Influence of ionic liquids on the electrical conductivity and morphology of PEDOT:PSS films

Small-molecule nonvolatile additives based on ionic liquids (IL) as electrical conductivity enhancer in Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) was studied. Ionic liquids were investigated in the synthesis of self-assembled, highly organized hybrid nanostructures due to their ability as supramolecular solvents. Different percentage of five ionic liquids, such as 1-butyl-3-methylimidazolium tetrafluoroborate (bmim) F 4 and 1-butyl-3-methylimidazolium bromide (bmim)Br were added to a PEDOT:PSScommercial dispersion. Films of pure PEDOT:PSS showed an average conductivity of 14 S cm-1, which corresponded to the value range given by the supplier. AFM images showed that IL induced the formation of a three-dimensional conducting network with smaller PEDOT domains. The ionic character of the films was significantly increased because of the presence of ionic liquids, which can be used effectively in optoelectronic devices.

Epoxy nanocomposites with aligned carbon nanofillers by external electric fields

This paper presents systematic studies on aligning carbon nanofillers in epoxy by external fields, either electric fields or magnetic fields, to create nanocomposites with greatly improved mechanical and electrical properties. Carbon nanofibers (CNFs) and graphene nanoplatelets (GnPs) were observed to align along the field direction in the epoxy resin. Compared to the unmodifed epoxy and those with randomly-oriented carbon nanofillers, the nanocomposites with aligned carbon nanofillers showed significantly higher fracture toughness and electrical conductivity along the direction of the external field. Compared with randomly-oriented nanofillers, aligned GnPs and CNFs produced 40% and 27% improvement in fracture energy at 1.0 wt%, bringing the total increase in fracture energy over the neat polymer to more than 10 times. Several key toughening mechanisms were identified through fractographic analysis, which was used to develop predictive models to quantify the increases in the value of GIc as a result of 1-D and 2D carbon nanofillers. The present findings suggest that aligning carbon nanofillers presents a very promising technique to create multi-scale reinforcement with greatly increased electric conductivity and fracture toughness.

Use of fluorescein as a ground water tracer in brackish water aquifers

A drift and pumpback experiment was conducted in a brackish water sandfill. The sandfill was reclaimed from the sea in the eastern part of Singapore and contains sands with low organic and clay/silt contents. The high salinity in the ground water precludes the use of chloride and bromide as tracers in such an environment, and a field experiment was conducted to assess the viability of using fluorescein as a tracer in brackish water aquifers. Nitrate was used as a second tracer to serve as a check. Initial laboratory studies showed that fluorescence was unaffected over the range of electrical conductivity and pH of the ground water. Results from the field experiment show that fluorescein appears to behave conservatively.

Excellent electrochemical performance of LiFe0.4Mn0.6PO4 microspheres produced using a double carbon coating process

Composite LiFe0.4Mn0.6PO4/C microspheres are considered advanced cathode materials for electric vehicles and other high-energy density applications due to their advantages of high energy density and excellent cycling stability. LiFe0.4Mn0.6PO4/C microspheres have been produced using a double carbon coating process employing traditional industrial techniques (ball milling, spray-drying and annealing). The obtained LiFe0.4Mn0.6PO4 microspheres exhibit a high discharge capacity of around 166 mA h g-1 at 0.1 C and excellent rate capabilities of 132, 103, and 72 mA h g-1 at 5, 10, and 20 C, respectively. A reversible capacity of about 152 mA h g-1 after 500 cycles at a current density of 1 C indicates an outstanding cycling stability. The excellent electrochemical performance is attributed to the micrometer-sized spheres of double carbon-coated LiFe0.4Mn0.6PO4 nanoparticles with improved electric conductivity and higher Li ion diffusion coefficients, ensuring full redox reactions of all nanoparticles. The results show that the advanced high-energy density cathode materials can be produced using existing industry techniques.

Improving the toughness and electrical conductivity of epoxy nanocomposites by using aligned carbon nanofibres

There is an increasing demand for high performance composites with enhanced mechanical and electrical properties. Carbon nanofibres offer a promising solution but their effectiveness has been limited by difficulty in achieving directional alignment. Here we report the use of an alternating current (AC) electric field to align carbon nanofibres in an epoxy. During the cure process of an epoxy resin, carbon nanofibres (CNFs) are observed to rotate and align with the applied electric field, forming a chain-like structure. The fracture energies of the resultant epoxy nanocomposites containing different concentrations of CNFs (up to 1.6wt%) are measured using double cantilever beam specimens. The results show that the addition of 1.6wt% of aligned CNFs increases the electrical conductivity of such nanocomposites by about seven orders of magnitudes to 10^-2S/m and increases the fracture energy, G<inf>Ic</inf>, by about 1600% from 134 to 2345J/m². A modelling technique is presented to quantify this major increase in the fracture energy with aligned CNFs. The results of this research open up new opportunities to create multi-scale composites with greatly enhanced multifunctional properties.