[Paper Review] Surface bubble nucleation phase space

James R. T. Seddon, E. Stefan Kooij+3 more|Data Archiving and Networked Services (DANS)|Oct 26, 2010

nanoparticles nucleation surface interactions4 citations

TL;DR

This study maps the phase space for surface nanobubble nucleation on hydrophobized silicon by independently controlling liquid temperature and dissolved gas concentration. It reveals that nanobubbles form only within a narrow, distinct region of this phase space (100–110% gas saturation), and crucially, supersaturation is not required—instead, nucleation depends on precise thermal and concentration conditions during liquid deposition, with micropancakes forming at higher temperatures and concentrations beyond the nanobubble regime.

ABSTRACT

Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobised silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this phase space, occurring for gas concentrations of approximately 100-110%. Below the nanobubble phase we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles.

Motivation & Objective

• To resolve contradictions in nanobubble nucleation mechanisms reported in prior studies.
• To determine whether supersaturation of dissolved gases is a necessary condition for surface nanobubble formation.
• To map the phase space of nanobubble nucleation by independently varying liquid temperature and dissolved gas concentration.
• To identify conditions under which nanobubbles form versus micropancakes or no gaseous domains.
• To provide a systematic, contamination-free method for nucleating nanobubbles or avoiding them in industrial applications.

Proposed method

• Hydrophobized silicon wafers were prepared using perfluorodecyltrichlorosilane to create a stable, non-wettable surface.
• Liquid temperature and dissolved gas concentration were controlled independently using a temperature-controlled hotplate and an oximeter for real-time gas concentration monitoring.
• Pure water was prepared via a Millipore Simplicity 185 system and gas concentration was measured in mg/L and percentage saturation.
• A custom AFM liquid cell allowed in situ imaging of the substrate with hydrophilic, Au-coated Si3N4 probes at 90% set point and ~15–25 kHz resonance frequency.
• Liquid was rapidly deposited onto the substrate (within 5–6 s) at defined T and gas concentration, followed by 10-minute AFM scans over 2×2 µm areas.
• Data were collected across varying liquid temperatures and gas concentrations to map nucleation behavior in a two-dimensional phase space.

Experimental results

Research questions

• RQ1 Is supersaturation of dissolved gases a necessary condition for surface nanobubble nucleation on hydrophobized substrates?
• RQ2 How do independent variations in liquid temperature and dissolved gas concentration affect the formation of nanobubbles versus micropancakes?
• RQ3 What is the precise region of phase space where nanobubbles nucleate reliably without supersaturation?
• RQ4 Why do nanobubbles persist for days despite rapid theoretical dissolution timescales?
• RQ5 Can the nucleation of nanobubbles or micropancakes be selectively controlled without cross-contamination from methods like ethanol-water exchange?

Key findings

• Nanobubbles nucleate only within a narrow, distinct region of the phase space defined by liquid temperature and dissolved gas concentration, specifically at gas concentrations of approximately 100–110% saturation.
• Supersaturation of dissolved gases is not a requirement for nanobubble nucleation; nanobubbles form even when the liquid is undersaturated relative to the substrate temperature after cooling.
• Below the nanobubble nucleation threshold, no gaseous domains form on the substrate, indicating a clear transition zone with no nucleation.
• Above the nanobubble regime, micropancakes—micron-sized, nanometer-high gaseous domains—form preferentially, especially when the liquid cools significantly after deposition.
• The transition to micropancake formation occurs when the liquid must cool to the substrate temperature after deposition, suggesting micropancakes are condensed adsorbates from the liquid phase.
• A 'safe zone' exists in the phase space where neither nanobubbles nor micropancakes form, enabling contamination-free operation in industrial processes like immersion lithography.