Browsing by Author "Chang, Jia-Yaw"

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pH-Responsive One-Dimensional Periodic Relief Grating of Polymer Brush-Gold Nanoassemblies on Silicon Surface
(2012-04-01)
Chen, Jem-Kun
;
Pai, Ping-Chun
;
Chang, Jia-Yaw
;
Fan, Shih-Kang
;
材料科學與工程學系
In this work, we focus on the fabrication of the nanoassemblies consisting of the poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes and gold nanoparticles (AuNPs). The employed process involves grafting of the PDMAEMA chains on an underlying substrate in a brush conformation followed by the immobilization of surface functionalized AuNPs by means of physical interaction (electrostatic attraction, entanglement, and hydrogen bonding). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy have been employed to characterize the prepared PDMAEMA-AuNP nanoassemblies. Polymer brushes possessing various thicknesses have been found to suppress the nanoparticles' aggregation and, hence, facilitate the surface coverage. Furthermore, we patterned the PDMAEMA-AuNP nanoassemblies as an one-dimensional periodic relief grating (OPRG). The subwavelength structure of OPRG has the optical features including artificial refractive index, form birefringence and resonance and band gap effects. A mean refractive index of the PDMAEMA-AuNP nanoassemblies can be controlled by the filling factors of the OPRG structure, so that a desired distribution of refractive index of the polymer brushes-gold OPRG under various stimuli can be realized. The employed approach is simple and highly versatile for the modification of surfaces with a wide range of NPs.
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
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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]
Using a CD-like microfluidic platform for uniform calcium alginate drug carrier generation
(2007-01-01)
Liu, Ming-Kai
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Huang, Keng-Shiang
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Chang, Jia-Yaw
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Wu, Chun-Han
;
Lin, Yu-Cheng
In this paper the manipulation of monodisperse Ca-alginate microparticles using a polymer'-based CD-like microfluidic platform and a reaction of external gelation is presented. Our strategy was based on associating the rapid injection molding process for cross-junction microchannel with the sheath focusing effect to form uniform water-in-oil (w/o) emulsions. These fine emulsions, consisting of 1.5% w/v Na-alginate, were then dripped into an oil solution containing 20% w/v calcium chloride (CaCl2) to accomplish Ca-alginate microspheres in an efficient manner. We have demonstrated that one can control the size of Ca-alginate microparticles from 20 mu m to 50 mu m in diameter (with a variation less than 10%) by altering the relative sheath/sample flow rate ratio. Experimental data showed that for a given fixed dispersed phase flow (sample flow), the emulsion size decreased as the average velocity of the continuous phase (oil flow) increased. The proposed CD-like microfluidic platform is capable of generating relatively uniform micro-droplets and has the advantages of active control of droplet diameter, simple and low cost process, and high throughput.