Highly Thermoconductive, Strong Graphene-Based Composite Films by Eliminating Nanosheets Wrinkles

Abstract

Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices. However, when flexible graphene nanosheets are assembled into macroscopic thermally conductive composites, capillary forces induce shrinkage of graphene nanosheets to form wrinkles during solution-based spontaneous drying, which greatly reduces the thermal conductivity of the composites. Herein, graphene nanosheets/aramid nanofiber (GNS/ANF) composite films with high thermal conductivity were prepared by in-plane stretching of GNS/ANF composite hydrogel networks with hydrogen bonds and π-π interactions. The in-plane mechanical stretching eliminates graphene nanosheets wrinkles by suppressing inward shrinkage due to capillary forces during drying and achieves a high in-plane orientation of graphene nanosheets, thereby creating a fast in-plane heat transfer channel. The composite films (GNS/ANF-60 wt%) with eliminated graphene nanosheets wrinkles showed a significant increase in thermal conductivity (146 W m^-1 K^-1) and tensile strength (207 MPa). The combination of these excellent properties enables the GNS/ANF composite films to be effectively used for cooling flexible LED chips and smartphones, showing promising applications in the thermal management of high-power electronic devices.

Keywords: Aramid nanofiber; Graphene; In-plane stretching; Thermal conductivity; Wrinkles elimination.

Fig. 1

Thermal conductivity and mechanical properties of GNS/ANF composite films with eliminated nanosheets wrinkles. a, b Schematic diagram of heat transfer in composite films with eliminated nanosheet wrinkles and with nanosheet wrinkles. c Comparison of thermal conductivity and tensile strength of the composite films with eliminated nanosheets wrinkles and with nanosheet wrinkles. d Comparison of thermal conductivity and tensile strength of the composite films with eliminated nanosheets wrinkles with previously reported thermal management materials with nanosheets wrinkles. Reference data are listed in Table S1

Fig. 2

Preparation of GNS/ANF films with eliminated nanosheets wrinkles by in-plane stretching strategy. a Schematic illustration of the fabrication process of GNS/ANF films with eliminated nanosheets wrinkles. b TEM image of graphene with wrinkles. c SEM image of spontaneously dried GNS/ANF composite aerogel. d, e SEM image of constrained dried GNS/ANF composite aerogel and films. f, g Raman spectra of GNS, ANF, GNS/ANF composite films and illustration of the existence of π–π interaction between GNS and ANF. h Stress–strain curves of GNS/ANF composite hydrogels. i GNS/ANF composite films with eliminated nanosheets wrinkles can lift heavy weights and be folded into origami crane and boat. Scale bar: 500 nm (b), 10 μm (c, d), 3 μm (e)

Fig. 3

Wrinkles regulation and thermal conductivity enhancement of composite films. a, b Surface SEM images. c AFM images. d, e Cross-sectional SEM images and f WAXS patterns for GNS/ANF films by in-plane stretching for (1) 0%; (2) 5%; (3) 10%; and (4) 15%. g Orientation factor change. h, i Thermal diffusivity and thermal conductivity of GNS/ANF-60, 50, 40 wt% films by different in-plane stretching ratio. j Tensile stress–strain curves of GNS/ANF-60 wt% films by different in-plane stretching ratio. Scale bar: a 30 μm, b 10 μm, d 10 μm, e 3 μm

Fig. 4

Principle of improving the thermal conductivity of GNS/ANF films by eliminating GNS wrinkles through in-plane stretching. a Schematic diagram of the GNS supercell, ANF supercell. b The PDOS versus frequency results of GNS and ANF. c, d Raman spectra of ANF films, GNS and GNS/ANF films with different in-plane stretching ratio. e, f FTIR spectra. g Density for GNS/ANF films by different in-plane stretching ratio. h, i Modeling and temperature distribution of GNS/ANF films by in-plane stretching for 0% (up), and 15% (down)

Fig. 5

Thermal management demonstration of GNS/ANF composite films with eliminated GNS wrinkles. a GNS/ANF composite films integrated into the backside of a flexible LED chip. b Image of the front side. c Infrared thermal images. d Surface temperature evolution curves of a flexible LED chip with working time. e, f Pure ANF, GNS/ANF-0% and GNS/ANF-15% integrated into a smartphone. g Thermal infrared images of smartphone under different working conditions