Martin-Gallego et al. Nanoscale Research Letters 2011, 6:610 http://www.nanoscalereslett.com/content/6/1/610 Table 1 Thermal conductivity of epoxy nanofluids and nanocomposites Neat resin 0.2 wt.% MWNT 0.4 wt.% MWNT 0.6 wt.% MWNT 0.8 wt.% MWNT 1 wt.% MWNT 0.6 wt.% f-MWNT 0.6 wt.% SWNT 1 wt.% FGS 1 wt.% Graphite 1 wt.% GO Kliq (W/mK) 0.150 ± 0.001 0.162 ± 0.004 0.176 ± 0.009 0.202 ± 0.004 0.220 ± 0.001 0.250 ± 0.001 0.180 ± 0.001 0.180 ± 0.001 0.150 ± 0.001 0.176 ± 0.005 0.150 ± 0.001 Ksol (W/mK) 0.22 ± 0.07 - - 0.29 ± 0.05 - 0.38 ± 0.07 - - 0.36 ± 0.04 - - This result can be explained by the presence of the functional groups, hydroxyl and carbonyl, that act as scattering points on the surface where phonons can be transferred from the nanotube crystalline structure into the insulating polymer matrix. This behavior has already Page 4 of 7 been observed in cured resins [27,28], but not in the pre-cured state. The addition of nano-dispersed FGS caused no improvement of the K in the liquid resin. To better understand this result, we also measured dispersions of both the starting natural graphite and GO. The natural graphite showed a slight enhancement of K, while no improvement was observed in the oxidized system. These results support the previous discussion of the negative effect of the presence of functional groups on the nanoparticle surfaces [29], the presence of only one carbon layer, and the large SSA (see Figure 3). Hence, FGS cannot be considered as suitable fillers to enhance the K of liquid resins. The enhancement in the K of MWNT nanofluids were fitted with the Hamilton-Crosser [30] model (Equation 1) traditionally used to predict the thermal enhancement of solid/liquid suspensions: Ke = 1 + Kf n (α − 1) φ (α + n − 1) − (α − 1) φ (1) Figure 3 Schema of the phonon coupling losses and the boundary phonon scattering at the nanoparticle interphase.