Competition and Synergy in Programmable Open Microfluidics: Thermal Fields vs Structural Heterogeneities

Functional structured surfaces have garnered wide interest in open microfluidics, where external fields like magnetic, optical, electrical, and thermal fields are crucial. While thermal fields provide simplicity and early utility in liquid manipulation, their interplay with structural effects remains underexplored compared to other field-driven methods. We present a programmable microfluidic platform involving heterogeneous structured surfaces grafted with thermoresponsive macromolecules, allowing control of surface wettability through global/local thermal fields. Structural heterogeneity enables asymmetric interfacial forces to achieve tunable directional liquid transport via thermo-mediated wettability. We reveal a competitive yet synergistic mechanism between local thermal fields and structural effects: thermal fields can override structural guidance to redirect liquid motion, while their synergy greatly enhances liquid operation performance, increasing the antigravity transport critical angle from 2.3° to 41.8°. Building upon these insights, we deploy localized heating units to show programmable liquid patterns and cascade chemical reactions, advancing thermal-regulated microfluidics for diagnostic/synthetic applications.