Controlling intermolecular dynamics to achieve liquid-phase directional molecular assembly of semiconducting polymers on self-assembled monolayers

Minh Nhat Pham¹, Chun-Jen Su², Yu-Ching Huang³, Kun-Ta Lin¹, Ting-Yu Huang¹, Yu-Ying Lai¹, Chen-An Wang², Yong-Kang Liaw¹, Ting-Han Lin¹, U-Ser Jeng², Jrjeng Ruan¹, Bang-Yu Hsu^1*

¹Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan
²Taiwan Photon Source, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
³Materials Engineering, Ming Chi University of Technology, New Taipei City, Taiwan

* Presenter:Bang-Yu Hsu, email:hsubon@mail.ncku.edu.tw

In solution-processed semiconducting polymers, the morphologies are influenced by the interactions between solutes, solvents, and substrates. These random interactions occur at the nanoscale and result in macroscopically disordered structures. Achieving long-range order is challenging due to the lack of control over dynamic states in current solution processes. In this presentation, we propose a molecular-level approach that matches the spatial dynamics between weakly bonded polymers and self-assembled monolayers (SAMs) at the sub-nanoscale. By optimizing the dynamic scale within 2.5 Å between polymer side chains and SAMs on nanogrooved substrates, we observe directional molecular assembly that transforms random aggregates into unidirectional fibers. This assembly process significantly increases the anisotropic stacking ratio from 1 to 11. Our study includes a Flory-Huggins-based molecular stacking model which accurately predicts the order and interdigitation angles of polymers on different SAMs, as confirmed by morphological and spectroscopic analyses. The resulting long-range ordering spans over 3 orders of magnitude in length, ranging from the smallest 7.3 nm random crystallites to >14 μm unidirectional fibers. This research sheds light on the control of random intermolecular interactions and offers a means of molecular controllability in solution-based processes.

Keywords: self-assembled monoalyers, semiconducting polymers, directional molecular assembly, long-range ordering