Other straight chain amphiphilic compounds

However, it is possible to introduce two new factors into the problem of multilayer structure, either of which can influence structure in an interesting way. It is possible to replace the ordinary hydrocarbon chain by a perfluorinated chain and it is possible to dip over a subphase containing a trivalent cation. The perfluorinated carbon chain has a helical structure which produces a chain which appears to be approximately cylindrical. The handedness of a chain is determined randomly so that an equal number of right handed and left handed molecules exist in a given batch. 

Completely perfluorinated carboxylic acids have never been deposited with total success as LB films, as it is very difficult to synthesise materials of this nature containing more than 12 carbon atoms. Unfortunately, it is not possible to form stable monolayers at the air/water surface or dip successfully when making use of such short chains. Nakahama et al. [143] claim to have carried out these processes using a subphase containing aluminium ions. However, extensive efforts to reproduce these results which were made in the author s laboratory proved unsuccessful. Naselli et al. [144] studied the partially perfluorinated material 

Various efforts have been made to form LB films of fatty acids using a subphase containing trivalent cations. Reference has already been made to the pioneering work of Wostenholme and Schulman [77J and the review article by Binks [78], Two recent attempts have been made to carry out such a programme by Prakash et al. [146J and Ohe et al. [147]. Both groups of workers made use of trivalent iron in the subphase and had some success, but X-ray diffraction data showed that the films obtained were far less well ordered than films dipped over divalent cations. 

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The most commonly used amphiphiles to build L-B hlms for tribological applications are the straight chain hydrocarbon compounds with simple functional groups such as the fatty acids, including stearic acids, arachidic acids, and behenic acids [32], but other amphiphilic molecules, e.g., 2,4-heneicosanedione and 2-docosylamina-5-nitropyridine, are also applied in some cases. There are two major systems of self-assembled monolayers, namely the alkylsilance derivatives (e.g., OTS, octadecyltrichlorosilane) on hydroxylated surfaces and the alkanethiols on metal substrates, which have been investigated extensively to examine their properties as solid lubricants and protective surface films [31 ]. 

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