Micelle diameter

In the separation tests with the use of a UF membrane, the rejection efficiency for the Cjg cationic surfactants was found to be in the range 90-99%, whereas for the C12 surfactants it ranged from 72 to 86%, when the feed concentration of each surfactant was greater than its corresponding CMC value. Therefore, UF rejection efficiency seems to be dependent on the respective hydrated micelle diameter and CMC value. In conclusion, the study showed that for cationic surfactants removal, if the feed concentration of a surfactant is higher than its CMC value, then the UF membrane process is found to be the best. However, if the feed concentration of a surfactant is less than its CMC value, then ion exchange is the best process for its removal. 

The size of the micelles is significantly increased by the addition of monomer up to a diameter of 4.5-5 nm. However, the size of the monomer droplets is stilt very much larger than that of the micelles (diameters up to 1 pm). In emulsion polymerization, one generally uses 0.5-5 wt% of emulsifier relative to monomer. With the usual oil-in-water emulsions, the water content varies from half to four times the amount of monomer. 

Blanch and coworkers [145] investigated in detail the solubilization properties of a-chymotrypsin and alcohol dehydrogenase (ADH) in RMs prepared by the above three techniques. Protein solubilization in RMs greatly depends on the method used for protein addition as well as on the size of the protein and of the RM. For the dry addition method protein solubilization is strongly dependent on micelle size whereas for the injection method it is less dependent. For smaller proteins like a-chymotrypsin (diameter of 44 A), maximum solubilization occurred when the micelle diameter was 50 - 60 A. For larger proteins like ADH... 

Poly (ethylene glycol)-poly(glutamic acid) block copolymers containing cis-diamine-dichloroplatinum, (IV), were prepared by Kataoka [3]. The micelle diameters were roughly 22 nm, and these block copolymers were used as antineoplastic drug delivery agents. 

Block copolymers of 23b and alkyl methacrylates [158] and diblock copolymers of 23b with 2-(diethylamino)ethyl methacrylate (23b-DEAEM), 2-(diisopropylamino)ethyl methacrylate (23b-DIPAEM), or 2-(N-morphoHno) ethyl methacrylate (23b-MEMA) exhibited reversible pH-, salt-, and temperature-induced micellization in aqueous solution under various conditions. The micelle diameters were 10-46 nm [238]. The micelles of these hydropho-bically modified polybetaines consist of coronas from 23b and cores from polyDEAEM, polyDIPAEM, or polyMEMA. In aqueous solution, the 23b-MEMA diblock copolymers form micelles with cores of polyMEMA above an upper critical micelle temperature of about 50 °C, and reversibly betainized-DMAEM core micelles below a lower critical micelle temperature of approximately 20 °C [239]. 

The general observation from DLS studies is that the apparent hydrodynamic diameter increases as the pressure is decreased towards a phase boundary (where surfactant and water will precipitate to form a second phase). Figures 2 and 3 show DLS results for AOT/water micelles in supercritical xenon (at 25 C) and ethane (at 37 C), respectively. Results are presented for [H20]/[A0T] molar ratios (W) of 1 (a) and 5 (b). All measurements were obtained In single-phase systems at constant W. The apparent hydrodynamic micelle diameter decreases with increasing pressure or density of the continuous phase in both fluids. The second cumulant in Equation 1, which is a qualitative measure of the polydispersity of the system, is very close to zero for all conditions of this study. There is no statistically... 

Because a solution containing a high concentration of nonsolvent can be presumed to be of the Sol 2 type and close to gelation. Immersion into a nonsolvent bath and subsequent gelation will be accompanied by less gel concentration than would occur If the solution were further removed from the perimeter of the solubility envelope. The result is that the micelle diameter in Sol 2, as well as the porosity and permeability of the final membrane. 

Figure 13. Interferogram of film formed from solution of nonionic detergent (Enordet AE1215-30, 0.052 mol/L). As the film thins, less light is reflected. Formation of metastable states of uniform thickness is revealed by steps . The height of the step corresponds to the thickness of film. The width of the steps is proportional to the lifetimes of respective metastable states. The vertical distance between steps corresponds to micelle diameter, about 10 nm. (Reproduced with permission from reference 54. Copyright 1990 Steinkopff Verlag Darmstadt.)...

Hanaoka et al.were able to control the Rh particle to a similar size of 4-4.2 nm. In our case, by increasing our water/surfactant ratio to 70, an average size of 9.75 nm Pd particle with 16% metal loading was obtained (Table 1). Thus, our results agree with the observations that diameter of metal nanoparticles synthesized inside the micelle system depends on micelle diameter (the included material < the aqueous core) which critically depends on water/surfactant ratio used. The subsequent application of the silica-gel coating onto these micelle stabilized metal nanoparticle does not seem to seriously alter... 

A reversed I2 structure of globular aggregates packed in a cubic array also has been reported recently for some surfactants [46-49], despite previous doubts about their existence. Here it appears that the micelles are spherical, but of two different sizes (Fig. 8). For reversed micelles the alkyl chain packing constraints no longer limit the micelle diameter, hence the coexistence of two spherical micelles of different sizes is more plausible than with the Ij phases. The Fd3m phase is well established now [48, 49], but again, there appear to be several other distinct symmetries possible in the I2 region [48]. It is likely that the confusion in this area will be resolved in the next few years as the surfactant structures necessary for both I] and I2 phases are now clear, hence we can obtain the phases with many more surfactant types. 

Figures 36 and 37 show that the hexadecane induces the formation of an 12 cubic phase, whereas the much more polarizable p-xylene, which can reside at the chain/wa-ter interface, induces a lamellar phase. As expected with the increase in micelle diameter, all the phases have their boundaries shifted to higher volume fractions with hexadecane addition.

The micelle diameter can be calculated by measuring the micelle diffusion coefficient using the technique of dynamic light scattering (DLS). If one assumes that aU micelles are spherical in shape, the radius of a micelle in solution may be calculated by using the Stokes-Einstein relation ... 

The surfactant diffusion data were compared with the molecular weight (MW) and diffusion data of selective proteins from the literature to estimate pseudo-molecular weights (PMW) of the surfactant micelle in Figure 6.9 [19]. The correlation indicates that the PMW of Tween 80 and RC-520 micelles was 92,000 and 346,000, respectively. A rule of thumb is that the MWCO of a UF membrane should be at least one-half of the solute to be separated. Thus, a new tool was developed where the relationship between the micelle diameter, diffusion coefficient and a PMW could be used to screen high MWCO membranes for SBUF appfications. 

---