Nanoscale Self-Assembly of Poly(3-hexylthiophene) Assisted by a Low-Molecular-Weight Gelator toward Large-Scale Fabrication of Electrically Conductive Networks

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Polymer Science and Engineering


Achieving self-assembly of conjugated polymers is necessary to harness their charge transport properties in various applications, including field-effect transistors, sensors, and conductive gels for biomedical applications. Although many processes have been investigated, there are still opportunities for developing new strategies that can lead to materials with improved performances. Particularly, large-scale fabrication of three-dimensional conductive networks formed by the self-assembly of conjugated polymers and low-molecular-weight gelators (LMWGs), but with conjugated polymers at much lower quantity, would be advantageous. LMWGs can be selected from an extensive library of available systems and can be directed to self-assemble in various conditions. However, the simultaneous self-assembly of LWMGs and conjugated polymers is not fully understood. Here, we report a simple pathway for the self-assembly of poly(3-hexylthiophene) (P3HT), a conjugated polymer, in chloroform in the presence of di-Fmoc-l-lysine, an LMWG. Di-Fmoc-l-lysine was selected as the LMWG because it does not have significant interactions with P3HT. P3HT and di-Fmoc-l-lysine in chloroform form gels with decreasing temperature. UV-vis spectroscopy provides an insight into the photophysical response of the gelation process, revealing the self-assembly of P3HT in the gel network. The scattering experiments further capture the self-assembly of the P3HT network. The nanofibrillar microstructure has been captured using atomic force microscopy (AFM) for the gels without and with P3HT, where both P3HT and di-Fmoc-l-lysine form nanofibers independently. Both these nanofibers coexist and intermingle, displaying conductive domains in the dried films captured by conductive AFM. The conductive nanofibers form a percolated network in the dried samples, leading to bulk electrical conductivity similar to that of pristine P3HT films. This is achieved with only 20% P3HT content and the balance insulating di-Fmoc-l-lysine molecules. Our results provide a fundamental understanding of the self-assembly of P3HT in the presence of an LMWG, resulting in a conductive nanofibrillar network. Such knowledge can readily be implemented in other conjugated polymeric systems. The approach presented here has potential applications towards fabricating conductive gels for biomedical and sensor applications and large-scale processing of thin films for optoelectronic applications.

Publication Title

ACS Applied Nano Materials

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