be either hydrophobic based (oil-in-water creams, O/W) or aqueous based (water-in-oil creams, W/O). Whether a cream is O/W or W/O is dependent on the properties of the system used to stabilize the interface between the phases. Given the fact that there are two incompatible phases in close conjunction, the physical stability of creams is always tenuous, but may be maximised by the judicious selection of an appropriate emulsion stabilizing system. In most pharmaceutical emulsions, stabilizing systems are comprised of either surfactants (ionic and/or non-ionic), polymers (non-ionic polymers, polyelectrolytes or biopolymers) or mixtures of these. The most commonly used surfactant systems are sodium alkyl sulphates (anionic), alkylammonium halides... 

A surprising result was obtained for both cationic gel-anionic surfactant systems The metal-containing samples appear not less ordered than the initial polyelectrolyte gel-surfactant complexes despite the diminished amplitudes of the peaks. For the PDADMACl-SDBS system, the average distance between... 

This family of noncovalently bonded PLCs may also include polyelectrolyte + surfactant complexes which, as will be seen, can also give rise to liquid crystalline mesophases. In these complexes there is only a flexible alkyl chain attached to the ionic head group in the small molecule constituent, with no rigid aromatic core present. Since surfactants themselves are frequently thermotropic liquid crystals, it is not surprising that their complexes with polyelectrolytes may produce PLCs, in both cases driven by the incompatibility between the ionic and aliphatic parts leading to amphitropic systems [27]. 

Thalberg, K. and Lindman, B., Polyelectrolyte-ionic surfactant systems phase behavior and interactions, in Surfactants in Solution, Mittal, K. and Shah, D.O. (eds.). Plenum Press, New York, 1991, pp. 11, 243. 

Complex coacervation is similar to simple coacervation where another complimentary polyelectrolyte is used. Gelatin and gum arabic is a well-estabHshed system for microencapsulation by complex coacervation. Mayya et al. have reported a two-layer encapsulation of paraffin oil, based on a primary layer of interface active polyelectrolyte-surfactant complex, followed by a second layer of the conjugate polyelectrolyte-polyelectrolyte complex [41]. The procedure involves the dispersion of paraffin oil in 1% gelatin solution (pH adjusted to 6.5) containing SDS having concentration less than its CMC, followed by drop-wise addition of the solution of the other polyelectrolyte (1% gum arabic) into the dispersion. The pH is then ad-... 

Successful attempts have been made to modify/minimize preeipitation in polyelectrolyte/oppositely charged surfactant systems. Laurent and Scott (65) reported such an effect with the addition of simple salts and defined a critical electrolyte concentration (c.e.c.) at which precipitation is totally inhibited. (See Chapter 5 and also Section III.E below.) Likewise, Dubin et al. (66,67) have found inhibitory effects on adding nonionic surfactants to these mixed polymer/surfactant systems, presumably a result of mixed micelle formation. 

Surface tension studies, yielding results similar to the above, have been obtained on other combinations of polyelectrolyte/oppositely charged surfactant systems. These include poly-L-lysine/SDS (75), carboxymethylcellulose/alkyl TAB surfactants (76), and sulfonated polyacrylamide/DTAB (77,78) combinations. 

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