Running-in behavior of internally plasma-treated silicone tubing

• Quantitative characterization of running-in behavior of metal–plastic contact.
• Systematic physical and chemical diagnostics to identify cause of running-in.
• Development of a method for diminishing running-in behavior.
• Specific experiments performed for metal coils sliding in plastic tubing.

When employed in biomedical applications, the bore of silicone tubing must be modified to become highly lubricious, for example, by means of plasma treatment. In this context, the determination of the degree of lubricity is normally accomplished with the aid of a frictional tribopartner. In practice, this determination is made uncertain and overly lengthy due to running-in behavior. The focus of this investigation is to characterize the running-in behavior, diagnose the factors that contribute to its existence, and develop means by which to eliminate the running-in process. The tribological system that was studied may be categorized as polymer/metal frictional interaction. It was discovered by systematic experimentation that transfer of material, rather than traditional wear, is at the root of the encountered running-in phenomena. These investigations included frictional-based and chemical-detection methodologies. Once the fundamental cause of the running-in behavior had been discovered and confirmed, a method for eliminating running-in was proposed and experimentally validated.