Douglas C. Dahn

Elastic energy and staging in intercalation compounds

Abstract We present a simple model for the elastic energy associated with the intercalation of a layered host lattice. The model accounts for the staging phenomena observed in many intercalation systems and is compared with Safrans theory of staging. The model is used to discuss the thermodynamic behaviour of Li x TiS 2 and is shown to give a good account of the experimental observations.

Phase mixtures and staging in intercalated LixNbSe2

Abstract We present experimental evidence for the existence at room temperature of staged compounds in the Li x NbSe 2 system. For x in the range .27 ⩽ × ⩽ 1, a stage 1 structure is observed. For × ≅ .14 and × ≅ .08, stage 2 and stage 3 structures, respectively, are seen. For other values of x in the range 0 ⩽ × ⩽ .27, coexisting phase mixtures are observed.

Capacitance-based sensor for monitoring bees passing through a tunnel

A sensor has been developed to monitor objects passing through tunnels using a capacitance bridge. While the sensor concept is easily adaptable to a wide range of objects or organisms which pass through an enclosed area, our version of the sensor was designed specifically for monitoring bumblebee colonies. Other bee sensors have been developed based on optical methods of detection. The capacitance sensor provides all the information of the optical sensors and additional information on the bee size and velocity. The sensor is expected to provide entomologists with more efficient methods of studying the foraging activities of bees.

Nanomaterials Based on Polyanilines and MoSe2

Polyaniline, poly(N-methyl aniline), poly(2-ethyl aniline) and poly(2-propyl aniline) were intercalated into layered molybdenum diselenide by using the exfoliation/restacking property of LixMoSe2. MoSe2 was reacted with n-butyllithium to form LixMoSe2. The LixMoSe2 was exfoliated in N-methylformamide (NMF) with the help of ultrasonication which lead to the formation of single layers of MoSe2. Addition of NMF solutions of the polymers to the exfoliated layers resulted in their intercalation into MoSe2. The products were characterized by powder X-ray diffraction. Fourier transform infra-red spectroscopy, and four-probe van der Pauw technique electrical conductivity measurements are reported here for the first time.

Scanning tunneling microscopy of unbroken chloroplasts

Abstract Mainsbridge and Thundat [J. Vac. Sci. Technol. B 9 (1991) 1259] recently reported STM images of chloroplast components. The goal of our work was to investigate the effects of sample preparation and imaging conditions, and to more clearly identify some of the structures that appear in chloroplast images. We have imaged gold-coated chloroplasts in air, and bare chloroplasts in solution. Results obtained include images of whole chloroplasts several micrometers in diameter, and images which show molecular-scale structure on the chloroplast outer membrane.

Intercalation of Poly(bis-(methoxyethoxyethoxy)phosphazene) into Lithium Hectorite

Poly(bis-(methoxyethoxyethoxy)phosphazene) (MEEP) intercalated into lithium hectorite was investigated for its potential application as a solid polymer electrolyte in lithium-ion polymer batteries. Varying amounts of MEEP were intercalated into lithium hectorite, and the physical properties of the nanocomposites were monitored using powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and attenuated total reflectance spectroscopy. Alternating current (AC) impedance spectroscopy was used to determine the ionic conductivity of the nanocomposites when complexed with lithium triflate salt.

Exfoliated Nanocomposites Based on Polyaniline and Tungsten Disulfide

Nanocomposite materials consisting of polyaniline (PANI) and exfoliated WS2 were synthesized. The WS2 was prepared by reacting tungstic acid with thiourea at 500°C under nitrogen flow. Samples were prepared with a WS2 content of 1, 5, 7.5, 10, 12.5, 15, 20, 37, and 64% by mass. An improvement in the electronic conductivity value of the PANI was observed through the incorporation of exfoliated WS2. The electronic conductivity of PANI-15%WS2 was 24.5 S/cm, an eightfold increase when compared to pure PANI. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR) provided evidence that the nanocomposites are in an exfoliated state. XRD and TEM showed that the nanocomposites were completely amorphous, suggesting lack of structural order in these materials, while their EPR signals were considerably narrower compared to pure PANI, indicating the formation of genuine exfoliated systems. Furthermore, our research showed that WS2 can be used as a filler to improve activation energy of decomposition of the polymer. By using the Ozawa method, we studied the decomposition kinetics for the nanocomposites, as well as for the pure polymer. The activation energy for the decomposition of pure PANI was found to be 131.2 kJ/mol. Increasing the amount of WS2 to 12.5% in the PANI increases the activation energy of decomposition to 165.4 kJ/mol, an enhancement of 34.2 kJ/mol over the pure polymer.

Intercalation of Poly[Oligo(Ethylene Glycol) Oxalate] into Vanadium Pentoxide Xerogel: Preparation, Characterization and Conductivity Properties

We report, for the first time, the intercalation of poly[oligo(ethylene glycol) oxalate] (POEGO) and POEGO lithium salt (LiCF3SO3) complex (POEGO-LiCF3SO3) into vanadium pentoxide xerogel (V2O5nH2O). The effect of changing the polymer concen‐ tration on the interlayer expansion of the layered host was studied, and the optimal intercalation ratio was determined to be 1:2. The intercalates were characterized by powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and AC impedance spectroscopy.

Polymer Nanocomposite Materials Based on Carbon Nanotubes

In the past two decades, mobile devices have decreased significantly in size and yet their capabilities and storage capacities continue to grow dramatically. Not unexpectedly, the energy demands of these devices are rather substantial, which has led to a huge increase in the level of research into batteries. In recent years, millions of dollars of research funding have been directed towards the development of more efficient battery systems, with a large focus on lithium ion batteries. These batteries are among the most popular for devices with high energy demands due to their high energy capacities. However, despite the impressive performance of lithium ion batteries to date, there is still significant room for improvement. Lithium ion batteries have progressed significantly since they were first developed in the early 1970s. These early systems consisted of lithium metal anodes combined with titanium disulfide cathodes; however, they demonstrated limited cell potentials and these chalcogenidic cathodes were soon replaced by layered oxide systems (Whittingham, 1976). Many such layered oxides were studied by the Goodenough group (Thackeray et al., 1983; Mizushima et al., 1980) with great success which led to the commercialization of these batteries in the early 1990s. These batteries were marketed by the electronics giant, the Sony Corporation, and they consisted of a lithium cobalt dioxide, LiCoO2, cathode and a graphitic anode (Nazri & Pistoia, 2004). Lithium metal anodes were discarded earlier in favour of safer systems such as graphite due to the dangers associated with recharging. In the years since the commercialization of lithium ion batteries, there have been many modifications to the three components of the cell: the anode, the cathode and the electrolyte. However, due to the low cost and relative efficiency of graphite as the anode system, very little work has been done in this area. Nonetheless, recently, silicon and germanium nanowires have demonstrated great potential as possible anode materials (Chan et al., 2008a; Chan et al., 2008b). It has long been known that silicon has a greater capacity for lithium ions than does graphite; however, previous attempts employing silicon particles and thin films have demonstrated significant degradation of the materials upon cycling. With these novel nanowires, this degradation is not observed. A small increase in the diameter of the nanowires occurs upon lithium intercalation, but this expansion is reversible upon the removal of the lithium ions. Research is still continuing into these materials due to their enhanced lithium storage capacities; however, these systems are plagued by their considerable expense when compared to graphite. Therefore,