Nowadays, the materials commonly used to fabricate thermoelectric devices are tellurium, lead and germanium. These materials ensure from one side the best thermoelectric performances, but exhibit drawbacks in terms of availability, sustainability, cost and manufacturing complexity. Moreover, they do not guarantee a safe and cheap implementation in wearable thermoelectric applications. Here, p-and n-type flexible thermoelectric textiles are produced with sustainable and low-cost materials through green and scalable processes. Cotton is functionalized with inks made with biopolyester and carbon-nanomaterials. Depending on the nanofiller, i.e. graphene nanoplatelets, carbon nanotubes or carbon nanofibers, positive or negative Seebeck coefficient values are obtained, achieving also a remarkable value of electrical conductivity of 55 S cm -1 using carbon nanotubes. The best bending and washing stability are registered for the carbon nanofibers-based biocomposites, which increase their electrical resistance by 5 times after repeated bending cycles and only of the 30% after washing. Finally, in-plane flexible thermoelectric generators are fabricated and characterized coupling the best p-and n-type materials, achieving an output voltage of ~ 1.65 mV and a maximum output power of ~ 1.0 nW by connecting only 2 p/n thermocouples at a temperature difference of 70°C.
International audienceWe report on the ultrafast vibrational response of single copper nanowires investigated by femtosecond transient reflectivity measurements. The oscillations of the sample reflectivity are correlated with individual modes of resonance for wires with a diameter ranging from 100 to 500 nm and are compared with 2D finite element simulation. Fluctuation of the sample-substrate coupling is illustrated through its effect on the damping rate. We demonstrate elastic confinement in free standing wires which allowed the detection of up to the third harmonic of the breathing mode. By removing the energy relaxation channel towards the substrate, we obtained nano-oscillators with quality factors up to 130. Finally, taking advantage of the very high spectral resolution achieved on free standing wires, we could observe the elastic coupling between two close wires via their polymer cladding. (C) 2013 AIP Publishing LLC
We report on gigahertz acoustic phonon waveguiding in free-standing single copper nanowires studied by femtosecond transient reflectivity measurements. The results are discussed on the basis of the semianalytical resolution of the Pochhammer and Chree equation. The spreading of the generated Gaussian wave packet of two different modes is derived analytically and compared with the observed oscillations of the sample reflectivity. These experiments provide a unique way to independently obtain geometrical and material characterization. This direct observation of coherent guided acoustic phonons in a single nano-object is also the first step toward nanolateral size acoustic transducer and comprehensive studies of the thermal properties of nanowires.
The synthesis of
a naphthalene diimide bithiophene copolymer P(EO-NDIT2)
with branched, base-stable, and purely ether-based side chains is
presented. Stille polycondensation leads to high molecular weights
that are limited by methyl transfer and eventually T2 homocouplings.
While extensive solution aggregation hampers molecular weight determination
by conventional methods, NMR spectroscopy allows identification of
both T2- (H and methyl) and NDI-related (methyl) end groups, enabling
the determination of absolute number average molecular weights larger
than M
n,NMR ∼100 kg/mol. Solvent-
and temperature-dependent aggregation in solution is investigated
by NMR and UV–vis spectroscopy. These results are used for
solution doping of P(EO-NDIT2) with N-benzimidazole-based n-dopants.
Spin coating from heated chlorobenzene solutions and using 4-(2,3-dihydro-1,3-dimethyl-1H-benzoimidazol-2-yl)-N,N-diisopropylaniline (N-DiPrBI) as the dopant leads to homogeneous
films with highest conductivities up to 10–2 S/cm.
Generally, N-DiPrBI concentrations as low as ∼5 wt % are sufficient
to increase conductivity by orders of magnitude. Strikingly, maximum
power factors up to 0.11 μW/mK2, although limited
by conductivity, are achieved for the highest molar mass sample at
a low dopant concentration of 2 wt % N-DiPrBI only.
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