Stearic acid, molecular model

Another concept that has been used freely and frequently in analyzing the coefficient of friction in lubricated sliding involves the dependence of the shear strength of a monomolecular film of fatty acid on the contact pressure, but no detailed model has ever been advanced to show the relation between shear strength and the molecular structure of the film. Bowers and Zisman [45] wrote the following relation for the "bulk" coefficient of friction of stearic acid ... 

Radioisotopic tracer techniques were applied to study the coadsorption of n-octadecane and stearic acid on a metal surface immersed in a n-octadecane solution of stearic acid. Dual labeling was employed for determining the surface concentrations of both n-octadecane and stearic acid. n-Octadecane was labeled with tritium and stearic acid with carbon-14. The results of half-hour adsorption experiments provide direct proof of coadsorption of polar and nonpolar materials on iron, copper, silver, and platinum surfaces. The films produced on silver and copper by 19-hour adsorption consisted of approximately one molecular layer of stearic acid and two molecular layers of octadecane. A new model is proposed to describe the structure of this thick coadsorbed film. 

Fig. 7.5. The solid-gel interface of a stearic acid/phenyl octane gel on HOPG (correlation averaged) together with an atomscale model of the molecular arrangement. Frame size is 25nm xllnm. Vsampie = 700mV, iuas = SOpA [16].

A novel analytieal tool for the selective detection of local water inside soft mol. assemblies (hydrophobic cores, vesicular bilayers, and micellar structures) suspended in bulk water has been presented. Through the use of dynamic nuclear polarization (DNP), the NMR signal of water is ampUfied, as it interacts with stable radicals that possess about 658 times higher spin polarization. Stable nitroxide radicals covalently attached along the hydrophobic tail of stearic acid molecules that incorporate themselves into surfactant-based micelle or vesicle structures have been used, allowing to study the local water content and fluid viscosity inside oleate micelles and vesicles and Triton X-100 micelles to serve as model systems for soft molecular assembhes. ... 

Fig. 1.8. Molecular models representing the three-dimensional structure of stearic and oleic acid. The cis configuration of the double bond of oleic acid produces a curvature of the carbon chain...

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