Browsing by Author "Tu, Yi-Hsuan"

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Bamboo-like nanostructures prepared using template-based wetting methods: Molecular arrangements of polyimide and carbon tubes in cylindrical nanopores
(2019-12-17)
Tu, Yi-Hsuan
;
Liu, Chih-Ting
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Chu, Chien-Wei
;
He, Hung-Chieh
;
Chang, Chun-Wei
With excellent mechanical and physical properties, polyimides (PIs) possess diverse applications in different fields. PI-based materials can also be converted to carbon materials by high temperature carbonization processes. The fabrication and properties of PI-based nanomaterials and corresponding carbon nanomaterials, however, have been less investigated, especially the packing behaviors of the polymer chains. In this work, we study the fabrication and characterization of PI nanostructures using the solution wetting (SW) method and the solvent-annealing-induced nanowetting in templates (SAINT) method. Poly(amic acid) (PAA) tubes are first prepared using anodic aluminum oxide (AAO) membranes. After thermal imidization and carbonization processes, PI and carbon tubes can be obtained, respectively. Bamboo-like structures are also observed in the tubes, which can be attributed to the Marangoni effect induced by the gradient of the surface tensions during the solvent evaporation process. Moreover, the laser Raman micro-spectroscopy results show that the packing behaviors of the polymer chains in the nanostructures prepared by the SAINT method are better than those prepared by the SW method, indicating that the solvent annealing process can improve the chain packing while assisting the infiltration of polymer chains in the nanopores.
Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers
(1970-01-01)
Li, Jia-Wei
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Chiu, Yu-Jing
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Chang, Chia-Jui
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He, Hung-Chieh
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Tu, Yi-Hsuan
Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI-based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp(2) bonding between carbon atoms.
From Block Copolymer Nanotubes to Nanospheres: Nonsolvent-Induced Morphology Transformation Using Porous Templates
(2018-11-27)
Chang, Chun-Wei
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Tu, Yi-Hsuan
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Luo, Ke-Hsuan
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Chen, Jiun-Tai
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Block copolymer nanostructures have attracted great attention because of the wide range of applications such as sensors and drug delivery. The fabrication of block copolymer nanostructures with controlled morphologies and sizes, however, is still challenging. Here, we study the fabrication of nanotubes and nanospheres of polystyrene-block-polybutadiene (PS-b-PBD) using anodic aluminum oxide (AAO) templates. When PS-b-PBD solutions in N-methyl-2-pyrrolidone are introduced into the nanopores of the AAO templates applying the traditional solution wetting method, PS-b-PBD nanotubes can be obtained. When PS-b-PBD solutions in the nanopores are in contact with a nonsolvent, acetic acid, PS-b-PBD nanospheres are formed. Two possible mechanisms are proposed to discuss the formation of the nonsolvent-driven morphology transformation, including the Rayleigh-instability-type transformation mechanism and the nucleation and growth mechanism. The effect of the polymer concentrations on the internal morphologies of the PS-b-PBD nanostructures is discussed; at higher concentrations, PS-b-PBD nanocapsules can also be prepared. Furthermore, core-shell PS-b-PBD/polymethylmethacrylate nanospheres can be fabricated using this strategy with polymer blend solutions. This work not only demonstrates a simple strategy to control the morphologies of block copolymer nanostructures but also deepens the understanding of the interactions between polymer solutions and solvents.
Microwave-annealing-induced nanowetting of block copolymers in cylindrical nanopores
(2018-01-07)
Chang, Chun-Wei
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Cheng, Ming-Hsiang
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Ko, Hao-Wen
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Chu, Chien-Wei
;
Tu, Yi-Hsuan
Block copolymers have attracted great attention because of their abilities to self-assemble into well-ordered microphase-separated structures. To generate nanopatterns of block copolymers with long-range ordering and low-defect densities in shorter time scales, microwave annealing has recently been applied. Microwave annealing, however, has so far only been used for block copolymer bulks and thin films. In this work, we discover that microwave annealing can be successfully applied to three-dimensional block copolymer nanostructures by studying the infiltration and microphase separation of block copolymers in cylindrical nanopores upon microwave irradiation. Cylinder-forming and lamella-forming poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) are introduced into the nanopores of anodic aluminum oxide (AAO) templates. In addition, AAO templates with different pore sizes are used to study the effect of the commensurabilities between the pore diameters and the repeating periods of the block copolymers on the morphologies of the block copolymer nanostructures.
Microwave-annealing-induced nanowetting: a rapid and facile method for fabrication of one-dimensional polymer nanomaterials
(2015-01-01)
Chang, Chun-Wei
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Chi, Mu-Huan
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Chu, Chien-Wei
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Ko, Hao-Wen
;
Tu, Yi-Hsuan
Template wetting methods have been broadly applied to fabricate diverse one-dimensional polymer nanomaterials. The currently used template wetting methods, however, have shortcomings and disadvantages such as long processing times, thermal degradation, and difficulties in controlling the lengths. In this work, we develop a novel microwave-annealing-induced nanowetting (MAIN) method to fabricate one-dimensional polymer nanomaterials using porous anodic aluminum oxide (AAO) templates. Upon microwave annealing, the polymer chains are infiltrated into the nanopores of the AAO templates, and the morphologies of the polymer nanomaterials can be controlled by the annealing conditions. The growth rates of the polymer nanomaterials using the MAIN method are faster than those using the traditional thermal annealing method. This work not only provides a time-saving method to fabricate one-dimensional polymer nanomaterials with controlled morphologies, but also offers a better understanding of the effect of microwave annealing on the wetting behaviors of polymer melts.
Porous Polyimide and Carbon Nanotubes: Solvent Vapor-Induced Transformation in the Nanochannels of Anodic Aluminum Oxide Templates
(2019-04-01)
He, Hung-Chieh
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Tu, Yi-Hsuan
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Li, Jia-Wei
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Lin, Yu-Liang
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Chen, Jiun-Tai
Polyimides (PIs) have attracted wide attention because of their exceptional thermal stability and applications in areas such as printed circuit boards and multichip modules. It remains a great challenge, however, to control the morphologies and properties of PI-based nanomaterials, especially porous PI-based nanotubes. In this work, a versatile method to fabricate porous PI nanotubes via the template method is developed, with a solvent vapor-induced transformation process. First, polyamic acid (PAA) solutions are used as precursors and infiltrated into the nanochannels of anodic aluminum oxide templates, forming PAA nanotubes. After the samples are annealed in tetrahydrofuran or dimethylformamide vapors, depression of the PAA tubes occurs, causing the formation of pores. The porous PAA nanotubes can be further converted to porous PI and carbon nanotubes by imidization and carbonization processes, respectively. The pore sizes of the porous nanomaterials can be controlled by changing the type of the annealing solvent and the solvent annealing time.
Selective solvent-induced reconstruction in confined space: one-dimensional mesoporous block copolymer structures in cylindrical nanopores
(2017-06-14)
Chang, Chun-Wei
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Chi, Mu-Huan
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Ko, Hao-Wen
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Chu, Chien-Wei
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Fang, Zhi-Xuan
We investigate the formation of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) nanostructures confined in cylindrical nanopores via a novel selective solvent-induced reconstruction process. The key factors of the morphologies of the nanostructures are determined, including the choice of solvents, the molecular weights of the polymers, and the pore diameters of the templates.