Chi-Ching Kuo

Synthesis, Morphology, and Sensory Applications of Multifunctional Rod−Coil−Coil Triblock Copolymers and Their Electrospun Nanofibers

We report the synthesis, morphology, and applications of conjugated rod-coil-coil triblock copolymers, polyfluorene-block-poly(N-isopropylacrylamide)-block-poly(N-methylolacrylamide) (PF-b-PNIPAAm-b-PNMA), prepared by atom transfer radical polymerization first and followed by click coupling reaction. The blocks of PF, PNIPAAm, and PNMA were designed for fluorescent probing, hydrophilic thermo-responsive and chemically cross-linking, respectively. In the following, the electrospun (ES) nanofibers of PF-b-PNIPAAm-b-PNMA were prepared in pure water using a single-capillary spinneret. The SAXS and TEM results suggested the lamellar structure of the PF-b-PNIPAAm-b-PNMA along the fiber axis. These obtained nanofibers showed outstanding wettability and dimension stability in the aqueous solution, and resulted in a reversible on/off transition on photoluminescence as the temperatures varied. Furthermore, the high surface/volume ratio of the ES nanofibers efficiently enhanced the temperature-sensitivity and responsive speed compared to those of the drop-cast film. The results indicated that the ES nanofibers of the conjugated rod-coil block copolymers would have potential applications for multifunctional sensory devices.

Morphology and pH Sensing Characteristics of New Luminescent Electrospun Fibers Prepared from Poly(phenylquinoline)‐block‐Polystyrene/Polystyrene Blends

New luminescent electrospun (ES) fibers for pH-tunable colorimetric sensors were prepared from binary blends of poly(phenylquinoline)-block-polystyrene (PPQ-b-PS)/polystyrene (PS) with a single-capillary spinneret. The PPQ-b-PS aggregated domain sizes in the ES fibers prepared from dichloromethane (CH(2) Cl(2) ), chlorobenzene (CB) and chloroform (CHCl(3) ) were 1.5 ± 0.5, 2.2 ± 0.4 and 4.1 ± 1.1 µm, respectively. Such variation on the aggregation size led to the red-shifting photoluminescence spectra changing from green, to yellow, and orange. ES fibers prepared from CH(2) Cl(2) exhibited pH-tunable photoluminescence and the emission maximum varied from 532 to 560 nm as the pH value changed from 7 to 1. The study demonstrated that the ES fibers prepared could have potential applications for sensory devices.

Non-woven and aligned electrospun multicomponent luminescent polymer nanofibers: effects of aggregated morphology on the photophysical properties

In this paper, the morphology and photophysical properties of non-woven and aligned ES nanofibers prepared from the ternary blends of poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) / poly(2,3-dibutoxy-1,4-phenylene vinylene) (DB-PPV) / poly(methyl methacrylate) (PMMA) using a single-capillary spinneret are reported. Various PFO and DB-PPV phase-separated structures in the ES nanofibers were found by two different solvents: ellipsoidal DB-PPV (10-40 nm) and fiber-like PFO (20-40 nm) in the PMMA using chloroform, while fiber-like DB-PPV (10-20 nm) and fiber-like PFO (20-30 nm) using chlorobenzene. Such different PFO and DB-PPV structures resulted in various energy transfer/emission colors in the ES nanofibers. Moreover, highly aligned luminescence PFO/DB-PPV/PMMA blend ES nanofibers prepared from chlorobenzene showed a much higher polarized emission than the non-woven and the emission colors changed from blue to greenish-blue to green as the DB-PPV composition increased. The different polarized emission characteristics between PFO and DB-PPV in the ES nanofibers also led to varied emission colors at different angles. The present study suggests the morphologies and emission characteristics of the multicomponent ES nanofibers could be efficiently tuned through solvent types and blend ratios of semiconducting polymers.

Highly ordered luminescent microporous films prepared from crystalline conjugated rod-coil diblock copolymers of PF-b-PSA and their superhydrophobic characteristics

We have successfully prepared three crystalline conjugated rod–coil diblock copolymers of poly[2,7-(9,9-dihexylfluorene)]-block-poly(stearyl acrylate) (PF-b-PSA), PF7-b-PSA64, PF7-b-PSA93, and PF7-b-PSA166, via the combination of a Suzuki coupling reaction and atom transfer radical polymerization. The crystalline comb-like PSA coil segment effectively formed the highly ordered microporous films through a “breath figure” (BF) process. On the other hand, the blue-emission band of the PF block was blue-shifting and became narrower as the PSA block was increased. The effects of block ratio, humidity, and solution concentrations on the porous structures were studied. The longer PSA block length, larger humidity, and higher copolymer concentration formed a more regular PF-b-PSA microporous structure. The images of SEM and scanning laser confocal microscope of the PF7-b-PSA166 microporous film showed that all bubbles were independent and perfectly monodisperse with a pore diameter ca. 1.85 μm. Furthermore, a rod-co-valley-like structure exhibited superhydrophobicity (contact angle up to 163 ± 0.3°), which was obtained from the peeled skin layer of the ordered PF7-b-PSA166 microporous surface. The experimental results revealed that multifunctional ordered microporous films could be successfully prepared from crystalline conjugated rod–coil block copolymers.

Ultra metal ions and pH sensing characteristics of thermoresponsive luminescent electrospun nanofibers prepared from poly(HPBO-co-NIPAAm-co-SA)

Novel multifunctional fluorescent electrospun (ES) nanofibers were prepared from random copolymers of poly{2-{2-hydroxyl-4-[5-(acryloxy)hexyloxy]phenyl}benzoxazole}-co-(N-isopropylacrylamide)-co-(stearyl acrylate)} (poly(HPBO-co-NIPAAm-co-SA)) using free-radical polymerization, followed by electrospinning. The moieties of HPBO, NIPAAm, and SA were designed to exhibit zinc ion (Zn2+) and pH sensing, thermoresponsiveness, and physical cross-linking, respectively. The ES nanofibers prepared from the P4 copolymer (1 : 93 : 6 composition ratio for HPBO/NIPAAm/SA), showed ultrasensitivity to Zn2+ (as low as 10−8 M) because of the large blue-shifting of 75 nm of the emission maximum and the 2.5-fold enhancement of the emission intensity. Furthermore, the nanofibers exhibited a substantial volume (or hydrophilic–hydrophobic) change during the heating and cooling cycle between 10 °C and 40 °C, attributed to the low critical solution temperature of the thermoresponsive NIPAAm moiety. Such temperature-dependent variation of the prepared nanofibers under the presence of Zn2+ or basic conditions led to a distinct on-off switching of photoluminescence. The high surface-to-volume ratio of the prepared ES nanofibers significantly enhanced their sensitivity compared to that of thin films. These results indicated that the prepared multifunctional ES nanofibers could be potentially used in metal ion, pH, and temperature sensing devices.

Water-Resistant Efficient Stretchable Perovskite-Embedded Fiber Membranes for Light-Emitting Diodes

Cesium lead halide perovskite nanocrystals (NCs) with excellent intrinsic properties have been employed universally in optoelectronic applications but undergo hydrolysis even when exposed to atmospheric moisture. In the present study, composite CsPbX3 (X = Cl, Br, and I) perovskite NCs were encapsulated with stretchable (poly(styrene-butadiene-styrene); SBS) fibers by electrospinning to prepare water-resistant hybrid membranes as multicolor optical active layers. Brightly luminescent and color-tunable hydrophobic fiber membranes (FMs) with perovskite NCs were maintained for longer than 1 h in water. A unique remote FMs packaging approach was used in high-brightness perovskite light-emitting diodes (PeLEDs) for the first time.

RGB-Switchable Porous Electrospun Nanofiber Chemoprobe-Filter Prepared from Multifunctional Copolymers for Versatile Sensing of pH and Heavy Metals

Novel red-green-blue (RGB) switchable probes based on fluorescent porous electrospun (ES) nanofibers exhibiting high sensitivity to pH and mercury ions (Hg2+) were prepared with one type of copolymer (poly(methyl methacrylatete-co-1,8-naphthalimide derivatives-co-rhodamine derivative); poly(MMA-co-BNPTU-co-RhBAM)) by using a single-capillary spinneret. The MMA, BNPTU, and RhBAM moieties were designed to (i) permit formation of porous fibers, (ii) fluoresce for Hg2+ detection, and (iii) fluoresce for pH, respectively. The fluorescence emission of BNPTU (fluorescence resonance energy transfer (FRET) donor) changed from green to blue as it detected Hg2+. The fluorescence emission of RhBAM (FRET acceptor) was highly selective for pH, changing from nonfluorescent (pH 7) to exhibiting strong red fluorescence (pH 2). The full-color emission of the ES nanofibers included green, red, blue, purple, and white depending on the particular pH and Hg2+-concentration combination of the solution. The porous ES nanofibers with 30 nm pores were fabricated using hydrophobic MMA, low-boiling-point solvent, and at a high relative humidity (80%). These porous ES nanofibers had a higher surface-to-volume ratio than did the corresponding thin films, which enhanced their performance. The present study demonstrated that the FRET-based full-color-fluorescence porous nanofibrous membranes, which exhibit on-off switching and can be used as naked eye probes, have potential for application in water purification sensing filters.

Novel highly aligned, double-layered, hollow fibrous polycarbonate membranes with a perfectly tightly packed pentagonal pore structure fabricated using the electrospinning process

Highly aligned, tightly packed, single-, double-, and mixed-layer polycarbonate (PC) hollow fibrous membranes were prepared using two-fluid coaxial electrospinning. Polyethylene oxide (PEO) was used as the core, and PC was used as the shell; the PEO was subsequently extracted. The effects of the polymer concentration and spinning voltage on the morphologies and mechanical properties of the membranes were explored. At a PC concentration of 20 wt% and voltage of 8 kV, a hollow fibrous membrane (PC20-8) with a perfectly packed double-layered structure, high alignment of 97%, and distinct pentagonal pores (different from the typical quadrangle pore structure) was prepared. This membrane had the highest Youngs modulus and tensile strain, 1.8 GPa and 700%, respectively. The observed results suggest that highly aligned hollow fibrous membranes with favorable mechanical properties, particularly PC20-8, have potential for application in guide conduits for nerves, vascular scaffolds, and biomedical devices.

Self-powered wireless temperature sensor with piezoelectric energy harvester fabricated with metal-MEMS process

This paper presents a self-powered wireless temperature sensor powered with a micro piezoelectric energy harvester. The piezoelectric energy harvester is a cantilever beam design fabricated with metal-MEMS process on stainless steel substrates. The energy harvester is tuned to have resonant frequency around 120Hz and the bimorph version can generate more than 400μW power output when driven with vibration levels of 1.5g acceleration at resonance. A shaker simulated the vibrations of motors general seen in air conditioning system with a vibration level around 0.5g is used to drive the piezoelectric energy harvesters and has a power output around 50μW power. An interfacing circuit with energy buffer is used to accumulate electrical energy in a capacitor and then turn on the Bluetooth wireless module to send temperature readings measured from internal temperature sensor to a smartphone intermittently. The Bluetooth module can be turn on for around 1 second to send the readings to a smartphone for every 1.5 minutes.

Novel Magnet and Thermoresponsive Chemosensory Electrospinning Fluorescent Nanofibers and Their Sensing Capability for Metal Ions

Novel multifunctional switchable chemosensors based on fluorescent electrospun (ES) nanofibers with sensitivity toward magnetism, temperature, and mercury ions (Hg2+) were prepared using blends of poly(N-isopropylacrylamide)-co-(N-methylolacrylamide)-co-(Acrylic acid), the fluorescent probe 1-benzoyl-3-[2-(2-allyl-1,3-dioxo-2,3-dihydro-1Hbenzo[de]isoquinolin-6-ylamino)-ethyl]-thiourea (BNPTU), and magnetite nanoparticles (NPs), and a single-capillary spinneret. The moieties of N-isopropylacrylamide, N-methylolacrylamide, acrylic acid, BNPTU, and Iron oxide (Fe3O4) NPs were designed to provide thermoresponsiveness, chemical cross-linking, Fe3O4 NPs dispersion, Hg2+ sensing, and magnetism, respectively. The prepared nanofibers exhibited ultrasensitivity to Hg2+ (as low as 10−3 M) because of an 80-nm blueshift of the emission maximum (from green to blue) and 1.6-fold enhancement of the emission intensity, as well as substantial volume (or hydrophilic to hydrophobic) changes between 30 and 60 °C, attributed to the low critical solution temperature of the thermoresponsive N-isopropylacrylamide moiety. Such temperature-dependent variations in the presence of Hg2+ engendered distinct on–off switching of photoluminescence. The magnetic ES nanofibers can be collected using a magnet rather than being extracted through alternative methods. The results indicate that the prepared multifunctional fluorescent ES nanofibrous membranes can be used as naked eye sensors and have the potential for application in multifunctional environmental sensing devices for detecting metal ions, temperature, and magnetism as well as for water purification sensing filters.