Surface activity, in water

These reactions are slowed by addition of chemically inert organic solvents to water and are generally slower in micelles than in water, although the effect is often small. The micellar inhibition has been discussed in terms of water activity, or more likely polarity, being somewhat lower at the micellar surface than in water (Menger et al., 1981). 

Silicone surfactants are specialty surfactants that are primarily used in applications that demand their unique properties. Most applications are based on some combination of their (a) low surface tension, (b) surface activity in nonaqueous media, (c) wetting or spreading, (d) low friction or tactile properties, (e) ability to deliver silicone in a water-soluble (or dispersible) form, (f) polymeric nature or (g) low toxicity. The major applications will be discussed briefly in following sections. 

For example, alkylbenzene is slightly surface active in nonaqueous media but is insoluble in water, Addition of a single S03H group to the molecule imparts solubility and excellent surfactant characteristics in water but insolubility... 

The CF3(CF2)5- group in the sodium suUbsuccinate derivatives of Gol din and co-workers (65) is remarkably surface active. In these molecules, the silicon and fluorine atoms are far apart, a separation that may be preserved when adjacent molecules are oriented at the air-water surface and... 

The design, preparation, and characterization of Ru02-Ti02 catalytic surfaces active in the photo-oxidation of water have been described. Chemical hydrolysis is used to produce islands of RUO2-H2O on submicron-size Ti02... 

Cellulose ethers swell or are colloidally soluble. They all raise viscosity and have specific rheology profiles (seeO Fig. 18). Many cellulose ethers are surface-active, and they reduce the surface activity of water by about 20 to 25% depending on type. Cellulose ethers are generally compatible with other hydrocolloids and many other substances. The field has recently been reviewed by Majewicz et al. [95]. The primary manufacturers of industrial cellulose ethers are listed in O Table 14. 

Second-order rate constants in the micelles (k2m) do not depend in any obvious way upon the hydrophobicities of the reactants or, for anionic nucleophiles, upon the surfactant counterion. The relatively small inhibitory micellar medium effect on reactions of nonionic nucleophiles is readily explained by the lower polarity of the micellar surface relative to water (32, 33). The generally small effects of the medium upon the ionic reactions are also understandable because water activity and ionic hydration are similar at the micellar surface and in water (34, 35, 38). 

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