Caishan Yan | Searcharxiv

arXiv2025

State-dependent friction for a moving liquid contact line over rough solid surfaces

Solid friction between two rough surfaces is often observed to increase logarithmically over time due to contact creeping. An intriguing question is whether a similar aging effect occurs in contact line (CL) friction over rough substrates. Here, we report a systematic experimental study of CL friction using a hanging-fiber atomic force microscope (AFM) to measure the frictional force as a liquid CL moves across a fiber surface with different coatings under a well-controlled time protocol. State- (or time-)dependent CL friction is observed for the fiber surface with different textures in both the advancing and receding directions. The experimental findings are explained by a phenomenological model that links mesoscale CL friction to the microscopic relaxation of metastable air bubbles or liquid droplets trapped in the interstices of a rough surface. This model offers a general aging mechanism relevant to a wide range of liquid-solid interfaces.

cond-mat.soft↗

arXiv2023

Elasticity-Controlled Jamming Criticality in Soft Composite Solids

Soft composite solids are made of inclusions dispersed within soft matrices. They are ubiquitous in nature and form the basis of many biological tissues. In the field of materials science, synthetic soft composites are promising candidates for building various engineering devices due to their highly programmable features. However, when the volume fraction of the inclusions increases, predicting the mechanical properties of these materials poses a significant challenge for the classical theories of composite mechanics. The difficulty arises from the inherently disordered, multi-scale interactions between the inclusions and the matrix. To address this challenge, we systematically investigated the mechanics of densely filled soft elastomers containing stiff microspheres. We experimentally demonstrated how the strain-stiffening response of the soft composites is governed by the critical scalings in the vicinity of a shear-jamming transition of the included particles. The proposed criticality framework quantitatively connects the overall mechanics of a soft composite with the elasticity of the matrix and the particles, and captures the diverse mechanical responses observed across a wide range of material parameters. The findings uncover a novel design paradigm of composite mechanics that relies on engineering the jamming properties of the embedded inclusions.

cond-mat.soft↗