Contact line mobility of nanoparticle suspension

Microdroplets of complex fluids or molten substances have played a pivotal tool as building blocks in bioprinting and bottom-up fabrication. Control of their behavior, specifically their spreading on solid surfaces, is paramount to the precision and accuracy of these technologies. While the spreading dynamics of pure liquids or microparticle suspensions have been extensively investigated for years, the spreading behavior of nanoparticle suspension microdrop has been rarely studied to date. Here, utilizing an in-house inkjet system that can generate single microdroplets in the diameter range from 50 μm to 80 μm on demand, we observed the spreading behavior of aqueous microdrops containing particles of various sizes on hydrophilic surfaces. Notably, the expanding radius of nanoparticle suspension surpassed that of pure water microdrops at the same Weber number. To understand this behavior, we visualized the flow field near the moving contact line of the nanoparticle suspension drops. We suggest possible mechanisms behind enhanced contact line mobility of nanoparticle suspension based on our experimental results. Our findings shed new light on the wetting behavior of nanoparticle suspensions, and they hold potential for further refining the precision and accuracy of microdroplet-based applications.