Polar long chain compounds

Techniques for spreading monolayers of polar long chain compounds on mercury in a Langmuir type film balance, and for measuring their surface area-pressure properties, have been described by one of the present authors (3). Using these techniques, it has proved possible to measure continuously the change in contact angle of a water droplet superposed on the monolayer, as the film pressure is controllably varied. This has now been done for monolayers of the normal C12-C20 fatty acids and the normal primary Ci4-Ci8 alcohols on the mercury substrate. 

The contact angle of 70° observed for a drop of methylene iodide is a criterion for the existence of an oleophobic film whose top surface is composed of an array of methyl groups. However, observation of such a contact angle is not a demonstration that the film formed by retraction of an adsorbing surface from a solution of a polar long-chain compound is... 

Surfactants are long-chain compounds containing a hydrophobic tail and an ionic head. In polar solvents the surfactants arrange themselves in a spherical structure known as a micelle in which the hydrophobic tails form the... 

As expected, LC separation of the dichloromethane/acetone SPE eluate in the RP-mode, presented as FIA-APCI-MS(+) in Fig. 2.12.13, was impossible because the alkyl ethoxy amines as cationic surfactants could not be eluted under conventional RP-separation conditions [37, 53]. The use of methane sulfonic acid for ion-pairing resulted in the separation of the compounds in the methanol eluate as shown as TIC (d) and selected ion trace masses (m/z 504 (a), 670 (b), and 802 (c)) in Fig. 2.12.14. Here, the short-chain ethoxy amines were eluted later than the more polar long-chain homologues [39]. 

The emulsifiers are generally long chain compounds with polar groups, such as soaps of various kinds, long chain sulphonic acids and alkyl sulphates. The function of an emulsifier is to lower the interfacial tension between the dispersed phase and the dispersion medium so as to facilitate the mixing of the two liquids. 

Waxes are esters of fatty acids with long chain primary alcohols (Figure 12.2). The fatty acid is usually straight chain which may be saturated or mono-unsat-urated although occasionally branched chain or hydroxy acids are found. They are extremely non-polar compounds and are relatively inert chemically but they can be hydrolysed using a strong alkali, such as potassium hydroxide, a process called saponification. 

Tn previous communications (7, 9, 10, H, 12) from this laboratory results have been presented on association reactions between long-chain ionic and long-chain polar compounds. The results have implications regarding the properties of interfaces, including those present in certain biological systems. The latter aspects have been emphasized by Schulman and Rideal (22). 

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