Polyethylene surfactant molecules

It must be pointed out here that the relative solubilities of the hydrophilic and lipophilic parts of an emulsifier (surfactant molecule) change with temperature as a result, the HLB value also changes. This phenomenon is very prominent for non-ionic emulsifiers containing polyethylene oxide (PEO)-type hydrophilic groups. At higher temperatures, such emulsifiers become less soluble in water and hence, stabilize W/O emulsions, and vice versa (see also Section 1.3). Ionic surfactants are more likely to stabilize O/W emulsions at high temperatures [38]. 

In contrast, because of the flexible nature of polyethylene oxide, the polymer segments can penetrate the polar surface of the micelles and modify the nature, of that interface. Assuming that polymer segments shield about 10 (per surfactant molecule) of the hydrocarbon core area of the micelle from water, ( Pnterfacial is approximately -1.2 RT, takii the hydrocarbon water interfacial tension to be 50 dynes/cm. A can be estimated in a manner similar to that used... 

A third example of a surfactant molecule which forms a lyotropic SmC analog phase in water is the ionic amphiphile reported by Ujiie et al. [9] (Fig. 5.1c). The molecule possesses a polyethylene imine unit, analog to the polyethylene glycol units of the Schafheude molecule. 

The crystallization of a commercial surfactant like Brij 97 on cooling is hindered by the presence of entrapped water (and, in quaternary system B, of dissolved butanol too) within the voids formed between the unequal headgroups and by the nonuniformity of the chains of the surfactant itself. Heating the system leads to the release of surfactant molecules. The subsequent glass transition is sometimes reflected as a broad step in the thermogram (not seen in Fig. 22). Such a step was observed between -80°C and -70°C in the polyethylene oxide-water system [96]. 

In the presence of polyethylene oxide MW 300,000 at a concentration of 0.025 g liter , variations in pH and ionic strength have no effect on elution volumes and a single calibration curve is obtained as shown in Figure 4 and Table II. This behavior presumably also results from modification of the glass surface by the polyethylene oxide surfactant, but in this case charge effects appear to be completely suppressed and the effective pore diameter and volume reduced. Such an interpretation is also in accord with the fact that the elution voliomes are lower with polyethylene oxide than with Tergitol, since Tergitol is a much smaller molecule than the polyethylene oxide. 

As with fullerenes, carbon nanotubes are also hydrophobic and must be made soluble for suspension in aqueous media. Nanotubes are commonly functionalized to make them water soluble although they can also be non-covalently wrapped with polymers, polysaccharides, surfactants, and DNA to aid in solubilization (Casey et al., 2005 Kam et al., 2005 Sinani et al., 2005 Torti et al., 2007). Functionalization usually begins by formation of carboxylic acid groups on the exterior of the nanotubes by oxidative treatments such as sonication in acids, followed by secondary chemical reactions to attach functional molecules to the carboxyl groups. For example, polyethylene glycol has been attached to SWNT to aid in solubility (Zhao et al., 2005). DNA has also been added onto SWNT for efficient delivery into cells (Kam et al., 2005). 

It is, of course, possible to prepare a molecule that has both polar and nonpolar characteristics. This is the basis of surfactant chemistry. Typically, a nonpolar molecule is modified by sulfonation. The well-known Pluronic family of surfactants is based on block polymerization of polypropylene oxide (the hydrophobe) and polyethylene oxide (the hydrophUe). It is conceptually possible to build a polyurethane 2005 by CRC Press LLC... 

Example 12.1. The CMC of C12E7 is 0.083 mM at room temperature. By SANS and dynamic light scattering the mean hydrocarbon core radius was found to be 1.70 nm at a surfactant concentration of 2 mM [532], The mean aggregation number is 64. If we divide the total surface area of the core by the number of surfactants, we get the area per molecule at the core radius. It is 47r (1.7 nm)2 /64 = 0.57 nm2. The cross-sectional area of polyethylene oxide is below 0.2 nm2. So, more than half the core area is exposed to aqueous or at least to a polar medium. 

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