Browsing by Author "Chen, Jiun-Tai"

Now showing 1 - 20 of 90

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.
Annealing Effect on Electrospun Polymer Fibers and Their Transformation into Polymer Microspheres
(2012-02-27)
Fan, Ping-Wen
;
Chen, Wan-Ling
;
Lee, Ting-Hsien
;
Chen, Jiun-Tai
;
應用化學系
Electrospinning is a simple and convenient technique to produce polymer fibers with diameters ranging from several nanometers to a few micrometers. Different types of polymer fibers have been prepared by electrospinning for various applications. Among different post-treatment methods of electrospun polymer fibers, the annealing process plays a critical role in controlling the fiber properties. The morphology changes of electrospun polymer fibers under annealing, however, have been little studied. Here we investigate the annealing effect of electrospun poly(methyl methacrylate) (PMMA) fibers and their transformation into PMMA microspheres. PMMA fibers with an average size of 2.39 mu m are first prepared by electrospinning a 35 wt% PMMA solution in dimethylformamide. After the electrospun fibers are thermally annealed in ethylene glycol, a non-solvent for PMMA, the surfaces of the fibers undulate and transform into microspheres driven by the Rayleigh instability. The driving force of the transformation process is the minimization of the interfacial energy between the polymer fibers and ethylene glycol. The sizes of the microspheres fit well with the theoretical predictions. Longer annealing times are found to be required at lower temperatures to obtain the microspheres.
Anthradithiophene-based liquid crystal molecules: High carrier mobilities enhanced by rubbed polyimides for the application in organic field-effect transistors
(2018-06-01)
Wang, Wei-Chih
;
Yeh, Tien-Tien
;
Liau, Wei-Lung
;
Chen, Jiun-Tai
;
Hsu, Chain-Shu
We synthesize three liquid crystal molecules with angular anthradithiophene (a-ADT) as the core for the application in organic film-effect transistors (OFETs). Thiophene-octyl group and thiophene-dodecyl group are introduced on both sides of the a-ADT core to yield compounds Bis-C8T-a-ADT and Bis-C12T-a-ADT. Moreover, thiophene-dodecyl group is attached to the a-ADT core on one side to yield compound C12T-a-ADT. The synthesized compounds are measured by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) to determine their mesomorphic properties. Compound Bis-C8T-a-ADT shows nematic and smectic A phases while both compounds Bis-C12T-a-ADT and C12T-a-ADT reveal smectic A phases. The optical and electrochemical properties of the compounds are characterized by UV-vis spectroscopy and cyclic voltammetry (CV). The HOMO levels for Bis-C8T-a-ADT and Bis-C12T-a-ADT are estimated to be -5.27 eV while the HOMO level of C12T-a-ADT is estimated to be -5.34 eV. The low-lying HOMO levels of the molecules indicate their great oxidation stability in OFET devices. The carrier mobilities are observed to increase 10-1000 times using rubbed polyimide (PI), resulting from the better arrangements of the liquid crystal molecules, and excellent carrier mobilities of 1.06 and 1.02 cm(2)/Vs are obtained from compounds Bis-C12T-a-ADT and C12T-a-ADT, respectively.
Asymmetric Polymer Particles with Anisotropic Curvatures by Annealing Polystyrene Microspheres on Poly(vinyl alcohol) Films
(2016-11)
Tseng, Hsiao-Fan
;
Cheng, Ming-Hsiang
;
Jeng, Kai-Sheng
;
Li, Jia-Wei
;
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.
Asymmetries in Porous Membranes: Fabrication of Anodic Aluminum Oxide Membranes with Double-Sized Nanopores and Controlled Surface Properties
(2019-06-13)
Liu, Chih-Ting
;
Lin, Yu-Liang
;
Chu, Chien-Wei
;
Chang, Chun-Wei
;
Chiu, Yu-Jing
Recently, anodic aluminum oxide (AAO) membranes with ordered and monodispersed nanopores have attracted significant attention because the pore sizes and lengths of the AAO membranes can be systematically controlled by changing the anodization parameters. Asymmetries of geometry, wettability, charge, and polarity in nanoporous AAO membranes are now highly desired for applications such as drug delivery, membrane filtration, and catalysis. Although the asymmetries in AAO membranes have been widely studied, AAO membranes whose nanopores simultaneously possess more than two asymmetric properties still need to be developed. In this work, we present a simple method to fabricate asymmetric AAO membranes by combining the post-treatments with the three-step anodization method. The asymmetries of the AAO membranes simultaneously possessing larger nanopores with higher hydrophobicity and smaller nanopores with lower hydrophobicity are characterized by scanning electron microscopy, water contact angle measurements, and energy-dispersive X-ray spectroscopy. Using the asymmetric AAO membranes, nanowires of polystyrene and poly(styreneb/ock-dimethylsiloxane) with double-sized diameters are also fabricated via the melt and solvent wetting methods, exhibiting that the AAO membranes with double-sized diameters can be used as the templates for generating double-sized polymer nanowires.
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
;
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.
Blending Homopolymers for Controlling the Morphology Transitions of Block Copolymer Nanorods Confined in Cylindrical Nanopores
(2017-06-21)
Cheng, Ming-Hsiang
;
Hsu, Yu-Chen
;
Chang, Chun-Wei
;
Ko, Hao-Wen
;
Chung, Pei-Yun
The microphase separation of block copolymers in confined geometries has been widely investigated over the last few decades. The controllability and versatility of the confinement-induced morphologies, however, are still difficult to be achieved because of the limited experimental parameters in the process of fabricating the confined nanostructures. In this work, we study the morphology transitions of lamellae forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) nanorods confined in the nanopores of anodic aluminum oxide (AAO) templates. The nanorods are formed by solvent-assisted template wetting, and the morphologies are compared to those in the bulk state. By blending PS-b-PDMS with homopolystyrene (hPS), the morphologies of the nanorods can be controlled because of the changes of the effective volume fractions. Special morphology transitions from concentric lamellar morphology, to multihelical morphology, and finally to spherical-like morphology are observed by increasing the weight ratios of hPS. hPS with different molecular weights is also applied to investigate the effect of hPS on the morphologies of the PS-b-PDMS/hPS blend nanostructures. The unusual morphologies are further confirmed by a selective removal process, which also generates nanochannels for possible refilling with functional materials.
Block Copolymer Micelle Nanotubes by the Solvent-Annealing-Induced Nanowetting in Anodic Aluminum Oxide Templates
(2015-11-01)
Yao, I-Chun
;
Cheng, Ming-Hsiang
;
Chen, Jiun-Tai
;
應用化學系
;
Department of Applied Chemistry
Block copolymer micelles are generally formed by the self-assembly of amphiphilic copolymer molecules in aqueous medium. Although different types of block copolymer micelles have been studied, the self-assembly behavior of block copolymer micelles in confined geometries have been rarely studied. In this work, the fabrication of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) micelle nanotubes in the cylindrical nanopores of anodic aluminum oxide templates using a solvent-annealing-assisted wetting method is presented. The PS-b-P4VP chains wet the pore walls in the form of micelles when the sample is annealed in the vapor of toluene, a good solvent for PS and a nonsolvent for P4VP. The formation of the PS-b-P4VP micelle nanotubes instead of nanorods implies that the micelles wet the nanopores in the complete wetting regime. This study not only contributes to a deeper understanding of the self-assembly behavior of block polymer micelles in confined geometries, but also provides more possible variations and design freedoms in the application of block copolymer micelles.
Block copolymer micelles confined in cylindrical nanopores: Effects of annealing solvents and hybridization
(2020-05-01)
Cheng, Ming-Hsiang
;
Yao, I-Chun
;
Chiu, Tang-Yao
;
Chen, Jiun-Tai
;
交大名義發表
Amphiphilic block copolymer micelles have been intensively investigated and applied into various research fields for decades. One of the most promising characteristics for block copolymer micelles is the selective incorporation of metal precursors in the cores or coronas of the micelles. By combining with nanoporous membranes, aligned polymer nanostructures can be generated, facilitating the applications such as nanolithography and catalysis. The morphology transitions and controllability of block copolymer micelles in confined geometries, however, have seldom been studied. In addition, for hybrid micelles in which polymer segments are selectively incorporated with inorganic metal precursors, the relationship between hybridization and morphologies of polymer nanostructures in the confined states is still under discussion. In this work, we investigate the effects of annealing solvents and hybridization with metal precursors (gold(III) chloride trihydrate (HAuCl4 center dot 3H(2)O)) on the morphologies of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer micelles confined in the nanopores of anodic aluminum oxide (AAO) templates. Tuned by the annealing solvent vapors and the selective ion complexation between HAuCl4 and P4VP cores, various morphologies can be effectively controlled, such as the spherical-micelles-in-rod morphology, the parallel-cylinders-in-rod morphology, and the hemispherical-micelles-in-rod morphology. This study not only investigates the effects of annealing solvent vapors and hybridization on the morphologies of block copolymer micelles confined in cylindrical nano-geometries but also offers a viable route for preparing metal nanoparticles embedded in porous templates.
Competition Between Effects of Pore Sizes and Annealing Solvents on the Morphology Manipulation of 3D Block Copolymer Nanostructures Using Anodic Aluminum Oxide Templates
(2016-06)
Chu, Chiang-Jui
;
Chung, Pei-Yun
;
Chu, Chien-Wei
;
Cheng, Ming-Hsiang
;
Chi, Mu-Huan
In this work, the morphologies of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) nanostructures using solvent-induced wetting in the nanopores of anodic aluminum oxide (AAO) templates are investigated. AAO templates with three different pore sizes (approximate to 200, approximate to 60, and approximate to 30 nm) are used in this work to differentiate the effect of confinement and annealing solvents. Different from the results by the traditional wetting methods, two major effects are identified in affecting the morphologies. At larger pore sizes, the morphologies of the nanostructures are mainly affected by the annealing solvent. At smaller pore sizes, however, the morphologies are mainly controlled by the confinement effect (pore sizes).
Confinement Effects on the Optical Properties and Chain Conformations of Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) Nanotubes
(2016-09)
Chu, Chien-Wei
;
Jeng, Kai-Sheng
;
Chi, Mu-Huan
;
Tsai, Chia-Chan
;
Cheng, Ming-Hsiang
Although many fabrication methods of conjugated polymer nanostructures have been developed, the effects of confinement on the morphologies, chain conformations, and optical properties of conjugated polymers are still not well understood. In this work, poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT), a light-emitting conjugated polymer, is used to fabricate nanotubes by a solution wetting method using anodic aluminum oxide templates. The property changes under the nanoscale confinement have been investigated. The morphologies of F8BT nanostructures are characterized by scanning electron microscope, transmission electron microscope, and laser scanning confocal microscope. The data show the hollow morphologies and no or low crystallinity of the nanostructures. The optical properties are also measured using UV-vis absorption, photoluminescence, and confocal Raman spectroscopy. The spectroscopy data indicate that F8BT polymer chains have less intermolecular interactions and coplanarity under the confinement effect.
Conjugated polymer nanostructures for organic solar cell applications
(2011)
Chen, Jiun-Tai
;
Hsu, Chain-Shu
;
應用化學系
;
Department of Applied Chemistry
Recently, there has been tremendous progress in the development of polymer-based organic solar cells. Polymer-based solar cells have attracted a great deal of attention because they have the potential to be efficient, inexpensive, and solution processable. New materials, nanostructures, device designs, and processing methods have been developed to achieve high device efficiencies. This review focuses on the fabrication techniques of conjugated polymer nanostructures and their applications for organic solar cells. We will first introduce the fundamental knowledge of organic solar cells and emphasize the importance of nanostructures. Then we will discuss different strategies for fabricating conjugated polymer nanostructures, including topics such as polymer nanowires, nanoparticles, block copolymers, layer-by-layer deposition, nanoimprint lithography, template methods, nanoelectrodes, and porous inorganic materials. The effects of the nanostructures on the device performance will also be presented. Efficiencies higher than 10% are expected for polymer-based solar cells by using new materials and techniques.
Controlled Assembly of Polymer-Tethered Gold Nanorods via a Rayleigh-Instability-Driven Transformation: Implications for Biomedical Applications
(2019-05-01)
Chiu, Tang-Yao
;
Cheng, Ming-Hsiang
;
Chang, Chun-Wei
;
Ko, Hao-Wen
;
Chen, Jiun-Tai
We study the assembly and morphology transformation of gold nanorods tethered with polystyrene ligands (AuNRs@PS). The AuNRs@PS nanotubes are first fabricated in the nanopores of anodic aluminum oxide (AAO) templates by the solution wetting method. When the samples are thermally annealed, the Rayleigh-instability-driven transformations of the nanostructures are triggered by the decrease of the interfacial energies between the nanotubes and the inner air cylinders. Four different morphologies are identified: nanotubes (I), undulated structures (II), Rayleigh-instability-induced structures (III), and nanorods (IV). The morphology diagrams of the AuNRs@PS structures using different thermal annealing temperatures and times are also made, showing that the morphology transformation rates are higher at higher annealing temperatures. This work has implications to be applied in different fields such as biomedical applications.
Controlled self-assemblies of polystyrene-block-polydimethylsiloxane micelles in cylindrical confinement through a micelle solution wetting method and Rayleigh-instability-driven transformation
(2017-08-28)
Ko, Hao-Wen
;
Higuchi, Takeshi
;
Chang, Chun-Wei
;
Cheng, Ming-Hsiang
;
Isono, Komei
Block copolymer micelles have been extensively discussed for many decades because of their applications, such as lithography and drug delivery. However, controlling the morphologies of nanostructure assembly using block copolymer micelles as building elements remains a great challenge. In this work, we developed a novel route to induce micelle assembly in confined geometries. Polystyrene-block-polydimethylsiloxane (PS-b-PDMS) micelle solutions were used to prepare micelle nanostructures, and the critical parameters affecting the morphologies were determined. Micelle nanorods, micelle nanospheres, and multi-component nanopeapods were prepared by wetting anodic aluminum oxide (AAO) templates with micelle solutions. Rayleigh-instability-driven transformation was discovered to play an important role in controlling the morphologies of the micelle nanostructures. This study not only proposes a versatile approach to preparing block copolymer micelle nanostructures, but it also provides deeper insight into the controlling factors of block copolymer micelle morphologies in cylindrical confinement.
Curved block copolymer nanodiscs: structure transformations in cylindrical nanopores using the nonsolvent-assisted template wetting method
(2019-11-07)
Lin, Yu-Liang
;
Cheng, Ming-Hsiang
;
Chang, Chun-Wei
;
Chu, Chien-Wei
;
Liu, Chih-Ting
In this work, we study the structure transformations of cylinder-forming polystyrene-block-polydimethylsiloxane (PS31k-b-PDMS14.5k) confined in cylindrical nanopores. PS-b-PDMS nanotubes, nanospheres, and curved nanodiscs are ingeniously prepared by a facile template wetting strategy using anodic aluminum oxide (AAO) templates. Quantitative analyses of the structure transformations from nanospheres to curved nanodiscs are also conducted, showing that the lengths of the curved nanodiscs can be controlled by adjusting the annealing temperature and time. Furthermore, the PDMS domains of the nanostructures can be selectively etched using HF solutions, generating porous PS nanostructures. This work not only offers versatile routes to prepare block copolymer nanostructures with controlled shapes but also provides a deeper understanding of the structure transformation of block copolymers in confined geometries.
Curved polymer nanodiscs by wetting nanopores of anodic aluminum oxide templates with polymer nanospheres
(2014)
Chi, Mu-Huan
;
Kao, Yi-Huei
;
Wei, Tzu-Hui
;
Lee, Chih-Wei
;
Chen, Jiun-Tai
Although nanostructures with diverse morphologies have been fabricated, it is still a great challenge to prepare anisotropic two-dimensional (2-D) nanostructures, especially non-planar disc-like nanostructures. In this work, we develop a simple method to prepare curved polymer nanodiscs with regular sizes by wetting polymer nanospheres in the nanopores of anodic aluminum oxide (AAO) templates. Polystyrene (PS) nanospheres are first fabricated by using a non-solvent-assisted template wetting method. By annealing the PS nanospheres in the nanopores of AAO templates, curved PS nanodiscs can be produced. The length and morphology of the curved PS nanodiscs can be controlled by the wetting conditions such as the annealing temperatures and times. For some stacked nanospheres, the annealing process can result in the formation of helix-like nanostructures. To demonstrate the universality of this work, this approach is also applied to poly(methyl methacrylate) (PMMA), another common polymer, and similar results are obtained.
Dewetting of polymer thin films on modified curved surfaces: preparation of polymer nanoparticles with asymmetric shapes by anodic aluminum oxide templates
(2018-04-21)
Liu, Chih-Ting
;
Tsai, Chia-Chan
;
Chu, Chien-Wei
;
Chi, Mu-Huan
;
Chung, Pei-Yun
We study the dewetting behaviors of poly(methyl methacrylate) (PMMA) thin films coated in the cylindrical nanopores of anodic aluminum oxide (AAO) templates by thermal annealing. Self-assembled monolayers (SAMs) of n-octadecyltrichlorosilane (ODTS) are introduced to modify the pore surfaces of the AAO templates to induce the dewetting process. By using scanning electron microscopy (SEM), the dewetting-induced morphology transformation from the PMMA thin films to PMMA nanoparticles with asymmetric shapes can be observed. The sizes of the PMMA nanoparticles can be controlled by the original PMMA solution concentrations. The dewetting phenomena on the modified nanopores are explained by taking into account the excess intermolecular interaction free energy (AG). This work opens a new possibility for creating polymer nanoparticles with asymmetric shapes in confined geometries.
Dewetting of Swollen Poly(3-hexylthiophene) Films during Spin-Coating Processes: Implications for Device Fabrication
(2018-05-01)
Chung, Pei-Yun
;
Cheng, Ming-Hsiang
;
Tseng, Hsiao-Fan
;
Liu, Chih-Ting
;
Chiu, Tang-Yao
Poly(3-hexylthiophene) (P3HT) films have been usually prepared by spin-coating for the applications of electronic devices such as organic photovoltaic devices (OPV) and organic field-effect transistors (OFETs). The wetting and dewetting behaviors of the swollen P3HT films during the spin-coating processes, however, are still poorly understood. In this work, we investigate the dewetting behaviors of P3HT thin films and the formation of ring structures during the spin-coating process by controlling the spin rates and the solution temperatures. Quantitative studies of the dewetting phenomena are conducted by measuring the sizes of the ring structures of the dewetting patterns. It is observed that the sizes of the ring structures are larger at lower spin rates because of the longer dewetting times allowed during the spin-coating processes. More importantly, the dewetting behaviors of the P3HT films are discovered to be affected by the formation of the P3HT nanowhiskers (nanowires). This work offers a deeper understanding of the dewetting behaviors of swollen P3HT films during the spin-coating processes, which is crucial for the development of P3HT-based optoelectronic devices.
Effect of Nonsolvent on the Formation of Polymer Nanomaterials in the Nanopores of Anodic Aluminum Oxide Templates
(1970-01-01)
Lee, Chih-Wei
;
Wei, Tzu-Hui
;
Chang, Chun-Wei
;
Chen, Jiun-Tai
;
應用化學系
"We study the effect of nonsolvent on the formation of polymer nanomaterials in the nanopores of porous templates. Water (nonsolvent) is added into a poly (methyl methacrylate) (PMMA) solution in dimethylformamide (DMF) confined in the nanopores of an anodic aluminum oxide (AAO) template. Water forms a wetting layer on the pore wall and causes the PMMA solution to be isolated in the center of the nanopore, resulting in the formation of PMMA nanospheres or nanorods after the solvent is evaporated. The formation of the polymer nanomaterials induced by nonsolvent is found to be driven by the Rayleigh-instability-type transformation. Without adding the nonsolvent, PMMA chains precipitate on the walls of the nanopores after the solvent is evaporated, and PMMA nanotubes are obtained."
Effect of the Polymer Concentration on the Rayleigh-Instability-Type Transformation in Polymer Thin Films Coated in the Nanopores of Anodic Aluminum Oxide Templates
(2015-03-03)
Tsai, Chia-Chan
;
Chen, Jiun-Tai
;
應用化學系
;
Department of Applied Chemistry
We study the Rayleigh-instability-type transformation of polystyrene (PS) thin films coated in the nanopores of anodic aluminum oxide (AAO) templates. The PS thin films are fabricated using a solution-wetting method, in which the wall thicknesses are controlled by the concentrations of the polymer solutions and the diameters of the nanopores. By thermal annealing, the surfaces of the thin films undulate and the morphologies transform from nanotubes to Rayleigh-instability-induced nanostructures (short nanorods) and long nanorods. To understand the mechanism of the morphology transformation further, we construct the morphology diagrams by annealing the PS thin films at different temperatures and times. We observe that the morphology diagrams of the PS thin films prepared by different concentrations are similar, indicating that the transformation kinetics are not affected by the film thicknesses. The values of the undulation wavelengths, however, are controlled by the film thicknesses and the diameters of the nanopores.