Achieving a Collapsible, Strong, and Highly Thermally Conductive Film Based on Oriented Functionalized Boron Nitride Nanosheets and Cellulose Nanofiber

Abstract

Boron nitride nanosheet (BNNS) films receive wide attention in both academia and industry because of their high thermal conductivity (TC) and good electrical insulation capability. However, the brittleness and low strength of the BNNS film largely limit its application. Herein, functionalized BNNSs (f-BNNSs) with a well-maintained in-plane crystalline structure were first prepared utilizing urea in the aqueous solution via ball-milling for the purpose of improving their stability in water and enhancing the interaction with the polymer matrix. Then, a biodegradable and highly thermally conductive film with an orderly oriented structure based on cellulose nanofibers (CNFs) and f-BNNSs was prepared just by simple vacuum-assisted filtration. The modification of the BNNS and the introduction of the CNF result in a better orientation of the f-BNNS, sufficient connection between f-BNNS themselves, and strong interaction between f-BNNS and CNF, which not only make the prepared composite film strong and tough but also possess higher in-plane TC. An increase of 70% in-plane TC, 63.2% tensile strength, and 77.8% elongation could be achieved for CNF/f-BNNS films, compared with that for CNF/BNNS films at the filler content of 70%. Although at such a high f-BNNS content, this composite film can be bended and folded. It is even more interesting to find that the in-plane TC could be greatly enhanced with the decrease of the thickness of the film, and a value of 30.25 W/m K can be achieved at the thickness of ∼30 μm for the film containing 70 wt % f-BNNS. We believe that this highly thermally conductive film with good strength and toughness could have potential applications in next-generation highly powerful and collapsible electronic devices.

Highly Thermoconductive, Thermostable, and Super‐Flexible Film by Engineering 1D Rigid Rod‐Like Aramid Nanofiber/2D Boron Nitride Nanosheets

“…[29,30] For instance, with the addition of 50 wt% BNNS, the thermal conductivity of CNF/BNNS paper only reaches 10-20 W m −1 K −1 , significantly less than those of metals such as iron and copper. [24] On the contrary, the addition of additives at high levels (>30 wt%) results in undesired mechanical losses resulting from composite brittleness. In addition to these thermoconductive limitations, conventional polymer nanofiber without aromatic rings in the backbone also cannot tolerate high temperatures (i.e., beyond 200 °C), which impedes the utilization of these materials as heat sink papers in elevated temperature applications.…”

“…The absence of strong van der Waals interactions and divergent phonon vibration modes between polymer nanofiber and BNNS are also obstructions to thermal enhancement at low filler percolation thresholds . For instance, with the addition of 50 wt% BNNS, the thermal conductivity of CNF/BNNS paper only reaches 10–20 W m −1 K −1 , significantly less than those of metals such as iron and copper . On the contrary, the addition of additives at high levels (>30 wt%) results in undesired mechanical losses resulting from composite brittleness.…”

“…[14][15][16][17][18][19][20] Among the possibilities, the utilization of a 1D polymer nanofiber combined with 2D boron nitride nanosheets (BNNS) has been reported to be one of the most efficient approaches. [21][22][23][24] Since a 1D polymer nanofiber can serve as a basic unit to connect the 2D BNNS planes along the fiber axis, it is often effective in constructing effective thermoconductive pathways. Moreover, in contrast to the bulk randomcoiled polymer morphology, the contact thermal resistance between polymer nanofiber and BNNS is reduced, hence decreasing the phonon scattering among the interacting units.Despite the advantages noted above, previous reports have typically involved the use of 1D polymer nanofibers such as cellulose nanofiber (CNF) or electrospun nanofiber mainly constituted of macromolecular chains with long and soft segments.…”

Synergistic effects on the enhancement of thermal conductive properties of thermal greases

“…The XRD pattern of GF reveals the characteristic diffraction peak (002) at 2θ = 26.5 ° with d ‐spacing of 0.34 nm, which is attributed to a partially ordered crystal structure of GF. For h‐BN, the diffraction peaks are corresponding to the (002), (100), (101), (102), and (004) planes of h‐BN, respectively . Besides, the (002) peak of h‐BN is strong and sharp, manifesting that the in‐plane crystalline structure is quite intact without obvious damage.…”

“…For h-BN, the diffraction peaks are corresponding to the (002), (100), (101), (102), and (004) planes of h-BN, respectively. 32,33 Besides, the (002) peak of h-BN is strong and sharp, manifesting that the in-plane crystalline structure is quite intact without obvious damage. The XRD pattern of HPC shows no distinct diffraction peaks, which indicates the HPC is amorphous.…”