Effect of Surfactant on Electrochemically Generated Surface Nanobubbles

Abstract

Surfactants, mimics of contamination, play an important role in nanobubble nucleation, stability, and growth at the electrode surface. Herein, we utilize single-molecule fluorescence microscopy as a sensitive imaging tool to monitor nanobubble dynamics in the presence of a surfactant. Our results show that the presence of anionic and nonionic surfactants increase the rate of nanobubble nucleation at all potentials in a voltage scan. The fluorescence and electrochemical responses indicate the successful lowering of the critical gas concentration needed for nanobubble nucleation across all voltages. Furthermore, we demonstrate that the accumulation of surfactants at the gas–liquid interface changes the interaction of fluorophores with the nanobubble surface. Specifically, differences in fluorophore intensity and residence lifetime at the nanobubble surface suggest that the labeling of nanobubbles is affected by the nature of the nanobubble (size, shape, etc.) and the structure of the gas–liquid interface (surfactant charge, hydrophobicity, etc.).

Single-Molecule Interactions at a Surfactant-Modified H2 Surface Nanobubble

“…A platinum wire acts as a quasi-reference electrode (Pt QRE) for which water oxidation is presumably the dominant reference reaction [2H 2 O → 4H + + 4e − + O 2(g) ]. 28 Hence, the thermodynamic potential for water reduction [2H 2 O + 2e − → H 2(g) + 2OH − ] occurs on the ITO electrode at −1.23 V versus the Pt QRE. After a sufficient voltage is applied at the electrode, the accumulation of free H 2 gas at the surface reaches a saturated concentration favorable for heterogeneous nanobubble nucleation.…”

“…27 During our investigation of nanobubble nucleation in the presence of a surfactant, we noticed that the lifetime and intensity of the labeling fluorophore at surfactant-coated nanobubbles were drastically different from those of "clean" nanobubbles. 28 Although fluorophore interaction at biological targets has been investigated, the governing phenomenon affecting fluorophore interaction at the gas−liquid interface of a surface nanobubble remains largely unknown. 29 Furthermore, we recognized the unique opportunity of probing single-fluorophore dynamics via systematic changes to the gas−liquid interface through the adsorption of surfactants with different charges, hydrophobicities, surface activities, and other chemical properties.…”

Emerging Optical Microscopy Techniques for Electrochemistry

“…This type of optical imaging of the appearance or disappearance of optical features, primarily used with model metal NPs, was extended to visualize and quantify in situ the formation or dissolution of a variety of other materials, such as gas nanobubbles (79)(80)(81)(82)(83) or ionic crystals (84), and holds promise for high-throughput monitoring of structural deformations of nanoelectrocatalysts under operating conditions (85). The technique can be easily extended to the study of various phase formation processes as long as they can be triggered electrochemically, either by direct electrodeposition or indirectly by local electrolysis.…”

Nanobubble Labeling and Imaging with a Solvatochromic Fluorophore Nile Red

“…from different fluorophore adsorption behaviors via TIRF measurement. 34 George et al stated that when the surfactant is enriched at the air−water interface, the polar head group favors the aqueous phase while the nonpolar tail prefers to be in the gas phase. 35 However, there has been a lack of direct studies on exploring other properties of the gas/ liquid interface (e.g., hydrophobicity).…”

“…Our group further demonstrated that accumulation of surfactants at the bubble surface affects the structure of the gas/liquid interface (charge, hydrophobicity, etc.) from different fluorophore adsorption behaviors via TIRF measurement . George et al stated that when the surfactant is enriched at the air–water interface, the polar head group favors the aqueous phase while the nonpolar tail prefers to be in the gas phase .…”