Surface Science and

Nano-Tribology Laboratory

Tribology: the science of interacting surfaces in relative motion. It encompasses the study of friction, wear and lubrication.

Friction The force known as friction is defined as a resistance encountered when one body moves relative to another body with which it is in contact.

Wear  Wear is defined as either mass or volume of material, removed or displaced from a body which is repeatedly stressed in mechanical contact with another body or bodies.

Lubrication The primary purpose of a lubricant is to separate the contacting surfaces and thereby reduce friction and wear.

    We have used a modified SPM and other instrument to study tribological properties of coating/substrate systems and polymeric coatings at micro- and nano-scale.

    We also use the Nanoindenter to make controlled damage then look at the damage with the SPM to analyze it. We are able to investigate the modes of damage caused by different amounts of force, scraping speeds, indentation methods, etc. and relate them to the mechanical properties of the materials.

     We have used a modified SPM to study mechanical properties of nanomaterial.  One of our  projects is “Investigation of the Radial Compression of Carbon Nanotubes with a Scanning Probe Microscope.”, and the results have been published on Physical Review Letters.
 

     Corrosion has drawn great interest of scientists and engineers and has been a focused research topic for decades, due to its enormous economic impact. While progress has been made, we are still far away from total control of it, and its mechanism has not been clearly understood, especially in micro and nano-scale. Electrochemical Impedance Spectroscopy (EIS) has been proven as a valid technique to investigate corrosion. The newly developed Localized Electrochemical Impedance Spectroscope (LEIS) will further allow us to measure the impedance dot by dot with a resolution of microns while it scans across the surface of sample. Combined with Scanning Probe Microscope (SPM), which can image surface morphology with nano and sub-nano resolution, we can study the corrosion mechanism in micro and nano-scale. 

In recent years there has been increased awareness of the environmental impact of antifouling coatings used on the hulls of marine vessels to discourage the settlement of marine life.  The long established marine fouling coating has been to add toxins (usually containing tin or copper) to the coatings. It has been shown that the leaching of these toxins, in particular tributyltin (TBT), causes damage to many non-targeted marine animals.  This has lead to the use of nontoxic coating systems to control marine fouling.    These nontoxic coatings have a low surface energy and low elastic modulus, making them difficult for marine life to adhere to. In the last few years silicone coatings have been demonstrated to provide the best foul release properties.  This laboratory has been employed by the U.S. Navy to characterize the morphology and nano-tribological properties of several such non-toxic fouling release coating systems.

Our study of the tribological properties of coatings/materials has focused on the mar/scratch resistance.

We used a modified SPM with home-made probe to study mar/scratch resistance of coatings, starting from early 90s. Currently, we use NanoIndenter XP to make controlled damage, and use SPM to examine the damage and study and analyze the mechanisms. Using these instruments, we can measure the micro mar resistance (MMR), and different responses of the coatings/materials to the scratch stress, i.e. elastic recovery, plastic deformation, and abrasive wear (mass loss), quantitatively, as well as identify the critical force for rough trough, at which the damage mode transits from mar to rough trough, the critical force for cracking, for delamination and for chipping.

Five distinguishable damage modes, mar, rough trough, crack, delamination, and chipping.