Tailored control of evaporation flux for uniform coffee-ring patterns in multiple nanofluid droplets

Document Type

Article

Publication Date

8-21-2025

Department

Department of Mechanical and Aerospace Engineering

Abstract

The present study proposes a straightforward approach to achieving consistent particle deposition patterns in multiple nanofluid droplet evaporation systems by strategically placing de-ionized (DI) water droplets without nanoparticles at both ends of the nanofluid droplet array. A proof-of-concept investigation was conducted through a combination of experimental and numerical analyses for a five-droplet evaporation system, consisting of three nanofluid droplets and two DI water droplets, to control vapor shielding effects. This study also examined contact-line dynamics, vapor concentration distribution, and evaporation flux during the evaporation process. The findings revealed inconsistent coffee-ring patterns formed by the three nanofluid droplets, without the addition of DI water droplets. In contrast, when DI water droplets were placed at both ends of the array, we were able to fabricate nearly consistent coffee-ring patterns. Specifically, the consistency of the coffee-ring patterns improved with an increase in DI water droplet volume, achieved by tailoring the evaporation flux near the droplet edges. Increased DI water volume also extended the total evaporation time due to enhanced vapor accumulation. Moreover, DI water droplets exhibited pinning-depinning behavior during evaporation, whereas nanofluid droplets remained pinned for longer durations as particle aggregation delayed the depinning process.

Publication Title

Physics of Fluids

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