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Polymers and Their Composites for Thermoelectric Applications
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Polymers in Energy Conversion and Storage, 2022
According to Equation (15.3), a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity in polymers are required to maximize ZT [25]. In pristine semiconducting polymers, the low electrical conductivity ranging from 10−3 to 10−8 S cm−1 leads to a low power factor (less than 1 μW m−1 K−2). Figure 15.2a shows the chemical structures of several semiconducting polymers for thermoelectric materials that include polyacetylene (PA) [40–44], polypyrrole (PPy) [45–47], polythiophene (PT) [48, 49], poly(3hexylthiophene) (P3HT) [50, 51], poly(3,4-ethylenedioxythiophene) (PEDOT) [52, 53], and polyaniline (PANI) [54]. Doping can improve electrical conductivity and the power factor of polymers [17, 55]. Semiconducting polymers can be oxidized (p-doped) [56] or be reduced (n-doped) [14, 16, 17, 57]. For example, a low power factor in pristine polyacetylene is 0.17 μW m−1 K−2 [44]. After doping by iodine, the measured power factor value in the doped polyacetylene was 400 μW m−1 K−2 [44]. However, thermoelectric applications using polyacetylene are limited, because it is unstable in air [17]. Figure 15.2 shows the chemical structures of selected semiconducting polymers (Figure 15.2a) and dopants (Figure 15.2b) for thermoelectric devices. Common dopants include poly(styrene sulfonate) (PSS), tosylate (Tos), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and nitrosonium tetrafluoroborate (NOBF4).
Progress in Optically Transparent Conducting Polymers
Published in Sun Sam-Shajing, Sariciftci Niyazi Serdar, Organic Photovoltaics, 2017
Venkataramanan Seshadri, Gregory A. Sotzing
In 1992 Pomerantz et al. [42] reported the synthesis and polymerization of thieno[3,4-b]pyrazines. Thieno[3,4-b]pyrazine (36) closely resembles 31 except that the carbons next to the β-positions of the thiophene are replaced by nitrogen atoms. They also reported soluble alkyl derivatives of the polypyrazine. They had calculated that the quinonoid form of the polymer is more stable than the aromatic form and claimed that even the aromatic form of the polymer is planar. These prompted the synthesis of the poly(thieno[3,4-b]pyrazines) by chemical methods as the resultant polymers were expected to be soluble. Poly(2,3-dihexylthieno[3,4-b]pyrazine) was shown to exhibit a band edge gap of 1.14 eV with a λmax at 875 nm in solution. The polymer film showed a λmax at 287 and 915 nm with a band edge gap of 0.86–1.02 eV. They also reported that upon doping the dark blue-black polymer solution in chloroform with nitrosonium tetrafluoroborate the solution turned light yellow. Schrof et al. [43] prepared a number of copolymers using a tool kit of bis(trimethylstannyl) thiophenes and dihalo thiophenes with fused pyrazine rings. All of these polymers were reported to show an absorption edge >900nm and also a λmax > 600 nm. The different copolymers (37–43) made by this group are shown in Figure 22.16 with the corresponding peak absorption for each of the copolymers.
Conjugated Polymers
Published in A. Sezai Sarac, Nanofibers of Conjugated Polymers, 2017
A strong electron acceptor (oxidizing agent) can be used to dope positively, a neutral conjugated material or to undope a negatively doped material, for example, nitrosonium tetrafluoroborate (NOBF4) and halogen gases (I2, etc.).
Low voltage tunable cholesteric liquid crystal based on electrochemical process
Published in Liquid Crystals, 2022
Yaqian Zhang, Wanli He, Yongfeng Cui, Lei Zhang, Yuzhan Li, Zhou Yang, Dong Wang, Hui Cao
According to the experimental design ratio, samples were composed of certain amount of LC matrix doped with chiral dopant R5011, a string of electrochemical chiral molecules CD-Fc, and equimolar amounts of single-electron oxidant Nitrosonium Tetrafluoroborate (NOBF4). Then, 4 mL of anhydrous dichloromethane and anhydrous ethanol solvent were added, and sonicated with shaking to obtain a uniformly mixed solution. Next, centrifuge tubes were moved to a vacuum oven at 60°C to evaporate solvent under reduced pressure for 10 h. Finally, samples were poured into the non-functionalised liquid crystal cell by siphoning.