Kosuke Suzuki

Spiral Alignment of Fullerene Microcrystals via Dewetting

We demonstrate the autonomous formation of spiral patterns made of fullerene C60 microcrystals via dewetting process on a solid substrate. We also succeeded in enlarging the spiral size by introducing a pillar that worked as an artificial core of the spiral. In situ observation of spiral formation revealed the stable inbound rotation of the pinning front about the meniscus region close to the pillar. The spacing ratio of the spiral, R(θ) n+1/R(θ) n , was 1.2,which indicates the formation of a logarithmic spiral.

Tunable Friction Through Microwrinkle Formation on a Reinforced Rubber Surface

A new system is presented for controlling of friction through manipulating the contact between a rigid indenter and a porous-film-embedded polydimethylsiloxane (PDMS) rubber surface that can buckle to form regular microwrinkles depending on the applied lateral compression. The effect of this change in topography on friction is investigated with a fixed surface chemistry at the sliding interface to ensure a consistent value of adhesive shear strength per unit area of contact. With a wrinkled surface, a shorter stick–slip period and corresponding lower average force of friction are observed when compared to a flat PDMS surface. Based on the framework of Bowden–Tabor’s adhesive friction model, this result is attributed to a decrease in the contact area caused by an increase in the effective modulus and the distribution of interfacial contacts on the wrinkles. These results therefore imply that a shape-tunable microstructure is an effective approach to developing surfaces with dynamically tunable tribological properties.

Self-organized target and spiral patterns through the “coffee ring” effect

We studied the precipitation pattern of fullerene C60 nanocrystals generated through the evaporation of a confined liquid bridge. In contrast to the usual coffee ring pattern, both target and spiral patterns were observed. The characteristics of the pattern critically depended on the concentration of the solution, the temperature, and the level of vacuum. In addition, the morphology of the microscopic precipitates varied greatly as a function of these experimental parameters. This pattern formation can be interpreted as a two-step rhythmic nucleation/precipitation of fullerene crystals during receding motion of the contact line. Symmetric motion of the contact line produces a target pattern, and the propagation of distortion of the liquid interface caused by a disturbance generates a spiral pattern.