Capillary rise on legs of a small animal and on artificially textured surfaces mimicking them.

Marie Tani,Takahiko Hariyama,Ko Okumura,Masatsugu Shimomura,Daisuke Ishii,Shuto Ito,Dario Pisignano

doi:10.1371/journal.pone.0096813

Abstract

The wharf roach Ligia exotica is a small animal that lives by the sea and absorbs water from the sea through its legs by virtue of a remarkable array of small blades of micron scale. We find that the imbibition dynamics on the legs is rather complex on a microscopic scale, but on a macroscopic scale the imbibition length seems to simply scale linearly with elapsed time. This unusual dynamics of imbibition, which usually slows down with time, is advantageous for long-distance water transport and results from repetition of unit dynamics. Inspired by the remarkable features, we study artificially textured surfaces mimicking the structure on the legs of the animal. Unlike the case of the wharf roach, the linear dynamics were not reproduced on the artificial surfaces, which may result from more subtle features on the real legs that are not faithfully reflected on the artificial surfaces. Instead, the nonlinear dynamics revealed that hybrid structures on the artificial surfaces speed up the water transport compared with non-hybrid ones. In addition, the dynamics on the artificial surfaces turn out to be well described by a composite theory developed here, with the theory giving useful guiding principles for designing hybrid textured surfaces for rapid imbibition and elucidating physical advantages of the microscopic design on the legs.

Highlights

A micropatterned surface that imbibes liquids efficiently would lead to broad technological applications for liquid transport in areas ranging from microfluidics and biomedical mixing devices to fuel transport but has been plagued with a problem that imbibition dynamics generally slows down with time and limits applications for long-distance transport
We found that the imbibition on the legs of the wharf roach Ligia exotica proceeds with linearly in time on the scale of podite
The unusual dynamics advantageous for long-distance water transport seems to result from repetition of unit dynamics

Summary

Introduction

A micropatterned surface that imbibes liquids efficiently would lead to broad technological applications for liquid transport in areas ranging from microfluidics and biomedical mixing devices to fuel transport but has been plagued with a problem that imbibition dynamics generally slows down with time and limits applications for long-distance transport. The dynamics in the central region of the HT paths can be explained well by the theory, the dynamics are faster than the corresponding dynamics on the CT paths, due to the edge effect (including the effect of joints on which the edge pattern is present) This speed-up effect is clearly visible in the insets in Fig. 3 2a–2c, except for two exceptional cases, in which L or W is small: it seems that the edge effect tends to play an efficient role when the length scales in the edge pattern are small enough compared with those in the central pattern, as on real legs. This edge effect is further understood in a systematic way from Fig. 3 2d: the edge effect measured through (1{w)D=DB increases as wDB=(1{w)DS decreases

Conclusion

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