Experimental Study on Fracture Structure of Sumi-Wari

TL;DR

This study investigates how variations in subphase viscosity influence fracture patterns in sumi ink films, revealing the coupling between surface tension, subphase properties, and film mechanics through experiments and a phenomenological model.

Contribution

It introduces a novel experimental and modeling approach to understanding fracture pattern formation in sumi films influenced by subphase viscosity.

Findings

Crack spike number increases with glycerol concentration.

Effective stiffness of sumi film decreases with higher glycerol levels.

Numerical simulations match experimental crack patterns and dynamics.

Abstract

Local variations in surface tension can induce complex fracture dynamics in thin interfacial films. Here, we investigate the fracture patterns that emerge when a localized surface-tension perturbation is applied to a sumi film supported on a water-glycerol subphase. Sumi is a traditional Japanese carbon black ink, and this process, referred to as sumi-wari, produces aesthetically pleasing, star-shaped crack patterns with multiple spikes radiating from the perturbation site. The number of crack spikes increases with the viscosity of the subphase, controlled here by the addition of glycerol. Atomic force microscopy measurements reveal that the effective stiffness of the sumi f ilm decreases as glycerol concentration increases. This suggests a strong coupling between the subphase properties and the mechanics of the sumi film. To capture the dynamics of sumi-wari, a phenomenological model is outlined, based on an overdamped equation of motion for particles connected by breakable springs. Numerical simulations reproduce both the morphology and the experimental trends of sumi-wari: the number of cracks and their temporal evolution depend on the spring stiffness, mirroring the behavior observed for subphases with different viscosities. These findings demonstrate how the interplay between surface-tension gradients, subphase properties, and film mechanics governs local fracture and pattern formation in fluid-supported thin films