Friction and Scratch Resistance of Polymer Liquid Crystals: Effects of Magnetic Field Orientation

Abstract

We have studied PET/0.6 PHB, an alternating copolymer in which PET is poly(ethylene terephthalate) and PHB is p-hydroxybenzoic acid with the mole fraction of 0.6 PHB. It is a longitudinal polymer liquid crystal (PLC) with the LC sequences in the main chain and oriented along the chain backbone. Material not subjected to the magnetic field, specimens oriented along and perpendicularly to the flux of the magnetic field, were investigated. Static friction, dynamic friction, scratch penetration depth, and healing of the material were determined. Static and dynamic friction parameters for oriented samples have significant higher values for oriented samples. The best scratch resistance is found for the sample aligned along the magnetic field. The results are explained in terms of morphology revealed by scanning electron microscopy and phase structures.

Sliding wear, viscoelasticity, and brittleness of polymers

“…We have shown how a polymer liquid crystal oriented in a magnetic field shows different values of recovery f in function of the angle between the scratching and the field orientation direction. 18 Other orientable polymers might show similar effects. Another source of information on tribological behavior is molecular-dynamics computer simulations.…”

“…The instrument and procedure have been described previously. [17][18][19] The test consists of 15 scratches by a diamond tip along the same groove. Each material was tested under constant loads of 5.0, 10.0, and 15.0 N at room temperature (25°C).…”

Poly(methyl acrylate) plus Mesoporous Silica Nanohybrids: Mechanical and Thermophysical Properties

“…Tribological properties deserve more attention [34], given the gradual replacement of metallic components by polymeric ones. The present approach has been applied to PMA; applying it to thermosets might be worthwhile -also given the large and still increasing range of application of epoxies [35 -37].…”

Probing polymer chain constraint and synergistic effects in nylon 6-clay nanocomposites and nylon 6-silica flake sub-micro composites with nanomechanics

“…The change in H/E may have important implications for tribological applications where performance often is correlated with parameters such as H/E and H 3 /E 2 , with higher H 3 /E 2 commonly resulting in a higher load for non-elastic deformation, and higher wear resistance to wear as has been achieved by cross-linking ultra-high molecular weight polyethylene (UHMWPE) for replacement of hip prostheses. 37 The tribology and wear of polymers and polymer-based composites is complicated by viscoelastic recovery and brittleness, [38][39][40] with Brostow and co-workers reporting a direct correlation between a brittleness index and scratch recovery. 40 Although wear resistance may improve by adding silicate layers to nylon 6, this has been associated with an increase in brittle modes of deformation such as the formation of brittle cracks during scratching.…”