Superhydrophobic property enhancement on guard ring micro-patterned PDMS with simple flame treatment

Abstract

In this study, a simple flame treatment was conducted to improve hydrophobicity of PDMS surfaces with a square guard ring (SGR) structure. In a scratch test, it was found that a surface with a pattern of circular rings and eight stripe supporters (C-RESS) (width: 2.0 μm, height: 5.0 μm) with the SGR structure (width: 20 μm, height: 100 μm) had the highest durability and no collapsing structures were found. After the surface with the pattern of the C-RESS with the SGR structure was simple flame-treated at 700 °C ± 20 °C for 20 s, a unique flower-like nano-structure was developed on the surface and average surface roughness increased from 210.5 to 450.4 nm. The C-RESS with the SGR structure exhibited superhydrophobic properties with water and ethylene contact angle of 159.2°± 1.6°and 157.9°± 3.2°, respectively. The unique surface topology and nano-structure become attractive because of the combination of its high durability and excellent superhydrophobic properties. Therefore, the flame-treated surface with the pattern of the C-RESS with the SGR structure is expected to be one of the promising antifouling technologies in various applications.

Fabrication of High Aspect Ratio Micro-Structures with Superhydrophobic and Oleophobic Properties by Using Large-Area Roll-to-Plate Nanoimprint Lithography

“…These patterns were arranged in a square array. Si master molds of both the PIL and C-RESS micro-structure were fabricated by a conventional photolithography and deep reactive ion etching (DRIE) process [ 34 , 36 ]. In this experiment, the resolution of the lithographic exposure tool called Nikon stepper, model NSR2005i8A (Miyagi Nikon Precision Co., Ltd., Miyaki, Japan) is 0.5 µm.…”

“…This prevents getting mold damage from hard PDMS residues in a poor demolding process. The HMDS molecules form a self-assembled monolayer (SAM) onto the Si surface of which the non-polar methyl groups repel water droplets inducing a slight hydrophobicity onto the Si surface (WCA: 60°–80°) with correspondingly good PDMS mold release properties [ 34 , 36 ]. Subsequently, the PDMS mixture (Sylgard 184, curing agent: 10 wt%, Sigma-Aldrich, St. Louis, MO, USA) was poured onto the Si master molds containing either the PIL or C-RESS pattern [ 34 , 36 ].…”

“…The HMDS molecules form a self-assembled monolayer (SAM) onto the Si surface of which the non-polar methyl groups repel water droplets inducing a slight hydrophobicity onto the Si surface (WCA: 60°–80°) with correspondingly good PDMS mold release properties [ 34 , 36 ]. Subsequently, the PDMS mixture (Sylgard 184, curing agent: 10 wt%, Sigma-Aldrich, St. Louis, MO, USA) was poured onto the Si master molds containing either the PIL or C-RESS pattern [ 34 , 36 ]. After curing in a convection oven at 75 °C for 120 min, the PDMS-PIL and PDMS-C-RESS patterns were released from their Si master mold by peeling them by hand, resulting in samples as schematically shown in Figure 4 c. A flat PDMS (PDMS-FLT) surface was also fabricated from a non-patterned Si surface as a control sample.…”

“…Moreover, PDMS has a great degree of flexibility during the patterning process due to its relatively high toughness and high elongation at break (>150%) [ 32 , 33 ]. Based on all of these benefits combined, PDMS becomes one of the best material choices that is widely used to fabricate surfaces with superhydrophobic properties using a soft lithography process [ 32 , 34 , 35 ]. A flat PDMS surface only shows hydrophobic properties with a WCA of 107–110° [ 36 ].…”

“…A flat PDMS surface only shows hydrophobic properties with a WCA of 107–110° [ 36 ]. Therefore, the fabrication of a rough surface with engineered hierarchical micro-/nano-structures having controlled geometries by the soft lithography process is needed to make PDMS become superhydrophobic [ 33 , 34 ]. Regarding our previous work, PDMS surfaces patterned with a conventional square-like pillar pattern arranged in a square array can demonstrate superhydrophobicity (WCA > 150°) when r and A.R.…”