Pamela L. Dickrell

Sliding orientation effects on the tribological properties of polytetrafluoroethylene

The chemical inertness, high melting point, and intrinsic lubricity of polytetrafluoroethylene (PTFE) have been used to develop solid lubricating parts for operation in extreme environments, from frying pans to satellites. The atomic-level mechanisms associated with friction and wear at PTFE surfaces are elucidated here by systematic investigations of the frictional anisotropy measured with respect to chain orientation. In particular, a combination of atomic-scale simulations, nanometer-scale atomic force microscopy experiments, micrometer-scale microtribometers experiments, and macroscale pin-on-disk experiments are used. Data across these length scales, from both the computational and experimental approaches, provide a consistent view of the mechanisms by which the structural orientation of PTFE contributes to its unique tribological properties.

Effects of laser repetition rate on corneal tissue ablation for 193‐nm excimer laser light

The goal of the present work is to assess whether bovine corneal ablations generated at laser repetition rates of up to 400 Hz are comparable to ablations performed at rates consistent with current clinical laser systems.

A fractional coverage model for gas–surface interaction in reciprocating sliding contacts

A model of fractional coverage in reciprocating sliding contact is developed. The sliding velocity profiles, the contact pressure distribution, the lengths of the slider or wear-track, and the periods of dwell where the slider is held stationary at the turn around locations are all variables. The model is evaluated for the condition of a constant fully reversing sliding speed with a uniform contact pressure and dwell. Plots are presented for surface area fractional coverage as a function of position illustrating the effects of individually varying vapor pressure, velocity, load, and dwell. The prediction of a steady state friction coefficient dependence on position is discussed, as well as the locations of maximum and minimum friction coefficient. The model predicts coverage to be enhanced by decreasing loads, decreasing sliding speeds, increasing gas pressures, and increasing periods of dwell.

Novel Ionic Liquid Lubricants for Aerospace and MEMS

Room temperature ionic liquids (RTILs) are molten salts with melting points at or below room temperature. RTILs have recently been recognized as novel lubricants. Only a few have previously been evaluated.Copyright

Development and Delivery of an Online Graduate Certificate in Materials Characterization for Working Professionals

Within materials science and engineering industries there exists a need for continual professional development and lifelong learning. University materials science and engineering departments and materials related centers have highly qualified instructional faculty, and course management infrastructure that can be utilized to deliver needed continuing education to working professionals via distance learning. This work examines the development and first year delivery results of an online graduate certificate in modern materials characterization techniques for working scientists and engineers.

Frictional and Electrical Properties of Multiwalled Carbon Nanotubes

This presentation examines the tribological properties and contact resistance of oriented capped carbon multiwalled nanotube (MWNT) films. Highly anisotropic tribological behavior of MWNT films oriented in mutually orthogonal directions is observed. The average values of coefficient of friction varied from high values (μ = 0.795) for vertically aligned nanotubes grown on rigid substrates to low values (μ = 0.090) for the same nanotubes dispersed flat on the same substrates. The results were insensitive to humidity, which is in contrast to graphite materials. The multiwalled nanotube layers also had a monotonic decrease in friction coefficient with increased surface temperature in both orientations, having a 32% drop in friction coefficient over a 73°C temperature rise. Preliminary results from contact resistance measurements of nanotube films grown through a porous alumina are investigated as a function of applied static load.© 2005 ASME

NANO-TRIBOLOGY OF A POLYTETRAFLUOROETHYLENE TRANSFER FILMS USING MOLECULAR DYNAMICS SIMULATION AND MICROTRIBOMETRY

Polytetrafluoroethylene (PTFE) is a well known solid lubricant and polymer nanocomposites based on PTFE are considered to be promising materials for tribological applications in space. Like other polymer materials, many properties of PTFE depend on morphology. In this study, molecular dynamics (MD) simulations are performed to examine the effect of chain configuration on the frictional behavior of PTFE at the molecular level and compared to microtribological studies on aligned transfer films of PTFE.