New Catanionics as suitable additives for oily formulations, especially lubricants

The lifespan and efficiency of various types of machinery is often limited by the performance of its lubricated interfaces, which are formed by two interacting surfaces and a lubricant. The job of the lubricant is to separate the surfaces and to decrease friction and wear. There is a constant quest for more efficient lubricants. Ionic Liquids possess many unusual physico-chemical properties compared to molecular liquids including, but not limited to, high polarity, high conductivity, high thermal stability, and a wide liquid range even down to low temperatures. Such properties are essential for formulating lubricants for interfaces in challenging applications like aerospace and wind turbines. Recently, a new family of Ionic Liquid has been deeply investigated. These Ionic Liquids contain surfactants as structural element, therefore they are known as SAILs, Surface Active Ionic Liquids. Due to their unique properties resulting from the combination of an Ionic Liquid and a surfactant, these substances could be interesting for being a high-performance lubricant. The motivation and concept of this thesis can be summarised by the following ideas. First, the synthesis of different anionic parts based on alkyl ether carboxylic acids. These kinds of molecules are well known as anionic surfactants, with a modular molecule shape. The physico-chemical properties are adjustable by variation of the alkyl chain as well as the alkoxylation type and degree. As purity is the key for Ionic Liquids, propylene oxide instead of ethylene oxide has been chosen for the alkoxylation. This relates to a narrower oligomer distribution as well as less remaining non-reacted alcohol and it makes the resulting molecule more oil soluble and less water soluble. A second advantage of the introduction of a certain degree of propylene oxide to the alcohol is the lowered melting point, due to the sterical hindrance of the methyl group in the three-dimensional network. The linking of the acetic acid group to the propoxylated alcohol directly leads to the anionic surfactant. The crucial step of this synthesis is the removal of all by-products as well as the needed high conversion degree to the resulting anionic surfactant. By using a suitable industrial synthesis and purification route, all anionic surfactants could be directly produced in industrial scale. As symmetric quaternary ammonium compound, three different molecules have been selected. Tetramethyl, tetraethyl and tetrabutyl, differ in the alkyl chains at the nitrogen atom, therefore also the influence of the molecular shape of the cation could be investigated and the best candidate for the application as lubricant could be defined. These products are also available in large scales from the market. In the second part, the synthesised compounds were characterised with respect to their potential as lubricant or lubricant additive. Typical lubricants or additives have to fulfil different requirements. They should show low electric conductivity and a good handling in terms of liquid flow behaviour, like low viscosity combined with low melting point and high thermal stability. Besides these parameters, also a good solubility in natural oils, like rape-seed oil, as well as low hygroscopic behaviour is preferred for this kind of future application. Following physico-chemical parameters of the prepared Ionic Liquids have been evaluated: density, viscosity, conductometry, melting, thermal stability, hygroscopy and oil solubility. These factors have then been correlated to the different molecular structures like C-chain lengths, propoxylation-degrees and size of the corresponding cation. In the last part of the thesis, all prepared Ionic Liquids have been tested as neat oil as well as additive in natural oil, rape-seed oil, concerning their potential as lubricant. For this investigation, a modular rheometer has been used. On this rheometer, the film forming properties, the lowest friction coefficient and the resulting lowest sliding speed have been correlated to the molecular structures of different Catanionics