Title

The tribology of functionally-terminated oligomer films

Date of Completion

January 1994

Keywords

Plastics Technology

Degree

Ph.D.

Abstract

In order to minimize the damage to sliding surfaces caused by friction and wear, lubricants are usually dispersed between the surfaces. A particularly important class of lubricants are boundary layer lubricants whose film thickness is generally less than the average roughness of the mating surfaces. Demands on the performance of boundary lubricants in a variety of tribological applications has continued to grow. The boundary lubricating properties of a novel class of thin film formers called functionally-terminated oligomers (FTO's) was investigated. Langmuir-Blodgett films of diamine and diacid polydimethylsiloxane, diacid 1,2-hydrogenated polybutadiene, and diacid perfluoropolyether, all with molecular weights of approximately 2000-3000 g/mole, were deposited on to silicon wafer substrates and friction tested against a silicon nitride pin using a pin-on-disk apparatus. At low temperatures (T = 19$\sp\circ$C), monolayer films of the diacid perfluoropolyether gave the smallest friction coefficients and best wear protection of the silicon surfaces at low loads. This was attributed to the superior load bearing properties of the highly fluorinated oligomer. At higher loads, all of the FTO's gave high friction and wear of silicon. A technique was developed that transformed siloxane and metal soaps of arachidic acid to SiO$\sb{x}$ and metal oxide films. The high temperature (T = 300$\sp\circ$C) lubricating properties of these films on silicon was studied. While all of the films lowered the friction coefficient of silicon, only the metal oxide films of manganese lowered the wear rate of silicon significantly at this temperature. This was attributed to the high hardness of the manganese coating. ^