Browsing by Author "Li, Jia-Wei"

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Alignment-Improved and Diameter-Reduced Electrospun Polymer Fibers via the Hot-Stretching Process
(1970-01-01)
Hsu, Hsun-Hao
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Chiu, Yu-Jing
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Li, Jia-Wei
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Tseng, Hsiao-Fan
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Chang, Kai-Chieh
Electrospinning is one of the most facile and versatile techniques to prepare polymer fibers ranging from micrometers to nanometers. Although several parameters can be tuned to control the sizes and morphologies of electrospun fibers, many obstacles are still encountered as the target sizes of the fibers are getting smaller; for example, the sizes of the fibers can be effectively reduced by lowering the polymer solution concentrations but beaded or beads-on-string structures are usually formed. To overcome such obstacles, here a simple technique to prepare alignment-improved and diameter-reduced fibers without bead formation by hot-stretching electrospun fibers at temperatures higher than the glass transition temperatures of the polymers is developed. Polystyrene and poly(methyl methacrylate) are both used in this work as model materials. The relationship between the draw ratio and diameter of the fibers is quantitatively analyzed, demonstrating the control of the fiber diameters. Moreover, higher degrees of alignment improvement at the middle part of the fibers than those at the end part is observed, which results in lower water contact angles at the middle part of the fibers. This work provides a useful post-treatment technique to control the sizes and orientations of electrospun polymer fibers.
Asymmetric Polymer Particles with Anisotropic Curvatures by Annealing Polystyrene Microspheres on Poly(vinyl alcohol) Films
(2016-11)
Tseng, Hsiao-Fan
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Cheng, Ming-Hsiang
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Jeng, Kai-Sheng
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Li, Jia-Wei
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Chen, Jiun-Tai
Anisotropic polymer particles such as Janus particles have attracted significant attention in recent years because of their unique properties and unusual self-assembly behavior. Most anisotropic polymer particles synthesized so far, however, only have different chemical regions compartmentalized on the particles. It remains a great challenge to fabricate anisotropic polymer particles with different shapes within a single particle. A novel approach is developed to prepare anisotropic polymer particles that contain two hemispheres with different curvatures by annealing polystyrene microspheres on poly(vinyl alcohol) films. During the annealing process, the polymer microspheres gradually sink into the polymer films and transform to asymmetric polymer particles, driven by the surface and interfacial tensions of the polymers. Selective removal techniques are also used to confirm the morphologies of the asymmetric particles.
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.
Fabrication and Thermal Insulation Properties of Bamboo-Shaped Polymer Fibers by Selective Solvent Vapor Annealing
(2018-12-01)
Chiu, Yu-Jing
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Chiu, Han-Lun
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Tseng, Hsiao-Fan
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Wu, Bo-Hao
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Li, Jia-Wei
Fibrillar materials have gained much attention recently because of their unique properties and potential applications. Although many methods have been developed to fabricate materials, it remains challenging to prepare fibrillar materials containing multicomponent materials or even with complex structures. Here, a facile strategy is developed to fabricate bamboo-shaped fibers by treating electrospun polymer core-shell fibers with solvent vapor annealing. Electrospun polystyrene (PS)/poly(methyl methacrylate) (PMMA) core-shell fibers are first prepared by electrospinning PS/PMMA blend solutions via a phase separation process. When the PS/PMMA core-shell fibers are annealed with the vapor of cyclohexane, which swells and delocalizes the PS domains selectively, the fibers transform into bamboo-shaped structures. The bamboo-shaped structures can be further examined by swelling and delocalizing the PMMA domains selectively, revealing the undulated PS structures. The thermal insulation properties of the fibers with bamboo-shaped structures are observed to be enhanced compared with the original polymer core-shell fibers.
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.
Preparation and thermal dissipation of hollow carbon fibers from electrospun polystyrene/poly(amic acid) carboxylate salt core-shell fibers
(2020-05-05)
Li, Jia-Wei
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Hsu, Hsun-Hao
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Chang, Chia-Jui
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Chiu, Yu-Jing
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Tseng, Hsiao-Fan
Polyimides (PIs) possess great mechanical properties, outstanding thermal stability, solvent inertness, and the ability to be converted into carbon by thermal carbonization. Although studies on carbon materials derived from PIs have been conducted, PI-derived one-dimensional (1D) carbon materials with high surface areas, especially carbon tubes or hollow carbon fibers, have been rarely investigated. In this work, we provide a simple and facile method to prepare hollow carbon fibers by carbonizing hollow PI fibers. Blend solutions of poly(amic acid) carboxylate salts (PAAS) and polystyrene (PS) are electrospun to form core-shell PS/PAAS fibers, in which the PS and PAAS domains are used as sacrificial and precursor materials, respectively. By imidizing the PAAS to PI and selectively removing PS, hollow PI fibers can be obtained. Finally, the hollow PI fibers are carbonized to form hollow carbon fibers. The fiber samples at different stages are examined by thermal gravimetric analysis (TGA), Raman spectrometry, Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The infrared images show that the thermal energy transfer rates of the hollow carbon fibers are higher than those of the hollow PI and PS/PI core-shell fibers, which can be attributed to the better thermal conductivity of carbon resulting from the covalent sp(2) bonding between carbon atoms and the high surface area of the hollow structure.
Radial Linear Polymer Patterns Driven by the Marangoni Instability and Lateral Phase Separation for the Formation of Nanoscale Perforation Lines
(2019-05-01)
Wu, Bo-Hao
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Chang, Kai-Chieh
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Hsu, Hsun-Hao
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Chiu, Yu-Jing
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Chiu, Tang-Yao
Phase separation under convection, related to the Marangoni instability, is critical in the development of advanced polymer processing technologies. The formation mechanisms of polymer patterns driven by the phase separation under convection, however, still require further investigations. In this work, we study the phase separation of polystyrene (PS)/poly(methyl methacrylate) (PMMA) bilayer films during the spin-coating processes. PMMA film-coated glass substrates are dripped by PS solutions in toluene before spinning. The concentration gradients of the PS solutions and the swollen PMMA films cause the surface tension-driven Marangoni instability; lateral phase separations also occur during the spin-coating processes, forming the interesting and uncommon radial linear patterns with nanoscale heights on the PS/PMMA bilayer films. By changing the solution waiting time and spin rates, the surface morphologies of the PS/PMMA bilayer films can be controlled. At longer waiting times, the higher degrees of swelling of the PMMA films by the solvents allow the formation of the polymer patterns; at higher spin-coating rates, the faster solvent evaporation improves the ordering of the polymer patterns. Furthermore, the morphologies of the PS/PMMA bilayer films can be confirmed using the selective removal technique; the PS films with linear-arranged cavities and the PMMA films with bumps can be obtained using acetic acid and cyclohexane, respectively. Finally, a proof of concept on the potentials in applying the cavities-containing PS films for nanoscale perforation lines is also demonstrated.
Sequential Selective Solvent On-Film Annealing: Fabrication of Monolayers of Ordered Anisotropic Polymer Particles
(2020-08-05)
Tseng, Hsiao-Fan
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Liang, Xiaobin
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Liu, Chih-Ting
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Chiu, Yu-Jing
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Li, Jia-Wei
Although various strategies have been developed to prepare anisotropic polymeric particles, it remains challenging to fabricate monolayers of anisotropic polymeric particles, which can extend the applications of anisotropic particles. Here, we develop a novel and facile approach to fabricate monolayers of anisotropic polymeric particles. Monolayers of polystyrene (PS) microspheres with a mean diameter of 10 mu m are deposited on glass substrates coated with poly(methyl methacrylate) films, followed by sequential selective solvent on-film annealing processes. Monolayers of anisotropic polymeric particles, such as the snowman-like PS particles, are successfully fabricated. Such unique structures possess the long-range ordering of monolayers (the structure factor) and the anisotropic geometry of individual particles (the form factor). The nanomechanical properties of the PS particles are also characterized using atomic force microscopy force volume measurements, showing a decrease in the Young's moduli of the PS particles owing to the looser packing of the polymer chains. This work provides the most facile and versatile strategy by far to fabricate monolayers of ordered anisotropic polymeric particles, which arc inaccessible by other traditional means.
Solvent On-Film Annealing (SOFA): Morphological Evolution of Polymer Particles on Polymer Films via Solvent Vapor Annealing
(2017-07-11)
Tseng, Hsiao-Fan
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Cheng, Ming-Hsiang
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Li, Jia-Wei
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Chen, Jiun-Tai
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應用化學系
Over the past few decades, anisotropic polymer particles are of significant interest because of their unique properties which can be applied in various areas, such as drug delivery, biotechnology, and electronics. Most approaches to synthesize anisotropic polymer particles, however, are complicated, and the three-dimensional shapes of the anisotropic particles are usually difficult to be controlled. In this work, we develop a solvent on-film annealing (SOFA) method to fabricate anisotropic polymer particles by studying the morphological evolution of polystyrene (PS) microspheres on poly(methyl methacrylate) (PMMA) films annealed in toluene vapor. At different annealing stages, the isotropic PS microspheres gradually transform to anisotropic PS particles with different morphologies, such as UFO-, cymbal-, peanut-, and bowl-shaped particles. The morphology evolution is driven by the surface and interfacial tensions during the annealing processes and can be confirmed by a selective removal technique. Acetic acid, a selective solvent for PMMA, and cyclohexane, a selective solvent for PS, are also used as the annealing solvents to further investigate the effect of the annealing solvent.
Solvent-Induced Shape Recovery of Anisotropic Polymer Particles Prepared by a Modified Thermal Stretching Method
(2018-07-17)
Lo, Yu-Ching
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Tseng, Hsiao-Fan
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Chiu, Yu-Jing
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Wu, Bo-Hao
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Li, Jia-Wei
Anisotropic polymer particles have attracted great attention because of their unique properties and potential applications in various areas, such as microelectronics, drug delivery, and medical imaging. The fabrication and morphology control, especially the shape recovery, of anisotropic polymer particles, however, remains a challenging task. In this work, we develop a novel strategy to fabricate anisotropic polymer particles by thermally stretching poly(vinyl alcohol) (PVA) films embedding polystyrene (PS) microspheres using a weight. Depending on the preannealing condition, anisotropic PS particles with two different shapes, sharp-headed and blunt-headed PS particles, can be obtained. The PVA films can be selectively removed by isopropanol/water, releasing the anisotropic PS particles. By adding tetrahydrofuran (THF), a good solvent for PS, into the PS particle-containing solutions, the anisotropic particles gradually transform back to spheres to reduce the total interfacial energies. The shape recovery rates of the polymer particles can be controlled by the amount of the added THF. This work not only provides a simple and feasible route to fabricate anisotropic polymer particles but also contributes to a deeper understanding in the solvent-induced shape recovery process from anisotropic polymer particles to polymer spheres.
Sunny-Side-Up Egg-Shaped Structures: Surface Modification To Form Anisotropic Polymer Particles Driven by the Plateau-Rayleigh Instability as Fluorescence Manipulation Platforms
(2019-02-26)
Chiu, Yu-Jing
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Liu, Chih-Ting
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Weng, Chang-Ching
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Chiu, Tang-Yao
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Li, Jia-Wei
The Plateau-Rayleigh instability is a phenomenon driven by the reduction of the surface energies, in which a liquid cylinder transforms to a series of droplets with distinct spacing. This instability phenomenon is also applied broadly for the transformation of cylindrical materials to spherical particles in homogeneous environments. The demonstration of the instability in heterogeneous environments, however, has been less studied. Here, we study the Plateau-Rayleigh instability of electrospun polystyrene (PS)/poly(methyl methacrylate) (PMMA) core-shell fibers annealed on n-octadecyl-trichlorosilane (ODTS)-modified glass substrates with toluene vapors. After the annealing procedures, the PS/PMMA core-shell fibers transform to anisotropic sunny-side-up egg-shaped polymer structures, driven by the reduction of the total surface and interfacial energies. Quantitative analyses are performed on the sizes of the structures. Fluorescent fibers are also prepared by electrospinning and annealed on the ODTS-modified substrates, demonstrating the potential application as fluorescence manipulation platforms.
Two-Step Solvent On-Film Annealing (2-SOFA) Method: Fabrication of Anisotropic Polymer Particles and Implications for Colloidal Self-Assembly
(2018-09-01)
Tseng, Hsiao-Fan
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Chiu, Yu-Jing
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Wu, Bo-Hao
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Li, Jia-Wei
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Chen, Jiun-Tai
In recent years, anisotropic polymer particles have gained increased interest owing to their special properties and broader applications, such as drug delivery, optical traps, and e-paper display. Most strategies to produce anisotropic polymer particles, however, require sophisticated instruments or additional surfactants. Here, we develop a simple and versatile method, the two-step solvent on-film annealing (2-SOFA) technique, to make anisotropic polymer particles with different shapes. Polystyrene (PS) microspheres spin-coated on poly(methyl methacrylate) (PMMA) films are chosen as model materials. By sequentially annealing the PS/PMMA composites in different solvent vapors, anisotropic polymer particles with distinctive and diverse shapes can be produced, such as half-eaten-peach-shaped, snowman-shaped, and bowler-hat-shaped morphologies. An exquisite selective removal strategy is applied to check the morphologies of the PS/PMMA composite films and to comprehend the transformation mechanism at different annealing steps and times. For particles merged from multiple microspheres, quantitative studies are also performed to figure out the relationships between the sizes of the merged particles and the numbers of the original microspheres. These results have implications for colloidal self-assembly.