Role of Nanostructure of Adsorbed Layers in Lubrication
Surfactants and polymers added to boundary lubrication systems adsorb on solid surfaces and form a protective film. Effectiveness of boundary lubricants has often been attributed to the adsorption affinity and the integrity of the adsorbed film. Such adsorption is influenced by additives introduced into the system to reduce thermal degradation, corrosion, sludge formation, foaming etc. There are many interactions that can take place between the additives and the surfactants and the base oil leading in addition to adsorption effects, a number of interfacial and colloidal phenomena such as micellization, precipitation and solubilization as well as flocculation of particulate matter in the fluid . Clearly the adsorption and integrity of the adsorbed film will depend on the molecular geometry of the interacting species. For example, among various saturated mono-, bi-, and tricyclic aromatics, alkanes, and polyethers tested as lubricating fluids by Hentschel , the “irregularly shaped molecules” yielded high traction coefficients whereas molecules with a “thread-like shape and minimum structural subunits or functional groups” yielded low coefficients. Evidently ability of molecules to undergo intramolecular as well as intermolecular motions is important in maintaining the integrity of the lubricating films.
KeywordsAdsorbed Layer Boundary Lubricant Adsorbed Film Surfactant Adsorption Surface Aggregate
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