Browsing by Author "Wang, Chien-Lung"

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2,2 '-Bis(trifluoromethyl)biphenyl as a building block for highly ambient-stable, amorphous organic field-effect transistors with balanced ambipolarity
(2016-01-01)
Chaing, Chi-Jui
;
Chen, Jyh-Chien
;
Kuo, Yu-Ju
;
Tsao, Hsiang-Yen
;
Wu, Kuan-Yi
Novel conjugated polymers, PBPV-TPA, PBPV-CBZ, PBPV-MEH and PBPV-FLO, consisting of trifluoromethyl-substituted biphenyl (2,2'-bis(trifluoromethyl)biphenyl, CF3-BP) as the acceptor with various aromatic donors (triphenylamine TPA, carbazole CBZ, 2-(2-ethylhexyloxy)-5-methoxybenzene MEH and fluorene FLO, respectively) have been successfully synthesized. Their amorphous features, confirmed by wide-angle X-ray scattering, small-angle X-ray scattering and atomic force microscopy, are attributed to lateral side chains on the CBZ, MEH and FLO units, and the propeller geometry of the TPA unit. By integration of CF3-BPs into the polymer backbone, the ambipolarities and well-balanced charge mobilities of OFETs based on these polymers were successfully demonstrated. OFETs based on PBPV-FLO exhibit the highest hole mobility of 0.0152 cm(2) V-1 s(-1) and electron mobility of 0.0120 cm(2) V-1 s(-1). In addition, these OFETs also exhibit annealing-free characteristics and ambient stability. The OFET performance without encapsulation remained nearly unchanged in ambient conditions for up to 90 days. This could be attributed to the enhanced oxidative stability from their relatively deep HOMO energy levels and better moisture resistance from the trifluoromethyl substitution. Considering the ambipolar, annealing-free and ambient-stable properties of these CF3-BP-based amorphous conjugated polymers, the electron-accepting CF3-BP unit can be considered as a promising building block in preparing the easily processable conjugated polymers used in high-stability optoelectronic applications.
2,2 \'-Bis(trifluoromethyl)biphenyl as a building block for highly ambient-stable, amorphous organic field-effect transistors with balanced ambipolarity
(2016-01-01)
Chaing, Chi-Jui
;
Chen, Jyh-Chien
;
Kuo, Yu-Ju
;
Tsao, Hsiang-Yen
;
Wu, Kuan-Yi
Novel conjugated polymers, PBPV-TPA, PBPV-CBZ, PBPV-MEH and PBPV-FLO, consisting of trifluoromethyl-substituted biphenyl (2,2\'-bis(trifluoromethyl)biphenyl, CF3-BP) as the acceptor with various aromatic donors (triphenylamine TPA, carbazole CBZ, 2-(2-ethylhexyloxy)-5-methoxybenzene MEH and fluorene FLO, respectively) have been successfully synthesized. Their amorphous features, confirmed by wide-angle X-ray scattering, small-angle X-ray scattering and atomic force microscopy, are attributed to lateral side chains on the CBZ, MEH and FLO units, and the propeller geometry of the TPA unit. By integration of CF3-BPs into the polymer backbone, the ambipolarities and well-balanced charge mobilities of OFETs based on these polymers were successfully demonstrated. OFETs based on PBPV-FLO exhibit the highest hole mobility of 0.0152 cm(2) V-1 s(-1) and electron mobility of 0.0120 cm(2) V-1 s(-1). In addition, these OFETs also exhibit annealing-free characteristics and ambient stability. The OFET performance without encapsulation remained nearly unchanged in ambient conditions for up to 90 days. This could be attributed to the enhanced oxidative stability from their relatively deep HOMO energy levels and better moisture resistance from the trifluoromethyl substitution. Considering the ambipolar, annealing-free and ambient-stable properties of these CF3-BP-based amorphous conjugated polymers, the electron-accepting CF3-BP unit can be considered as a promising building block in preparing the easily processable conjugated polymers used in high-stability optoelectronic applications.
A Facile PDMS-Assisted Crystallization for the Crystal-Engineering of C-60 Single-Crystal Organic Field-Effect Transistors
(2015-08-05)
Wu, Kuan-Yi
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Wu, Tzu-Yi
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Chang, Shu-Ting
;
Hsu, Chain-Shu
;
Wang, Chien-Lung
A high-performance lithium-ion capacitor with carbonized NiCo2O4 anode and vertically-aligned carbon nanoflakes cathode
(2019-11-01)
Cheng, Chung-Fu
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Li, Xiang
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Liu, Kewei
;
Zou, Feng
;
Tung, Wei-Yao
Lithium ion capacitors (LICs) are energy storage devices integrating the complementary features of both supercapacitors and lithium ion batteries to simultaneously reach high energy and power densities. One of the major challenges in LIC technology is the kinetic imbalance between the faradaic insertion anode and capacitive cathode. Therefore, the design of electrode materials is crucial to enhance the rate performance of anode and the capacitance of the cathode in LIC devices. In this work, novel LICs were demonstrated with nanostructured cathode and anode. A vertically-aligned carbon nanoflakes (VACNFs) cathode provided high electrochemically active surface area and excellent conductivity, while a metal organic framework (MOF) derived carbonized nickel cobalt oxide (cNiCo(2)O(4)) anode ensured fast conversion reactions and remarkable cyclability. Electrochemical characterization of individual electrode confirmed that both electrodes exhibited good electron and ion transport capability. The LICs were fabricated with optimized electrode active materials loading to deliver high energy densities at desired charge/discharge rates. The devices exhibited energy density up to 136.9W h/kg (at 200 W/ kg). At higher power density of 40 kW/kg, under which a full charge-discharge can be finished within 4 s, the LICs could still deliver an energy density of 26.44W h/kg. The devices also showed a good cycle stability (approximate to 90% capacitance retention after 9000 cycles, under current density of 4 A/g) within the voltage range of 1-4.2 V.
A New sp2-sp2 Dialkylethylene-Bridged Heptacyclic Ladder-Type Arene for High Efficiency Polymer Solar Cells
(2013-04-01)
Wu, Jhong-Sian
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Lai, Yu-Ying
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Cheng, Yen-Ju
;
Chang, Chih-Yu
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Wang, Chien-Lung
A new dithienobenzo-carbazole (DTBC) heptacyclic arene using sp2-sp2 dialkylethylene moiety as the bridge was successfully synthesized by Suzuki-Miyaura cross-coupling reaction. This facile benzoannulation planarizes the conjugated framework with the concomitant introduction of four octyl substituents, making the newly designed copolymer PDTBCDTBT exhibit solution processability, superior absorption ability, lower-lying HOMO energy level, and crystalline nature. The solar cell using PDTBCDTBT has produced a high efficiency of 6.2%, which outperforms the corresponding sp3-hybridized C-bridged, Si-bridged and N-bridged analogous polymers.
A Supramolecular "Double-Cable" Structure with a 129(44) Helix in a Columnar Porphyrin-C-60 Dyad and its Application in Polymer Solar Cells
(2012-11-01)
Wang, Chien-Lung
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Zhang, Wen-Bin
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Sun, Hao-Jan
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Van Horn, Ryan M.
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Kulkarni, Rahul R.
A novel porphyrin-C-60 dyad (PCD1) is designed and synthesized to investigate and manipulate the supramolecular structure where geometrically isotropic [such as [60]fullerene (C-60)] and anisotropic [such as porphyrin (Por)] units coexist. It is observed that PCD1 possesses an enantiomeric phase behavior. The melting temperature of the stable PCD1 thermotropic phase is 160 degrees C with a latent heat (Delta H) of 18.5 kJ mol(-1). The phase formation is majorly driven by the cooperative intermolecular PorPor and C60C60 interactions. Structural analysis reveals that this stable phase possesses a supramolecular double-cable structure with one p-type Por core columnar channel and three helical n-type C-60 peripheral channels. These double-cable columns further pack into a hexagonal lattice with a = b = 4.65 nm, c = 41.3 nm, alpha = beta = 90 degrees and gamma = 120 degrees. The column repeat unit is determined to possess a 129(44) helix. With both donor (D; Pro) and acceptor (A; C-60) units having their own connecting channels as well as the large D/A interface within the supramoleculassr double-cable structure, PCD1 has photogenerated carriers with longer lifetimes compared to the conventional electron acceptor [6,6]-phenyl-C-61-butyric acid methyl ester. A phase-separated columnar morphology is observed in a bulk-heterojunction (BHJ) material made by the physical blend of a low band-gap conjugated polymer, [poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothia-diazole)] (PCPDTBT), and PCD1. With a specific phase structure in the solid state and in the blend, PCD1 is shown to be a promising candidate as a new electron acceptor in high performance BHJ polymer solar cells.
A Versatile Method to Enhance the Operational Current of Air-Stable Organic Gas Sensor for Monitoring of Breath Ammonia in Hemodialysis Patients
(2019-04-01)
Yu, Shang-Yu
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Tung, Tin-Wei
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Yang, Hong-Yu
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Chen, Guan-Yu
;
Shih, Che-Chi
Point-of-care (POC) application for monitoring of breath ammonia (BA) in hemodialysis (HD) patients has emerged as a promising noninvasive health monitoring approach. In this context, many organic gas sensors have been reported for BA detection. However, one of the major challenges for its integration with affordable household POC application is to achieve stable performance for accuracy and high operational current at low voltage for low-cost read-out circuitry. Herein, we exploited the stability of the Donor Acceptor polymer on the cylindrical nanopore structure to realize the sensors with a high sensitivity and stability. Then, we proposed a double active layer (DL) strategy that exploits an ultrathin layer of Poly(3-hexylthiophene-2,5-diyl) (P3HT) to serve as a work function buffer to enhance the operational current. The DL sensor exhibits a sustainable operational current of microampere level and a stable sensing response even with the presence of P3HT layer. This effect is carefully examined with different aspects, including vertical composition profile of DL configuration, lifetime testing on different sensing layer, morphological analysis, and the versatility of the DL strategy. Finally, we utilize the DL sensor to conduct a tracing of BA concentration in two HD patients before and after HD, and correlate it with the blood urea nitrogen (BUN) levels. A good correlation coefficient of 0.96 is achieved. Moreover, the feasibility of DL sensor integrated into a low-cost circuitry was also verified. The results demonstrate the potential of this DL strategy to be used to integrate organic sensor for affordable household POC devices.
Ambient-Stable, Annealing-Free, and Ambipolar Organic Field-Effect Transistors Based on Solution-Processable Poly(2,2 \'-bis(trifluoromethyl)biphenyl-alt-2,5-divinylthiophene) without Long Alkyl Side Chains
(2015-01-28)
Chiang, Chi-Jui
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Chen, Jyh-Chien
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Tsao, Hsiang-Yen
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Wu, Kuan-Yi
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Wang, Chien-Lung
An ambipolar conjugated polymer CF3-PBTV, poly(2,2-bis(trifluoromethyl)biphenyl-alt-2,5-divinylthiophene), consisting of thienylenevinylene as the donor and trifluoromethyl-substituted biphenyl as the acceptor has been successfully synthesized. CF3-PBTV shows solution-processability without electrically insulating long alkyl side chains. Grazing incidence X-ray diffraction results suggest a nearly equal population of flat-on and end-on domains in CF3-PBTV thin film. The excellent ambipolarity of CF3-PBTV is demonstrated by well-equivalent charge mobilities of 0.065 and 0.078 cm(2) V-1 s(-1) for p- and n-channel, respectively. The organic field-effect transistors (OFET) also shows very high on/off ratio (approximate to 10(7)) which is attributed to the relatively large bandgap and low-lying highest occupied molecular orbital (HOMO) of CF3-PBTV. The OFET performance barely changes after the device is stored in ambient conditions for 90 days. The ambient-stability is attributed to the enhanced oxidative stability from its low-lying HOMO and the better moisture resistance from its fluorine contents. The performance of CF3-PBTV based OFET is annealing independent. It is noteworthy that the solution-processable, ambipolar, and thienylenevinylene-containing conjugated polymer without any long alkyl side chains is reported for the first time. And to the best of our knowledge, it is the first ambient-stable, annealing-free OFET with well-equivalent ambipolarity.
An active guarding circuit for giga-hertz substrate noise suppression
(2007)
Chao, Hao-Ming
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Wang, Chien-Lung
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Wuen, Wen-Shen
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Wen, Kuei-Ann
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電子工程學系及電子研究所
This paper presents an active guarding circuit employing noise decoupling and inversion feedback for substrate noise suppression in high frequency up to GHz. Proposed inversion feedback circuit can efficiently suppress substrate noise up to GHz range by introducing a zero within an amplitude controller. The noise decoupling circuit not only provides a decoupling path, but also senses the noise level for the amplitude controller to perform noise cancellation. By applying the proposed active guarding circuit, the noise suppression of passive guard ring can be improved more than 14dB in the frequency range from DC to 1GHz and 7.2dB up to 5GHz. For 1dB degradation of noise suppression performance, the input noise level can be up to 90mV at 1MHz and 86mV at 1GHz, respectively.
Chemical mimicry of viral capsid self-assembly via corannulene-based pentatopic tectons
(2019-08-01)
Chen, Yu-Sheng
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Solel, Ephrath
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Huang, Yi-Fan
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Wang, Chien-Lung
;
Tu, Tsung-Han
Self-assembly of twelve pentatopic tectons, which have complementary edges or can be linked using either digonal or trigonal connectors, represents the optimal synthetic strategy to achieve spherical objects, such as chemical capsids. This process requires conditions that secure uninterrupted equilibria of binding and self-correction en route to the global energy minimum. Here we report the synthesis of a highly soluble, deca-heterosubstituted corannulene that bears five terpyridine ligands. Spontaneous self-assembly of twelve such tectons with 30 cadmium(II) cations produces a giant icosahedral capsid as a thermodynamically stable single product in high yield. Nuclear magnetic resonance (NMR) methods, mass spectrometry analyses, small-angle X-ray scattering, transmission electron microscopy, and atomic force microscopy indicate that this spherical capsid has an external diameter of nearly 6 nm and shell thickness of 1 nm, in agreement with molecular modeling. NMR and liquid chromatography evidences imply that chiral self-sorting complexation generates a racemic mixture of homochiral capsids.
Cofacial Versus Coplanar Arrangement in Centrosymmetric Packing Dimers of Dipolar Small Molecules: Structural Effects on the Crystallization Behaviors and Optoelectronic Characteristics
(2016-07-20)
Chou, Shu-Hua
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Kang, Hao-Wei
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Chang, Shu-Ting
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Wu, Kuan-Yi
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Bazan, Guillermo C.
Two D-pi-A-A molecules (MIDTP and TIDTP) composed of an electron-rich ditolylamino group (D) and an electron-deficient 5-dicyanovinylenylpyrimidine (A-A) fragment bridged together with indeno[1,2-b]thiophene (IDT) were synthesized. These molecules provide an opportunity to examine in-depth the impact of side-chain variations (methyl vs p-tolyl) on the crystallization behaviors, solid-state morphology, physical properties, and optoelectronic characteristics relevant for practical applications. X-ray analyses on single-crystal structures indicate that methyl-substituted MIDTP forms coplanar antiparallel dimers via C-H center dot center dot center dot S interactions and organizes into an ordered slip-staircase arrays. In contrast, p-tolyl-bearing TIDTP shows cofacial centrosymmetric dimers via pi-pi interactions and packs into a less-ordered layered structures. The X-ray diffraction analyses upon thermal treatment are consistent with a superior crystallinity of MIDTP, as compared to that of TIDTP. This difference indicates a greater propensity to organization by introduction of the smaller methyl group versus the bulkier p-tolyl group. The increased propensity for order by MIDTP facilitates the crystallization of MIDTP in both solution-processed and vacuum-deposited thin films. MIDTP forms solution-processed single-crystal arrays that deliver OFET hole mobility of 6.56 x 10(-4) cm(2) V-1 s(-1), whereas TIDTP only forms amorhpous films that gave lower hole mobility of 1.34 x 10(-5) cm(2) V-1 s(-1). MIDTP and TIDTP were utilized to serve as donors together with C-70 as acceptor in the fabrication of small-molecule organic solar cells (SMOSCs) with planar heterojunction (PHJ) or planar-mixed heterojunction (PMHJ) device architectures. OPV devices based on higher crystalline MIDTP delivered power conversion efficiencies (PCEs) of 2.5% and 4.3% for PHJ and PMHJ device, respectively, which are higher than those of TIDTP-based cells. The improved PCEs of MIDTP-based devices are attributed to better hole-transport character.
Concentration-dependent self-assembly structures of an amphiphilic perylene diimide with tri(ethylene glycol) substituents at bay positions
(2017-01-01)
Wang, Xin
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Zeng, Ting
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Nourrein, Mohamed
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Lai, Bo-Han
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Shen, Kaiwen
In this work, an amphiphilic perylene diimide (1,7-TEG-PDI-C12) that bears two hydrophilic triethylene glycol (TEG) chains at its bay position, and two hydrophobic dodecyl chains at its imide position was synthesized to identify the roles of concentration and H-bonding on the self-assembly morphology of the amphiphilic PDI. Since 1,7-TEG-PDI-C12 was prepared from the reaction of two bifunctional reactants, TEG and N, N'-bis(n-dodecyl)- 1,7-dibromo-perylene-3,4: 9,10-tetracarboxylic diimide, careful choices of solvent, base, and the stoichiometry of crown ether and base were found to be critical in reaching high reaction yield under mild conditions. TEM and SEM results revealed the abundant concentration-dependent self-assembly morphologies of 1,7-TEG-PDI-C12. Characterization results including UV-vis, fluorescence, NMR, IR and XRD analysis show that the formation of the self-assembled structure is a synergetic result of the intermolecular pi-pi interaction and H-bonding of 1,7-TEG-PDI-C-12.
Conformational Preferences and the Phase Stability of Fullerene Hexa-adducts
(2016-07-20)
Wu, San-Lien
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Hong, Chen-Yang
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Wu, Kuan-Yi
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Lan, Shih-Ting
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Hsieh, Chou-Ting
Molecular conformation and the assembly structure determine the spatial arrangements of the constituent units and the functions of a molecule. Although, fullerene hexa-adducts (FHAs) have been known as functional materials with great versatility, their conformational preferences and phase stability remain a complicate issue. By choosing bithiophene (T-2) and dodecyl bithiophene (C12T2) as the peripheral units of FHA, and using microscopic, scattering and diffraction characterizations, our study reveals how the intramolecular interaction and environmental stimulus affects the conformational preferences and phase stability of FHAs.
Control of preferred orientation with slow crystallization for carbon-based mesoscopic perovskite solar cells attaining efficiency 15%
(2017-01-14)
Tsai, Cheng-Min
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Wu, Guan-Wei
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Narra, Sudhakar
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Chang, Hung-Ming
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Mohanta, Nayantara
To produce mesoscopic carbon-electrode-based solar cells free of a hole-conduction layer, we developed a simple one-step drop-cast method (temperature 20 degrees C, relative humidity 50%) to grow uniform and compact perovskite nanocrystals via slow crystallization (SC). X-ray diffraction (XRD) results indicated that perovskite nanocrystals produced inside the mesoporous TiO2/Al2O3/C layers according to our SC approach with N-methyl-2-pyrrolidone (NMP) as a precursor solvent showed a preferred orientation at facet (004) with large crystalline grains, whereas those produced with other solvents or via thermal annealing (TA) methods showed greater intensity at facet (220) with small crystals. After the SC (NMP) procedure was completed, additional TA treatment would change the preferred orientation from (004) back to facet (220), which would break the connectivity and lose the uniformity of the crystals, causing the grains to become significantly smaller. Transient photoluminescence (PL) decay profiles of the SC devices made with four precursor solvents, NMP, g-butyrolactone (GBL), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), were recorded to show the trend of charge separation kinetics of the perovskite crystals inside the mesoporous films, which is consistent with the trend of the corresponding device performance showing the same order. The SC (NMP) device attained the best efficiency of power conversion (PCE), 15.0%, with average value (13.9 +/- 0.5%), which is much superior to those devices from either the traditional one-step TA (DMF) method (5.2 +/- 1.0%) or the traditional sequential TA method (10.1 +/- 0.7%). This work emphasizes the significance of the control of preferred orientation of perovskite nanocrystals using the SC approach, to obtain high-performance carbon-based mesoscopic solar cells with excellent reproducibility and stability.
Crystal Structure and Molecular Packing Behavior of Poly(2,3-diphenyl-1,4-phenylenevinylene) Derivatives Containing Alkyl Side-Chains
(2013-01-08)
Ren, Xiang-Kui
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Wu, Yu-Chun
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Wang, Shao-Jie
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Jiang, Shi-Dong
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Zheng, Jun-Feng
Phase behavior and crystal structure of a series of poly(2,3-diphenyl-5-alkyl-p-phenylenevinylene) (denoted as DPn-PPV, where n represents the carbon number of the alkyl side-chain, n = 6, 8, 10, 12) were studied using differential scanning calorimetry, one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction (WAXD), and selected area electron diffraction (SAED). The experimental results reveal that DPn-PPV exhibits one crystalline phase at low temperatures. On the basis of 2D WAXD and SAED patterns obtained from the oriented samples, the crystal structures are determined to be orthorhombic for DP6-PPV and monoclinic for DP8-PPV, DP10-PPV, and DP12-PPV. To account for the unusually large unit cell dimensions, we propose that the unit cell of DPn-PPV contains 4 chains (8 chemical repeat units). The complex crystal structure can be attributed to the longitudinal and transverse offsets between the neighboring chains, which shall be mainly due to the requirement of minimizing the steric hindrance caused by the attached pendent groups and maximizing the pi-pi interaction between the chains. The molecular packing scheme was simulated by using Cerius(2) software, of which the result agrees with the experimental data. The polarized UV-vis absorption and polarized solid-state photoluminescence (PL) property of these polymers was also investigated. The PL spectra indicated that the light emitted from the oriented film was preferentially polarized parallel to the shear direction, implying that DPn-PPV may potentially be useful in linearly polarized luminescence devices.
Crystal structure and molecular packing of an asymmetric giant amphiphile constructed by one C-60 and two POSSs
(2014-08-18)
Lin, Ming-Champ
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Hsu, Chih-Hao
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Sun, Hao-Jan
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Wang, Chien-Lung
;
Zhang, Wen-Bin
Based on our recent understanding and development of functionalized molecular nanoparticles (MNPs) as building blocks for constructing various giant molecules, we report our efforts on design and synthesis of an asymmetric giant amphiphile, diBPOSS-C-60, composed of one [60]fullerene (C-60) covalently linked with two isobutyl-functionalized polyhedral oligomeric silsesquioxane (BPOSS) MNPs. Its crystal structure and molecular packing were investigated. The compositional asymmetry between C-60 and BPOSS led to a "sandwich-layered" molecular packing scheme, where a single layer of C-60 is sandwiched between double BPOSS layers: a so-called "one-and-half-layered" structure. Within these layers, the molecules further organized into crystalline arrays. Interestingly, this compound can be viewed as size amplification of a class of atomically thin, two-dimensional layered transition metal dichalcogenides with the "one-and-half-layered" structure. 2014 Elsevier Ltd. All rights reserved.
Crystal structure and molecular packing of an asymmetric giant amphiphile constructed by one C-60 and two POSSs
(2014-08-18)
Lin, Ming-Champ
;
Hsu, Chih-Hao
;
Sun, Hao-Jan
;
Wang, Chien-Lung
;
Zhang, Wen-Bin
Based on our recent understanding and development of functionalized molecular nanoparticles (MNPs) as building blocks for constructing various giant molecules, we report our efforts on design and synthesis of an asymmetric giant amphiphile, diBPOSS-C-60, composed of one [60]fullerene (C-60) covalently linked with two isobutyl-functionalized polyhedral oligomeric silsesquioxane (BPOSS) MNPs. Its crystal structure and molecular packing were investigated. The compositional asymmetry between C-60 and BPOSS led to a "sandwich-layered" molecular packing scheme, where a single layer of C-60 is sandwiched between double BPOSS layers: a so-called "one-and-half-layered" structure. Within these layers, the molecules further organized into crystalline arrays. Interestingly, this compound can be viewed as size amplification of a class of atomically thin, two-dimensional layered transition metal dichalcogenides with the "one-and-half-layered" structure. 2014 Elsevier Ltd. All rights reserved.
Cylindrical micelles of a POSS amphiphilic dendrimer as nano-reactors for polymerization
(2018-02-21)
Weng, Jing-Ting
;
Yeh, Tso-Fan
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Samuel, Ashok Zachariah
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Huang, Yi-Fan
;
Sie, Jyun-Hao
A low generation amphiphilic dendrimer, POSS-AD, which has a POSS core and eight amphiphilic arms, was synthesized and used as a nano-reactor to produce well-defined polymer nano-cylinders. Confirmed by small-angle X-ray scattering (SAXS), Raman and NMR spectrometry, monodispersed cylindrical micelles that contain a hydrophilic cavity with a diameter of 2.09 nm and a length of 4.26 nm were produced via co-assembling POSS-AD with hydrophilic liquids, such as H2O and HEMA in hydrophobic solvents. Taking the HEMA/POSS-AD cylindrical micelles as nano-reactors, polymerization of HEMA within the micelles results in polymer nano-cylinders (POSS-AD NPs) with a diameter of 2.24 nm and a length of 5.02 nm. The study confirmed that despite the inability to maintain specific shape in solution, low generation dendrimers form well-defined nano-containers or nano-reactors, which relies on co-assembling with hydrophilic guest molecules. These nano-reactors are robust enough to maintain their shape during the polymerization of the guest molecules. Polymer nano-cylinders with dimensions less than 10 nm can thus be produced from the HEMA/POSS-AD micelles. Since the chemical structure of low-generation dendrimers and the contents of the co-assembled nano-reactors can be easily adjusted, the concept holds the potential for the further developments of low-generation amphiphilic dendrimers.
Directional Solution Coating by the Chinese Brush: A Facile Approach to Improving Molecular Alignment for High-Performance Polymer TFTs
(2017-09-13)
Lin, Fang-Ju
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Guo, Cheng
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Chuang, Wei-Tsung
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Wang, Chien-Lung
;
Wang, Qianbin
Directional solution coating by the Chinese brush provides a facile approach to fabricate highly oriented polymer thin films by finely controlling the wetting and dewetting processes under directional stress. The biggest advantage of the Chinese brush over the normal western brush is the freshly emergent hairs used, whose unique tapered structure renders a dynamic balance of the liquid within the brush by multiple forces when interacting with the liquid. Consequently, the liquid is steadily held within the brush without any unexpected leakage, making the liquid transfer proceed in a well-controllable manner. It is demonstrated that the Chinese brush coating enables the crystallization of the polymer and the self-assembly of conjugated backbones to proceed in a quasi-steady state via a certain direction, which is attributed to the controllable receding of the three-phase contact line during the dewetting process by the multiple parallel freshly emergent hairs. The as-prepared polymer thin films exhibit over six times higher charge-carrier mobility compared to the spin-coated films, which therefore provides a general approach for high-performance organic thin-film transistors.
Estimating Percent Crystallinity of Polyethylene as a Function of Temperature by Raman Spectroscopy Multivariate Curve Resolution by Alternating Least Squares
(2017-03-07)
Samuel, Ashok Zachariah
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Lai, Bo-Han
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Lan, Shih-Ting
;
Ando, Masahiro
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Wang, Chien-Lung
We have recently demonstrated a methodology to estimate the percent crystallinity (PC) of polymers directly with Raman spectroscopy and multivariate curve resolution (MCR) by alternating least-squares (ALS). In the MCR-ALS methodology, the Raman spectrum of a semicrystalline polymer is separated into two constituent components (crystalline and molten/amorphous) and their corresponding concentrations. The methodology necessitates that the Raman spectrum at any temperature be a linear combination of two MCR spectral components (one molten and one crystalline). This is true in the case of simple systems such as crystalline pendant alkyl domains in polymers (Samuel et al. Anal. Chem. 2016, 88, 4644). However, in the case of main chain polymer crystals (e.g., polyethylene), the situation can be complicated owing to several molecular changes in the lattice in addition to conformational reorganizations during melting. Under this circumstance, a simple two-state model may not be adequate and we describe the modifications required to treat such systems, keeping the basic principles of the proposed methodology unchanged. A comparative study with wide-angle X-ray scattering (WAXS) and Raman spectroscopy is also performed to substantiate our findings. In addition to estimating percent crystallinity (PC), our methodology is capable of revealing additional information, such as interchain interactions in crystal lattice, that in principle will help distinguishing polymorphic transformations, subtle changes in lamellar lattice dimensions, and other phase changes in polymers.