Effect of the Conformation Changes of Polyelectrolytes on Organic Thermoelectric Performances
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Article www.springer.com/13233 pISSN 1598-5032 eISSN 2092-7673
Effect of the Conformation Changes of Polyelectrolytes on Organic Thermoelectric Performances Kyungwho Choi1 Jihun Son2 Yong Tae Park3 Jung Sang Cho4 Chungyeon Cho*,2
1
School of Aerospace & Mechanical Engineering, Korea Aerospace University, Goyang-si, Gyeonggi 10540, Korea 2 Department of Carbon Convergence Engineering, College of Engineering, Wonkwang University, Iksan 54538, Korea 3 Department of Mechanical Engineering, Myongji University, 116 Myongji-ro, Cheoin-gu, Yongin, Gyeonggi 17058, Korea 4 Department of Engineering Chemistry, Chungbuk National University, Gaesin-Dong, Seowon-Gu, Cheongju 28644, Korea Received February 7, 2020 / Revised May 15, 2020 / Accepted June 6, 2020
Abstract: The relationship between the conformation of a polyelectrolyte and the performance of organic thermoelectric multilayers was studied. The conformational change of a weak polyelectrolyte via controlling assembling pH gave rise to a different thermoelectric behaviour in thin films. Organic thermoelectric multilayers were fabricated by alternately depositing bilayers (BL) of a positively-charged polyaniline (PANi) and multiwalled carbon nanotubes (MWNT), stabilized in poly(acrylic acid) (PAA), via a layer-by-layer assembly technique. The electrical conductivity and Seebeck coefficient of PANi/MWNT-PAA nanocomposites were measured by varying assembly pH of PAA solutions. Altering the deposition pH of PAA resulted in different thermoelectric performances. A 40 BL thin film (~210 nm thick) of PANi/MWNT-PAA assembled at pH 2.5/6.5 exhibited electrical conductivity of 95.2 S/cm and a Seebeck coefficient of 35 μV/K. This translates to a power factor of 11.7 μW/m∙K2, which is 50 times higher than that of the same film with all components deposited at pH 2.5. Enhancement of thermoelectric behaviour in PANi/MWNT-PAA nanocomposites is attributed to a conjugated π-π network, together with a tightly packed nanostructure. Keywords: layer-by-layer assembly, polyelectrolytes, power factor, electrical conductivity.
1. Introduction The energy crisis is ongoing and getting worse, as the world demand for energy on the limited natural resources have been rapidly increasing.1,2 Environmental concerns over traditional energy sources such as fossil fuels stimulate many researchers to find alternative energy sources. To date, various techniques have been developed to harvest energy mechanically, electronically, magnetically, thermally, and biochemically.3-5 Thermoelectric (TE) materials have been proved to be effective means of converting heat, which is wasted more than half of the energy produced, into useful electricity. The thermoelectric conversion efficiency depends on the dimensionless figure-of-merit (ZT), ZT = S2σ/κ, where S stands for the Seebeck coefficient (also called the thermopower); σ is electrical conductivity; κ is thermal conductivity; and T is absolute temperature. A power factor (PF = S2·σ) is also used to measure the TE performance due to the difficulties in measur
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