The Origin of the “Snap-In” in the Force Curve between AFM Probe and the Water/Gas Interface of Nanobubbles
Abstract
Snap-in operation: The origin of the “snap-in” in the force curve between the atomic force microscopy (AFM) probe and the water/gas interface of a nanobubble is investigated by PeakForce quantitative nanomechanics. The phenomenon is attributed to hydrophobic interactions caused by hydrophobic contamination or surfactant absorption on the AFM probe or the nanobubble. Conventional plasma cleaning treatment is shown to remove the effect.
Abstract
The long-range attractive force or “snap-in” is an important phenomenon usually occurring when a solid particle interacts with a water/gas interface. By using PeakForce quantitative nanomechanics the origin of snap-in in the force curve between the atomic force microscopy (AFM) probe and the water/gas interface of nanobubbles has been investigated. The snap-in frequently happened when the probe was preserved for a certain time or after being used for imaging solid surfaces under atmospheric conditions. In contrast, imaging in liquids rarely induced a snap-in. After a series of control experiments, it was found that the snap-in can be attributed to hydrophobic interactions between the water/gas interface and the AFM probe, which was either modified or contaminated with hydrophobic material. The hydrophobic contamination could be efficiently removed by a conventional plasma-cleaning treatment, which prevents the occurring of the snap-in. In addition, the adsorption of sodium dodecyl sulfate onto the nanobubble surface changed the water/gas interface into hydrophilic, which also eliminated the snap-in phenomenon.





