Theory of the photothermally generated Seebeck voltage in harmonic regime

In this paper, a general theory of the photothermally induced Seebeck voltage in the harmonic regime is presented. Conditions highlighting coupling effects between temperature and electric fields are reported. In the frequency domain, thermoelectric materials are governed by two regimes separated by a cut-off frequency. Below this point, there is no manifestation of coupling on the voltage response. In its vicinity and beyond, coupling appears through an effective Seebeck coefficient and an effective thermal conductivity. From this last quantity, the figure of merit can be, in principle, theoretically determined from the ratio of thermal conductivities obtained respectively at high and low frequencies or from the maximum value of the complex thermal conductivity argument at the cut-off frequency

Heat treatment of commercial polydimethylsiloxane PDMS precursors: Part II. Thermal properties of carbon-based ceramic nanocomposites

International audienc

Quantitative thermal wave phase imaging of an IR semi-transparent GaAs wafer using IR lock-in thermography

International audienc

Carbon Nanotubes Blended Nematic Liquid Crystal for Display and Electro-Optical Applications

In this paper, we investigate a commercial nematic liquid crystal (LC) mixture namely E7 dispersed with small concentrations of multi-walled carbon nanotubes (MWCNTs). The dielectric and electro-optical characterizations have been carried out in the homogeneously and vertically aligned LC cells. The electro-optical response of LC molecules has been enhanced by 60% after the addition of MWCNTs, which is attributed to the reduced rotational viscosity in the composites. MWCNTs act like barricades for ionic impurities by reducing them up to ∼34.3% within the dispersion limit of 0.05 wt%. The nematic–isotropic phase transition temperature (TNI) of the E7 LC has also been shifted towards the higher temperature, resulting in a more ordered nematic phase. The enhanced birefringence and orientational order parameter in the LC-MWCNTs are attributed to π-π electron stacking between the LC molecules and the MWCNTs. The outlined merits of the LC-MWCNTs composites evince their suitability for ultrafast nematic-based electro-optical devices

Carbon Nanotubes Blended Nematic Liquid Crystal for Display and Electro-Optical Applications

In this paper, we investigate a commercial nematic liquid crystal (LC) mixture namely E7 dispersed with small concentrations of multi-walled carbon nanotubes (MWCNTs). The dielectric and electro-optical characterizations have been carried out in the homogeneously and vertically aligned LC cells. The electro-optical response of LC molecules has been enhanced by 60% after the addition of MWCNTs, which is attributed to the reduced rotational viscosity in the composites. MWCNTs act like barricades for ionic impurities by reducing them up to ∼34.3% within the dispersion limit of 0.05 wt%. The nematic–isotropic phase transition temperature (TNI) of the E7 LC has also been shifted towards the higher temperature, resulting in a more ordered nematic phase. The enhanced birefringence and orientational order parameter in the LC-MWCNTs are attributed to π-π electron stacking between the LC molecules and the MWCNTs. The outlined merits of the LC-MWCNTs composites evince their suitability for ultrafast nematic-based electro-optical devices

General approach of the photothermoelectric technique for thermal characterization of solid thermoelectric materials

International audienceThis work focuses on the photothermoelectric (PTE) technique allowing the thermal characterization of solid-state thermoelectric (TE) materials. Previously, this technique was restricted to TE materials having low electrical conductivities. Here, the PTE technique is extended and generalized to all solid-state TE materials with low or high electrical conductivities. This is achieved by taking into account the Gaussian shape of the thermal excitation source. The formalism of this new methodology is developed and the procedure for extracting thermal parameters is proposed. For illustration, two different TE materials are studied with relatively high electrical conductivity (Bi2Te2.4Se0.6) and relatively low electrical conductivity (Bi2Ca2Co1.7Ox). The thermal properties of these two materials (thermal diffusivity, effusivity and conductivity) are found and compared to those obtained by the photothermal radiometry which is a well established technique. The good concordance between the results obtained by these two techniques demonstrates the relevance of the generalized PTE technique. One of the main advantages of this technique is its non use of an external sensor