Micropattern-controlled wicking enhancement in hierarchical micro/nanostructures

Wicking in hierarchical micro/nanostructured surfaces has attracted significant attention due to its potential applications in thermal management, moisture capturing, drug delivery, and oil recovery. Although some studies have shown that hierarchical structures enhance wicking over micro-structured...

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Bibliographic Details
Published in:Soft matter 2019, Vol.15 (32), p.6518-6529
Main Authors: Rokoni, Arif, Kim, Dong-Ook, Sun, Ying
Format: Article
Language:English
Subjects:
Capillarity
Dependence
Drug delivery
Drug delivery systems
Micropatterning
Nanorods
Nanostructure
Oil recovery
Product design
Scaling
Silicon substrates
Structural hierarchy
Thermal management
Zinc oxide
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Summary:Wicking in hierarchical micro/nanostructured surfaces has attracted significant attention due to its potential applications in thermal management, moisture capturing, drug delivery, and oil recovery. Although some studies have shown that hierarchical structures enhance wicking over micro-structured surfaces, others have found very limited wicking improvement. In this study, we demonstrate the importance of micropatterns in wicking enhancement in hierarchical surfaces using ZnO nanorods grown on silicon micropillars of varying spacings and heights. The wicking front over hierarchical surfaces is found to follow a two-stage motion, where wicking is faster around micropillars, but slower in between adjacent pillar rows and the latter stage dictates the wicking enhancement in hierarchical surfaces. The competition between the added capillary action and friction due to nanostructures in these two different wicking stages results in a strong dependence of wicking enhancement on the height and spacing of the micropillars. A scaling model for the propagation coefficient is developed for wicking in hierarchical surfaces considering nanostructures in both wicking stages and the model agrees well with the experiments. This microstructure-controlled two-stage wicking characteristic sheds light on a more effective design of hierarchical micro/nanostructured surfaces for wicking enhancement. Micropattern-controlled two-stage wicking dynamics dictate the enhancement of wicking in hierarchical micro/nanostructured surfaces over bare microstructures.
ISSN:1744-683X
1744-6848
DOI:10.1039/c9sm01055f