Tribological properties of carbon nanotube–polyethylene oxide composite coatings

The effect of polyethylene oxide (PEO) inclusion in carbon nanotube (CNT) coating on the tribological properties of the composite coating was investigated. CNT/PEO composite coatings with 12 different weight fractions were fabricated by using the spin-coating method on pre-cleaned Si (1 0 0) substrates. Wear tests were performed using a reciprocating tribo-tester under an applied load of 10 mN and a speed of 4 mm/s. A 1.6 mm diameter stainless-steel ball was used as the pin and the corresponding Hertzian contact pressure was calculated to be ∼20 kPa. From the experimental results, it was shown that the steady-state friction coefficients for the CNT/PEO coatings gradually decreased from ∼0.47 to ∼0.3 as the concentration of PEO increased from 0 wt.% to 75 wt.%. The wear volume of the CNT/PEO composite coating rapidly increased with increasing amount of PEO when the weight fraction of PEO was comparatively low. The wear volume reached the maximum value for 87/13 wt.% of CNT/PEO coating and showed a continuous decrease in the wear volume with further increase in the PEO weight fraction. Morphological analyses of the wear pattern revealed that wear mechanism of the composite coating varied with respect to PEO concentration. The overall experimental results demonstrated that the tribological properties of CNT-based coatings could be significantly improved by adding an optimum amount of PEO. The reason for such an improvement was attributed to the enhancement of interfacial forces within the composite coating due to the presence of PEO.