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Research Papers

Improving Surface Hydrophobicity by Microrolling-Based Texturing

[+] Author and Article Information
Man-Kwan Ng

Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: manng2015@u.northwestern.edu

Ishan Saxena

Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: ishanSaxena2013@u.northwestern.edu

Kornel F. Ehmann

Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: k-ehmann@northwestern.edu

Jian Cao

Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: jcao@northwestern.edu

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received August 26, 2015; final manuscript received May 18, 2016; published online June 30, 2016. Assoc. Editor: Shiv G. Kapoor.

J. Micro Nano-Manuf 4(3), 031001 (Jun 30, 2016) (8 pages) Paper No: JMNM-15-1064; doi: 10.1115/1.4033680 History: Received August 26, 2015; Revised May 18, 2016

A two-pass microrolling-based texturing (μRT) process was utilized to improve the hydrophobicity of aluminum surfaces. Square micropillars were fabricated on aluminum sheets by two mutually orthogonal forming passes by a roller pretextured with microgrooves. Subsequently, the droplet contact angle was measured to evaluate the hydrophobicity of the surface. Results show that surfaces with μRT-imprinted textures have higher contact angles than nontextured surfaces indicating improved hydrophobicity. Furthermore, the process has led to the creation of hierarchical valleylike features on top of each of the micropillars caused by the pile-up effect during the forming process. It was hypothesized that such hierarchical features positively contribute to the improved hydrophobicity of the surface. This hypothesis was validated by testing surfaces with a similar hierarchical textured pattern produced by laser-induced plasma micromachining (LIPMM). The effects of various aspects of texture geometry including surface area-to-volume ratio and groove aspect ratio on the surface contact angle and the anisotropy of the contact angles were investigated.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Illustrations of rolls with (a) grooves and (b) grids

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Fig. 2

Cross-sectional optical image of a microrolling-based textured titanium

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Fig. 3

Schematic of the pile-ups on liquid adhesion in the hypothesis: (a) textures with no pile-ups and (b) texture with edge pile-ups

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Fig. 4

A desktop microrolling mill (DμRM)

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Fig. 5

A pretextured roll

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Fig. 6

Tooth profile in the middle section of the pretextured roll

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Fig. 7

Schematic of the LIPMM process

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Fig. 8

(a) 3D and (b) two-dimensional (2D) images of a coarse square pattern produced with the right section of the pretextured roll in μRT

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Fig. 9

(a) 3D and (b) 2D images of a fine square pattern produced with the middle section of the pretextured roll in μRT

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Fig. 10

(a) 3D and (b) 2D images of an LIPMM textured surface with flat-top square pattern

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Fig. 11

(a) 3D and (b) 2D images of an LIPMM textured surface with valley-topped square pattern

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Fig. 12

Mean contact angles of different textured surfaces produced by μRT

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Fig. 13

Photos of contact angles on different textured surfaces produced by μRT

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Fig. 14

Topography of a μRT-textured surface

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Fig. 15

Mean contact angles of different LIPMM textured surfaces

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Fig. 16

Photos of contact angles on different textured surfaces produced with LIPMM

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Fig. 17

Effect of groove aspect ratio on contact angle of μRT-produced surfaces

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Fig. 18

Effect of surface area-to-volume ratio on contact angle of μRT-produced surfaces

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Fig. 19

Contact angles on different μRT-textured surfaces

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Fig. 20

Photos of contact angles on grooves oriented in different directions

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