Characterizing Hydrogen Microbubble Stiffness Properties Using Atomic Force Microscopy

Abstract

In the past decades, bubbles have been gaining extensive attentions for their wide range of applications, especially those at the micro-scale. Research on the bubbles' mechanical properties is necessary for better implementations. Precise measurement of the microbubbles' mechanical properties (e.g. stiffness and adhesion) relies largely on delicate manipulation technologies in aqueous environment. As a consequence, atomic force microscopy (AFM) has been widely adopted in this field. Bubble stiffness is an important indicator to reflect the stability. Existing studies mainly focused on statistic property of the microbubbles' stiffness, which may omit delicate specific characteristics of a single microbubble. In this letter, as an instance, AFM-based stiffness measurement of a single hydrogen microbubble has been carried out. The electrochemistry method was adopted to generate stable hydrogen microbubbles. By using force volume mode of a commercial AFM, the temperature-dependent stiffness property of the microbubble was studied. Furthermore, stiffness map of a single microbubble was captured, which shows location-dependent anisotropic characteristic, contradicting the preassumption that stiffness of bubbles should be isotropic. To explain this phenomenon, the contact condition between the AFM tip and the bubble surface is considered as the key reason that induces the anisotropic observation, and a corresponding model is established to verify this hypothesis.