Doping Effect of Poly(vinylidene fluoride) on Carbon Nanofibers Deduced by Thermoelectric Analysis of Their Melt Mixed Films
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Date
2024
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Abstract
The effect of temperature on the electrical conductivity (sigma) and Seebeck coefficient (S) of n-type vapor grown carbon nanofibers (CNFs) and poly(vinylidene fluoride) (PVDF) melt-mixed with 15 wt% of those CNFs is analyzed. At 40 degrees C, the CNFs show stable n-type character (S=-4.8 mu V<middle dot>K-1) with an sigma of ca.165 S<middle dot>m-1, while the PVDF/CNF composite film shows an sigma of ca. 9 S<middle dot>m-1 and near-zero S (S=-0.5 mu V<middle dot>K-1). This experimental reduction in S is studied by the density functional tight binding (DFTB) method revealing a contact electron transfer from the CNFs to the PVDF in the interface. Moreover, in the temperature range from 40 degrees C to 100 degrees C, the sigma(T) of the CNFs and PVDF/CNF film, successfully described by the 3D variable range hopping (VRH) model, is explained as consequence of a thermally activated backscattering mechanism. On the contrary, the S(T) from 40 degrees C to 100 degrees C of the PVDF/CNF film, which satisfactorily matches the model proposed for some multi-walled carbon nanotube (MWCNT) doped mats; however, it does not follow the increase in S(T) found for CNFs. All these findings are presented with the aim of discerning the role of these n-type vapor grown carbon nanofibers on the sigma and S of their melt-mixed polymer composites.
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Keywords
Carbon nanofibers, Poly(vinylidene fluoride), Seebeck coefficient, P-type doping, Density functional based tight binding, Variable range hopping