Micelle ionization degree

C=surfactant concentration). The micelle ionization degree the CMC was taken as the ratio of the slopes of the specific conductivity C curves above and below CMC. The CMC and micelle ionization degpree were also determined for SDS in the presence of N-methylpyrrolidone (NMP), as a function of the NMP concentration. Indeed NMP can be considered as the repeat unit of PVP. The comparison of the results for NMP and PVP then allows one to assess the part of the change of the micelles properties due to the polymeric character of the additive. 

Figures 1 and 2 show the changes of CMC and micelle ionization degree 3 of the various surfactant-polymer systems, and of the SDS-NMP system, as a function of the concentration Cp of polymer or NMP (in g. per 100 ml of solution).

Figure 2 Variation of the micelle ionization degree at the CMC with the polymer concentration for the systems SDS-NMP ( ) SDS-POE (O) SDS-PVP ( ) TTAB-POE (X) and TTAB-PVP (+).

The cmc and micelle ionization degrees near the cmc (9) were determined by emf measurements using a specific bromide ion electrode (Orion 9435), in conjunction with a double junction reference electrode (Orion 9002) and a millivoltmeter (Orion 701A). Some determinations were also performed by means of conductivity. It was noted that emf measurements yielded cmc values slightly lower than those obtained from the equivalent conductivity vs. (concentration) plots. This, however, is of no importance in this work where we are only interested in relative changes. 

This expression of I/Tj is veiy similar to Equation 3.9 except for the correcting term F. In Equation 3.17 a is the experimentally accessible micelle ionization degree and y=... 

Van Paassen [57] describes the CMC of some polyether carboxylates with different fatty chains and EO degrees (Fig. 2). In an extensive study, Binana-Limbele et al. [59] investigated the micellar properties of the alkylpolyether carboxylates of the general formula CnH + OCF CH OCI COONa with n = 8, x = 5, and n = 12 and x = 5,1, and 9, by means of electrical conductivity (CMC, apparent micellar ionization degree) and time-resolved fluorescence probing (micelle aggregation number A7) as a function of temperature and surfactant concentration (Table 1). 

From the apparent ionization degree it was concluded that the EO chain probably behaves as part of the headgroup. As with Aalbers [49], a low surface charge of the sodium alkyl ether carboxylate micelles was mentioned. The micelle aggregation number N increases with the C chain much more than for the corresponding nonionic surfactants. In the case of C8 there was no influence of temperature. A small decrease was found with increasing EO, but much smaller than in the case of nonionics. 

As exemplified above, most of the studies on anionic polyelectrolyte block copolymer micelles have been carried out on P(M)AA-containing copolymers. The ionization degree of these anionic blocks is strongly dependent on... 

TABLE 8.1 Critical Micelle Concentration, Degree of Aggregation, and Effective Fractional Ionization for Several Surfactants With and Without Added Salt... 

The experimental techniques used to obtain the properties necessary to derive the kinetic constants of interest from the ultrasonic relaxation times have been previously described in detail [2,3]. Briefly, the degree of micelle ionization (P) and the binding constant (Ka) of an alcohol to mixed micelles were obtained from specific conductivity measurements as a function of surfactant concentration at various fixed alcohol compositions. The binding constant was determined from the slopes of the curves above the cmc, as proposed by Abu-Hamdiyyah et al... 

Changes of solution pH can induce micellization not only because of a decrease in the ionization degree of one block, but also because of the development of secondary interactions, like hydrogen bonds. An example of the above situation is the solution behavior of the PVA-PAA block copolymer [32]. The particular copolymer was almost molecularly dissolved in aqueous media at neutral or alkaline environments. However, the formation of aggregates was observed at low pH values, not only because of deprotonation of the PAA block but also due to the development of intermolecular hydrogen bonds between the PAA and PVA blocks. 

The increase of the ionization degree of SDS micelles upon addition of POE explains the increase of relaxation rate of the Na" " counterions observed in a previous NMR study. Moreover, the very large values of 3 at the CMC indicate that the first SDS micelles formed on, and bound to, the polymer at low C must be of much smaller size, or aggreation number than the micelles formed in water. 

At eqnifibrinm, the micelles have a net charge that is demonstrated by electrophoretic mobility experiments, for example, in an electric field, cationic micelles migrate toward a negative electrode. Typically, the surface charge at equilibrium is about 10-40% of the total number of micellized surfactant molecules. The net surface charge is numerically equal to the micellar degree of ionization (or ionization degree), a, which is experimentally obtained from the measured concentration of counterions to the aqueous pseudophase, [X ], corrected for the unimer concentration cmc, (5). A variety of methods may be used, for example, ion selective electrodes, conductivity NMR,... 

Benrraou M, Bales BL, Zana R (2003) Effect of the nature of the counterion on the properties of anionic surfactants. 1. cmc, ionization degree at the cmc and aggregation number of micelles of sodium, cesium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, and tetrabutylammonium dodecyl sulfates. J Phys Chem B 107 13432-13440... 

A. Critical Micelle Concentration and Miceile Ionization Degree... 

In this experiment the degree of ionization of CTAB micelles is determined by measuring the change in slope of solution electrical conductivity (k) versus total concentration (C) as the solution goes through the critical micelle concentration (cmc). That this information is suffi-... 

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