Charge transport studies in fluorene – Dithieno[3,2-b:2′,3′-d]pyrrole oligomer using time-of-flight photoconductivity method

Charge mobility characteristics of a newly synthesised 2,6-bis[2-(9,9-dihexyl-9H-fluorene)]-N-(4-hexylphenyl)-dithieno[3,2-b:2′,3′-d]pyrrole oligomer (DTP-FLU) was studied as a function of electric field and temperature using time-of-flight photoconductivity measurement. It is found that the DTP-FLU oligomer is a hole transporting material with a hole mobility of 7.7 × 10^?6 cm²/Vs at an applied electric field of 2.9 × 10⁵ V/cm at 298 K. The dependence of hole mobility with applied electric field and temperature is studied in detail by analyzing the experimental results using the Bassler’s Gaussian disorder model and Correlated disorder model. The energetic disorder parameter (σ) = 100 meV, mobility pre-factor (μ_∞) = 6.1 × 10^?4 cm²/Vs and positional disorder parameter (Σ) = 2.4 were extracted using Gaussian disorder model. The film morphology and photophysical properties of this new oligomer are also studied in detail.     

Investigations on the Structural Damage in Human Erythrocytes Exposed to Silver,Gold, and Platinum Nanoparticles

Human erythrocytes or red blood cells (RBCs), which constitute 99% of blood cells, perform an important function of oxygen transport and can be exposed to nanoparticles (NPs) entering into the human body during therapeutical applications involving such NPs. Hence, the haemocompatibility of the Ag, Au, and Pt NPs on human RBCs is investigated. The parameters monitored include haemolysis, haemagglutination, erythrocyte sedimentation rate, membrane topography, and lipid peroxidation. The findings suggest that platinum and gold NPs are haemocompatible compared to Ag NPs. Erythrocytes exhibit significant lysis, haemagglutination, membrane damage, detrimental morphological variation, and cytoskeletal distortions following exposure to Ag NPs at a concentration of 100 µg mL^?1. Exposure of Ag⁺ to RBCs shows no lysis or deterioration, implying that the observed toxicity is solely due to NPs. The haemolyzed erythrocyte fraction has the ability to induce DNA damage in nucleated cells. Additionally, multiple pits and depressions are observed on RBC membrane following exposure to Ag NPs (50 µg mL^?1 onwards). Hence, it is apparent that Ag NPs exhibit toxicity on RBCs and on other cells that are exposed to NP‐mediated haemolyzed fractions.     

Cost-Benefit Model for the Construction of Tornado Shelters

Tornadoes have been identified as one of the leading causes of death and injuries among natural disasters in the United States. Shelters play an important role in tornado mitigation efforts, since tornado-related mortality and injury rates are higher when tornado shelters are not available. This paper describes a methodology to address the viability of construction of tornado shelters in areas which have significant tornado hazards. A cost-benefit model that estimates the relative advantages of three tornado shelter construction strategies was developed and tested. The model accounts for factors such as probability of tornado occurrence, historical death and injury rates, economic incentives, and local construction and maintenance costs. The implications of factors such as useful life period, discount rate, and occupancy on the viability of the shelter were also studied. Relevance of this model to decision makers, as well as future needs for the model, is discussed.     

Structurally modified poly(methyl methacrylate) electrospun nanofibers as better host matrix for noble metal nanoparticles

Poly(methyl methacrylate) (PMMA) nanofibers are proved as good host matrix for various nanomaterials. Here, the possibilities offered by the process of electrospinning are exploited for the production of pure and structurally modified surface roughened and coaxial hollow PMMA electrospun nanofibers with unique advantages and surface characteristics, which is proved through various structural analyses. The host matrix nature of these pure and structurally modified surface roughened and coaxial hollow PMMA nanofibers to gold nanoparticles (AuNPs) are proved through different structural and morphological analyses. The host matrix nature of pure and structurally modified surface roughened and coaxial hollow PMMA nanofibers to AuNPs are compared with that of pure PMMA nanofibers by comparing their structural and optical properties. It is found here that, the surface roughened PMMA nanofibers act as better host matrix with more uniform distribution of particles and intensity enhancement than the pure and coaxial hollow PMMA nanofibers. Pure and coaxial hollow PMMA nanofibers show almost two times enhancement in intensity while the surface roughened PMMA nanofibers show almost five times enhancement in intensity after incorporating AuNPs. The host matrix nature of PMMA nanofibers is thus proved to be improved by making structural modifications on PMMA nanofibers in a simple and cost-effective way. This makes them more suitable and adaptable in their applications. This superior property of surface roughened PMMA nanofibers over pure PMMA nanofibers can be used in all the application fields of PMMA nanofibers like optical works, catalytically supporting agents, antibacterial supporting systems and so on.     

Functionalization of surfactant wrapped graphene nanosheets with alkylazides for enhanced dispersibility

A facile and simple approach for the covalent functionalization of surfactant wrapped graphene sheets is described. The approach involves functionalization of dispersible graphene sheets with various alkylazides and 11-azidoundecanoic acid proved the best azide for enhanced dispersibility. The functionalization was confirmed by infrared spectroscopy and scanning tunneling microscopy. The free carboxylic acid groups can bind to gold nanoparticles, which were introduced as markers for the reactive sites. The interaction between gold nanoparticles and the graphene sheets was followed by UV-vis spectroscopy. The gold nanoparticle-graphene composite was characterized by transmission electron microscopy and atomic force microscopy, demonstrating the uniform distribution of gold nanoparticles all over the surface. Our results open the possibility to control the functionalization on graphene in the construction of composite nanomaterials.     

Cationic surfactant mediated exfoliation of graphite into graphene flakes

A simple and effective method for the preparation of a few layered graphene nanoflakes directly from graphite has been successfully demonstrated. Mild ultrasonication of highly ordered pyrolytic graphite, in presence of a cationic surfactant cetyltrimethylammonium bromide and acetic acid yielded graphene nanoflakes, which formed a stable colloidal suspension in organic solvent such as N,N-dimethyl formamide. Scanning and transmission electron microscopic analyses showed that the dispersed phase consist of mainly few layered graphene nanoflakes. Average thickness of the flakes was found to be ∼1.18 nm. Energy dispersive X-ray analysis indicated the absence of graphene oxide. Field emission measurements for the nanoflakes showed a turn on voltage of 7.5 V/μm and emission current densities of 0.15 mA/cm².     

Flexible conductive graphene/poly(vinyl chloride) composite thin films with high mechanical strength and thermal stability

The fabrication and characterization of ultrathin composite films of surfactant-wrapped graphene nanoflakes and poly(vinyl chloride) is described. Free-standing composite thin films were prepared by a simple solution blending, drop casting and annealing route. A significant enhancement in the mechanical properties of pure poly(vinyl chloride) films was obtained with a 2 wt.% loading of graphene, such as a 58% increase in Young’s modulus and an almost 130% improvement of tensile strength. Thermal analysis of the composite films showed an increase in the glass transition temperature of the polymer, which confirms their enhanced thermal stability. The composite films had very low percolation threshold of 0.6 vol.% and showed a maximum electrical conductivity of 0.058 S/cm at 6.47 vol.% of the graphene loading.