Difference between revisions of "Patterned Superhydrophobic Surfaces: Toward a Synthetic Mimic of the Namib Desert Beetle"

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In this paper, the authors reported a method to make hydrophilic or superhydrophilic patterns on a superhydrophobic surface inspired by the Stenocara beetle's back. The details of experimental methods are described in the paper. Using their methods, they made an array of hydrophilic spots with size of 750 um onto a superhydrophobic surface by selected delivery of polyelectrolytes to the surface in a mixed water/2-propanol solvent. Then, the samples were characterized by various methods. From contact angle measurements, the advancing contact angle of water in the patterned region was 144' and the receding contact angle was 12'. They also tested their samples by spraying a mist of water onto the surface. As shown in Fig. 1, small water droplets (~250 um) did not wet the superhydrophobic surface and formed almost perfect spheres and most of the droplets did not stay on the superhydrophobic areas and formed large water droplets in the patterned hydrophilic region by coalescence of small drops.
 
In this paper, the authors reported a method to make hydrophilic or superhydrophilic patterns on a superhydrophobic surface inspired by the Stenocara beetle's back. The details of experimental methods are described in the paper. Using their methods, they made an array of hydrophilic spots with size of 750 um onto a superhydrophobic surface by selected delivery of polyelectrolytes to the surface in a mixed water/2-propanol solvent. Then, the samples were characterized by various methods. From contact angle measurements, the advancing contact angle of water in the patterned region was 144' and the receding contact angle was 12'. They also tested their samples by spraying a mist of water onto the surface. As shown in Fig. 1, small water droplets (~250 um) did not wet the superhydrophobic surface and formed almost perfect spheres and most of the droplets did not stay on the superhydrophobic areas and formed large water droplets in the patterned hydrophilic region by coalescence of small drops.
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[[Image:Fig 1 (Zhai et al).jpg|thumb|center|600px| '''Fig. 1''' (a) Small water droplets sprayed on a (PAA/PAH/silica nanoparticle/semi-fluorosilane) superhydrophobic surface with an
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array of hydrophilic domains patterned with a 1% PAA water/2-propanol solution (scale bar = 5 um). (b) Sprayed small water droplets accumulate on the patterned hydrophilic area shown in
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(a) (scale bar = 750 um).]]
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[[Image:Fig 2 (Zhai et al).jpg|thumb|center|600px| '''Fig. 2''' 750 um wide canals built on a patterned superhydrophobic surface: (A) A water droplet (1.5 mm diameter) spreads along a hydrophilic canal comprised of 4 bilayers of PAH/SiO<sub>2</sub>; (B) A water droplet (1.5 mm diameter) spreads along a superhydrophilic canal comprised of 14 bilayers of PAH/SiO<sub>2</sub>.]]
  
 
==References==  
 
==References==  

Revision as of 16:56, 28 March 2009

By Sung Hoon Kang


Title: Patterned Superhydrophobic Surfaces: Toward a Synthetic Mimic of the Namib Desert Beetle

Reference: L. Zhai, M. C. Berg, F. C. Cebeci, Y. Kim, J. M. Milwid, M. F. Rubner, and R. E. Cohen, Nano Lett. 6, 1213-1217 (2006).

Soft matter keywords

superhydrophobic surface, hydrophilic pattern, contact angle, Namib desert beetle

Abstract from the original paper

The present study demonstrates a surface structure that mimics the water harvesting wing surface of the Namib Desert beetle. Hydrophilic patterns on superhydrophobic surfaces were created with water/2-propanol solutions of a polyelectrolyte to produce surfaces with extreme hydrophobic contrast. Selective deposition of multilayer films onto the hydrophilic patterns introduces different properties to the area including superhydrophilicity. Potential applications of such surfaces include water harvesting surfaces, controlled drug release coatings, open-air microchannel devices, and lab-on-chip devices.

Soft matter example

(not done yet)

In the Namib Desert where there is limited water source for plants and animals, there are very interesting creatures that have unique ways to collect water from the atmosphere. For example, the Stenocara beetle utilizes its wings with hydrophilic/superhydrophobic patterns to acquire water from fog-laden wind. At dawn, the Stenocara beetle leans its body toward the wind to collect small water droplets in the fog. Then, these small water droplets coalesce and become bigger droplets. When the droplets reach certain sizes, they roll down into the beetle's mouth. Parker and his colleagues reported that the structure of the beetle's back provided this unique ability to collect water [1]. According to their study, the beetle's back has an array of hydrophilic bumps with ~ 100 um in diameter on a superhydrophobic background. As a result, small water droplets in a fog are collected on the hydrophilic area and coalesce. When the weight of the droplet is big enough to overcome the adhesion forces of the hydrophilic region, it is detached from the surface and rolls down the superhydrophobic surface to the mouth of the beetle. In addition to this example of water collection, patterned surfaces with different wetting properties can be useful for many applications including microfluidic channels and rapid evaluation of complex bioactivities [2-4].


In this paper, the authors reported a method to make hydrophilic or superhydrophilic patterns on a superhydrophobic surface inspired by the Stenocara beetle's back. The details of experimental methods are described in the paper. Using their methods, they made an array of hydrophilic spots with size of 750 um onto a superhydrophobic surface by selected delivery of polyelectrolytes to the surface in a mixed water/2-propanol solvent. Then, the samples were characterized by various methods. From contact angle measurements, the advancing contact angle of water in the patterned region was 144' and the receding contact angle was 12'. They also tested their samples by spraying a mist of water onto the surface. As shown in Fig. 1, small water droplets (~250 um) did not wet the superhydrophobic surface and formed almost perfect spheres and most of the droplets did not stay on the superhydrophobic areas and formed large water droplets in the patterned hydrophilic region by coalescence of small drops.

Fig. 1 (a) Small water droplets sprayed on a (PAA/PAH/silica nanoparticle/semi-fluorosilane) superhydrophobic surface with an array of hydrophilic domains patterned with a 1% PAA water/2-propanol solution (scale bar = 5 um). (b) Sprayed small water droplets accumulate on the patterned hydrophilic area shown in (a) (scale bar = 750 um).
Fig. 2 750 um wide canals built on a patterned superhydrophobic surface: (A) A water droplet (1.5 mm diameter) spreads along a hydrophilic canal comprised of 4 bilayers of PAH/SiO2; (B) A water droplet (1.5 mm diameter) spreads along a superhydrophilic canal comprised of 14 bilayers of PAH/SiO2.

References

(not done yet)

1. A. R. Parker, C. R. Lawrence, Nature 414, 33-34 (2001).

2. P. Lam, K. J. Wynne, G. E. Wnek, Langmuir 18, 948-951 (2002).

3. C. M. Niemeyer, D. Blohm, Angew. Chem. Int. Ed. 38, 2865-2869 (1999).

4. D. MacBeath, S. L. Schreiber, Science 289, 1760-1763 (2000).