Surfactants behavior

Zhu, J., Shi, Z. (2003). ESI-MS studies of polyether surfactant behaviors in reversed-phase HPLC system. Int. J. Mass Spectrom. 226(3), 369-378. 

Polymer/Surfactant Interactions. Interaction between polymers and surfactants was recently reviewed by Robb (11) and surfactant association with proteins by Steinhardt and Reynolds (12). Polymer/surfactant interactions are highly dependent on the chemical nature of the polymer and the surfactant. In general, surfactants tend to associate with uncharged polymers in aggregates rather than individual surfactant molecules interacting with the macro-molecule. The ability of surfactants to form micelles is thought to be an important factor in the role of surfactant behavior in interactions with polymers. Individual surfactant... 

With monomeric molecules, the aggregation number of micelles is determined by equilibrium thermodynamics. In polymeric molecules, however, topological constraints are imposed on the system. If the degree of polymerization exceeds the aggregation number of the monomeric micelle, unsaturated sites of the polymeric molecules become available (directed to the aqueous phase) and inter-molecular interactions (agglomeration) occur. In the case of polymer with Mw= 6.23x105, typical surfactant behavior was found. 

Florence (1983) provide a comprehensive reference for the use of surfactants in drug formulation development. The treatment by Florence (1981) of drug solubilization in surfactant systems is more focused on the question at hand and provides a clear description of surfactant behavior and solubilization in conventional hydrocarbon-based surfactants, especially nonionic surfactants. This chapter will discuss the conventional surfactant micelles in general as well as update the reader on recent practical/commercial solubilization applications utilizing surfactants. Other uses of surfactants as wetting agents, emulsiLers, and surface modiLers, and for other pharmaceutical applications are nc emphasized. Readers can refer to other chapters in this book for details on these uses of surfactant Polymeric surfactant micelles will be discussed in Chapter 13, Micellization and Drug Solubility Enhancement Part II Polymeric Micelles. 

Based on their data for sorption onto a lake sediment, Kiewiet et al. (1996) derived an equation predicting sorption coefficients of CnEOms as a functions of alkyl chain length and the number of oxyethylene units. Di Toro et al. (1990) proposed a model for description of sorption of anionic surfactants which includes sorbent properties (organic carbon content, cation exchange capacity, and particle concentration) and the CMC as a function of the solution properties (ionic strength, temperature). The CMC is used as a relative hydrophobicity parameter. Since the model takes the contribution of electrostatic as well as hydrophobic forces explicitly into account, it is an example of an attempt to model surfactant behavior on the basis of the underlying mechanisms. 

The key feature of Inisurfs is their surfactant behavior. They form micelles and are adsorbed at interfaces, and as such they are characterized by a critical micelle concentration (CMC) and an area/molecule in the adsorbed state. This influences both the decomposition behavior and the radical efficiency, which are much lower than those for conventional, low molecular weight initiators. Tauer and Kosmella [4] have observed that in the emulsion polymerization of styrene, using an Inisurf concentration above the CMC resulted in an increase in the rate constant of the production of free radicals. This was attributed to micellar catalysis effects as described, for example, by Rieger [5]. Conversely, if the Inisurf concentration was below the CMC the rate constant of the production of free radicals decreased with an increase in the Inisurf concentration, which was attributed to enhanced radical recombination. Also note that a similar effect of the dependence of initiator efficiency on concentration was reported by Van Hook and Tobolsky for azobisisobutyronitrile (AIBN) [6]. 

Successfully developing a surface engineering strategy based on surfactant behavior at interfaces requires surface characterization techniques that can validate and quantify surface chemistry changes. This review describes the role of two surface chemistry analysis techniques that have proven highly successful in surfactant analysis x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). In Section II, the methods by which these techniques analyze surface chemistry are described. In Section III, recent examples of their application in surfactant-based surface engineering are described. 

Such telechelic polyesters show typical surfactant behavior after neutralization with various amines (mono- and diethanol amine, etc...). Micellization has been studied by photon correlation spectroscopy. 

As an approach to investigating the complex chemistry of natural foams, humic substances (compounds sufficiently nonpolar at pH 2.0 to be isolated by reverse phase on XAD-8 and recovered in 0.1 N sodium hydroxide) were isolated from aquatic foam and associated stream water for chemical characterization and investigations into surfactant behavior. Humic substances were chosen because they represent natural organic compounds present in natural waters that are sufficiently nonpolar at pH 2.0 to be isolated by XAD-8 adsorption. As surfactants also possess moderately nonpolar characteristics it follows that humic substances may contain a significant surfactant component. We hypothesized that foam would be enriched in humic substances compared to stream samples and would show increased hydrophobicity, aliphaticity, and decreased carboxylation in order to sustain surface-active behavior. 

Table 1 Trends for material and external variables that promote Type III surfactant behavior...

The n. idea is useful in describing systematically the properties of the low tension state (19). It has similar status to the "optimal salinity" favored by other authors 0-5). The one considers the oil required to give the best low tension when all other variables are held constant, the other looks for the salinity required for low tension against a given oil. Similar information about surfactant behavior is yielded in both cases. 

To achieve the above-mentioned objective, the following processes have to be considered (a) formation of H+ at an oxidized anode area (decrease of pH) and OH at a reduced cathode area (increase of pH) (b) dissociation of soluble compounds within an entire length of cell (c) movement of cations and anions into respective electrodes (d) displacement of negatively charged and pH-dependent colloidal particles of clays toward the anode (e) formation of pH-dependent complexes of EDTA-metals and their transport toward the anode (f) electroos-motic transport of inert particles (phenanthrene compound) toward the cathode (g) amphoteric surfactant behavior (in the presence of a variable pH within the cell), formation of micelles, and desorption of phenanthrene (h) displacement of micelles and their transformation and (i) transport and removal of conditioning liquids. 

The surface tension measurements demonstrated that all compounds with a lipophilic alkyl chain of more than 12 carbon atoms display surfactant behavior and self-aggregate into micelles above the critical micellar concentration (cmc). The cmc values decrease from 1 x 10 to 2.5 x 10 while the hydrocarbon chain length increases and the usual linear variation of log cmc versus number of carbon atoms was observed. Moreover the variation of the counter-anion X shows the cmc values in the HEA-Ci series decrease from Cl>Br>BF4>Ms>I and finally the determination of the cmc value of the surfactant affords the possibility to optimize the efficiency of the colloidal catalyst in biphasic liquid-liquid systems (vide infra). The... 

An example of surfactant behavior in conventional liquid solvents is shown in Fig. 3 for the nonionic C12EO5-water-heptane system [12]. The upper boundary of the narrow one-phase region, shown by open circles, is the solubilization boundary. The lower boundary, shown by filled circles, is the haze point curve. AOT systems have the same kind of phase behavior, but since AOT is anionic the relative positions of the solubilization and haze point... 

It is seen that the effect of the surfactant on the adhesion strength of polymer is related not only to the surface but also to the bulk properties of surfactant. Let us now pass to considering the details of surfactant behavior in ohgomeric and polymeric solutions. 

Recently, Chatterjee et al [57] examined the problem of CMC in organic solutions in some detail in case of non-ionic surfactants of the Span and Tween series (see Section 2.2) with an eye toward the effect of the surfactant behavior on the synthesis of particles in the water pool . The choice of the relatively pH-... 

FIGURE 1.13 Idealized diagram showing surfactant behavior. 

Surfactants also occur as lining material in the lungs. Diseases associated with malfunctioning of these tissues or processes often involve surfactant behavior. 

An investigation of surfactant behavior at the liquid/iiquid interface with sum-frequency vibrationai spectroscopy... 

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