Lateral Force Microscopy of Interfacial Nanobubbles: Friction Reduction and Novel Frictional Behavior

Abstract

Atomic force microscopy is used to conduct single-asperity friction measurements at a water-graphite interface. Local mapping of the frictional force, which is based on the degree of the cantilever twisting, shows nearly friction-free when a tip scans over a nanobubble. Surprisingly, apart from being gapless, the associated friction loop exhibits a tilt in the cantilever twisting versus the tip’s lateral displacement with the slope depending on the loading force. The sign of the slope reverses at around zero loading force. In addition, the measured normal and lateral tip-sample interactions exhibit unison versus tip-sample separation. Theoretical analysis, based on the balance of forces on the tip originated from the capillary force of the nanobubble and the torsion of the cantilever, offers quantitative explanations for both the tilted friction loop and the unison of force curves. The analysis may well apply in a wider context to the lateral force characterization on cap-shaped fluid structures such as liquid droplets on a solid substrate. This study further points to a new direction for friction reduction between solids in a liquid medium.

Evolution process and stabilization mechanism of different gas nanobubbles based on improved statistical analysis

“…Nowadays, many experimental techniques have been proposed and developed to investigate the NBs, which generally can be divided into bulk [19] and interfacial. [20,21] The detection and characterization methods for interfacial NBs include AFM, [22][23][24][25][26] soft X-ray microscopy, [27,28] rapid cryofixation/freeze fracture, [29][30][31] neutron reflectivity measurements, [32] and optical visualization; [33] for bulk NBs, methods include light scattering (dynamic light scattering [DLS], nanoparticle tracking analysis [NTA]), [18][19]34] cryo-electron microscopy, [29] transmission electron microscopy along with freeze-fractured replication, [30] in situ liquid transmission electronic microscopy, [35][36][37] total internal reflection fluorescence microscopy, [38] quartz crystal microbalance analysis, [39] and resonant mass measurements. [40] Among these, resonant mass measurements can simply and convincingly distinguish NBs from solid (or liquid emulsion) nanoparticles.…”

Force Spectroscopy Revealed a High-Gas-Density State near the Graphite Substrate inside Surface Nanobubbles

“…Force spectroscopy has been widely used in the field of nanobubble research. For example, Yang et al studied the friction reduction behavior of an AFM probe sliding through nanobubbles on highly ordered pyrolytic graphite (HOPG) . To estimate the gas density inside surface nanobubbles, here we propose performing standard force spectroscopy experiments by using AFM (Figure ).…”

Nucleation of Capillary Bridges and Bubbles in Nanoconfined CO2

“…Capillary processes are at the center of a wide range of phenomena, including the onset of phase transitions in confined geometries, − the control of friction between sliding surfaces, − or the formation of capillary liquid bridges during inflammatory processes of the lungs. , These fluid contacts can actually take place over vastly different length scales and have been reported for colloidal systems − and in nanotribology and nanolithography. − Recent advances on the theoretical front have led to the extension of capillary theory (CT), whose tenets are rooted in a macroscopic approach, to nanoscopic systems by connecting the free energy barrier of nucleation for the fluid contacts to the contributions arising from the surface tension …”