�\[diffusion\](a)-(f) are snapshots captured from the top at time $t$, where (a) $t=0$ s, (b) 0.03 s, (c) 0.07 s, (d) 0.13 s, (e) 0.20 s and (f) 0.30 s, respectively. In Fig. \[diffusion\], $t=0$ corresponds to the time at which the chalk powders started moving on the water. The diffusion of camphor molecules under the rectangular boat leads to the motion of chalk powders on the water surface. As shown in Fig. \[diffusion\](a), all regions of the surface were covered by chalk powders with a gray color at $t=0$. The chalk powders started moving at $t=0.03$ s, and the water surface without powders was observed as a white region around the boat in Fig. \[diffusion\](b). The area of the white region grew with time (Figs. \[diffusion\](b)-(d)). The boat stayed at the same position before $t\sim0.2$ s (Figs. \[diffusion\] (a)-(e)), although the powders moved. The camphor boat, then, started to move after $t\sim0.2$ s (Fig. \[diffusion\](f)). In this process, the chalk powders were carried by not only the camphor diffusion but also fluid flow induced by the motion of the boat.

![\[diffusion\] Snapshots on the expansion of the camphor molecular layer at (a) $t=0$ s, (b) 0.03 s, (c) 0.07 s, (d) 0.13 s, (e) 0.20 s and (f) 0.30 s, respectively. Chalk powders were dispersed on the solution surface for visualization of the camphor layer. The white and gray regions indicate the camphor layer and the region rich in floating chalk powders, respectively.](sup.2_1.2.eps){width="7cm"}

![\[diffusion2\] (a) Relationship between time $t$ and $r^{2}$, where $r$ is the longest distance between the edge and the center of the area from which chalk powders were swept out. $t=0$ corresponds to the time at which chalk powders on the solution started moving. Closed circles, open squares, and closed triangles show the data for glycerol concentrations $p=0~\%$ ($\mu=$ 0.92 mPa$\cdot$s), $p=40~\%$ ($\mu=4.03$ mPa$\cdot$s), and $p=70~\%$ ($\mu=25.80$ mPa$\cdot$s), respectively. (b) An expanded one for 0 s $<t<0.8$ s in (a), and solid line