Browsing by Author "Wang, Jing-Hong"

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Fabrication of biomimetic device with PS-b-PNIPAAm copolymer pillars mimicking a gecko foot pad
(2012-11-01)
Chen, Jem-Kun
;
Wang, Jing-Hong
;
Cheng, Chih-Chia
;
Ko, Fu-Hsiang
;
應用化學系
Inspired by the climbing aptitude of geckos, a gecko's foot pad can alternately attach to and detach from almost any kind of surface. We firstly fabricated a multi-layer thin film with electrodes as a thermal device that could adjust the surface temperature by applying voltage. We sequentially used very-large-scale integration (VLSI) process and atom-transfer radical-polymerization (ATRP) process to generate well-defined pillar patterns of polymerized styrene as seta analogues and successively grafted n-isopropylacrylamide (NIPAAm) as thermally responsive terminating of the pillars to mimic the configuration of a real gecko's foot pad. Our fabrication strategy exploits surface textures of polystyrene (PS) and thermally responsive terminating of PNIPAAm, which could generate alternately ca. 88.1 and 11.3 nN of adhesive force at 0.2 and 2 V of applying voltage, respectively. The results indicate that the adjustable adhesive ability of the copolymer brushes could approach the climbing aptitude of a gecko much more closely through voltage tuning. The advantage of the processing strategy described here is the potential to fabricate a device of an artificial foot pad to mimic the climbing aptitude of geckos vividly. (C) 2012 Elsevier B.V. All rights reserved.
Reversible Hydrophobic/Hydrophilic Adhesive of PS-b-PNIPAAm Copolymer Brush Nanopillar Arrays for Mimicking the Climbing Aptitude of Geckos
(2012-03-29)
Chen, Jem-Kun
;
Wang, Jing-Hong
;
Fan, Shih-Kang
;
Chang, Jia-Yaw
;
材料科學與工程學系
Inspired by the adjustable adhesive ability of the gecko foot pad, alternately attaching to and detaching from where they climb, we used a fabrication process to generate well-defined pillar patterns of polymerized styrene and successively grafted n-isopropylacrylamide (NIPAAm) as thermally responsive terminating of the pillars. By varying the geometry of the patterns including aspect ratio and duty ratio (solid fraction), the respective roles of the geometry the pattern features on the static water contact angle (WCA), hysteresis, adhesive, and friction force at 25 and 50 degrees C have been systemically investigated. The fabrication strategy exploits surface textures of polystyrene (PS) and thermally responsive terminating of PNIPAAm as the artificial foot pad surface, which could generate alternately ca. 93.9 and 8.7 nN of adhesive force at 25 and 50 degrees C, respectively. The results indicate that the adjustable adhesive ability of the copolymer brushes could approach the climbing aptitude of a gecko much more closely. We develop a bioinspired artificial analog by using two common methods including atom-transfer radical polymerization (ATRP) and photolithography to adjust adhesion reversibly on a silicon surface. The advantage of the processing strategy described here is the potential to fabricate a device of an artificial foot pad to mimic the climbing aptitude of geckos vividly.
Reversibly Thermoswitchable Two-Dimensional Periodic Gratings Prepared from Tethered Poly(N-isopropylacrylamide) on Silicon Surfaces
(2013-04-24)
Chen, Jem-Kun
;
Wang, Jing-Hong
;
Cheng, Chih-Chia
;
Chang, Jia-Yaw
;
應用化學系
In this study we used atom transfer radical polymerization to graft poly(N-isopropylacrylamide) (PNI-PAAm) onto flat Si substrates. We then applied very large-scale integration and reactive ion etching sequentially to generate 200-nm-scale hole arrays of tethered PNIPAAm as two-dimensional periodic concave gratings (2DPCGs) on the Si surfaces. The hole array structures of tethered PNIPAAm could be created and erased reversibly at 25 and 40 degrees C, respectively, leading to significant. changes in the effective refractive index (n(eff)). The values of neff of the 2DPCGs were related to the depth of their holes generated after etching for various times, resulting in a color change from blue to red that could be observed by the naked eye at incident angles of 10-20 degrees. Moreover, we used effective-medium theory to calculate the filling factors of air inside the 2DPCGs to verify the structural changes of the tethered PNIPAAm. Such designed 2DPCGs of thermorespective hydrogel films have potential applications in temperature-responsive optical devices [e.g., as antireflection structured surfaces (ARSs)] that operate at both visible and near-infrared wavelengths.
Thermally switchable adhesions of polystyrene-block-poly (n-isopropylacrylamide) copolymer pillar array mimicking climb attitude of geckos
(2012-09-17)
Chen, Jem-Kun
;
Wang, Jing-Hong
;
Chang, Jia-Yaw
;
Fan, Shih-Kang
;
材料科學與工程學系
Inspired by the gecko foot pad, we fabricated polystyrene-block-poly(N-isopropylacrylamide) (PS-b-PNIPAAm) copolymer pillar array to mimic climbing attitude of a gecko, alternately attach to and detach from a surface. The pillar array structure of the PS segment significantly enhances both of the hydrophilic and hydrophobic property of PNIPAAm segment tips at 25 and 50 degrees C, respectively, which could generate alternating adhesive forces of approximately 120 and 11 nN. The dramatic change in adhesive and friction force difference at 25 and 50 degrees C may guide the design of bio-inspired artificial analogues, which could approach gecko's climbing behavior. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754135]