Micelle molecular weight

It is also possible to determine simultaneously by GPC the micelle molecular weight and aggregation number. It is important to ensure that the integrity of polymeric micelles during their elution through the size exclusion column is maintained. Adsorption of the polymer on the column may prove to be a problem (Yokoyama et al., 1993), especially at concentrations close to the CMC, where micelles consist of large loose aggregates (Jones and Leroux, 1999). 

S. Ikeda, S. Ozeki and M. Tsunoda, Micelle molecular weight of dodecyldimethylammonium chloride in aqueous solutions, and the transition of micelle shape in concentrated NaCl solutions, J. Colloid Interface Sci. 73 (1980) 27-37. 

The determination of the molecular weight was complicated by the lack of data at low angles, and a simple Zimm plot analysis of the curve (Kc/Rq)c=0 could not be performed in a straightforward way (as suggested by Eq. 4), since it would lead to an underestimated value of the micelle molecular weight. However, from the downward curvature of these different plots we were able to deduce that the scattering particles present in solution had a rod-like shape. 

Fig. 4. Tetradecyltrimethylammonium bromide at 25 . Effect of alcohols on the micelle molecular weight, as determined from light scattering (CD butanol (+) pentanol and (O) hexanol.

The complex changes of molecular weight of TTAB micelles in H2O-O.IM KBr upon addition of pentanol may be explained in terms of a distribution of alcohol between different micelle solubilization sites. In H2O, the alcohol may essentially be dissolved in the palissade layer, thereby decreasing the molecular weight by the effects discussed above. In H2O-O.IM KBr, pentanol is salted out of water and may preferentially dissolve into the micelle hydrophobic core, thereby increasing the micelle molecular weight. 

A quantitative analysis of the above kinetic results on the basis of Aniansson s theory of mixed micelles is not possible at the present time because it requires the knowledge of such quantities as the total micelle molecular weight at every concentration of alcohol and detergent, and the micelle composition. Work is now in progress in our laboratory in order to determine these quantities. 

The effect of alcohols on dilute micellar solutions is to decrease the cmc and micelle molecular weight and to increase the micelle ionization. Also, the exchange of detergent ions between micelles and surrounding solution and the micelle formation-dissolution are strongly accelerated upon addition of alcohol (micelles become more labile in presence of alcohol). All these variations can be explained on the basis of the effects associated with the dissolution of alcohol into micelles, leading to mixed alcohol + detergent micelles. 

In Fig. 17 the micelle molecular weight (MMW) is plotted versus V y /Vo for different systems. The micelle molecular weights (MMW) were found from literature as measured by other methods, such as light scattering and diffusion. Fig. 17 shows that there exists a linear relation between log(MMW) and with few exceptions. 

This unusual variation of N with emulsifier concentration suggests that the monomer droplets were a locus for particle nucleation, which was demonstrated by the particles as small as 20nm formed by emulsification of 20% aqueous poly-p-sodium styrene sulfonate solutions under the same conditions. Moreover, the interfacial tension between 20% aqueous p-sodium styrene sulfonate and o-xylene containing dissolved Span 60 was O.OOlO.Ol dynes/cm. Emulsion droplets as small as 20nm could compete effectively as a locus for particle nucleation with the monomer-swollen micelles (cmc in benzene 0.0022 gm/cc micelle molecular weight 52800 aggregation number 94 (55)). Thus both the micelles and the monomer droplets are loci for particle nucleation. 

Figure 3.8 Logarithmic relation of apparent micelle molecular weight with ionic strength (0)25°C (A)30°C ( ) 35°C (D) data of Emerson and Holtzer [123]. From Hayashi and Ikeda [85] with permission.

The type of behavior shown by the ethanol-water system reaches an extreme in the case of higher-molecular-weight solutes of the polar-nonpolar type, such as, soaps and detergents [91]. As illustrated in Fig. Ul-9e, the decrease in surface tension now takes place at very low concentrations sometimes showing a point of abrupt change in slope in a y/C plot [92]. The surface tension becomes essentially constant beyond a certain concentration identified with micelle formation (see Section XIII-5). The lines in Fig. III-9e are fits to Eq. III-57. The authors combined this analysis with the Gibbs equation (Section III-SB) to obtain the surface excess of surfactant and an alcohol cosurfactant. 

Colloidal State. The principal outcome of many of the composition studies has been the delineation of the asphalt system as a colloidal system at ambient or normal service conditions. This particular concept was proposed in 1924 and described the system as an oil medium in which the asphaltene fraction was dispersed. The transition from a coUoid to a Newtonian Hquid is dependent on temperature, hardness, shear rate, chemical nature, etc. At normal service temperatures asphalt is viscoelastic, and viscous at higher temperatures. The disperse phase is a micelle composed of the molecular species that make up the asphaltenes and the higher molecular weight aromatic components of the petrolenes or the maltenes (ie, the nonasphaltene components). Complete peptization of the micelle seems probable if the system contains sufficient aromatic constituents, in relation to the concentration of asphaltenes, to allow the asphaltenes to remain in the dispersed phase. 

An increase in the rate of radical production in emulsion polymerisation will reduce the molecular weight since it will increase the frequency of termination. An increase in the number of particles will, however, reduce the rate of entry of radicals into a specific micelle and increase molecular weight. Thus at constant initiator concentration and temperature an increase in micelles (in effect in soap concentration) will lead to an increase in molecular weight and in rate of conversion. 

Ultrafiltration of micellar solutions combines the high permeate flows commonly found in ultrafiltration systems with the possibility of removing molecules independent of their size, since micelles can specifically solubilize or bind low molecular weight components. Characteristics of this separation technique, known as micellar-enhanced ultrafiltration (MEUF), are that micelles bind specific compounds and subsequent ultrafiltration separates the surrounding aqueous phase from the micelles [70]. The pore size of the UF membrane must be chosen such, that the micelles are retained but the unbound components can pass the membrane freely. Alternatively, proteins such as BSA have been used in stead of micelles to obtain similar enan-tioselective aggregates [71]. 

The progression of an ideal emulsion polymerization is considered in three different intervals after forming primary radicals and low-molecular weight oligomers within the water phase. In the first stage (Interval I), the polymerization progresses within the micelle structure. The oligomeric radicals react with the individual monomer molecules within the micelles to form short polymer chains with an ion radical on one end. This leads to the formation of a new phase (i.e., polymer latex particles swollen with the monomer) in the polymerization medium. 

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