Engineering the band gap of BN and BC2N nanotubes based on T-graphene sheets using a transverse electric field: Density functional theory study

A new class of nanotubes formed by rolling boron nitride (BN) and boron carbonitride (BC2N) sheets in the form of T-graphene is suggested in this work. The structural and electronic properties of these nanotubes, named T-BNNTs and T-BC2NNTs, are systematically studied by density functional theory (DFT) calculations. The tubes with different chirality and size are considered. Their structural stability is evaluated by calculation of cohesive energy and ab-initio molecular dynamics simulation. The results confirm the thermal stability of the considered T-BNNTs and T-BC2NNTs. The calculated electronic band structures and density of states reveal that the T-BNNTs are insulators, independent of their size and chirality. The T-BC2NNTs show both metallic and semiconducting properties. Our results indicate that the electronic properties of T-BNNTs and T-BC2NNTs can be successfully tuned by applying an external electric field, which makes the application of these tubes in nanoelectronic devices more promising

Towards friction and adhesion from high modulus microfiber arrays

Unlike traditional pressure sensitive adhesives, the natural setal arrays of gecko lizards achieve dry adhesion with stiff, keratinous material. This remarkable property has inspired a new class of adhesive and high friction microstructures composed of stiff materials that, like natural setae, have an elastic modulus greater than 1 GPa. In contrast to softer materials, such as rubber and low molecular weight acrylates, stiff materials have the advantage of wear and creep resistance and represent a wide range of polymers, metals, and ceramics that include materials that are also temperature resistant and biocompatible. This work presents progress in the design and fabrication of synthetic gecko adhesives with particular attention to the principles of contact mechanics and elasticity that are essential in formulating accurate design criteria

Engineering Composites Made from Wood and Chicken Feather Bonded with UF Resin Fortified with Wollastonite: A Novel Approach

Wood-composite panel factories are in shortage of raw materials; therefore, finding new sources of fibers is vital for sustainable production. The effects of chicken feathers, as a renewable source of natural fibers, on the physicomechanical properties of medium-density fiberboard (MDF) and particleboard panels were investigated here. Wollastonite was added to resin to compensate possible negative effects of chicken feathers. Only feathers of the bodies of chickens were added to composite matrix at 5% and 10% content, based on the dry weight of the raw material, particles or fibers. Results showed significant negative effects of 10%-feather content on physical and mechanical properties. However, feather content of 5% showed some promising results. Addition of wollastonite to resin resulted in the improvement of some physical and mechanical properties. Wollastonite acted as reinforcing filler in resin and improved some of the properties; therefore, future studies should be carried out on the reduction of resin content. Moreover, density functional theory (DFT) demonstrated the formation of new bonds between wollastonite and carbohydrate polymers in the wood cell wall. It was concluded that chicken feathers have potential in wood-composite panel production

Improving Fire Retardancy of Beech Wood by Graphene

The aim of this paper was to improve the fire retardancy of beech wood by graphene. Six fire properties, namely time to onset of ignition, time to onset of glowing, back-darkening time, back-holing time, burnt area and weight loss were measured using a newly developed apparatus with piloted ignition. A set of specimens was treated with nano-wollastonite (NW) for comparison with the results of graphene-treated specimens. Graphene and NW were mixed in a water-based paint and brushed on the front and back surface of specimens. Results demonstrated significant improving effects of graphene on times to onset of ignition and glowing. Moreover, graphene drastically decreased the burnt area. Comparison between graphene- and NW-treated specimens demonstrated the superiority of graphene in all six fire properties measured here. Fire retardancy impact of graphene was attributed to its very low reaction ability with oxygen, as well as its high and low thermal conductivity in in-plane and cross-section directions, respectively. The improved fire-retardancy properties by the addition of graphene in paint implied its effectiveness in hindering the spread of fire in buildings and structures, providing a longer timespan to extinguish a fire, and ultimately reducing the loss of life and property. Based on the improvements in fire properties achieved in graphene-treated specimens, it was concluded that graphene has a great potential to be used as a fire retardant in solid wood species