Apparent stress-strain relationships in experimental equipment where magnetorheological fluids operate under compression mode

Abstract: This paper presents an experimental investigation of two different magnetorheological ( MR) fluids, namely, water-based and hydrocarbon-based MR fluids in compression mode under various applied currents. Finite element method magnetics was used to predict the magnetic field distribution inside the MR fluids generated by a coil. A test rig was constructed where the MR fluid was sandwiched between two flat surfaces. During the compression, the upper surface was moved towards the lower surface in a vertical direction. Stress-strain relationships were obtained for arrangements of equipment where each type of fluid was involved, using compression test equipment. The apparent compressive stress was found to be increased with the increase in magnetic field strength. In addition, the apparent compressive stress of the water-based MR fluid showed a response to the compressive strain of greater magnitude. However, during the compression process, the hydrocarbon-based MR fluid appeared to show a unique behaviour where an abrupt pressure drop was discovered in a region where the apparent compressive stress would be expected to increase steadily. The conclusion is drawn that the apparent compressive stress of MR fluids is influenced strongly by the nature of the carrier fluid and by the magnitude of the applied current

On the triplet state of poly(N-vinylcarbazole)

Triplet state properties including transient triplet absorption spectrum, intersystem crossing yields in solution at room temperature and phosphorescence spectra, quantum yields and lifetimes at low temperature as well as singlet oxygen yields were obtained for poly(N-vinylcarbazole) (PVK) in 2-methyl-tetrahydrofuran (2-MeTHF), cyclohexane or benzene. The results allow the determination of the energy value for the lowest lying triplet state and also show that triplet formation and deactivation is a minor route for relaxation of the lowest excited singlet state of PVK. In addition, they show the triplet state is at higher energy than reported heavy metal dopants used for electrophosphorescent devices, such that if this is used as a host it will not quench their luminescence.http://www.sciencedirect.com/science/article/B6TFN-4DTTJJC-7/1/b605edb9859b607f1a9b1c1348af029

Circulating tumour cell clusters: Insights into tumour dissemination and metastasis.

INTRODUCTION:Metastasis results in more than 90% of cancer related deaths globally. The process is thought to be facilitated by metastatic precursor cells, commonly termed circulating tumour cells (CTCs). CTCs can exist as single cells or cell clusters and travel through the lymphovasculature to distant organs where they can form overt metastasis. Areas covered: Studies have highlighted that CTC clusters, which may be homotypic or heterotypic in composition, have a higher metastatic potential compared to single CTCs. The characterisation of CTC clusters is becoming important as heterotypic clusters can provide a mechanism for immune evasion. This review summarises the latest advances in CTC cluster mediated metastasis and clinical significance. Expert Opinion: Comprehensive characterisation of CTC clusters is needed to understand the cell types and interactions within clusters, in order to identify ways in which to reduce CTC cluster mediated metastasis. The role of CTC clusters in prognosticating disease progression needs to be determined by documenting CTC clusters from the time of diagnosis over the course of therapy

Optical and Polarity Control of Donor–Acceptor Conformation and Their Charge-Transfer States in Thermally Activated Delayed-Fluorescence Molecules

This study reports two novel D–A–D molecules, 2,7-bis(phenothiazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPT-TXO2) and 2,7-bis(1-methylphenothiazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DMePT-TXO2), where the latter differs by only a methyl group incorporated on each of the donor units. DMePT-TXO2 in solution and in solid state shows dual charge-transfer (CT) emission. The CT states come from two distinctive conformations between the D and A units. Experiments show that the emission contribution of each state can be controlled by the polarity of the environment and by the excitation energy. Also, how the different conformers can be used to control the TADF mechanism is analyzed in detail. These results are important as they give a more in-depth understanding about the relation between molecular conformation and the TADF mechanism, thereby facilitating the design of new TADF molecules

Intramolecular Hydrogen Bonding in Thermally Activated Delayed Fluorescence Emitters: Is There Evidence Beyond Reasonable Doubt?

Intramolecular hydrogen bonding between donor and acceptor segments in thermally activated delayed fluorescence (TADF) materials is now frequently employed to─purportedly─rigidify the structure and improve the emission performance of these materials. However, direct evidence for these intramolecular interactions is often lacking or ambiguous, leading to assertions that are largely speculative. Here we investigate a series of TADF-active materials incorporating pyridine, which bestows the potential ability to form intramolecular H-bonding interactions. Despite possible indications of H-bonding from an X-ray analysis, an array of other experimental investigations proved largely inconclusive. Instead, after examining computational potential energy surfaces of the donor–acceptor torsion angle we conclude that the pyridine group primarily alleviates steric congestion in our case, rather than enabling an H-bond interaction as elsewhere assumed. We suggest that many previously reported “H-bonding” TADF materials featuring similar chemical motifs may instead operate similarly and that investigation of potential energy surfaces should become a key feature of future studies

Electron correlation effects in electron-hole recombination in organic light-emitting diodes

We develop a general theory of electron--hole recombination in organic light emitting diodes that leads to formation of emissive singlet excitons and nonemissive triplet excitons. We briefly review other existing theories and show how our approach is substantively different from these theories. Using an exact time-dependent approach to the interchain/intermolecular charge-transfer within a long-range interacting model we find that, (i) the relative yield of the singlet exciton in polymers is considerably larger than the 25% predicted from statistical considerations, (ii) the singlet exciton yield increases with chain length in oligomers, and, (iii) in small molecules containing nitrogen heteroatoms, the relative yield of the singlet exciton is considerably smaller and may be even close to 25%. The above results are independent of whether or not the bond-charge repulsion, X_perp, is included in the interchain part of the Hamiltonian for the two-chain system. The larger (smaller) yield of the singlet (triplet) exciton in carbon-based long-chain polymers is a consequence of both its ionic (covalent) nature and smaller (larger) binding energy. In nitrogen containing monomers, wavefunctions are closer to the noninteracting limit, and this decreases (increases) the relative yield of the singlet (triplet) exciton. Our results are in qualitative agreement with electroluminescence experiments involving both molecular and polymeric light emitters. The time-dependent approach developed here for describing intermolecular charge-transfer processes is completely general and may be applied to many other such processes.Comment: 19 pages, 11 figure

Conformational Dependence of Triplet Energies in Rotationally Hindered N‐ and S‐Heterocyclic Dimers: New Design and Measurement Rules for High Triplet Energy OLED Host Materials

A series of four heterocyclic dimers has been synthesized, with twisted geometries imposed across the central linking bond by ortho‐alkoxy chains. These include two isomeric bicarbazoles, a bis(dibenzothiophene‐S,S‐dioxide) and a bis(thioxanthene‐S,S‐dioxide). Spectroscopic and electrochemical methods, supported by density functional theory, have given detailed insights into how para‐ vs. meta‐ vs. broken conjugation, and electron‐rich vs. electron‐poor heterocycles impact the HOMO–LUMO gap and singlet and triplet energies. Crucially for applications as OLED hosts, the triplet energy (ET) of these molecules was found to vary significantly between dilute polymer films and neat films, related to conformational demands of the molecules in the solid state. One of the bicarbazole species shows a variation in ET of 0.24 eV in the different media—sufficiently large to “make‐or‐break” an OLED device—with similar discrepancies found between neat films and frozen solution measurements of other previously reported OLED hosts. From consolidated optical and optoelectronic investigations of different host/dopant combinations, we identify that only the lower ET values measured in neat films give a reliable indicator of host/guest compatibility. This work also provides new molecular design rules for obtaining very high ET materials and controlling their HOMO and LUMO energies

Pendant Homopolymer and Copolymers as Solution-Processable Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

Materials that display thermally activated delayed fluorescence (TADF) have recently been identified as the third generation emitters for organic light-emitting diodes (OLEDs). However, there are only a few reported examples of polymeric TADF materials. This study reports a series of polymers with an insulating backbone and varying ratios of 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide as a pendant TADF unit. Steady-state and time-resolved fluorescence spectroscopic data confirm the efficient TADF properties of the polymers. Styrene, as a comonomer, is shown to be a good dispersing unit for the TADF groups, by greatly suppressing the internal conversion and triplet–triplet annihilation. Increasing the styrene content within the copolymers results in relatively high triplet energy, small energy splitting between the singlet and triplet states (ΔEST), and a strong contribution from delayed fluorescence to the overall emission. Green emitting OLED devices employing these polymers as spin-coated emitting layers give high performance, which is dramatically enhanced in the copolymers compared to the homopolymer. Within the series, Copo1 with a regiorandom ratio of 37% TADF units:63% styrene units displays the best performance with a maximum external quantum efficiency (EQE) of 20.1% and EQE at 100 cd m–2 of 5.3%

The electronic structure of polyaniline and doped phases studied by soft X-ray absorption and emission spectroscopies

The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant X-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped (protonated) phases for both the carbon and nitrogen contents. The resonant X-ray emission spectra show depletion of the {\pi} electron bands due to the selective excitation which enhances the effect of symmetry selection rules. The valence band structures in the X-ray emission spectra attributed to the {\pi} bands show unambiguous changes of the electronic structure upon protonation. By comparing to X-ray absorption measurements, the chemical bonding and electronic configuration is characterized.Comment: 8 pages, 8 pictures, http://jcp.aip.org/resource/1/jcpsa6/v111/i10/p4756_s