Tunable coffee-ring effect on a superhydrophobic surface

A tunable coffee-ring effect (CRE) that enables the patterned deposition of nanoparticles (NPs) is obtained on a designed superhydrophilic and superhydrophobic composite surface of a titanium substrate. Low-adhesion superhydrophobic surfaces with picosecond laser-induced periodic surface structure and micro-nano hierarchical structure are investigated. The NPs are not only deposited in a small area of 0.045  mm², which is 265.56 times smaller than that of the original hydrophilic surface, but also in various patterns such as triangular, rectangular, and ecliptical besides the traditional circular shape. This controllable morphology of the CRE indicates a maneuvering capability of NPs in their common preservation form of suspension turbid liquid, even when the solution concentration reaches 1 mg/mL, which is promising for NP-printed circuit boards and site-specific delivery drugs.