Probing the Viscoelastic Property of Pseudo Free‐Standing Conjugated Polymeric Thin Films

Abstract

The understanding of the structure-mechanical property relationship for semiconducting polymers is essential for the application of flexible organic electronics. Herein pseudo free-standing tensile testing, a technique that measures the mechanical property of thin films floating on the surface of water, is used to obtain the stress-strain behaviors of two semiconducting polymers, poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(2-decyltetradecyl)-3,6-di(thiophen-2-yl)diketopyrrolo[3,4-c]pyrrole-1,4-dione-alt-thienovinylthiophene (DPP-TVT) donor-acceptor (D-A) polymer. To our surprise, DPP-TVT shows similar viscoelastic behavior to P3HT, despite DPP-TVT possessing a larger conjugated backbone and much higher charge carrier mobility. The viscoelastic behavior of these polymers is due to sub room temperature glass transition temperatures (T ), as shown by AC chip calorimetry. These results provide a comprehensive understanding of the viscoelastic properties of conjugated D-A polymers by thickness-dependent, strain rate dependent, hysteresis tests, and stress-relaxation tests, highlighting the importance of T for designing intrinsically stretchable conjugated polymers.

The Critical Role of Electron‐Donating Thiophene Groups on the Mechanical and Thermal Properties of Donor–Acceptor Semiconducting Polymers

“…[52] Briefly speaking, the polymer thin films (≈90 nm) were patterned into dog-bone shape by oxygen plasma etching process and floated on top of water before being further unidirectionally pulled at a strain rate of 5 × 10 −4 s −1 until the film fractures. Details about the tensile stage setup can be referred to our previous publication.…”

“…The details of the set-up were described in our previous publication. [52,54,55] The molecular weight is another factor that has been observed to critically influence the mechanical property of a given polymer, which was carefully tuned to be in the similar range, as shown in Table 1. To provide a fair comparison between different DPP polymers, conjugated polymers with relatively high molecular weights were targeted and synthesized, followed by processing into thin films of similar thickness, and annealing under the same temperature and time.…”

Glass Transition Phenomenon for Conjugated Polymers

“…However, the sample preparation is time consuming since it requires the stacking of several hundred layers of ultrathin film in order to meet the mass requirement . With the new developments of the nanocalorimetry, including flash DSC and AC‐chip calorimetry (We note here that the modulated DSC and the AC‐chip calorimetry are considered as dynamic measurements of T g ), which has the mass requirement of nanogram, measuring the T g of sub‐100 nm a single layer of polymer ultrathin film with DSC becomes possible and has drawn increasing attention …”

Enhanced miscibility and strain resistance of blended elastomer/π‐conjugated polymer composites through side chain functionalization towards stretchable electronics

“…Substrates were then rinsed with clean isopropanol and dried with a stream of air and further cleaned by 15 min of oxygen plasma. A common literature procedure was adapted to employ a sacrificial PEDOT/PSS layer for transfer printing onto PDMS substrates as described in detail for the applicable experiments below . P3Br x HT solutions were filtered with a 0.45 μm syringe filter and blends were filtered with both 0.8 μm and 0.45 μm syringe filters before spin coating for 60 s at 2000 rpm.…”