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Light-Induced Nanowetting: Erasable and Rewritable Polymer Nanoarrays via Solid-to-Liquid Transitions
(2020-08-12)
Lin, Kuan-Ting
;
Chen, Yu-Jia
;
Huang, Meng-Ru
;
Karapala, Vamsi Krishna
;
Ho, Jhih-Hao
Template wetting methods have been widely applied in the preparation of one-dimensional (1D) polymer nanomaterials. The pattern control using the template wetting methods, however, still remains a great challenge, mainly due to the nonselectivity of the polymers toward the environmental triggering. In this work, we present a facile light-induced nanowetting (LIN) method to fabricate patterned nanoarrays using anodic aluminum oxide (AAO) templates. Photoresponsive azobenzene-containing polymers (azopolymers) that exhibit light-induced reversible solidto-liquid transitions are used. Upon exposure to ultraviolet lights, the azopolymer chains can wet the nanopores of the AAO templates in a liquid state via capillary force. The azopolymer chains are then solidified by illuminating them with visible lights, resulting in the formation of azopolymer nanoarrays. Notably, using designed photomasks, the patterns of the nanoarrays can be ingeniously controlled with the characteristic of erasable and rewritable nanostructures.
Sequential Selective Solvent On-Film Annealing: Fabrication of Monolayers of Ordered Anisotropic Polymer Particles
(2020-08-05)
Tseng, Hsiao-Fan
;
Liang, Xiaobin
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Liu, Chih-Ting
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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.
Intelligent Environmental Sensing: Fabrication of Switchable, Reusable, and Highly Sensitive Gas Sensors with Spiropyran-Grafted Anodic Aluminum Oxide Templates
(2020-06-04)
Lee, Lin-Ruei
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Karapala, Vamsi Krishna
;
Lin, Yu-Liang
;
He, Hung-Chieh
;
Chen, Jiun-Tai
Monitoring undesired pH deviations in the surroundings is one of the most pervasive issues of environment and industry, and developing efficient, economical, portable, and reusable membranes for pH monitoring is urgently needed. Herein, we report novel smart nanomembranes (SNMs) that are made up of anodic aluminum oxide (AAO) templates grafted with spiropyran molecules. The ultraviolet and visible light responses of the SNMs under acid vapors are investigated. Under UV irradiation, the ring-closed spiropyran on the AAO templates transform to ring-opened merocyanine, which contains phenolate oxygen and can be further protonated by acids. Such a protonation process not only shows evident color changes but also endows SNMs with pH-responsive properties, which are further investigated by UV-vis diffuse reflectance spectroscopy. Furthermore, to demonstrate the pH-responsive properties of the SNM, common volatile acids such as hydrochloric acid, nitric acid, formic acid, and acetic acid are tested. The SNM shows conspicuous sensibility, reusability, and reversibility during the processes of irradiation, protonation, and deprotonation. Therefore, the newly developed SNM can be an excellent alternative to the existing pH sensors for the detection of pH variations in environment and industry.
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
;
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.
Dewetting of Swollen Poly(3-hexylthiophene) Films during Spin-Coating Processes: Implications for Device Fabrication
(2018-05-01)
Chung, Pei-Yun
;
Cheng, Ming-Hsiang
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Tseng, Hsiao-Fan
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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.
Reproducible and Bendable SERS Substrates with Tailored Wettability Using Block Copolymers and Anodic Aluminum Oxide Templates
(1970-01-01)
Lin, Yu-Liang
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Karapala, Vamsi Krishna
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Shen, Ming-Hui
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Chen, Yi-Fan
;
He, Hung-Chieh
Surface properties are essential for substrates exhibiting high sensitivity in surface-enhanced Raman scattering (SERS) applications. In this work, novel SERS hybrid substrates using polystyrene-block-poly(methyl methacrylate) and anodic aluminum oxide templates is presented. The hybrid substrates not only possess hierarchical porous nanostructures but also exhibit superhydrophilic surface properties with the water contact angle approximate to 0 degrees. Such surfaces play an important role in providing uniform enhanced intensities over large areas (relative standard deviation approximate to 10%); moreover, these substrates are found to be highly sensitive (limit of detection approximate to 10(-12) m for rhodamine 6G (R6G)). The results show that the hybrid SERS substrates can achieve the simultaneous detection of multicomponent mixtures of different target molecules, such as R6G, crystal violet, and methylene blue. Furthermore, the bending experiments show that about 70% of the SERS intensities are maintained after bending from approximate to 30 degrees to 150 degrees.
Interplay of Template Constraints and Microphase Separation in Polymeric Nano-Objects Replicated from Novel Modulated and Interconnected Nanoporous Anodic Alumina
(2018-01-01)
Bayat, Haider
;
Lin, Chia-Hua
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Cheng, Ming-Hsiang
;
Steuber, Marc
;
Chen, Jiun-Tai
We report on a versatile strategy to fabricate shape-controlled polymeric nano-objects with an internal compartmentalized structure by replication from pore-diameter-modulated and interconnected nanoporous anodized aluminum oxide (AAO). The AAO with modulated pore diameters is synthesized in a refined temperature-modulated hard anodization (TMHA) approach, by alternating the flow rate of an air stream cooling the electrolyte. Through pore-widening of the templates with modulated pore diameters, a stable interconnected 3D network with transversal ellipsoidal holes is fabricated as a second template structure. From these unprecedented template structures exhibiting modulated pores and an intricate 3D network structure, shape-controlled polymeric nano-objects are replicated using the melt wetting method with polystyrene homopolymer (PS) and cylinder-forming block copolymer polystyrene-block-polydimethylsiloxane (PS298-b-PDMS195). The replicated nanostructures are separated into individual anisotropically shaped nanocapsules by passing the replicas through a polycarbonate membrane followed by gentle sonication. Inside the nano-objects, the microphase separation of PS298-b-PDMS195 affords parallel aligned nanophases, in which domain sizes and morphologies are different compared to the unconfined bulk according to transmission electron microscopy analyses. These advanced AAO platforms and the nanoscale polymer replicas offer new routes for compartmentalized nano objects with potential future relevance for applications ranging from drug nanocarriers to biosensors.
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
;
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.

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