arXiv subjects

Michiko Shimokawa

Publications and source records attributed to Michiko Shimokawa.

6 recordsLinked to original sources

arXiv2025

Experimental Study on Fracture Structure of Sumi-Wari

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

nlin.PS↗

arXiv2020

Star shaped patterns caused by colloidal aggregation during the spreading process of a droplet

This research found that when an acidic solution with a low surface tension spread on the surface of a glycerol solution mixed with milk, a star shaped pattern was spontaneously formed on the surface in the horizontal plane during the spreading process. We investigated the emergence of the star shaped pattern owing to an interfacial instability in experiments using glycerol solutions with several viscosities and 2-methoxyethanol aqueous solutions, which are acidic solutions, with several concentrations. This result demonstrated that the star shaped pattern emerged in the high concentration of 2-methoxyethanol. We proposed a phenomenological model, based on our experimental results, which explains three points as follows; the spreading of the 2-methoxyethanol aqueous solution on the surface of the glycerol solution, the colloidal aggregation of the milk protein colloids caused by the denaturation that occurs when mixed with 2-methoxyethanol, and the accumulation of the aggregates toward the dent regions of the moving interface by a sweeping effect. The model reproduces the formation of the star shaped pattern which was similar to the experimental one. Furthermore, the model provided a phase diagram against the concentration of the 2-methoxyethanol solution and the viscosity of the glycerol solution as control parameters in our experiments. The phase diagram was close to that obtained from our experiments. The results suggest that the above three points are important for the formation of the star shaped pattern.

cond-mat.soft↗

arXiv2018

Power law observed in the motion of an asymmetric camphor boat under viscous conditions

We investigated the velocity of an asymmetric camphor boat moving on aqueous solutions with glycerol. The viscosity was controlled by using several concentrations of glycerol into the solution. The velocity decreased with an increase in the glycerol concentration. We proposed a phenomenological model, and showed that the velocity decreased with an increase in the viscosity according to power law. Our experimental result agreed with the one obtained from our model. The results provided an approximation that the characteristic decay length of the camphor concentration profile at the front of the boat was sufficiently shorter than that at the rear of the boat, which was difficult to measure directly.

nlin.PS↗

arXiv2017

Emergence of wrinkles during the curing of coatings

Wrinkles often emerge on a paint layer when a second coat of paint is applied on an already-coated substrate. Wrinkle formation occurs when the first layer absorbs organic solvent from the second layer. We set up experiments to mimic the double-coating process, focusing on the interaction between a paint layer and an organic solvent. In the experiments, we investigated the characteristic wavelengths of the wrinkles and the time of wrinkle emergence. We propose a simple model to explain (1) the buckling induced by swelling of the layer due to absorption of the organic solvent and (2) delamination of the layer from the substrate. A linear stability analysis of the model provides a relationship between the wavelengths and the characteristic timescale that agrees reasonably well with the data obtained from our experiments. Our results indicate that compression of the layer due to swelling and delamination are both important factors in the formation of wrinkles.

cond-mat.soft↗

arXiv2011

Surface pattern determined by vertical convection on Rayleigh-Taylor instability

Relationship between a surface pattern and vertical convections is studied in a condition of Rayleigh-Taylor instability. The vertical convections change with the case configuration and the aspect ratio r / h of the case, where r and h show radius of case and height of the lighter solution. Fractal pattern is observed at r < h, and cell pattern is formed at r > h. According to the changes of the surface pattern, the vertical convection transfers to some convections from coupled convections. This result shows that the surface pattern is strongly influenced by the vertical convection.

nlin.PS↗

arXiv2008

Annihilative fractals of coffee on milk formed by Rayleigh-Taylor instability

We have discovered a new fractal pattern, coffee exhibits on a horizontal surface, with a fractal dimension $1.88 \pm 0.06$, when a heavy coffee droplet interacts with the surface of lighter milk. Parts of coffee pattern on the surface disappear due to Rayleigh-Taylor instability, and the annihilative behavior produces the fractal pattern. Coffee fractals and the Sierpinski carpet have common features, such as the fractal dimension, annihilative behavior, and an exponential decrease of the pattern area. It is suggested the formation of fractal follows a rule similar to that of the Sierpinski carpet.

nlin.PS↗