NCAFM2023 Programme Booklet

Monday 1440 - 1500

ATOMIC FORCE MICROSCOPY MANIPULATION AND FRICTION MEASUREMENT OF NANOSCALE DROPLETS CONFINED BY TWO-DIMENSIONAL SHEETS

Chengfu Ma*, Yuhang Chen, Jiaru Chu

1 Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei 230026, China Email: chfuma@ustc.edu.cn

Pinning of droplets on solids is an omnipresent phenomenon in nature and in daily life that attracts intense research interest. Understanding the pinning behaviors of droplets is not only academically important but also key for many industrial applications such as self-cleaning surfaces, oil/water separation, and directional liquid transport. Here, we investigate the pinning behaviors of nanoscale droplets that are confined by a two-dimensional (2D) elastic sheet onto a substrate by using atomic force microscopy (AFM). The protection provided by the 2D elastic sheet to the droplets makes manipulating them and measuring their pinning forces by an AFM probe possible. This brings the study of the pinning effect of wetting into the micro- and nanometer scales. Our results reveal a time-dependent pinning effect of the confined nanodroplets. The droplets’ lateral retention forces are found to increase with increasing their resting times until saturations. Our analysis suggests that dissipation by fine deformations of the substrate, induced by vertical tensions at the contact lines, plays important roles in the droplet’s pinning. The creep of the deformation is suggested to result in the time dependence of the droplet’s pinning as well as the observed residual ridge structures left by droplets at their original contact lines after their spreads after long resting times.

Acknowledgements We thank the support from the National Natural Science Foundation of China (No. 52005476).

References [1] C. Ma, Y. Chen, and J. Chu. Time-dependent pinning of nanoblisters confined by two-dimensional sheets. Part 1: scaling law and hydrostatic pressure. Langmuir, 39(2), 701-708 (2023). [2] C. Ma, Y. Chen, and J. Chu. Time-dependent pinning of nanoblisters confined by two-dimensional sheets. Part 2: contact line pinning. Langmuir, 39(2), 709-716 (2023).

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