Boron nitride with high zeta potential via plasma processing in solution for preparation of polyrotaxane composite

Abstract

Plasma processing in solution is effective for the preparation of composites. To optimize the plasma processing in solution, a method that can be used to sufficiently evaluate the surface modifications is necessary. In this study, to identify such a method, hexagonal boron nitride (hBN) particles modified by plasma processing in solution and exhibiting different zeta potentials were used to prepare a polyrotaxane composite. Plasma processing in a hydroquinone solution yielded hBN particles with a high zeta potential, named HQpBN, and x-ray computed tomography showed a uniform dispersion of the HQpBN/polyrotaxane composite. The tensile strength and elongation of the HQpBN/polyrotaxane composite were twice as high as those of an unmodified hBN/polyrotaxane composite, in which hBN particles aggregated. These results demonstrate that the zeta potential of the modified particles can be used as an indicator to guide optimal surface modification during plasma processing in solution for the preparation of homogeneous composites.

Carbon Layer Formation on Hexagonal Boron Nitride by Plasma Processing in Hydroquinone Aqueous Solution

“…The formed carbon layer is expected to contain polar functional groups such as hydroxyl and carboxyl groups. − Indeed, in our previous paper, HQpBN was confirmed to have a higher negative zeta potential (−42.5 mV at pH 7) than pBN (−36.7 mV at pH 7), thus providing better dispersibility in a polymer . Furthermore, HQpBN was also found to maintain the thermal conductivity and electrical resistivity of hBN when used as a filler in composites.…”

“…24−26 Indeed, in our previous paper, HQpBN was confirmed to have a higher negative zeta potential (−42.5 mV at pH 7) than pBN (−36.7 mV at pH 7), thus providing better dispersibility in a polymer. 11 Furthermore, HQpBN was also found to maintain the thermal conductivity and electrical resistivity of hBN when used as a filler in composites. Thus, the carbon layer on HQpBN is expected to have reactive sites that will allow functionalization with any other groups.…”

“…Hydroquinone-aided plasma-modified hBN (HQpBN) particles were prepared using a previously reported method. 11 A plasma was generated in 900 mL of distilled water containing 5 g of hBN particles (Sigma−Aldrich, Ltd) and 10 g of hydroquinone (Wako Pure Chemical Corporation), using a bipolar pulsed power supply (Kurita Seisakujo, MPP-HV-04-300 kHz). A dispersion device based on cavitation (Nihon Spindle Mfg.…”

“…Hexagonal boron nitride (hBN), which has a graphite-like structure, has attracted attention due to its superior thermal conductivity and electrical insulating properties. In recent years, as a two-dimensional layered material, hBN has shown great potential in many applications in substrates for graphene electronics, − optical devices, , and composite materials. − In particular, polymer composites with hBN particles as thermally conductive and electrically insulating fillers are expected to act as thermal management materials to address heat accumulation in electronic devices with higher integration. − For such applications, the surface modification of hBN particles is essential to improve dispersibility in polymer matrices and form strong filler–polymer bonds, thus realizing organic/inorganic composites that combine the mechanical properties of polymer matrices with thermal conductivity at high filler contents. − Among surface modification techniques using dispersants , and oxidization, , plasma processing is an effective method for hBN surface modification because the highly energetic species in plasma can break stable B–N bonds and enable the in-plane functionalization of hBN. , Plasma in solution is particularly suitable for the surface modification of inorganic particles because stirring solution during the process can suppress particle agglomeration and promote effective reactions between particles and high-density excited species. ,,− However, even with plasma processing, it is difficult to make reactive hBN surfaces allowing designable functionalization because of the scarcity of reactive sites such as dangling bonds …”

“…Many researchers have studied carbon synthesis and deposition on materials using plasma processes, including nanographene synthesis using alcohol in-liquid plasma. − Nitrogen-doped carbon has also been synthesized on metal nanoparticles using plasma in solutions containing organic compounds such as N,N -dimethylformamide. , Furthermore, as low-pressure plasma processes, various diamond-like carbons have been synthesized by plasma-enhanced chemical vapor deposition, − and the direct growth of graphene on hBN by plasma-assisted molecular beam epitaxy has been reported. , In our previous studies, the modification of hBN particles by plasma in hydroquinone aqueous solution was found to improve their dispersibility in water and a polymer matrix with maintaining the thermal conductive and electrical insulating properties as fillers, , but the surface state was not clarified.…”