Large Interfacial Contact Research Articles

Damping Properties of Epoxy Films with Nanoscale Fillers

This study demonstrates improved damping in epoxy films using nanoscale fillers. The mechanism for damping improvement is related to frictional energy dissipation arising from interfacial sliding at the nanofiller-matrix interface. The combination of extremely large interfacial contact area, high aspect ratio, many interfaces, and low density implies that nanoscale fillers could be far more efficient with regard to damping augmentation than traditional fillers. In this study, three categories of nanoscale fillers are investigated; (1) silica nanoparticles, (2) silicon nanorods, and (3) silicon nanosprings. The nanofillers are dispersed in an epoxy matrix and the nanocomposite film is tested dynamically (in the shear mode) using an MTS-858 servohydraulic test facility. The results indicate that nanospring fillers generate greater energy dissipation than nanoparticles or nanorods. The material loss factor (or damping ratio) of the epoxy film (with silicon nanospring fillers) showed a 150% increase compared to the baseline (pure) epoxy. The nanocomposite damping materials developed here show the potential to overcome the limitations of traditional viscoelastic polymers and could help to efficiently deliver significant levels of damping to structural components.

Characterizing energy dissipation in single-walled carbon nanotube polycarbonate composites

In this study, single-walled carbon nanotube and bisphenol-A-polycarbonate composite beams were fabricated by a solution mixing process and dynamic (cyclic) load tests were performed to characterize energy dissipation. We report up to an order of magnitude (>1000%) increase in loss modulus of the polycarbonate system with the addition of 2% weight fraction of oxidized single-walled nanotube fillers. We show that the increase in damping is derived from frictional sliding at the nanotube-polymer interfaces. The nanoscale dimensions of the tubes not only result in large interfacial contact area, thereby generating high damping efficiency, but also enable seamless integration of the filler materials into the composite structure.

Biosorption of toxic metals from aqueous solutions by bacteria strains isolated from metal-polluted soils

The use of biological materials for effective removal and recovery of heavy metals from contaminated wastewaters has emerged as a potential alternative method to conventional treatment techniques. The aim of this paper was the laboratory study of biosorption of toxic metals from aqueous solution by the application of microorganisms ( Bacillus laterosporus or Bacillus licheniformis), isolated from polluted (metal-laden) soil. Microorganisms have a high surface area-to-volume ratio, because of their small size and therefore, they can provide a large contact interface, which would interact with metals from the surrounding environment. Microbial metal accumulation has received much attention during recent years, due to the potential use of microorganisms for treatment of metal-polluted water or wastewater streams. Two toxic metals were selected as typical examples: a cation (cadmium) and an oxyanion (hexavalent chromium, and promising results were obtained, under optimized conditions.