Modeling and Analysis of Micro-bubble Stiffness Measured by Atomic Force Microscopy

Abstract

In the past 50-60 years, the bubble has gained attention for its wide range of applications, especially in micro-scale. Research on the bubble's mechanical properties is necessary so that we can manipulate the bubble better (for better implementation). Precise measurement of the microbubble's mechanical properties (e.g., stiffness and surface tension) relies largely on delicate manipulation technology, as a result, atomic force microscopy (AFM) has been widely implemented. However, in previous AFM-scanned figures, microbubbles were usually captured with a relatively large distortion and the bubble topology was not clear enough to locate precisely the AFM probe so that further nanomanipulation or measurements could not occur. In this paper, AFM-based properties measurement of a single micro-bubble has been studied. An electrochemistry method was applied to generate stable bubbles. By using force volume mode, a single bubble was captured. The bubble, which should be isotropic, showed instead location-dependent anisotropic characteristics. In this case, the shape of the bubble (which influences the angle between the bubble's surface and the AFM tip) was proposed as the key reason to explain the anisotropic phenomenon, and a corresponding model was established to verify the hypothesis.