Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Thin Friction The rubbing motion between two surfaces is always hindered by friction, which is caused by continuous contacting and attraction between the surfaces. These interactions may only occur over a distance of a few nanometers, but what happens when the interacting materials are only that thick? Lee et al. (p. 76; see the Perspective by Müser and Shakhvorostov) explored the frictional properties of a silicon tip in contact with four atomically thin quasi–two dimensional materials with different electrical properties. For all the materials, the friction was seen to increase as the thickness of the film decreased, both for flakes supported by substrates and for regions placed above holes that formed freely suspended membranes. Placing graphene on mica, to which it strongly adheres, suppressed this trend. For these thin, weakly adhered films, out-of-plane buckling is likely to dominate the frictional response, which leads to this universal behavior. A universal trend is observed for the friction properties of thin films on weakly adhering substrates. Using friction force microscopy, we compared the nanoscale frictional characteristics of atomically thin sheets of graphene, molybdenum disulfide (MoS2), niobium diselenide, and hexagonal boron nitride exfoliated onto a weakly adherent substrate (silicon oxide) to those of their bulk counterparts. Measurements down to single atomic sheets revealed that friction monotonically increased as the number of layers decreased for all four materials. Suspended graphene membranes showed the same trend, but binding the graphene strongly to a mica surface suppressed the trend. Tip-sample adhesion forces were indistinguishable for all thicknesses and substrate arrangements. Both graphene and MoS2 exhibited atomic lattice stick-slip friction, with the thinnest sheets possessing a sliding-length–dependent increase in static friction. These observations, coupled with finite element modeling, suggest that the trend arises from the thinner sheets’ increased susceptibility to out-of-plane elastic deformation. The generality of the results indicates that this may be a universal characteristic of nanoscale friction for atomically thin materials weakly bound to substrates.

Frictional Characteristics of Atomically-Thin Sheets

Synchronously improved thermal conductivity and dielectric constant for epoxy composites by introducing functionalized silicon carbide nanoparticles and boron nitride microspheres.

It is an urgent need that defect repair can develop from simple device fixation to living tissue reconstruction, from short life function replacement to permanent regeneration repair. At present, bone transplantation has become the second largest transplantation surgery after blood transfusion, and artificial bone transplantation generates great hope for the repair and treatment of bone defect. In order to repair bone defect, artificial bone must have good biological properties and sufficient mechanical properties, and it should also have the shape matching to bone defect site and the connected porous structure. For structures and properties requirements of artificial bone, in this review three major challenges faced by artificial bone transplantation are systemtically analyzed and current methods and strategies to address these issues are discussed: 1) the need for developing a type of bone scaffold material with both biological and mechanical properties, 2) the need for realizing the controllable fabrication of individual shape and multistage pore structure of bone scaffold, 3) the need for realizing the transformation from man‐made structure to biological structure. Besides, it summarizes the advantages and disadvantages of these methods and discusses the potential future directions of structural and functional adaptive artificial bone for bone defect regeneration.

Structural and Functional Adaptive Artificial Bone: Materials, Fabrications, and Properties

Abstract Two-dimensional (2D) nanomaterial-reinforced polymer composites exhibit superior properties and multifunctional applications. Compared to lower dimensional nanomaterials such as nanotubes and nanoparticles, 2D nanomaterials show a larger surface area. The large surface area makes 2D nanomaterials more effectively restrict the mobility of polymer chains and yields better reinforcing efficiency than the lower-dimensional nanomaterials. To gain an in-depth understanding and extend the applications of polymer composites reinforced with 2D nanomaterials, this paper reviews the progress in the fundamentals of synthesis and applications of such composites. The motivation and improvement of adding 2D nanomaterials to polymer materials are introduced first, followed by the synthesis approaches and the properties of typical 2D nanomaterials, including graphene, boron nitride nanosheet, and molybdenum disulfide nanosheet. Based on the properties of 2D nanomaterials, polymer composites reinforced with different types of 2D nanomaterials are designed for structural application, thermal dissipation application, tribological application, three-dimensional printing composite structures, and strain sensing application. Afterwards, the significance of reinforcement–matrix interaction and its improving approach are reviewed. The current progress envisions that polymer composites reinforced with 2D nanomaterials can be used in the fields of aviation and aerospace for improving radiation shielding capacity and nanomedical engineering.

/pdf/two-dimensional-nanomaterial-based-polymer-composites-2krt09og.pdf

Yonghan Li

Papers

Mechanical and dielectric properties of functionalized boron nitride nanosheets/silicon nitride composites