Engineered Materials for Concentration of Microparticles from Evaporating Drops for Applications in Microplastics Detection

Micro- and nano-plastics (MNPs) are emerging environmental contaminants that are now ubiquitous throughout the natural environment, built environment, and even human bodies. Detecting and characterizing MNPs in aqueous environments remains challenging due to their low concentrations and diverse size distributions. We investigate the evaporation of drops containing MPs ranging from 26 nm to 3.1 μm on hydrophobic, superhydrophobic, and liquid-infused surfaces (LIS), focusing on how contact angle hysteresis (CAH) and MNP sizes influence deposit morphology. On hydrophobic and superhydrophobic substrates, stronger TCL pinning drives outward capillary flows, leading to ring-like or heterogeneous deposits that depend on particle size. In contrast, LIS, with minimal CAH, allows smooth TCL recession and suppresses size selectivity, producing compact deposits whose area scales with total particle mass. These insights demonstrate how surface design and CAH can be leveraged to efficiently concentrate microplastics from dilute solutions, advancing techniques for their detection and quantification.