Fundamental study of the initial agglomeration of lithium soap thickener in lubricating oil Report March 2019 Paul Shiller1, Nikhil Prasad1, and Gary Doll1 1 The University of Akron 1 Introduction This is an update of the progress of the project which started August 2018. There are two parts to this project •
The first is to physically manufacture soap thickened grease at the initial point of thickener agglomer-ation. – The initial point of thickener agglomeration is the critical micelle concentration. – For the Li-12hydroxy stearate thickener grease that concentration is between 3% and 5% soap concentration.
•
The second is to model the thickener agglomeration. – Modeling will initially consist of determining the attractive or repulsive force between thickener molecules. – After the forces are determined a molecular dynamics simulation will be constructed to match the results of testing the physical grease
2 Current Work Grease was formulated in the lab by mixing lithium hydroxide and 12-hydroxy stearic acid in an ISO VG 10 base oil. •
Multiple batches with concentrations of 3%, 4%, and 5% soap were formulated, see the appendix for procedure and recipe. – Moisture testing was performed to determine the end point of the reaction. – Cone on plate rheological testing was performed to determine if the critical micelle concentration was reached. * The determining factor is the relative position of the storage and loss moduli in the plateau region of an oscillating stress sweep rheology experiment. * If the storage modulus is above the loss modulus the thickener has formed. If the storage modulus is below the loss modulus the thickener has not formed yet. – Dynamic light scattering experiments were performed to determine the shapes and orientation of the agglomerates. * Results are inconclusive at this time due to the opaque nature of the mixtures
Thickener agglomeration modeling was started by calculating energies of interaction between thickener molecules •
Modeling was started by establishing the orientation of the Li-12hydroxystearate molecules relative to each other. – A semi-empirical method with a two body repulsion force was chosen to determine the interaction forces and energies – Initial calculations show a small van der Waals attraction between two Li-12hydroxystearate molecules. - 53 VOLUME 83, NUMBER 2
