Tuning structures of solution‐state aggregation and aggregation‐mediated assembly pathways of conjugated polymers is crucial for optimizing their solid‐state morphology and charge‐transport property. However, it remains challenging to unravel and control the exact structures of solution aggregates, let alone to modulate assembly pathways in a controlled fashion. Herein, aggregate structures of an isoindigo–bithiophene‐based polymer (PII‐2T) are modulated by tuning selectivity of the solvent toward the side chain versus the backbone, which leads to three distinct assembly pathways: direct crystallization from side‐chain‐associated amorphous aggregates, chiral liquid crystal (LC)‐mediated assembly from semicrystalline aggregates with side‐chain and backbone stacking, and random agglomeration from backbone‐stacked semicrystalline aggregates. Importantly, it is demonstrated that the amorphous solution aggregates, compared with semicrystalline ones, lead to significantly improved alignment and reduced paracrystalline disorder in the solid state due to direct crystallization during the meniscus‐guided coating process. Alignment quantified by the dichroic ratio is enhanced by up to 14‐fold, and the charge‐carrier mobility increases by a maximum of 20‐fold in films printed from amorphous aggregates compared to those from semicrystalline aggregates. This work shows that by tuning the precise structure of solution aggregates, the assembly pathways and the resulting thin‐film morphology and device properties can be drastically tuned.
The hierarchical assembly of conjugated polymers has gained much attention due to its critical role in determining optical/electrical/mechanical properties. The hierarchical morphology encompasses molecular-scale intramolecular conformation (torsion angle, chain folds) and intermolecular ordering (π–π stacking), mesoscale domain size, orientation and connectivity, and macroscale alignment and (para)crystallinity. Such complex morphology in the solid state is fully determined by the polymer assembly pathway in the solution state, which, in turn, is sensitively modulated by molecular structure and processing conditions. However, molecular pictures of polymer assembly pathways remain elusive due to the lack of detailed structural characterizations in the solution state and the lack of understanding on how various factors impact the assembly pathways. In this mini-review, we present possible assembly pathways of conjugated polymers and their characteristics across length scales. Recent advances in understanding and controlling of assembly pathways are highlighted. We also discuss the current gap in our knowledge of assembly pathways, with future perspectives on research needed on this topic.
Conductive polymer composites (CPCs) with positive temperature coefficients (PTC) are widely used in intelligent electric heating materials and temperature-sensitive electronic components due to their superior mechanical properties, stability of chemical...
Poly (3,4-ethylenedioxythiophene) (PEDOT) has been synthesized through a facile solid-state polymerization (SSP) approach. The polymerization was simply initiated by sintering the monomer, 2,5-dibro-3,4-ethylenedioxythiophene (DBEDOT), at the temperature of 80 °C. The SSP-PEDOT with the heating time for 24 hours has the maximum value of dielectric loss tangent (tanδε) in the frequency range of 2-18 GHz, which revealed that this sample has the best electromagnetic energy absorption ability. When the thickness of the sample reached 2 mm, the bandwidth with the reflection loss (RL) deeper than −10 dB is nearly 5.9 GHz (From 10.0 GHz to 15.9 GHz), and the maximum value of RL is about −50.1 dB at 11.2 GHz. These results demonstrate that SSP initiated at low temperature shows multi-practical application in the areas of military camouflage, and electronic devices protection.
Tuning structures of solution-state aggregation and aggregation-mediated assembly pathways of conjugated polymers is crucial for optimizing their solid-state morphology and charge transport property. However, it remains challenging to unravel and control the exact structures of solution aggregates, let alone to modulate assembly pathways in a controlled fashion. Herein, we largely modulate aggregate structures by tuning selectivity of the solvent towards the side chain vs. the backbone, which leads to three distinct assembly pathways: direct crystallization from side-chain associated amorphous aggregates, chiral liquid crystal (LC)-mediated assembly from semicrystalline aggregates with side-chain and backbone stacking, random agglomeration from backbone-stacked semicrystalline aggregates. Importantly, we demonstrate for the first time that the amorphous solution aggregates, compared with semicrystalline ones, lead to significantly improved alignment and reduced paracrystalline disorder in solid-state due to direct crystallization during the meniscus-guided coating process. Alignment quantified by dichroic ratio obtained from grazing incidence X-ray diffraction (GIXD) is enhanced by up to fourteen-fold, and the charge carrier mobility increases by a maximum of twenty-fold in films printed from amorphous aggregates compared to those from semicrystalline aggregates. This work shows that by tuning the precise structure of solution aggregates, one can drastically tune assembly pathways, and the resulting thin film morphology and device properties.
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