Cavitation-induced microjets tuned by channels with alternating wettability patterns

TL;DR

This study investigates how alternating wettability patterns on capillaries influence cavitation-induced microjets, revealing that specific coatings and geometries can control jet direction, size, and consistency.

Contribution

It introduces a novel approach of using patterned wettability to tune microjet behavior in capillaries, expanding control over jet dynamics and outcomes.

Findings

Hydrophobic strips direct jets along the channel axis.

Wettability patterns affect jet breakup and drop size.

Channel geometry and coatings influence jet consistency.

Abstract

A laser pulse focused near the closed end of a glass capillary partially filled with water creates a vapor bubble and an associated pressure wave. The pressure wave travels through the liquid toward the meniscus where it is reflected, creating a fast, focused microjet. In this study, we selectively coat the hydrophilic glass capillaries with hydrophobic strips along the capillary. The result after filling the capillary is a static meniscus which has a curvature markedly different than an unmodified capillary. This tilting asymmetry in the static meniscus alters the trajectory of the ensuing jets. The hydrophobic strips also influence the advancing contact line and receding contact line as the vapor bubble expands and collapses. We present thirteen different permutations of this system which includes three geometries and four coating schemes. The combination of geometry and coatings influences the jet breakup, the resulting drop size distribution, the trajectory of the jet tip, and the consistency of jet characteristics across trials. The inclusion of hydrophobic strips promotes jetting in line with the channel axis, with the most effective arrangement dependent on channel size.