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Sequential Selective Solvent On-Film Annealing: Fabrication of Monolayers of Ordered Anisotropic Polymer Particles
(2020-08-05)
Tseng, Hsiao-Fan
;
Liang, Xiaobin
;
Liu, Chih-Ting
;
Chiu, Yu-Jing
;
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.
Snake Tracks in Polymer Land: Wavy Polymer Structures via Selective Solvent Vapor Annealing
(2020-08-25)
Chiu, Yu-Jing
;
Weng, Chang-Ching
;
Tseng, Hsiao-Fan
;
Hsu, Hsun-Hao
;
Chen, Jiun-Tai
Wavy patterns are interesting geometric patterns and commonly seen in nature, such as serpentine streams or snake tracks in the sand. Although many efforts have been devoted to fabricating artificial wavy structures, it remains a great challenge to obtain wavy structures with controllable curvatures and desired functional properties. Here, we present an unprecedented approach to generate wavy polymer structures by annealing electrospun core-shell fibers on polymer films. Polystyrene (PS)/poly(methyl methacrylate) (PMMA) core-shell fibers, produced via the viscosity-induced phase separation in the electrospinning process, are annealed on PMMA films using vapors of acetic acid, a selective solvent for PMMA but not for PS. After the swollen PMMA chains of the PMMA shells are shed, the revealed PS cores start to buckle, driven by the elastic force from the strain release, forming the wavy structures. The degrees of the buckling, measured by the curvatures and the amplitudes of the wavy structures, are controlled by the annealing times. Furthermore, fluorescent properties are selectively introduced to the wavy structures using pyrene solutions or pyrene-containing vapors, demonstrating the potential application as fluorescent wavy materials.
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
;
Hsu, Hsun-Hao
;
Chang, Chia-Jui
;
Chiu, Yu-Jing
;
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.
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
;
Chiu, Yu-Jing
;
Wu, Bo-Hao
;
Li, Jia-Wei
;
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.
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
;
Chang, Kai-Chieh
;
Hsu, Hsun-Hao
;
Chiu, Yu-Jing
;
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.
The Effect of Solvent Vapor Annealing on Drug-Loaded Electrospun Polymer Fibers
(2020-02-01)
Chiu, Yu-Jing
;
Zhang, Ziwei
;
Dziemidowicz, Karolina
;
Nikoletopoulos, Christos-Georgios
;
Angkawinitwong, Ukrit
Electrospinning has emerged as a powerful strategy to develop controlled release drug delivery systems but the effects of post-fabrication solvent vapor annealing on drug-loaded electrospun fibers have not been explored to date. In this work, electrospun poly(epsilon-caprolactone) (PCL) fibers loaded with the hydrophobic small-molecule spironolactone (SPL) were explored. Immediately after fabrication, the fibers are smooth and cylindrical. However, during storage the PCL crystallinity in the fibers is observed to increase, demonstrating a lack of stability. When freshly-prepared fibers are annealed with acetone vapor, the amorphous PCL chains recrystallize, resulting in the fiber surfaces becoming wrinkled and yielding shish-kebab like structures. This effect does not arise after the fibers have been aged. SPL is found to be amorphously dispersed in the PCL matrix both immediately after electrospinning and after annealing. In vitro dissolution studies revealed that while the fresh fibers show a rapid burst of SPL release, after annealing more extended release profiles are observed. Both the rate and extent of release can be varied through changing the annealing time. Further, the annealed formulations are shown to be stable upon storage.
Alignment-Improved and Diameter-Reduced Electrospun Polymer Fibers via the Hot-Stretching Process
(1970-01-01)
Hsu, Hsun-Hao
;
Chiu, Yu-Jing
;
Li, Jia-Wei
;
Tseng, Hsiao-Fan
;
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.
Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers
(1970-01-01)
Li, Jia-Wei
;
Chiu, Yu-Jing
;
Chang, Chia-Jui
;
He, Hung-Chieh
;
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.
Hierarchical and Spiral Polymer Structures: Direct Electrospinning on Porous Anodic Aluminum Oxide Templates
(2019-08-01)
Liu, Ying-Hsuan
;
Chiu, Yu-Jing
;
Chen, Jiun-Tai
;
交大名義發表
;
應用化學系
Electrospun fibers with hierarchical structures have attracted a great deal of attention because they have distinct properties, such as large specific surface areas and high surface area-to-volume ratios, and can be applied to various fields. Here, a simple and versatile method is demonstrated to prepare electrospun fibers with hierarchical structures by directly electrospinning poly(methyl methacrylate) (PMMA) solutions on porous anodic aluminum oxide (AAO) templates. Hierarchical PMMA structures with micro- and nanometer scales can be generated. The two length scales of the hierarchical structures can be independently controlled; the first length scale is controlled by the electrospinning conditions, and the second length scale is controlled by the pore sizes of the AAO templates. By adding water in the polymer solutions, the evaporation of the solvents and the whipping instability of the solution jets can be manipulated. Consequently, spiral and hierarchical structures can be obtained. This study opens a promising avenue in fabricating electrospun polymer fibers with hierarchical structures, which should have great potential in a variety of applications, such as filtration, diagnosis, and tissue regeneration.
Hierarchical and Spiral Polymer Structures: Direct Electrospinning on Porous Anodic Aluminum Oxide Templates
(1970-01-01)
Liu, Ying-Hsuan
;
Chiu, Yu-Jing
;
Chen, Jiun-Tai
;
交大名義發表
;
應用化學系
Electrospun fibers with hierarchical structures have attracted a great deal of attention because they have distinct properties, such as large specific surface areas and high surface area-to-volume ratios, and can be applied to various fields. Here, a simple and versatile method is demonstrated to prepare electrospun fibers with hierarchical structures by directly electrospinning poly(methyl methacrylate) (PMMA) solutions on porous anodic aluminum oxide (AAO) templates. Hierarchical PMMA structures with micro- and nanometer scales can be generated. The two length scales of the hierarchical structures can be independently controlled; the first length scale is controlled by the electrospinning conditions, and the second length scale is controlled by the pore sizes of the AAO templates. By adding water in the polymer solutions, the evaporation of the solvents and the whipping instability of the solution jets can be manipulated. Consequently, spiral and hierarchical structures can be obtained. This study opens a promising avenue in fabricating electrospun polymer fibers with hierarchical structures, which should have great potential in a variety of applications, such as filtration, diagnosis, and tissue regeneration.

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