Biphasic Dip-Coating Composition and Method for Forming Polymer Thin Films Using the Same

Low-Volume Biphasic Dip-Coating for Semiconducting Polymer Thin Films Using Solubility Parameter Differences

This technology provides a composition for biphasic dip-coating and a method for forming semiconducting polymer thin films by forming a phase-separated interface with a high-density chlorinated amphiphilic solvent at the bottom and a polythiophene-xylene solution at the top. By setting the difference in Hansen solubility parameters between the two solvents to 0.9–2.4, solubility-induced aggregation of the polymer is triggered at the interface.

Conventional dip-coating processes require large amounts of polymer solution to fill the reservoir, making it difficult to scale up for large-area production. While biphasic dip-coating has been proposed as an alternative, there have been limitations due to a lack of established criteria for selecting solvent pairs that create a stable biphasic state and a poor understanding of how the bottom solvent affects the top polymer thin film.

This technology allows for the control of coating solution stability and thin-film surface crystallinity simply by switching the bottom solvent among chloroform, chlorobenzene, or dichlorobenzene. It significantly reduces solute consumption compared to single-phase dip-coating while producing thin films with superior molecular alignment and charge mobility. Applicable to the manufacturing of organic field-effect transistors and flexible/wearable electronic devices, it enables large-area printed electronics with reduced consumption of expensive conjugated polymer materials.

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Key Features:

• A composition for biphasic dip-coating in which a high-density chlorinated amphiphilic solvent—either chloroform, chlorobenzene, or dichlorobenzene—is positioned at the bottom, and a semiconducting polymer solution of polythiophene dissolved in xylene is positioned on top.
• A configuration where the difference in Hansen solubility parameters between the top and bottom solvents is 0.9 to 2.4, forming an interface through phase separation and inducing solubility-driven aggregation at that interface.
• A step of preparing a biphasic dip-coating solution by mixing polythiophene in xylene, heating to 85–90°C, and dropping the solution onto the amphiphilic solvent to form an interface.
• A configuration where a substrate is immersed in the biphasic dip-coating solution and then withdrawn to obtain a semiconducting polymer thin film with thickness controlled by the withdrawal speed, which is then applied to a field-effect transistor.

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This invention was developed with support from the Ministry of Education for the development of high-performance gas sensors based on phase-separated MOF/conjugated polymer hybrid thin films.

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