Plasmonic Microbubble Dynamics in Binary Liquids

TL;DR

This study investigates how plasmonic microbubbles grow and behave in binary water/ethanol solutions, revealing ethanol concentration-dependent dynamics and mechanisms behind bubble shrinkage.

Contribution

It provides the first detailed experimental analysis of plasmonic microbubble dynamics in binary liquids, highlighting the role of ethanol concentration and contact line depinning.

Findings

Microbubbles do not form at the solid-liquid interface below 67.5% ethanol.

In the 67.5%-80% ethanol range, bubbles exhibit three distinct growth phases.

Water recondensation causes the sudden bubble shrinkage during the second phase.

Abstract

The growth of surface plasmonic microbubbles in binary water/ethanol solutions is experimentally studied. The microbubbles are generated by illuminating a gold nanoparticle array with a continuous wave laser. Plasmonic bubbles exhibit ethanol concentration-dependent behaviors. For low ethanol concentrations (f_e) of < 67.5%, bubbles do not exist at the solid-liquid interface. For high f_e values of >80%, the bubbles behave as in pure ethanol. Only in an intermediate window of 67.5% < f_e < 80% do we find sessile plasmonic bubbles with a highly nontrivial temporal evolution, in which as a function of time three phases can be discerned. (1) In the first phase, the microbubbles grow, while wiggling. (2) As soon as the wiggling stops, the microbubbles enter the second phase in which they suddenly shrink, followed by (3) a steady reentrant growth phase. Our experiments reveal that the sudden shrinkage of the microbubbles in the second regime is caused by a depinning event of the three phase contact line. We systematically vary the ethanol concentration, laser power, and laser spot size to unravel water recondensation as the underlying mechanism of the sudden bubble shrinkage in phase 2.