Graphene‐based polymer composites with ultra‐high in‐plane thermal conductivity: A comparison study between optothermal Raman spectroscopy and laser flash method

Abstract

ABSTRACTWe developed a simple solution mixing and molding process for the incorporation of graphene nano‐flakes (GNFs) in polymer films. Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) and poly(ethylene‐co‐methacrylic acid) (PEMAA) were used for preparation of the samples. The orientation and stacking of GNFs were confirmed using a scanning electron microscope. The thermal conductivity values for these composites were obtained using (1) laser flash method (commercially available) and (2) an optothermal Raman (OTR) technique (homemade device). The former measures the thermal diffusivity (α) and one needs to measure the density (ρ) and the heat capacity (Cp) of the composites in order to measure the in‐plane thermal conductivity (κ = α.ρ.Cp), while the latter measures the in‐plane thermal conductivity directly from the relation between the excitation power and the position of the Raman resonance. The data obtained from Raman spectroscopy were analyzed, assuming heat propagation in three and two dimensions. The Raman results obtained based on the two‐dimensional model were very close to the results obtained using the laser flash method with less than 10% difference. The OTRspectroscopy was found to be a promising technique for measuring the in‐plane thermal conductivity of carbon‐based polymer composites. PVDF‐HFP and PEMAA composite films with very high in‐plane thermal conductivity (25 W m−1 K−1) were obtained through the incorporation of GNFs (20 wt % concentration). Considering a very low thermal conductivity of these polymers (<0.2 W m−1 K−1), this corresponds to a large enhancement of roughly 12 400%. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48927.