Micelle model

Fringed micelle model Frings acetator Frisium Frit... 

If the ordered, crystalline regions are cross sections of bundles of chains and the chains go from one bundle to the next (although not necessarily in the same plane), this is the older fringe-micelle model. If the emerging chains repeatedly fold buck and reenter the same bundle in this or a different plane, this is the folded-chain model. In either case the mechanical deformation behavior of such complex structures is varied and difficult to unravel unambiguously on a molecular or microscopic scale. In many respects the behavior of crystalline polymers is like that of two-ph ise systems as predicted by the fringed-micelle- model illustrated in Figure 7, in which there is a distinct crystalline phase embedded in an amorphous phase (134). 

Figure 8 Fringe-micelle model of crystalline polymers. (PramRef. 131,)...

The hydroxyethyl quaternary ammonium ion in (20) is a weak acid the pATa-value of the non-micellizing model compound, choline, is 12.8 (Haber-field and Pessin, 1982). Reactions of the alkoxide zwitterion are therefore followed at relatively high pH, and from the variation of rate constant with... 

This humic-micelle model is consistent with much of the reported information in the literature, especially with regard to the membrane-like behavior. Such a structure might explain the following findings reported by several authors [ 19, 44,254,293-297] ... 

It has been suggested that glass transition is an important physicochemical event that controls the phase transition process of starch (Biliaderis, 1998). According to Biliaderis (1998), the "fringe-micelle" model (Fig. 5.16) does not permit assignment of a definite Tg for most starches. This is because the change in heat capacity during phase... 

Titration results for the mixed erne s of the SDS/CgE4 and C12E2S/C8E4 systems as a function of their relative mole fraction in solution are shown in Figures 2 and 3, respectively. Here, the experimentally determined points are compared with calculated results from the nonideal mixed micelle model (solid line) and the ideal mixed micelle model (dashed line). Good agreement with the nonideal model is seen in each case. 

Figure 2. Cmc s of mixtures of SDS and CgE4 in distilled water (at 25°C). The plotted points are experimental data, the solid line is the result for the nonideal mixed micelle model with B = -3.3, and the dashed line is the result for ideal mixing.

The finding that the assumptions of the regular solution approximation do not hold for the mixed micellar systems investigated here suggests a re-examination of how the thermodynamics of mixing enter the nonideal mixed micelle model. 

The mixed cmc behavior of these (and many other) mixed surfactant systems can be adequately described by a nonideal mixed micelle model based on the psuedo-phase separation approach and a regular solution approximation with a single net interaction parameter B. However, the heats of micellar mixing measured by calorimetry show that the assumptions of the regular solution approximation do not hold for the systems investigated in this paper. This suggests that in these cases the net interaction parameter in the nonideal mixed micelle model should be interpreted as an excess free energy parameter. 

FIGURE 2.14 Schematic two-dimensional representation of a modified micelle model of the crystalline-amorphous structure of polymers. 

If the mixed micelle model already presented is used to predict the ionic surfactant monomer concentration, and a simple concentration—based solubility product is assumed to hold between the unbound counterion and monomer, the salinity tolerance of an anionic/nonionic surfactant mixture can be accurately predicted (91). supporting this view of the mechanism of tolerance enhancement by nonionic surfactant. 

The purpose of this paper will be to develop a generalized treatment extending the earlier mixed micelle model (I4) to nonideal mixed surfactant monolayers in micellar systems. In this work, a thermodynamic model for nonionic surfactant mixtures is developed which can also be applied empirically to mixtures containing ionic surfactants. The form of the model is designed to allow for future generalization to multiple components, other interfaces and the treatment of contact angles. The use of the pseudo-phase separation approach and regular solution approximation are dictated by the requirement that the model be sufficiently tractable to be applied in realistic situations of interest. 

The pseudo-phase separation approach has been successfully applied in developing a generalized nonideal multicomponent mixed micelle model (see I4) and it is Interesting to consider whether this same approach can be used to develop a generalized treatment for adsorbed nonideal mixed surfactant monolayers. The preferred form for suoh a model is that it be suitable (at least in principle) for treating multiple components and be extendable to other interfaoes and properties of interest suoh as oontaot angles. Earlier models (5, 18, 27) based on the pseudo-phase separation approach and... 

Results for the various binary mixed surfactant systems are shown in figures 1-7. Here, experimental results for the surface tension at the cmc (points) for the mixtures are compared with calculated results from the nonideal mixed monolayer model (solid line) and results for the ideal model (dashed line). Calculations of the surface tension are based on equation 17 with unit activity coefficients for the ideal case and activity coefficients determined using the net interaction 3 (from the mixed micelle model) and (equations 12 and 13) in the nonideal case. In these calculations the area per mole at the surface for each pure component, tOj, is obtained directly from the slope of the linear region in experimental surface tension data below the cmc (via equation 5) and the maximum surface pressure, from the linear best fit of... 

To this point, only models based on the pseudo—phase separation model have been discussed. Mixed micelle models utilizing the mass action model may be necessary for micelles with small aggregation numbers, as demonstrated by Kamrath and Franses ( ). However, even for large micelles, the fundamental basis for the pseudophase separation model needs to be examined. In micelles, how much solvent or how many counterions (bound or in the electrical double layer) should be included in the micellar pseudo-phase is unclear. The difficulty is normally surmounted by assuming that the pseudo—phase consists of only the surfactant components i.e., solvent or counterions are ignored. The validity of treating the micelle on a surfactant—oniy basis has not been verified. Funasaki and Hada (22) have questioned the thermodynamic consistency of such an approach. 

Fig. 7. Schematic representation of the fringed micelle model of crastalline polymers... 

Fig. 37a, b. Model proposed according to 31P-NMR signal shape of phase transition range. Membrane structure of mixed vesicles prepared from oppositely charged vesicles a inverse micelle model b bulge model of clusters with different spontaneous membrane bending [310]... 

Chapter 8 discusses self-assembly of surfactants to form micelles, models of micelliza-tion, use of micelles in catalysis and solubilization, and oil-in-water and water-in-oil microemulsions. 

It is sometimes argued that the reverse micelle terminology is an inappropriate comparison to aqueous micelles. Since water can be solubilized by these micelles, causing an increase in n, the reverse micelle model and vocabulary do seem useful for ternary systems. 

Xu et al. (1992) used light scattering to characterize micelles formed by a wide range of PS-PEO di- and tri-block copolymers in dilute solution in water. Although full analysis of the data was complicated by the tendency of the micelles to undergo secondary association, they did find that the micellar radius scaled as eqn 3.14, in agreement with the predictions of Halperin (1987). With values of p and RB from the star-like micelle model, Xu et al. (1992) were able to compute % parameters for the interactions of PEiO with water and with PS, in... 

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