# Epoxy/Glass Fiber Nanostructured p- and n-Type Thermoelectric Enabled Model Composite Interphases
## 1 Introduction
CNTs dispersed-inks deposition onto fibrous substrates are capable of to convert insulating reinforcing fibers to semi-conductive reinforcements for composites with modified interfacial shear strength (IFSS) and secondary additional properties. The resulting composite materials can be used for a wide range of applications, such as electrostatic charge dissipation, damage sensing, and energy harvesting. [PERSON] et al. reported on the strain, humidity and temperature sensing ability of hierarchical GFs, coated with commercial oxidized CNTs by electrical measurements [22]. [PERSON] et al. systematically examined the thermoelectric response of reinforcing fibers coated with CNTs [23], thermoelectric materials based on engineered polymer nanocomposites, and/or polymer/fiber composites [14; 24], appropriate for large-scale structural applications with thermal energy harvesting capabilities. It is common knowledge that energy loss is inevitable during the operation of an engine resulting in a fuel efficiency less than 50%. Most of the wasted energy is in the form of heat. For typical diesel engines, tests from as early as 2009 showed that, the heat lost by the exhaust was approximately a quarter of the energy produced by the utilized fuel [25]. Thermoelectric energy harvesting and pyroelectric energy harvesting exploitation, relying on the temperature change over distance and time, respectively. The aforementioned technologies constitute the two most common thermal energy harvesting methods. Thermoelectric (TE) conversion is a promising technique to recover temperature waste heat as electricity. In general, heat coming from temperature fluctuation in the environment can be reclaimed as electricity on account of the well-known 'Seebeck effect'. Thermoelectric materials exhibit the Seebeck effect, in which charge carriers move in response to temperature gradients. The Seebeck coefficient is directly related to the density of states, whereas the electrical conductivity can be limited by electronic and morphological defects. Charge carriers diffuse across the temperature gradient, creating an accumulation of charge and thus a potential difference, \(\Delta V\). The magnitude of this effect is described by the Seebeck coefficient (\(S\)) and is simply the voltage difference divided by the applied thermal gradient \(S=\Delta V/\Delta T\). The Seebeck coefficient is further used for the calculation of the power factor (\(PF=\sigma\times S^{2}\)), a well-established quantity for comparing the TE performance of different thermoelectric materials. Finally, the overall thermoelectric efficiency for specific temperature range applications of a material is classified by the dimensionless thermoelectric figure of merit, \(ZT\) (\(ZT=(\sigma\times S^{2})\times T/\kappa\)), where \(\sigma\) is the electrical conductivity, \(S\) is the Seebeck coefficient, \(\kappa\) is the thermal conductivity and \(T\) is the corresponding temperature. An efficient thermoelectric material presents a high value of ZT, combining high electrical and poor thermal conductor characteristics. The three thermoelectric parameters \(\sigma\), \(S\) and \(\kappa\) are correlated with the intrinsic carrier concentration of the material [26; 27; 28; 29]. Thermoelectric energy harvesting is a conventional technique for converting wasted thermal energy into the electrical power by means of thermoelectric element generators (TEGs). A typical TEG device consists of p-n junctions properly interconnected electrically in series and thermally in parallel. When a temperature gradient is established between the hot and the cold side, free electrons and holes are able to move towards specific directions and generate a potential difference proportional to the temperature difference between the p-type and n-type semiconductors. Compared to the traditional TEG devices, high performance flexible TEGs that exploit the nanotechnology advancements are being extensively reported [17; 30].