Nanoparticles in a Liquid: New State of Liquid?

Atoms at a solid surface have different co-ordination numbers, bond lengths, and bond angles, with manifest differences in chemical and physical properties of surface atoms relative to their counterparts in the bulk material. In materials where the fraction of atoms at or near the surface is relatively small (e.g. most bulk materials) the effects of surface atoms on macroscopic phenomena are often negligible. This is not true when materials are in the form of nanoparticles, where their highly subdivided state leads to a very high fraction of the total atoms residing at or near a surface. For nanoparticles, the differences between the bulk and surface properties of constituent atoms can often dominate the overall properties of the material. These effects manifest themselves as an increase in vapor pressure, a decrease in melting point, and/or an increase in surface tension/ surface energy when compared to their macroscopic counterparts. Nanoparticles also experience significant changes in optical and electronic properties due to quantum size effects and energetic effects initiated by the increasing contribution of the particle surface to the energy of particles.
 

Nano-Aluminum Thermite Formulations: Characterizing the Fate Properties of a Nanotechnology during Use

Nanothermites represent an emerging class of highly efficient propellants/explosive materials whose environmental impacts are poorly understood. In this work, several nanothermite formulations (e.g., Fe₂O₃/Al and Bi₂O₃/Al) were investigated following material transformation during end use. Combustion products were analyzed by SEM, EDS, and XRD. These products subsist with unique physical and chemical forms as compared to the original materials. The combustion process results in the formation of inert spinel structures in the case of the iron-based formulations, whereas Bi₂O₃/Al composites react fully, transforming to metallic bismuth and aluminum oxide. These products are largely resistant to wetting and evidence suggests that transport in aqueous environments would be limited. Due to the particle size ranges found, it is speculated that the main transport route for these materials is aerosolization. These data will ultimately establish a baseline for future studies aimed at an accurate determination of the fate of nanothermite formulations after use.
 

Effects of Nano-Wollastonite on Thermal Conductivity Coefficient of Medium-Density Fiberboard

Effect of wollastonite nanofibers on the improvement of thermal conductivity coefficient of medium-density fiberboard (MDF) was studied here to find a possible solution to decrease hot-press time as a bottle-neck during composite production. Nanowollastonite (NW) was applied at 10%, based on the dry weight of wood fibers. Density of the control MDF boards was 0.66 g/cm3. Thermal conductivity coefficient was measured using an apparatus based on Fourier’s Law for heat conduction. Results indicated that thermal conductivity was increased by 11.5% in NW-treated MDF boards in comparison to the control boards; thermal conductivity of control MDF was 0.099, whereas that of the NW-treated MDF boards was 0.110 (w/mk). It may then be concluded that higher thermal conductivity of wollastonite nanofibers, spread all over the MDF-matrix, resulted in the increased thermal conductivity coefficient of NW-treated boards. This increased thermal conductivity contributed to better resin cure in the core section of the MDF mat, resulting in improved physical and mechanical properties reported in prior studies.
 

Bundlet Model of Single- Wall Carbon, BC2N and BN Nanotubes, Cones and Horns in Organic Solvents

The existence of Single-wall C-nanocones (SWNCs), especially nanohorns (SWNHs) and BC2N/Boron Nitride (BN) analogues is discussed in organic solvents in cluster form. A theory is developed based on the bundlet model, describing distribution function by size. The phenomena present unified explanation in the model, in which free energy of (BC2N/BN )SWNCs involved in cluster, is combined from two components: volume one proportional to the number of molecules n in cluster and surface one, to n1/2. The model enables describing distribution function of (BC2N/BN )SWNC clusters by size. From geometrical differences, bundlet [(BC2N/BN )SWNCs]/ droplet (C60/B15C30N15/B30N30) models predict dissimilar behaviours. Various disclination (BC2N/BN )SWNCs are studied via energetic/ structural analyses. Several (BC2N/BN )SWNC’s ends are studied, which are different because of closing structure and arrangement type. Packing efficiencies and interaction-energy parameters of (BC2N/BN )SWNCs/SWNHs are intermediate between C60/ B15C30N15/B30N30 and (BC2N/BN )Single-wall C-nanotube (SWNT) clusters: in between behaviour is expected; however, properties of (BC2N/BN )SWNCs, especially (BC2N/BN )SWNHs, are calculated closer to (BC2N/BN )SWNTs. Structural asymmetry in different (BC2N/BN )SWNCs, characterized by cone angle, distinguishes properties of types: P2. BC2N/BN, especially species isoelectronic with C-analogues, may be stable.