# Epoxy/Glass Fiber Nanostructured p- and n-Type Thermoelectric Enabled Model Composite Interphases
## 5 Conclusions  
The scope of this research study was to introduce and evaluate functional interphases between modified GFs with p and n-type SWCNTs model epoxy composites. Efforts were devoted to the morphological inspection as well as the evaluation of the structural changes that might be caused by the functional nanocoated GFs in the presence of temperature gradients. The thermal stability of the nanocoated GF tows was investigated through thermogravimetric analysis (TGA). Additionally, the chemical and structural stability of the TE nanoparticle-coated GF tows were studied by Raman measurements at elevated temperatures. The Raman spectra of p-type SWCNTs coated GFs and n-type SWCNTs coated GFs were acquired at ambient conditions, as well as at temperature differences of 50 \({}^{\circ}\)C and 100 \({}^{\circ}\)C by performing measurements at 75 \({}^{\circ}\)C and 125 \({}^{\circ}\)C. The results indicated that both the p-type and n-type TE enabled GF tows are chemically and structurally stable. The effect of the integration of the modified nanocoated GFs into a conventional epoxy resin was evaluated. The TE performance of the functional GF tows was only slightly affected by the resin encapsulation. Both p and n-type SWCNTs model composites exhibited a combination of high electrical conductivity and Seebeck coefficient. N-type model composites exhibited higher electrical conductivity compared to the corresponding p-type, due to their higher intrinsic electrical properties, as measured on SWCNTs bucky paper films. Moreover, the n-type model composites exhibited excellent behavior as thermoelectric materials with remarkably high values of Seebeck coefficient very close to the properties of the bulk SWCNTs material. An epoxy-based TEG model composite was manufactured to demonstrate the potential application of the technology in a TE generator, using a pair of alternating p- and n-type junctions interconnected in series via a metallic junction. The interfacial shear strength for both p and n-type TE enabled model composites was assessed by tow pull-out tests. The presence of SDBS as surfactant for the dispersion of the SWCNTs affected negatively the IFSS when epoxy resin was used as a matrix leading to a slight reduction of the IFSS values for both systems comparatively to the reference one. Finally, the fractographic study of the tested samples revealed that the matrix-to-matrix failure was more dominant than fiber/matrix-to-matrix failure, indicating strong interfacial adhesion.  
Further optimization of the thermoelectric performance which involves the increase of both the electrical conductivity and the Seebeck coefficient could be as achieved via doping of SWCNTs, use of different types of SWCNTs and creating efficient p-n heterojunctions for the fabrication of TEG module devices. The generation of thermoelectricity using structural engineering materials that are routinely exposed to high temperatures will represent a breakthrough in multifunctional materials, rendering them an attractive technology for aerospace and automobile applications.  
G.K.: conceptualization, methodology, validation, writing, visualization; K.T.: formal analysis, review and editing; L.T.: conceptualization, review and editing; C.M.: validation; L.K.: validation; A.S.P.: review and editing, supervision and project administration. All authors have read and agreed to the published version of the manuscript.  
Co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH-CREATE-INNOVATE (project code: T1 EDK-03480).  
The authors declare no conflict of interest.