Connecting the Mechanical and Conductive Properties of Conjugated Polymers

Abstract

Both the mechanical deformability and electronic conductivity of conjugated polymers play important roles in the development of wearable and stretchable electronics. Despite the recent progress and emphasis on achieving highly stretchable and conductive devices, the correlation This article is protected by copyright. All rights reserved. 2 between the mechanical and conductive properties is poorly understood and remains mostly empirical. The future of flexible electronics relies on the ability to predict and tune the mechanical and conductive properties such that the molecular design of conjugated polymers can be optimized for various applications. Instead of seeking a direct correlation between mechanical and conductive properties, this Progress Report proposes to examine the common microstructural origin for mechanical performance and charge transport in conjugated polymers. Measurements of microstructural information, such as persistence length, chain entanglement, glass transition, liquid crystalline phase transition, and intercrystalline morphology, are desperately needed in the field of conjugated polymers in order to establish connections with both the mechanical/conductive properties and the chemical structures. Conventional experimental methods in the field of flexible polymer physics, such as linear viscoelastic rheometry, open up new avenues for characterizing these microstructural parameters, thereby providing a path towards predicting and designing the molecular structure of conjugated polymers with desired mechanical and conductive properties.

Glass Transition Phenomenon for Conjugated Polymers

“…However, AC‐chip calorimetry for P(DPPTTT) gives a T g of 22 °C, much higher than that from DMA, which is consistent with the conformational freedom of the structure . This suggests that extra caution needs to be paid when interpret the results from DMA . Following this trend, the T g of conjugated polymers can be engineered by controlling the sidechain fraction.…”

“…Although, in this case, T g can also be obtained from the peak of tan δ or E ′′, since the sample geometry is unspecified, it is not able to acquire the absolute modulus value. In addition, as pointed out by Xie and co‐workers, besides glass transition, other thermal transitions often observed in conjugated polymers, such as melting and smectic‐to‐isotropic transition, also lead to a peak in tan δ, which potentially could be challenging to accurately differentiate various phase transitions …”

“…In addition, as pointed out by Xie and co-workers, besides glass transition, other thermal transitions often observed in conjugated polymers, such as melting and smectic-to-isotropic transition, also lead to a peak in tan δ, which potentially could be challenging to accurately differentiate various phase transitions. [25,130] In addition to the extensional deformation, the material can also be measured under shear deformation. In this case, the disk-shaped sample is prepared and measured with a rotational rheometer, and the complex dynamic shear modulus G* (G* = G′ + iG′′, G′ and G′′ are storage modulus and loss modulus, respectively; tan δ = G′′/G′ and δ is the phase angle) is obtained.…”

The Polymer Physics of Multiscale Charge Transport in Conjugated Systems

“…The field‐effect mobility ratio of transistors comprising these two polymers is very similar to their elastic modulus ratio, shown in Figure . In light of the success in engineering desired mechanical properties of polyolefins, we believe that many opportunities exist not only to establish empirical correlations between mechanical and electrical properties, like the mobility–modulus relationship mentioned above, but also to shed light on the underlying structural origin and polymer physics for charge transport . This review highlights how these ideas and frameworks have been leveraged—and in some other cases extended—to gain insights on how polymer microstructure impacts charge transport in conjugated polymers.…”

“…Many theoretical tools and frameworks have been developed to describe how the single‐chain characteristics and microstructure in melts and solid states impact the bulk mechanical properties of commodity polymers . We argue that these tools and frameworks can also lend insight to charge transport in conjugated polymers because there can be a common microstructural origin for mechanical and electrical properties . For example, moderately crystalline P3HT is more flexible and ductile than highly crystalline PBTTT.…”