Advanced Functional Materials

Previous investigations of the field-effect mobility in poly(3-hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium-MW: Mn = 7 200 g mol−1; high-MW: Mn = 27 000 g mol−1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) and organic field-effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra-grain mobility depends only weakly on MW (being in the order of 10−2 cm2 V−1 s−1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature-dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium-MW P3HT undergo a “pre-melting” significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short-chain P3HT is strongly inhibited by the presence of disordered domains, while in high-MW P3HT the low-mobility disordered zones are bridged via inter-crystalline molecular connections.

We describe a new method towards bulk-heterojunction hybrid polymer solar cells based on composite films of zinc oxide (ZnO) and a conjugated polymer poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV). Spin-coating diethylzinc as a ZnO precursor and MDMO-PPV from a common solvent at 40 % humidity and annealing at 110 °C provides films in which crystalline ZnO is found to be intimately mixed with MDMO-PPV. Photoluminescence and photoinduced spectroscopy demonstrate that photoexcitation of these hybrid composite films results in a fast and long-lived charge transfer from the polymer as a donor to ZnO as ato be obtained n acceptor. Using the ZnO-precursor method, hybrid polymer solar cells have been made with an estimated air-mass of 1.5 (AM 1.5) energy conversion efficiency of 1.1 %. This new method represents a fivefold improved performance compared to similar hybrid polymer solar cells based on amorphous TiO2.

Improving the functional stability of shape memory alloys (SMAs), which undergo a reversible martensitic transformation, is critical for their applications and remains a central research theme driving advances in shape memory technology. By using a thin-film composition-spread technique and high-throughput characterization methods, the lattice parameters of quaternary Ti–Ni–Cu–Pd SMAs and the thermal hysteresis are tailored. Novel alloys with near-zero thermal hysteresis, as predicted by the geometric non-linear theory of martensite, are identified. The thin-film results are successfully transferred to bulk materials and near-zero thermal hysteresis is observed for the phase transformation in bulk alloys using the temperature-dependent alternating current potential drop method. A universal behavior of hysteresis versus the middle eigenvalue of the transformation stretch matrix is observed for different alloy systems. Furthermore, significantly improved functional stability, investigated by thermal cycling using differential scanning calorimetry, is found for the quaternary bulk alloy Ti50.2Ni34.4Cu12.3Pd3.1.

Biological photonic systems composed of anhydrous guanine crystals evolved separately in several taxonomic groups. Here, two such systems found in fish and spiders, both of which make use of anhydrous guanine crystal plates to produce structural colors, are examined. Measurements of the photonic-crystal structures using cryo-SEM show that the crystal plates in both fish skin and spider integument are ∼20-nm thick. The reflective unit in the fish comprises stacks of single plates alternating with ∼230-nm-thick cytoplasm layers. In the spiders the plates are formed as doublet crystals, cemented by 30-nm layers of amorphous guanine, and are stacked with ∼200 nm of cytoplasm between crystal doublets. They achieve light reflective properties through the control of crystal morphology and stack dimensions, reaching similar efficiencies of light reflectivity in both fish skin and spider integument. The structure of guanine plates in spiders are compared with the more common situation in which guanine occurs in the form of relatively unorganized prismatic crystals, yielding a matt white coloration.

ABSTRACT The rheological and adhesive properties of bis-urea functionalized low-molecular-weight polyisobutylenes (PIBUT) are investigated. The polymers, which can interact through supramolecular hydrogen bonds, can self-organize over times of the order of days at room temperature. This organized structure has been identified by small angle X-ray scattering (SAXS) and its rheological properties indicate the behaviour of a soft viscoelastic gel. The ordered structure can be disrupted by temperature and shear so that at 80 °C, the material behaves as a highly viscoelastic fluid and no SAXS peak is observed. When cooled back at room temperature, the PIBUT retrieves its ordered structure and gel properties after 20 h of annealing. This very slow molecular dynamics gives PIBUT a highly dissipative nature upon deformation, which combined with strongly interacting moieties results in very interesting adhesive properties both on steel surfaces but more importantly on typical low adhesion surfaces such as silicone. A strategy based on the controlled incorporation of supramolecular bonds in a covalently crosslinked network appears promising for the development of a new generation of highly interacting and dissipative soft adhesives.

Here, a novel method of immobilizing proteins with well-defined orientation directly on liquid crystal surfaces that allow subsequent real-time imaging of specific protein–protein binding events on these surfaces is reported. Self-assembly of nitrilotriacetic acid terminated amphiphiles loaded with Ni2+ ions at aqueous-liquid crystal interface creates a surface capable of immobilizing histidine-tagged ubiquitin through complex formation between Ni2+ and histidine. When these surfaces containing immobilized histidine-tagged ubiquitin are exposed to anti-ubiquitin antibody, the spatial and temporal of specific protein–protein binding events trigger orientational transitions of liquid crystals. As a result, sharp liquid crystal optical switching from dark to bright can readily be observed under polarized lighting. The protein–protein binding can be observed within seconds and only requires nanogram quantities of proteins. This work demonstrates a simple strategy to immobilize proteins with well-defined orientation on liquid crystal surfaces for real-time and label-free detection of specific protein–protein binding events, which may find use in biomedical diagnostics.

We report the evolution of structural, dielectric, ferroelectric and ferromagnetic properties in novel
(Pb1 − 3x/2Ndx)(Ti0.98 − yFeyMn0.02)O3 perovskite ceramics (x=0.08, 0 b y b 0.05). We found room-temperature ferroelectric polarization and ferromagnetismfor higher amount of iron ions (y ≥ 0.04). The paraelectric-ferroelectric phase transition occurred between 650 and 670 K for 0 ≤ y ≤ 0.05. Ferromagnetic hysteresis was measured at
different temperatures on samples with y ≥ 0.04. Detailed structural analysis evidenced the variation of unit cell parameters with y increasing, confirming the substitution of the iron element in the lattice. 57Fe Mössbauer spectroscopy evidenced that iron ions occupy Ti positions in the perovskite lattice, with the oxidation state Fe3+ and
two coordination types. X-ray photoelectron spectroscopy confirmed the presence of iron only as Fe3+ and, moreover, evidenced the presence of a substantial amount of Ti3+ ions in the structure. The presence of both Fe3+ (spin 5/2) in different coordinations aswell as Ti3+ (spin 1/2) magnetic ions in B-site positions drives the occurrence of
magnetic properties from low temperature to above room temperature, through superexchange Fe3+-O-Fe3+, Fe3+-O-Ti3+ and Ti3+-O-Ti3+ interactions. The finding of coexistent ferroelectric and ferromagnetic properties in these compounds ground the route to facile synthesis of multiferroics by simply doping a classical perovskite ferroelectric material like PbTiO3 with an adequate amount of transition magnetic ions.

International Journal of Recent advances in Physics (IJRAP) is a peer-reviewed, open access
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