1,908 research outputs found
The Interplay between Different Stimuli in a 4D Printed Photo-, Thermal-, and Water-Responsive Liquid Crystal Elastomer Actuator
Get PDFMulti-stimuli responsivity in 3D-printed objects is receiving much attention. However, the simultaneous interplay between different environmental stimuli is largely unexplored. In this work, we demonstrate direct ink writing of an oligomeric ink containing an azobenzene photo-switch with an accessible hydrogen bond allowing triple responsivity to light, heat, and water. The resulting printed liquid crystal elastomer performs multiple actuations, the specific response depending on the environmental conditions. Bilayer films formed by printing on a static substrate can rapidly change shape, bending almost 80 degrees if irradiated in air or undergoing a shrinkage of about 50 % of its length when heated. The bilayer film assumes dramatically different shapes in water depending on combined environmental temperature and lighting conditions
Solar power from plastics?
No full textColorful plastic panels collect and focus sunlight onto small solar cells, offering architects great design freedom in integrating solar-energy systems into the built environment
A concept for switchable, energy-generating ‘smart’ windows
No full textSmart’ windows, mostly based on chromogenic events triggered chemically, electrically or otherwise, are able to variably control the amount of light that passes into a room space, but make no use of the rejected light. Photovoltaic ‘windows’ such as those based on thin films or tiled photovoltaic cells, on the other hand, may used absorbed light to generate electricity, but are incapable of adjusting transparency. I propose to use fluorescent dye guests in a liquid crystal host sandwiched between glass panels as a new type of ‘smart’ window. The dye material absorbs a variable amount of light depending on its orientation, which may be altered at will by aligning the liquid crystal host through application of an electric field. The absorbed light, rather than being lost, is re-emitted by the fluorescent molecules. A significant fraction of this light becomes trapped in the glass window panels by total internal reflection, and becomes concentrated along the edges of the device. To the edges of the glass waveguides may be attached small photovoltaic cells for generation of electricity. In this work I discuss preliminary results on model ‘smart’ window systems. I demonstrate that there is a variation of absorption upon adjusting the voltage applied to the cell. While there is a concurrent decrease in the amount of light emitted from the edge as the transmission of the window is increased, the variation in edge output is less than the variation in transmission, due to enhanced efficiency of light transport as the dye molecules alter their alignments
Luminescent solar concentrators: Semiconductor solution
No full textThere are increasing public and private pressures for the adoption of renewable energy technologies, of which solar is anticipated to be a prime player1. As it becomes increasingly desirable to generate energy nearer the point of demand (such as within a city centre) it is also more apparent that additional features beyond electrical performance play an important role in solar power: aesthetics2 and perceived safety3 of the devices come to the fore. Because of their adaptability and attractive appearance, there is a burgeoning interest in luminescent solar concentrator (LSC) devices for use in urban areas4. LSCs are large plastic plates filled with luminescent materials that essentially redirect solar energy to small edge-attached photovoltaic (PV) cells to generate electricity (Fig. 1). The first steps have been made in integrating LSCs into public spaces5, 6. But while the silicon-based PV panel industry has experienced tremendous growth, there is still no commercial manufacturer of LSCs
Renewable energy : better luminescent solar panels in prospect
No full textDevices known as luminescent solar concentrators could find use as renewable-energy generators, but have so far been plagued by a major light-reabsorption effect. A new study offers a promising route to tackling this proble
Thermally stable sites for electron capture in directly ionized DNA : free radicals produced by the net gain of hydrogen at C5/C6 of cytosine and thymine in crystalline oligodeoxynucleotides
No full textElectron paramagnetic resonance (EPR) spectroscopy is used to study radical trapping in crystalline oligodeoxynucleotides exposed to 70 keV x-irradiation at 4 K and annealed to 240 K. The four oligomers studied were the Z form d(CGCACG:GCGTGC), two A forms, d(CCCTAGGG)2 and d(GTGCGCAC)2, and the B form d(CGCGAATTCGCG)2. In each of these oligomers, evidence was found for trapping of a cytosine radical formed by the net gain of a hydrogen at C6 and a proton at N3 (the Cyt(C6+H, N3+H+)+• radical). The data are consistent with the trapping of another cytosine radical formed by the net gain of hydrogen at C5 (the Cyt(C5+H, N3+H)+• or Cyt(C5+H)• radical). The well-known thymine radical formed by the net gain of hydrogen at C5 (Thy(C6+H)• radical) was observed in the Z- and B-form duplexes but not in the A-form duplexes. The relative yields of these three reduction species indicate that cytosine is comparable to, or better than, thymine as a stable trapping site for reductive damage. These three radicals, Cyt(C6+H, N3+H+)+•, Cyt(C5+H, N3+H)+•, and Thy(C6+H)•, account for 85% of the total irreversibly trapped electrons in samples irradiated at 4 K and annealed to 240 K. Extrapolation of these results to B-form DNA hydrated to 9 waters per nucleotide, x-irradiated at 4 K, and warmed to room temperature predicts end product yields of 0.04-0.06 µmol/J for 5,6-dihydrouracil and 0.03-0.05 µmol/J for 5,6-dihydrothymine
Using liquid crystals to improve the performance of luminescent solar concentrators
No full textThe luminescent solar concentrator (LSC) has been proposed as a cost-effective solution to bring electricity generation from sunlight into the built environment. The basic LSC design consists of a plastic plate containing or topped by a thin layer of fluorescent dyes. The dyes absorb sunlight and re-emit it at a longer wavelength. A fraction of this light is trapped by total internal reflection and becomes concentrated along the edges of the waveguide, where one can place small photovoltaic cells to convert the emitted light into electrical current. With its flexibility in color, shape, and size, it would appear ideally suited for exploitation by the architect for use in façades and other structures in the urban surroundings. However, limitations in performance have hindered widespread adoption of the devices. In this work I present modifications to the standard LSC using liquid crystals to assist in collecting, directing, and controlling both the incoming and emitted light in the device, as well as describing additional features to allow on-demand adjustment of transparency
Solar energy collectors with tunable transmission
No full textA new type of smart window is proposed that makes use of fluorescent dye guests in a liquid-crystal host sandwiched between glass panels. The dye absorbs a variable amount of light depending on its orientation, and re-emits this light, of which a significant fraction is trapped by total internal reflection at the glass–air interface, and becomes concentrated along the edges. Such a device could both generate electricity via an attached photovoltaic as well as allow user control of the amount of transmitted light. By applying a voltage across the cell, absorption could be varied 31%, while the usable light output only varied 11% due to the increased efficiency of light collection at homeotropic dye orientation
Free radical yields in crystalline DNA x-irradiated at 4 K
No full textThe objective of this work is to determine the extent to which various structural factors influence the yield of trapped free radicals, G(tfr), in DNA irradiated at 4 K. G(tfr) was measured in a series of 13 different oligodeoxynucleotides using electron paramagnetic resonance (EPR) spectroscopy. Each sample consisted of crystalline duplex DNA for which the crystal structure was verified to be that reported in the literature. We find that the G(tfr) of these samples is remarkably high, ranging from 0.55 to 0.75 micromol/J. The standard deviation in G(tfr) for a given crystal structure is generally small, typically less than +/-10%. Furthermore, G(tfr) does not correlate with DNA base sequence, conformation, counterion or length of base stacking. Two observations point to the importance of DNA packing: (1) The radical yields in crystalline DNA are greater than those determined previously for DNA films (0.2 to 0.5 micromol/J); and (2) the variability in G(tfr) is less in DNA crystals than in DNA films. We conclude that closely packed DNA maximizes radical trapping by minimizing the interhelical solvent space. Furthermore, the high efficiency of electron and hole trapping at 4 K is not consistent with DNA possessing properties of a metallic conductor. Indeed, it behaves as an insulator, whether it is in A-, B-, or Z-form and whether base stacking is short- (8 bp) or long-range (>1000 bp)
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