Volume 107, Number 6, September 2014
|Number of page(s)||6|
|Section||Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics|
|Published online||16 September 2014|
Evaporative microclimate driven hygrometers and hygromotors
1 School of Engineering and Applied Sciences, Harvard University - Cambridge, MA 02138, USA
2 Wyss Institute for Biologically Inspired Engineering, Harvard University - Cambridge, MA 02138, USA
3 Department of Physics, Harvard University - Cambridge, MA 02138, USA
Received: 18 July 2014
Accepted: 25 August 2014
A strip of paper placed on a hand spontaneously curls upwards. This simple observation illustrates the ability of a relatively homogeneous hygroscopic structural material, paper, to sense and respond to the microclimate near a non-equilibrium system, a moist evaporative boundary layer. We quantify this interaction using a simple experiment and show that it can be understood in terms of a minimal model. A small modification of this paper hygrometer that makes one or another surface partly hydrophobic using a crayon or tape allows us to create a hygro-oscillator or a hygromotor that converts transverse moisture gradients into lateral oscillations or directed motion. Our study shows how treating paper as a responsive structural material allows us to extract information and work from a microclimatic boundary layer, transforming a messenger to a machine.
PACS: 46.70.De – Beams, plates, and shells / 68.03.Fg – Evaporation and condensation of liquids
© EPLA, 2014
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