Near-field probe of thermal capillary fluctuations of a hemispherical bubble

TL;DR

This study measures nanoscale thermal capillary oscillations of a hemispherical bubble using an AFM cantilever, revealing resonance peaks, pinning of the contact line, and surface viscosity influenced by impurities.

Contribution

It introduces a method to probe thermal capillary fluctuations of a hemispherical bubble and measures surface viscosity at the nanoscale.

Findings

Resonance peaks in thermal oscillations spectrum

Pinning of the contact line on the substrate

Impurities alter surface rheology

Abstract

We report measurements of resonant thermal capillary oscillations of a hemispherical liquid gas interface obtained using a half bubble deposited on a solid substrate. The thermal motion of the hemispherical interface is investigated using an atomic force microscope cantilever that probes the amplitude of vibrations of this interface versus frequency. The spectrum of such nanoscale thermal oscillations of the bubble surface presents several resonance peaks and reveals that the contact line of the hemispherical bubble is pinned on the substrate. The analysis of these peaks allows to measure the surface viscosity of the bubble interface. Minute amounts of impurities are responsible for altering the rheology of the pure water surface.