Hydrogen peroxide-generated gases at asphalt-glass interface: Effect on surface cleaning and analysis by nanoscale surface imaging spectroscopy

The research herein focused on the first step of the phenomena of surface cleaning by hydrogen peroxide and advanced oxidation treatment, namely chronicling preferential accumulation of nanometer-scale gas bubbles at the solid-residue interface. To demonstrate this phenomenon, the authors coated asphalt onto a glass slide, then immersed the slide in 3% hydrogen peroxide (H₂O₂) at pH 9, then projected laser light against the opposing side of that glass slide at an angle. As a significant original contribution to science, nanoscale surface imaging quantitatively detected H₂O₂-induced bubbles that had 70-400 nm dimensions; and it revealed that these bubbles congregated along 50-80% of the asphalt coating's fringe. Tests further showed that when H₂O₂ and O₃ dosing was followed by cavitation and ultrasonics, organic coatings abruptly dislodged from silica grains. With the high resolution of this Surface Imaging Spectroscopy, this laser apparatus could discern between (a) the clear glass slide, (b) regions of asphalt adhesion to the glass, (c) infinite air, and (d) most significantly, regions where nanoscale gas bubbles congregated under the lip of asphalt's fringe. Microscopic cleaning process of the removal of asphalt from a glass surface has been observed directly. The authors have proposed the removal mechanism to be due to the formation of gas bubbles at the interface that accumulate underneath the edges of the asphalt coating. This accumulation eventually assisted the removal by prying the asphalt coating off the surface as the formation and reaction progressed along the interface.