Lubricating properties of liquid crystals

VI.3 Lubricating properties of Liquid Crystal VI.3.1 Pure LC or mixtures... 

Chemical structure, effect on lubricating properties of liquid crystals, 36,37f Cholesteric liquid crystals description, 49 structure, Af ... 

Ge LL, Chen LP, Guo R (2007) Microstructure and lubrication properties of lamellar liquid crystal in BrijSO/lBmimlPF HjO system. Tribol Lett 28 123-130... 

Despite the large number of liquid crystals reported in the literature, only a few classical TLCs and even fewer LLCs have been investigated for their tribological properties (1-8L A number of investigators have reported reduced coefficients of friction, reduced wear, reduced temperature in the contact zone and increased load-bearing properties between various surfaces when TLCs were used as lubricants by themselves or added to base oils. However, almost all of these studies were conducted under hydrodynamic conditions. Thus, we decided to... 

The term moisture, usually defined as wetness conferred by an unidentified liquid, is assumed here to be due to water. Thus, the scope of this article is the characterization of and consequences due to relatively small amounts of water associated with solids of pharmaceutical interest. Chemical stability, crystal structure, powder flow, compaction, lubricity, dissolution rate, and polymer film permeability are some properties of pharmaceutical interest that have been demonstrated to be influenced by the presence of moisture. Wet granulation, extrusion, spheronization, tray drying, freeze drying, spray drying, fluid-bed drying, tableting, and aqueous film coating are some unit operations that obviously depend on the amount and state of water present. 

Electrostatic interactions resulting from the polarity of the carbon-fluorine bond play an important role in the binding of fluorinated biologically active compounds to their effectors [22] (discussed in detail in Sections 4.5 and 4.6) and for the me-sophase behavior of fluorinated liquid crystals [23] (Section 4.4). The consequences of the low polarizability of perfluorinated molecular substructures have been put into commercial use for chlorofluorocarbon (CFG) refrigerants, fire fighting chemicals, lubricants, polymers with anti-stick and low-friction properties, and fluorosur-factants. 

To analyze such thermodynamic relations of different molecules, we will take the model system to be a homologous series of normal alkanes and alkenes, as very reliable and accurate data are available in the literature. Linear hydrocarbon chains, n-alkanes, are among the most common blocks of organic matter. They form part of the organic and biological molecules of lipids, surfactants, and liquid crystals and determine their properties to a large extent. As major constituents of oils, fuels, polymers, and lubricants, they also have immense industrial importance. Accordingly, their bulk properties have been extensively studied. 

New improved lubricating greases containing ash-free additives, the combination of lithium and calcium soaps to improve water resistance, the incorporation of functional polymers into the thickener matrix to improve spray-off properties and many more customer-specific solutions have been offered. In the pipeline are products containing functional soaps, nano particles (nested spheres) and lyotropic liquid crystals. In scientific terms, the trend is moving from know how to know why as more is understood about the actual mechanisms involved in grease lubrication. 

Despite the widespread belief that liquid crystals (LC) should have peculiar lubricating properties " there has been few publications on that subject. Since our early work we have not been able, either through computational research (Chem. Abstract, INSPEC) or cross referencing to find more than 40 references. In this review we will quote all of them and give a large place to our unpublished work. 

SURFACES constitute the boundaries of condensed matter, solids, and liquids. Surface chemistry explores the structure and composition of surfaces and the bonding and reactions of atoms and molecules on them. There are many macroscopic physical phenomena that occur on surfaces or are controlled by the electronic and physical properties of surfaces. These include heterogeneous catalysis, corrosion, crystal growth, evaporation, lubrication, adhesion, and integrated circuitry. Surface chemistry examines the science of these phenomena as well. 

As the changes of melting temperature and viscosity of post-precipitated liquid slag is not obvious, the discussion therefore focused on effects of crystallization on break temperature, crystallization temperature and lubrication property (Vi) of post-precipitated liquid slag. The effects of the property change on continuous casting of peritectic steel slab were also discussed. 

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