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Maximizing Poly(3-butylthiophene-2,5-diyl) Electrical Conductivity by Maximizing Transcrystal Growth

  • Bicknell, Edward Alexander
Publication Date
Jun 01, 2019
[email protected]
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Polymers are generally considered electrical insulators. Despite this, research in the mid 1970’s found that polymers consisting of a conjugated backbone structure could become electrically conductive upon doping.1 The conjugated polymer analyzed for this project was poly(3-butylthiophene-2,5-diyl) (P3BT). Transcrystals have been found as a way to promote electrical conductivity through mechanisms including π bond atomic orbital overlap and electron mobility.2 In theory, maximizing transcrystal length would also maximize P3BT electrical conductivity, increasing its applicable use in electronic devices. The goal of this project was to determine a methodological way to maximize P3BT electrical conductivity by producing the longest transcrystal length possible. This was attempted through two objectives. The first objective was to determine what solvent combination and solvent evaporation temperature (24°C and 26°C) would yield in the longest transcrystal length possible. The solvents investigated included carbon disulfide (CS2), 1,2-dichlorobenzene (DCB), liquid 1,2,4-trichlorobenzene (L-TCB), and solid 1,3,5-trichlorobenzene (S-TCB). The second objective was to determine if increasing transcrystal length would increase electrical conductivity. Three solutions of 2 wt.% P3BT were produced with the following solvent combinations: solution #1 (7wt.% L-TCB, 91wt.% CS2), solution #2 (7wt.% L-TCB, 91wt.% DCB), and solution #3 (7wt.% S-TCB, 91wt.% DCB). Transcrystals were nucleated from a carbon nanotube (CNT) aerogel fiber via a 24-hour controlled CS2 solvent evaporation. Polarized optical microscopy (POM) and scanning electron microscopy (SEM) were used to capture the transcrystal lengths and morphology of each condition analyzed. It became evident through the POM images that solution used had the largest impact on transcrystal length, while temperature had a smaller yet significant impact. Solution #1 produced the longest average transcrystal length of 44.8μm. This was followed by solution #2 and #3, with respective transcrystal lengths of 24.1μm and 1.6 μm. A solvent evaporation temperature at 24°C yielded slightly longer transcrystals than a solvent evaporation temperature at 26°C, with respective lengths of 26.2 μm and 20.8 μm. A correlation between transcrystal length and electrical conductivity remain inconclusive due to a limitation with the four-point probe testing apparatus and its ability to analyze transcrystals in a micrometer scale. Transcrystal formation proved unpredictable, demonstrated through several attempts to nucleate transcrystals under the same conditions. Overall, a methodological way to produce the longest transcrystal length possible has been established.

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