Order–disorder transitions in poly(3,4-ethylenedioxythiophene)

The commonly held perception that high conductivity in conducting polymers is linked to a high level of π-stacking order in the material is shown here to be of lesser importance in highly conducting poly(3,4-ethylenedioxythiophene) (PEDT), which has been prepared by chemical vapour phase polymerisation. Despite the fact that there is a highly energetic phase transition about 130 °C (110 J/g), and that this transition corresponds to a loss of the long-range π-stacking as observed in grazing angle XRD, the conductivity remains unchanged beyond the transition and only decreases by a factor of two when heating to above 200 °C. The XRD data suggest that order in two dimension remains above the phase transition measured by DSC and this order is sufficient to maintain a high level of electronic conductivity. Furthermore, as the ligand on the iron salt used in the synthesis is varied, the conductivity of the PEDT varies over two orders of magnitude. These phenomena cannot be explained by different degree of doping or crystallinity and it is proposed that the iron salt has an ordering effect during the vapour phase polymerisation.

High current density and drift velocity in templated conducting polymers

Conducting polymers prepared by a templated vapour phase polymerisation process involving solid phase transition metal complexes are found to produce polymers with charge carriers that exhibit maximum drift velocity in the range of 1 m/s. This super-mobility seems to be related to a high degree of ordering in the materials as evidenced by the X-ray diffraction data. This may result from a templated polymerisation process. The high mobility manifests itself as a capacity to sustain very high current densities (>10000 A/cm2); such high current densities are of importance in thin film conductor applications.

A new class of proton-conducting ionic plastic crystals based on organic cations and dihydrogen phosphate

Choline dihydrogen phosphate ([N_1.1.1.2OH]DHP) and 1-butyl-3-methylimidazolium dihydrogen phosphate ([C₄mim]DHP) were synthesized as a new class of proton-conducting ionic plastic crystals. Both [N_1.1.1.2OH]DHP and [C₄mim]DHP showed solid–solid phase transition(s) and showed a final entropy of fusion lower than 20 J K⁻¹ mol⁻¹ which is consistent with Timmerman’s criterion for molecular plastic crystals. The ionic conductivity of [N_1.1.1.2OH]DHP was in the range of 10⁻⁶ S cm⁻¹–10⁻³ S cm⁻¹ in the plastic crystalline phase. On the other hand, the ionic conductivity of [C₄mim]DHP showed about 10⁻⁵ S cm⁻¹ in the plastic crystalline phase. [N_1.1.1.2OH]DHP showed one order of magnitude higher ionic conductivity than [C₄mim]DHP in the temperature range where the plastic phase is stable.

Lithium doped N,N-dimethyl pyrrolidinium tetrafluoroborate organic ionic plastic crystal electrolytes for solid state lithium batteries

The organic ionic plastic crystal material N,N-dimethyl pyrrolidinium tetrafluoroborate ([C1mpyr][BF4]) has been mixed with LiBF4 from 0 to 8 wt% and shown to exhibit enhanced ionic conductivity, especially in the higher temperature plastic crystal phases (phases II and I). The materials retain their solid state well above 100 °C with the melt not being observed up to 300 °C. Interestingly the conductivity enhancement is highest with the lowest level of LiBF4 addition in phase II, but then the order of enhancement is reversed in phase I. In all cases, a conductivity drop is observed at the II → I phase transition (105 °C) which is associated with increased order in the pure matrix, as previously reported, although the conductivity drop is least for the highest LiBF4 amount (8 wt%). The 8 wt% sample displays different conductivity behaviours compared to the lower LiBF4 concentrations, with a sharp increase above 50 °C, which is apparently not related to the formation of an amorphous phase, based on XRD data up to 120 °C. Symmetric cells, Li/OIPC/Li, were prepared and cycled at 50 °C and showed evidence of significant preconditioning with continued cycling, leading to a lower over-potential and a concomitant decrease in the cell resistivity as measured by EIS. An SEM investigation of the Li/OIPC interfaces before and after cycling suggested significant grain refinement was responsible for the decrease in cell resistance upon cycling, possibly as a result of an increased grain boundary phase.

Pressure-induced structural transitions in MOO3·xH2O (x = 1/2, 2) molybdenum trioxide hydrates : a raman study

The high-pressure behaviors of M_OO₃·1/2H₂O and M_OO₃·2H₂O have been investigated by Raman spectroscopy in a diamond anvil cell up to 31.3 and 30.3 GPa, respectively. In the pressure range up to around 30 GPa, both M_OO₃·1/2H₂O and M_OO₃·2H₂O undergo two reversible structural phase transitions. We observed a subtle structural transition due to O−H···O hydrogen bond in M_OO₃·1/2H₂O at 3.3 GPa. We found a soft mode phase transition in M_OO₃·2H₂O at 6.6 GPa. At higher pressures, a frequency discontinuity shift and appearance of new peaks occurred in both M_OO₃·1/2H₂O and M_OO₃·2H₂O, indicating that the second phase transition is a first-order transition. The frequency redshift of the O−H stretching bands of M_OO₃·1/2H₂O and M_OO₃·2H₂O are believed to be related to the enhancement of the O−H···O weak hydrogen bonds under high pressures.

High-pressure spectroscopic study of hydrous and anhydrous Cs-exchanged natrolites

Structural phase transitions in hydrous Cs-exchanged natrolite (Cs-NAT-hyd) and anhydrous Cs-exchanged natrolite (Cs-NAT-anh) have been investigated as a function of pressure and temperature using micro-Raman scattering and synchrotron infrared (IR) spectroscopy with pure water as the penetrating pressure medium. The spectroscopic results indicate that Cs-NAT-hyd undergoes a reversible phase transition around 4.72 GPa accompanied by the discontinuous frequency shifts of the breathing vibrational modes of the four-ring and helical eight-ring units of the natrolite framework. On the other hand, we observe that Cs-NAT-anh becomes rehydrated at 0.76 GPa after heating to 100 °C and then transforms into two distinctive phases at 2.24 and 3.41 GPa after temperature treatments at 165 and 180 °C, respectively. Both of these high-pressure phases are characterized by the absence of the helical eight-ring breathing modes, which suggests the collapse of the natrolite channel and formation of dense high-pressure polymorphs. Together with the fact that these high-pressure phases are recoverable to ambient conditions, our results imply a novel means for radionuclide storage utilizing pressure and a porous material.

High-pressure structural transitions of Sc2O3 by X-ray diffraction, raman spectra, and ab initio calculations

The high-pressure behavior of scandium oxide (Sc₂O₃) has been investigated by angle-dispersive synchrotron powder X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 46.2 and 42 GPa, respectively. An irreversible structural transformation of Sc₂O₃ from the cubic phase to a monoclinic high-pressure phase was observed at 36 GPa. Subsequent ab initio calculations for Sc₂O₃ predicted the phase transition from the cubic to monoclinic phase but at a much lower pressure. The same calculations predicted a second phase transition at 77 GPa from the monoclinic to hexagonal phase.

Temperature-agile and structure-tunable optical properties of VO 2/Ag thin films

By integrating together VO2’s unique near-room-temperature (RT) semiconductor–metal (S–M) phase transition with a thin silver (Ag) layer’s plasmonic properties, VO2/Ag multilayers could present a much enhanced optical transmission change when increasing the temperature from RT to over VO2’s S–M phase-transition temperature. Changing VO2 and Ag layer thicknesses can also significantly tune their transmission and absorption properties, which could lead to a few useful designs in optoelectronic and energy-saving industries.

Combinational rate effects on the performance of nano-grained pseudoelastic Nitinols

Combinational loading-unloading rate effects were studied on the behavior of NiTi shape memory alloys (SMAs) under nanoindentation loads. While combinational loading rates showed negligible effects on the performance of NiTi SMAs, the combinational unloading rates did show significant effects on hysteresis energy. The heating-cooling phenomenon during the loading stage and the sole cooling during the unloading stage explain the effects. This study elucidates the nature of thermomechanical SMAs' behaviors during complex compressive loadings with the presence of solid-state phase transition.

Enhancing bi-functional electrocatalytic activity of perovskite by temperature shock : a case study of LaNiO3-ᵟ

Perovskite oxide offers an attractive alternative to precious metal electrocatalysts given its low cost and high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. The results obtained in this work suggest a correlation of crystal structure with ORR and OER activity for LaNiO3-?. LaNiO3-? perovskites with different crystal structure were obtained by heating at different temperatures, e.g., 400, 600, and 800 C followed by quenching into room temperature. Cubic structure (relative to rhombohedral) leads to higher ORR and OER activity as well as enhanced bi-functional electrocatalytic activity, e.g., lower difference in potential between the ORR at -3 mA cm-2 and OER at 5 mA cm -2 (?E). Therefore, this work shows the possibility to adjust bi-functional activity through a simple process. This correlation may also extend to other perovskite oxide systems.

An organic ionic plastic crystal electrolyte for rate capability and stability of ambient temperature lithium batteries

Reliable, safe and high performance solid electrolytes are a critical step in the advancement of high energy density secondary batteries. In the present work we demonstrate a novel solid electrolyte based on the organic ionic plastic crystal (OIPC) triisobutyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1444FSI). With the addition of 4 mol% LiFSI, the OIPC shows a high conductivity of 0.26 mS cm-1 at 22 °C. The ion transport mechanisms have been rationalized by compiling thermal phase behaviour and crystal structure information obtained by variable temperature synchrotron X-ray diffraction. With a large electrochemical window (ca. 6 V) and importantly, the formation of a stable and highly conductive solid electrolyte interphase (SEI), we were able to cycle lithium cells (LiLiFePO4) at 30 °C and 20 °C at rates of up to 1 C with good capacity retention. At the 0.1 C rate, about 160 mA h g-1 discharge capacity was achieved at 20 °C, which is the highest for OIPC based cells to date. It is anticipated that these small phosphonium cation and [FSI] anion based OIPCs will show increasing significance in the field of solid electrolytes.

Using a selective cadmium-binding peplipid to create responsive liquid crystalline nanomaterials.

A specific metal ion-responsive lipid liquid crystalline (LLC) dispersion system was fabricated, which can work in buffer solutions. The LLC matrix was prepared from phytantriol which spontaneously forms the reversed bicontinuous cubic phase in water, and a novel peptide-lipid conjugate (peplipid) consists of a myristate alkyl chain for anchoring into the phytantriol-based cubic bilayer and a peptide sequence for capturing a specific metal ion. The peplipid in its unbound state, when added into the phytantriol-based cubic system induces a positive effect on the bilayer curvature, resulting in the formation of the lamellar phase (vesicles) and the dispersion was transparent in appearance. Upon binding of the cadmium ion, the peplipid induces a negative effect on the lipid bilayer curvature and consequently leading to the formation of cubic phase and opaque appearance. In contrast, other metal ions, including buffering salts, could not sufficiently trigger the phase transition due to weak interaction with the peplipid. The high selectivity of metal ion interaction and triggered phase transition provide potential applications, such as in colloidal-mineral separation, triggered drug release and treatment of cadmium (II) pollution.

Lipid merging, protrusion and vesicle release triggered by shrinking/swelling of poly(N-isopropylacrylamide) microgel particles

Cell membrane changes its morphology during many physiological processes with the assistance of a solid support, such as the cytoskeleton, under an environmental stimulus. Here, a novel type of stimuli-responsive lipogel was fabricated, mimicking the changes of cell membrane. The lipogel was prepared from poly(N-isopropylacrylamide) (pNIPAM) microgel particle and phospholipid by a solvent-exchange method. The temperature dependent volume phase transition of pNIPAM triggers reversible transformation of the lipogel between a lipid vesicle-coated sun-like structure and a contracted hybrid sphere, through lipid merging and protrusion processes, respectively. By contrast, the salt induced pNIPAM phase transition leads to an irreversible vesicle release behaviour. The lipogel creates a unique platform for studying cell membrane behaviour and provides promising candidates in drug delivery and controlled release applications. © 2014 Elsevier B.V. All rights reserved.