Controlling Chiral Emergence of Conjugated Polymers by Meniscus-Guided Coating

The ubiquity of chiral structures and materials in nature has inspired researchers across various fields to investigate their properties and find possible applications. Many of these biological structures often show chirality at a supramolecular level and are the result of molecular self-assembly. Advancements in understanding these self-assembly processes have paved the way for the development of chiral structures from achiral soft materials, which have found multiple applications in chiral recognition and sensors, spintronics, circularly polarized luminescence, and chiral catalysis. Previous studies have reported the formation of chiral liquid crystal mesophases from achiral polymers through a multistep hierarchical self-assembly process that is induced by increasing the concentration beyond a critical point. In this work, we demonstrate the emergence of supramolecular chirality in the Landau Levich blade coating regime which has previously been left unexplored. The high-speed Landau Levich printing regime, in which film thickness and formation are controlled by the competition between viscous forces and surface tension, is often associated with lower crystallinity and alignment due to a lack of slow and controlled assembly. However, we show that by modulating the viscosity of the polymer solution, through the concentration and the polymer molecular weight, we were able to fabricate highly crystalline chiral films accompanied by global segregation of handedness. We further demonstrate that for a given solution, the chiral G factor can be controlled over a range of two orders of magnitude by simply varying the printing speed between the transition regime and the Landau Levich regime. Given the strong dependence of the chirality on the printing speed and solution viscosity, we hypothesize that the shear-induced stress from the blade motion, combined with the subsequent complex flow patterns that arise during printing, lead to chiral symmetry breaking in the deposited liquid film. The rapid drying process that follows, captures this transient chiral state, resulting in highly aligned and crystalline films with a unique morphology that shows alignment orthogonal to films found in the evaporation regime - a feature exclusive to the Landau-Levich regime with low viscosity solutions. These findings present a new potential approach to fabricate chiral thin films from achiral polymer solutions, and further tune the chirality by tuning the printing parameters without modifying the material system.