Double bonds, surfactant alkyl chains

What are typical values for the parameters k and kl The bending rigidity of surfactant films is typically of the order of 1-20 kBT at room temperature. Factors that reduce k are short alkyl chains, cosurfactants, double-chain surfactants with unequal chains, and cis-unsaturated bonds. For the saddle-splay modulus only few measurements have been done. It tends to be negative with an amount much smaller than the bending rigidity for the same system. 

The information includes location of double bonds In fatty acids, indentlficatlon of components in complex lipids, determination of compositions of anionic and cationic surfactants, and identification of long-chained alkyl substituents on phosphonium and ammonium ions. 

Perfluoro alkyl iodides add to both terminal and internal double bonds when the reaction is initiated by electron transfer from metals such as finely divided silver, copper powder, and lead with copper acetate. Using an -olefin and a perfluoro-alkyl-a, -diiodide, a perfluoro group can be inserted into a long-chain compound (118) (Figure 21). Deiodination of the product by catalytic reduction results in highly hydrophobic alkyl chains with interesting surfactant properties. 

The maximum amount of water solubilized into hydrocarbon solvents by ionic surfactants appears to increase with increase in the concentration of the surfactant, the valence of the counterion, and the length of the alkyl chain (Kon-no, 1971b) and with the introduction of double bonds into the hydrophobic group (Demchenko, 1971). Straight-chain compounds appear to solubilize less water than branched-chain ones, possibly because the former form micelles that are more compact and rigid than the latter (Frank, 1969 Kon-no, 1971c). 

Commercial polyoxyethylene surfactants contain a wide range of EO sizes, often with a reasonably defined alkyl chain. Bouwstra et al. [116] studied a commercial sample of Cg=C9EOi4 (i.e. a Cig chain with 9-10 cis double bond and a polydisperse EO group). It exhibits phase behavior similar to C12EOg... 

Commercial polyoxyethylene surfactants contain a wide range of EO sizes, often with a reasonably defined alkyl chain. Bouwstra and co-workers (130) have studied a commercial sample of Cq CqEOh (i.e. a Cig chain with 9-10 cis double bonds and a polydisperse EO group). The latter exhibits phase behaviour similar to C12EO8, with Ii, Hi, Vi and L phases. The Hi phase exits between 35.6 and 74.8 wt% surfactant and up to 84°C. The other phases exist over narrower concentration ranges and to lower temperatures. Similar studies have also been reported by Kunieda and co-workers (131, 132) for a wide range of commercial oleoyl EO derivatives again, the commercial actives behave like pure ones with a shorter EO size. 

It is worth noting that in the present case, the surfactants have three characteristics that prevent a liquid crystal from forming when the nonadsorbed alcohol situation is attained at and above octanol. First, it is a polyethoxylated nonionic surfactant, then it is a mixture of oligomers, and, on the other hand, it has a very branched alkyl chain. In effect, the alkylates of these commercial nonionics are synthesized by polymerizing C3 or C4 olefins. According to Markovnikov s rule, the polymerization attachment on the double bond takes place not at the ending carbon but at the second one, so that the polymer chain is regularly branched. Moreover, the oil is also a branched-structure molecule. 

The length and the shape of the alkyl chain are also quite important for the interaction of surfactants with CNTs longer and more branched alkyl groups are better than linear and straight ones. In addition, the merit of a dispersant containing double bonds, and with similar head group and tail length, was proved by particle size analysis of Tween-60 and Tween-80 nonionic surfactants. 

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