PVP/SDS system

Finally, we can briefly consider the effect of PVP on SDS micelles. We recall that the CMC and B changes upon addition of PVP suggested that this polymer interacts more strongly than POE with SDS. The results of Table I show that the value of I1/I3 at low C in the PVP-SDS system, is close to that in water. Also, the values of kg are small and they increase with C, contrarily to the POE-SDS system. These two facts suggest a specific interaction between PVP and pyrene which may keep pyrene exposed to water (large I1/I3), and slows down its diffusion in the micelle (small kg). More investigations on the PVP-SDS systems appear necessary before a definite conclusion can be drawn concerning this system. 

Finally, a third electromethod, namely electrical conductivity (k), has been employed. It is well known that micellization of an ionic surfactant like SDS leads to a slope change in its k versus concentration plot. Work by Jones (24) on the PEO/SDS system showed that intfoduction of PEO into the surfactant solution led to pre- and postmicellar breakpoints consistent with the Ti and T2 concepts mentioned above. Furthermore, interpretation of the conductivity data for PEO/SDS and PVP/SDS systems by Zana et al. provided confirmation that the degree of counterion (Na) binding for the complexes was considerably lower than that observed with simple SDS micelles (25). 

Figure 37 Effect of salt on the transition concentrations of 0.1% PVP/SDS systems corresponding salt effect on c.m.c. of SDS is included. (From Ref. 28.)...

FIGURE 14.13 Contrasting features of the polymer-surfactant interaction for the PVP/DTAC and PVP/SDS systems l(q=0) versus during SDS ramp (top) and during DTAC ramp (bottom), Cpyp=0.5mg ml" [57],... 

The enhancement of the PVP adsorbed amount at the alumina-water interface, due to its interaction with an anionic surfactant, depends on the nature of the surfactant, as has been pointed out by Esumi et al. [50]. They studied the adsorption behavior on alumina of a system composed of PVP and a double-chained anionic surfactant, sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT). In an aqueous solution. Aerosol OT interacts with PVP as shown by surface-tension measmements which evidence the two typical Q and Ca concentrations [18] (Fig. 13). Ci at 2 mmol/L is the same as for the PVP-SDS system or the PVP-LiDS pair. Ca of the SDS-PVP system is approximately two times that of the Aerosol OT-PVP pair (i.e., around 2.3 mmol/L and 1.3 mmol/L, respectively). 

Subsequent ultrasonic relaxation studies - also involved the PVP/SDS system. The reported results are very different from those on the same system given in Reference 225, in the sense that in the binding range the value of 1/Xx is claimed to be nearly independent of the surfactant concentration. This is apparently true for the data in References 226 and 227 (PVP/SDS systems) but certainly not for the results reported in Reference 228 for several other polymer/surfactant systems. There it is clearly seen that 1/Xi is nearly constant over a very short range of concentration but increases linearly with C in the binding range determined from ultrasonic velocity measurements, as predicted by Equation 3.9. Besides in Reference 226 to Reference 228, the range where 1/Xi is nearly... 

Historically, the first use of a specific surfactant ion electrode for polymer/surfactant studies seems to have been that of Birch et al. (17), who used aDS electrode to investigate the PVP/SDS and PEO/SDS systems, followed by Gilanyi and Wolfram (21), who studied the PVA/SDS and PEO/SDS systems. 

Behavior similar to that in Figure 9 has been authenticated for well-studied systems like PEO/SDS and PVP/SDS (34,35,38,39). 

The dependence of surface tension on surfactant concentration when such behavior occurs is illustrated in Figure 4.16 for the SDS-polyvinylpyrrolidone (PVP) system. The symbols Tj and Tj denote the CAC and the surfactant concentration where the polymer chains are saturated with micelles. The plots indicate that the polymer itself has some surface activity (i.e., surface tension decreases with increasing polymer concmtiation when little surfactant is present). Moreover, Tj is greater than the surfactant CMC and increases with increasing polymer concentration, as one would expect. It has been found that the surface tension curve does not vary significantly with polymer molecular weight except when the molecular weight is quite low (about 1500 for the SDS-PEO system). 

In solutions of polymers (PVP, PEG, PDDA) complete or partial neutralization of the negative charge of the anionic form of the initial metal complex was seem Similar behavior was observed for metal complexes comprising micelles (SDS). In the case of micellar system CTABr lanthanide bis-phthalocyanine predominantly existed in the anionic form. 

Figure 1 Variation of the CMC with the polymer concentration for the systems SDS-NMP ( ) SDS-POE (O) SDS-PVP ( ) TTAB-POE (X) and TTAB-PVP (+).

It is well established that the interaction of a nonionic polymer such as polyethyl-eneoxide (PEO) or polyvinylpyrrolidone (PVP) with an anionic surfactant such as SDS can impart polyelectrolyte-like properties to the nonionic polymer (54,80-82). This effect manifests as a significant increase in viscosity at a certain concentration (Ti or c.a.c. ) of the surfactant, which is independent of molecular weight, and this increase can be as high as fivefold. In addition to an increase in viscosity, these systems can exhibit considerable viscoelastic (82) effects, especially if the molecular weight of the polymer itself is already high. 

A typical ESR spectrum is shown in Fig. 2. As described, Xc can be calculated from the spectra. Shah and co-workers [35] used ESR to study the structure of microemulsion, and Rosen et al. [36] used ESR and found the microviscosity gradient in the middle phase of three-phase micellar systems. Shirhama et al. [37] and Witte et al. [38] have used ESR to study the interaction of SDS with PEO and PVP, yielding information on the structure of complex from the polymers and SDS. But the influence of the spin-label molecule on the microstructure should be considered. 

These studies were undertaken using a pressure-jump apparatus over the time range 10-10 sec. incorporating a rapid data capture and analysis system. The polymer, polyvinylpyrrolidone, PVP, (Aldrich) was used without further purification. Sodium dodecyl sulphate, SDS, (Henkel) was chosen as the surfactant system, since a considerable wealth of equilibrium data were already available involving this surfactant. SDS was purified by repeated recrystallisation from two solvents until the relaxation time at the CMC agreed with literature values. 

Table 13.3 gives the CMC, CAC, and PSP values for a number of polymer/surfactant systems. The variations of CAC with temperature and polymer concentration are also indicated. The ratio CAC/CMC depends on the type of polymer/surfactant combination. For example, the ratio CAC/ CMC is 0.26 for SDS/0.1% of PVP solution and 0.55 for SDS/0.1% PEO solution. This shows that even if the type of surfactant is the same, the CAC can be different for different polymers. Thus, the structure of polymer has a strong effect on the CAC. 

Systems of uncharged polymers and anionic surfactants are the most widely studied systems. The most popular neutral polymers are poly (ethylene oxide) (PEO) or poly(ethyleneglycol) (PEG), poly(propyleneoxide) (PPO), poly(vinyl pyrrolidone) (PVP), poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), hydroxypropylcellulose (HPC), ethylhydroxypropylcellulose (EHEC). Most frequently, they were studied with SDS. Other anionic surfactants, namely sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT), have also been the subjects of investigations in aqueous solution [18], as well as at the solid-liquid interface, as will be discussed later [46,50]. 

Probably the largest volume of published work in the field of surfactant-polymer interactions has involved surfactants and nonionic polymers such as polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polypropylene glycol (PPG), methyl cellulose (MC), and polyethylene oxide (POE). The preferred surfactant has been (of course ) the classic—sodium dodecylsulfate (SDS). The results of most studies with SDS and similar surfactants indicate that the more hydrophobic the polymer, the greater is the interaction with anionic surfactants. For a given anionic surfactant, it has been found that adsorption progresses in the order PVP > PPG > PVAc > MC > PEG > PVA. In such systems, the primary driving force for surfactant-polymer interaction will be van der Waals forces and... 

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