Determination of physical parameters of conducting polymers by photothermal spectroscopies

Abstract

Photothermal spectroscopies, photopyroelectric and photoacoustic, were used to obtain physical parameters of polyaniline–emeraldine base (PANI-EB) and poly(o-methoxyaniline)–emeraldine base (POMA-EB), such as thermic parameters like thermal diffusivity, thermal conductivity, and specific heat. These studies were done for PANI-EB and POMA-EB films in the 400<λ<900 nm wavelength range. The photopyroelectric intensity Vn(f ) and the phase Fn(f ) (f being the chopping frequency) for a given λ of the saturation part of the PPES spectrum signal were independently measured, as well as the intensity Vn(λ) and its phase Fn(λ). Equations of both the intensity and the phase of the PPES signal, taking into account the thermal and the optical characteristics of the PANI and POMA films and the pyroelectric detector, were used to fit the experimental results. It was observed that, in contrast with the strong doping dependence of the electrical conductivity, the thermal parameters of PANI films remained practically unchanged under doping. This apparent discrepancy is explained by the granular metal model of doped PANI.

Thermal characterization of doped polyaniline and its composites with CoPc

“…However, the order of variation is small in the case of thermal diffusivity as compared to electrical conductivity. 29 This is due to the fact that thermal energy transport mechanism in conducting polymers is dominated by phonon assisted mechanism, whereas electrical conduction is dominated by the variable range hopping process and metallic diffusion of electrons. 30 The effective thermal parameters of composites depend on the thermal properties of its constituents as well as on the microstructural parameters such as volume fraction of each phase, shape, size, and distribution of the particles.…”

Photoacoustic spectroscopy as an approach to assess chemical modifications in edible oils

“…The gas acts as a piston in order to produce a sound wave which is detected by a microphone connected to the chamber. [6][7][8][9][10] As the microphone signal is proportional to radiation absorption by the sample, PAS gives results similar to absorbance spectra, i.e., conventional optical absorption spectroscopy. Also, as the signal depends on the modulation of the radiation source, PAS is able to perform a depth profile of the absorption in the sample, that is, at high modulation frequencies absorption information about the sample near the surface is obtained, while at low modulation frequencies the data come from deeper within the sample.…”

“…5 The heat propagation across the whole chamber is governed by heat diffusion equations of each medium coupled via boundary conditions at the interfaces (T a = T b and k a dT a /dx = k b dT b /dx, a and b are adjacent media, T is temperature and k is thermal conductivity). After all mathematical treatment, the normalized photoacoustic signal (S n ) produced by the microphone is: [5][6][7][8][9][10]17 (2) where r s = b s /s s , b s is the sample optical absorption coefficient, s s = (1 + i)a s with i = (-1) ½ and a s = (p f /a s ) ½ , a s is the sample thermal diffusivity, b nm = k n a n /k m a m (n = g, s, b, that is, g = gas, s = sample, b = backing), and L S is the sample thickness. This equation is a complex mathematical function of the optical, thermal and geometrical parameters of the system, and it governs our results for all the chopper frequencies.…”

Determination of thermal and optical properties of ion implanted polyetheretherketone films by photothermal spectroscopies

“…The detected signal V͑ , t͒ is proportional to the pyroelectric coefficient p of the detector and to the temperature distribution along the detector thickness: 15,16,18,19,22,23 …”

“…[10][11][12][13] Among the PTS techniques, photoacoustic spectroscopy ͑PAS͒, 14 which is the most traditional one, and the more recent photopyroelectric spectroscopy 15 ͑PPES͒ have been used for studying thermal and optical properties of polymeric films and semiconductors. [16][17][18][19][20][21][22][23][24] In these techniques a pulsed light beam is absorbed in a solid sample and the converted heat diffuses into the bulk structure; the sample expansion, or the temperature gradient, is then detected by an appropriate sensor system. The detected signal depends on the optical and thermal properties of the sample: the optical absorption coefficient ␤͑͒ ͑ being the light wavelength͒, the nonradiative conversion efficiency ͑͒, the thermal conductivity k, and the thermal diffusivity coefficient ␣.…”