Optical micrographs of different concentrations (weight %) of untreated multi-walled carbon nanotubes (CNTs) suspended in epoxy resin (Araldite LY556): (a) 0.025%, (b) 0.05%, (c) 0.1% and (d) 0.5% CNTs. Optical depth = 130 μm. Temperature = 25°C. The CNTs were prepared by Prof. AH Windle's group at the Dept. of Materials Science and Metallurgy.