A Simple Route towards High-Concentration Surfactant-Free Graphene Dispersions

A simple solvent exchange method is introduced to prepare high-concentration and surfactant-free graphene liquid dispersion. Natural graphite flakes are first exfoliated into graphene in dimethylformamide (DMF). DMF is then exchanged by terpineol through distillation, relying on their large difference in boiling points. Graphene can then be concentrated thanks to the volume difference between DMF and terpineol. The concentrated graphene dispersions are used to fabricate transparent conductive thin films, which possess comparable properties to those prepared by more complex methods.Comment: 9 pages, 3 figure

ESTIMATION OF DEPROTONATION COEFFICIENTS FOR CHELATING ION EXCHANGE RESINS. COMPARISON OF DIFFERENT THERMODYNAMIC MODEL

The deprotonation of quinolic resin P-127 and iminodiacetic resin Amberlite IRC-718 has been studied. The process of salt transfer into the resin phase is considered to be an important contributor to the deprotonation process. Estimation of the salt transfer was based on the principle of equal activity of the salt in both phases at equilibrium. Two assumptions were made: sorbed alkali metal ions are not associated with functional groups, while all hydrogen ions are associated with functional groups. The associated hydrogen ions and functional groups do not contribute to the internal ionic strength value. Two thermodynamic models, describing the deprotonation of ion-exchange resin, were used and compared: the Gibbs-Donnan-based model of Bukata and Marinsky and the model proposed by Erik Hogfeldt. Thermodynamic characteristics of the resins’ deprotonation are obtained using two different thermodynamic approaches. Ho¨gfeldt’s three-parameter model provides a better agreement with experimental data. The fitting of the data to Marinsky’s method can be improved by taking into account the influence of the resins’ macroporosity; however, this requires an additional empirical parameter to describe the resin

Thin Films of Zinc Oxide Nanoparticles and Poly(acrylic acid) Fabricated by the Layer-by-Layer Technique: a Facile Platform for Outstanding Properties

The incorporation of nanoparticles into polyelectrolytes thin films opens the way to a broad range of applications depending on the functionality of the nanoparticles. In this work, thin films of ZnO nanoparticles and poly­(acrylic acid) (PAA) were built up using the layer-by-layer technique. The thickness of a 20-bilayer film is about 120 nm with a surface roughness of 22.9 nm as measured by atomic force microscopy (AFM). Thin ZnO/PAA films block UV radiation starting at a wavelength of 361 nm due to absorption by ZnO although the films are highly transparent. Due to their high porosity, these thin films show a broadband antireflection in the visible region, and thus they provide selective opacity in the UV region and enhanced transmittance in the visible region up to the near-infrared region. They are also superhydrophilic due to their high porosity and surface roughness

Processing and Characterization of Nano-structured ZrO₂/CoSb₃ Thermoelectric Composites

The addition of ceramic inclusion to a thermoelectric matrix could reduce the thermal conductivity of the composite, which is attributed to phonon scattering on the generated interfaces. The electrical conductivity of the composite, however, could also be reduced due to additional charge carrier scattering. The performance of the thermoelectric composite, therefore, depends on the resulting ratio of electrical conductivity to thermal conductivity, which results from the entire scattering effects on phonons and charge carriers. In the present work, nano-sized ZrO2 powders of different contents were dispersed into sub-micron-sized CoSb3 powders via ball milling. The as-milled powders were consolidated into dense compacts by hot pressing. The phase, the microstructure, and the thermoelectric properties of the prepared compacts were characterized. The correlation of phase, microstructure, and thermoelectric properties (electrical conductivity, thermal conductivity, and ratio of electrical conductivity to thermal conductivity), with the ceramic content and sintering temperature is presented. The results show how the performance of the investigated thermoelectric composites can be affected by the dispersion of nano-sized ceramic inclusions. It is noted that the selection of appropriate inclusion content is crucial to maintaining or improving the ratio of electrical conductivity to thermal conductivity