Morphology and Surface Properties of Roach Water Transport Arrays

We report on morphological studies of wharf roaches, Ligia exotica, which can passively absorb and transport water through the microscopic protrusions on their legs. We systematically investigated the geometrical variables of the protrusions on each podite of legs to reveal a particularized structural complexity. For the morphological analysis, each podite was split into nine different zones by grouping the protrusions with similar shapes and organization. The protrusions are shown to possess three different types of shapes located on each specific zone of the podite. In addition, the nanoscale surface morphologies of the protrusions on the wharf roach legs were probed by using atomic force microscopy, and the surface properties of the hairy arrays were determined for identifying the localized hydrophobicity distribution. The protrusion surface possessed a nanoscale periodic patterned texture, and both the valley and ridges of a periodic pattern on the protrusion surface exhibited an identical low surface energy. We suggest that the structural morphologies and distinct hydrophobicity of the protrusions can be critical in determining the directional wettability of an entire leg and important for designing a sturdy water transport and passive water-absorbing system without external energy consumption.