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John O | May 2019

Flexible nanocomposite demonstrates high strength and high thermal conductivity

By Josh Perry, Editor


Researchers from the Rice University (Houston, Texas) Brown School of Engineering developed a new nanocomposite with enhanced strength and thermal conductivity that they believe could be a superior high-temperature dielectric material for flexible electronics.


From left, postdoctoral researcher Anand Puthirath, academic visitor Fanshu Yuan and research scientist M.M. Rahman show the high-temperature flexible dielectric material invented at Rice University. (Jeff Fitlow/Rice University)


According to a report from the school, the nanocomposite combines 1-D polymer nanofibers and 2-D boron nitride nanosheets. Boron nitride is an electrical insulator but has high thermal conductivity.


“The nanofibers reinforce the self-assembling material while the ‘white graphene’ nanosheets provide a thermally conductive network that allows it to withstand the heat that breaks down common dielectrics, the polarized insulators in batteries and other devices that separate positive and negative electrodes,” the article explained.


The material is 12-15 microns thick and acted as a heat sink up to 250°C. Researchers demonstrated that the composite conducted heat four times better than the polymer alone.


“In its simplest form, a single layer of polyaramid nanofibers binds via van der Waals forces to a sprinkling of boron nitride flakes, 10% by weight of the final product,” the article continued. “The flakes are just dense enough to form a heat-dissipating network that still allows the composite to retain its flexibility, and even foldability, while maintaining its robustness. Layering polyaramid and boron nitride can make the material thicker while still retaining flexibility.”


The research was recently published in Advanced Functional Materials. The abstract read:


“Polymer dielectrics find applications in modern electronic and electrical technologies due to their low density, durability, high dielectric breakdown strength, and design flexibility. However, they are not reliable at high temperatures due to their low mechanical integrity and thermal stability.


“Herein, a self?assembled dielectric nanocomposite is reported, which integrates 1D polyaramid nanofibers and 2D boron nitride nanosheets through a vacuum?assisted layer?by?layer infiltration process. The resulting nanocomposite exhibits hierarchical stacking between the 2D nanosheets and 1D nanofibers.


“Specifically, the 2D nanosheets provide a thermally conductive network while the 1D nanofibers provide mechanical flexibility and robustness through entangled nanofiber–nanosheet morphologies. Experiments and density functional theory show that the nanocomposites through thickness heat transfer processes are nearly identical to that of boron nitride due to synergistic stacking of polyaramid units onto boron nitride nanosheets through van der Waals interactions.


“The nanocomposite sheets outperform conventional dielectric polymers in terms of mechanical properties (about 4–20?fold increase of stiffness), light weight (density ≈1.01 g cm−3), dielectric stability over a broad range of temperature (25–200 °C) and frequencies (103–106 Hz), good dielectric breakdown strength (≈292 MV m−1), and excellent thermal management capability (about 5–24 times higher thermal conductivity) such as fast heat dissipation.”


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