Polymeric Frameworks as Organic Semiconductors with Controlled Electronic Properties

The rational assembly of monomers, in principle, enables the design of a specific periodicity of polymeric frameworks, leading to a tailored set of electronic structure properties in these solid-state materials. The further development of these emerging systems requires a combination of both experimental and theoretical studies. Here, we investigated the electronic structures of two-dimensional polymeric frameworks based on triazine and benzene rings, by means of electrochemical techniques. The experimental density of states was obtained from quasi-open-circuit voltage measurements through galvanostatic intermittent titration technique, which we show to be in excellent agreement with first principles calculations performed for two and three-dimensional structures of these polymeric frameworks. These findings suggest that the electronic properties do not only depend on the number of stacked layers but also on the ratio of the different aromatic rings

Polylactic acid (PLA)/halloysite nanotube (HNT) composite mats: Influence of HNT content and modification

Polylactic acid (PLA)/halloysite nanotube (HNT) composite mats were successfully fabricated via electrospinning. Composite mats reinforced by both unmodified and modified HNTs with a dispersant BYK-9076 were prepared at the HNT contents of 0, 1, 5 and 10 wt%/v. The influence of HNT content and modification was investigated comprehensively, based on several characterisation techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, mechanical testing, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). Typical modified Halpin–Tsai model and modified Halpin–Tsai laminate hybrid model in conventional composite theory were used, which were found difficult to predict the entire experimental data of elastic moduli for PLA/HNT composite mats, possibly arising from the nanosized effect of HNTs and some electrospun PLA nanofibres within composite mats

Analytical Model for the Effect of Pressure on the Electronic Structure of Germanium Nanocrystals

The electronic structure modification of germanium nanocrystals under the condition of external pressure has been investigated, in order to gain a better understanding of their relevant properties. In this paper, an atomistic insight into the effect of size-pressure variation on the electronic structure of germanium nanocrystals (of 8, 16, 54 atoms) is performed. The effect of pressure on the structural and electronic properties of germanium nanocrystals has been investigated using the large unit cell within the framework of ab initio restricted Hartree-Fock theory and the linear combination of atomic orbital approximation included in Gaussian03 software by considering the effects of size and pressure. Cohesive energy, indirect band gap, valence bandwidth and bulk modulus are all obtained, which is consistent with understanding the interdependence of these quantities and their common atomistic origin originates with size- and pressure-induced change, leading to a variation of the crystal potential. Theoretical results are compared with the experimental measurements. The calculations show an agreement of the calculated lattice constant at equilibrium point, cohesive energy, valence bandwidth, and bulk modulus with the experimental data. Computed band gap is greater than the experimental value. That is what expected from Hartree-Fock method. Band gap shows a good trend compared to theoretical values. The calculations of the effect of pressure on the aforementioned properties are investigated. It is found that the valence bandwidth decrease with the increase of pressure, and cohesive energy decrease with the increase of tensile pressure in 8 atoms while it increase in both 16 and 54 atoms. Lattice constant increase with pressure in three crystals, and energy gap decrease with pressure in both 8, and 16 atoms crystals and increase with pressure in 54 atoms nanocrystal. The maximum value of pressure is taken to be 7.6 GPa, because beyond this value, the phase of Ge transforms from nanocrystals to another phase

Analytical Model for the Effect of Pressure on the Electronic Structure of Germanium Nanocrystals

The electronic structure modification of germanium nanocrystals under the condition of external pressure has been investigated, in order to gain a better understanding of their relevant properties. In this paper, an atomistic insight into the effect of size-pressure variation on the electronic structure of germanium nanocrystals (of 8, 16, 54 atoms) is performed. The effect of pressure on the structural and electronic properties of germanium nanocrystals has been investigated using the large unit cell within the framework of ab initio restricted Hartree-Fock theory and the linear combination of atomic orbital approximation included in Gaussian03 software by considering the effects of size and pressure. Cohesive energy, indirect band gap, valence bandwidth and bulk modulus are all obtained, which is consistent with understanding the interdependence of these quantities and their common atomistic origin originates with size- and pressure-induced change, leading to a variation of the crystal potential. Theoretical results are compared with the experimental measurements. The calculations show an agreement of the calculated lattice constant at equilibrium point, cohesive energy, valence bandwidth, and bulk modulus with the experimental data. Computed band gap is greater than the experimental value. That is what expected from Hartree-Fock method. Band gap shows a good trend compared to theoretical values. The calculations of the effect of pressure on the aforementioned properties are investigated. It is found that the valence bandwidth decrease with the increase of pressure, and cohesive energy decrease with the increase of tensile pressure in 8 atoms while it increase in both 16 and 54 atoms. Lattice constant increase with pressure in three crystals, and energy gap decrease with pressure in both 8, and 16 atoms crystals and increase with pressure in 54 atoms nanocrystal. The maximum value of pressure is taken to be 7.6 GPa, because beyond this value, the phase of Ge transforms from nanocrystals to another phase

In Situ Confocal Raman Mapping Study of a Single Ti-Assisted ZnO Nanowire

In this work, we succeeded in preparing in-plane zinc oxide nanowires using a Ti-grid assisted by the chemical vapor deposition method. Optical spatial mapping of the Confocal Raman spectra was used to investigate the phonon and geometric properties of a single ZnO nanowire. The local optical results reveal a red shift in the non-polar E2 high frequency mode and width broadening along the growth direction, reflecting quantum-confinement in the radial direction

Tribological properties of fabric self-lubricating liner based on organic montmorillonite (OMMT) reinforced phenolic (PF) nanocomposites as hybrid matrices

Organic montmorillonite (OMMT) reinforced phenolic (PF) nanocomposites with OMMT contents of 2 and 5 wt% were fabricated by the two-step OMMT intercalation process, resulting in the further increase of interlayer spacing of OMMT from 2.07 to 4.27 nm. Prepared OMMT/PF composites were found to possess a mix of intercalated and agglomerated clay structures via X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). Results obtained via differential scanning calorimetry (DSC) and thermogravimetry (TG) revealed that the thermal stability of PF matrices was enhanced by the incorporation of OMMT. With OMMT/PF nanocomposites as hybrid matrices, fabric self-lubricating liners were prepared to evaluate their tribological properties. Effects of OMMT on friction coefficient, wear loss and wear morphology of fabric self-lubricating liner, based on OMMT/PF nanocomposites, were studied via long-term friction and wear tests. Tribological properties of liners with different OMMT contents were investigated by imitating a high-velocity/light-load condition. The addition of OMMT appears to enhance the friction and wear properties of fabric self-lubricating liner, and the preferable OMMT content is around 2 wt%