20 research outputs found

    Neural-network quantum state study of the long-range antiferromagnetic Ising chain

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    We investigate quantum phase transitions in the transverse field Ising chain with algebraically decaying long-range antiferromagnetic interactions by using the variational Monte Carlo method with the restricted Boltzmann machine being employed as a trial wave function ansatz. In the finite-size scaling analysis with the order parameter and the second R\'enyi entropy, we find that the central charge deviates from 1/2 at a small decay exponent αLR\alpha_\mathrm{LR} in contrast to the critical exponents staying very close to the short-range (SR) Ising values regardless of αLR\alpha_\mathrm{LR} examined, supporting the previously proposed scenario of conformal invariance breakdown. To identify the threshold of the Ising universality and the conformal symmetry, we perform two additional tests for the universal Binder ratio and the conformal field theory (CFT) description of the correlation function. It turns out that both indicate a noticeable deviation from the SR Ising class at αLR<2\alpha_\mathrm{LR} < 2. However, a closer look at the scaled correlation function for αLR2\alpha_\mathrm{LR} \ge 2 shows a gradual change from the asymptotic line of the CFT verified at αLR=3\alpha_\mathrm{LR} = 3, providing a rough estimate of the threshold being in the range of 2αLR<32 \lesssim \alpha_\mathrm{LR} < 3

    Synthesis and Characterization of [Poly(3-dodecylthiophene)]<sub>2</sub>Poly(methyl methacrylate) Miktoarm Star Copolymer

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    We have introduced a facile synthetic route for well-defined [poly­(3-dodecylthiophene)]<sub>2</sub> poly­(methyl methacrylate) miktoarm star copolymer (P3DDT<sub>2</sub>PMMA) by using a click reaction. For this purpose, PMMA with two ethynyl groups (PMMA-(≡)<sub>2</sub>) and ω-azidopropyl-P3DDT were synthesized. We found that the use of alkyl linker (here, propyl group) between P3DDT and azido group is very essential to minimize the steric hindrance arising from bulky side group in P3DDT during the click reaction. When we employed a slightly excess amount of the ω-azidopropyl-P3DDT, we obtained a well-defined P3DDT<sub>2</sub>PMMA with a narrow molecular weight distribution (polydispersity index <1.20) after selective removal of the unreacted ω-azidopropyl-P3DDT in a crude product by using column chromatography. We also investigated self-assembled structure of P3DDT<sub>2</sub>PMMA by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). P3DDT<sub>2</sub>PMMA with weight fraction of P3DDT block (<i>w</i><sub>P3DDT</sub>) of 0.33 had lamellar microdomains, while a linear diblock copolymer (P3DDT-<i>b</i>-PMMA) with <i>w</i><sub>P3DDT</sub> = 0.37 showed cylindrical microdomains. Also, P3DDT<sub>2</sub>PMMA with <i>w</i><sub>P3DDT</sub> = 0.59 showed the HEX cylindrical microdomains of PMMA in the P3DDT matrix, whereas P3DDT-<i>b</i>-PMMA with <i>w</i><sub>P3DDT</sub> = 0.56 exhibited lamellar microdomains. More interestingly, P3DDT<sub>2</sub>PMMA with <i>w</i><sub>P3DDT</sub> of 0.76 showed hexagonally packed PMMA cylinders in the P3DDT matrix at molten state, and this morphology was maintained even after crystallization of the P3DDT block. This behavior is quite different from linear P3DDT-<i>b</i>-PMMA diblock with the same weight fraction of P3DDT because the latter shows fibril structures after P3DDT crystallization. These results imply that controlling the molecular architecture is an effective way to tune the morphology of P3AT-containing block copolymers

    Synthesis and self-assembly of amphiphilic and biocompatible poly(vinyl alcohol)-block-poly(l-lactide) copolymer

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    Well-defined amphiphilic and biocompatible poly(vinyl alcohol)block-poly(L-lactide) copolymers (PVA-b-PLLA) were synthesized by the combination of reversible addition-fragmentation chain transfer (RAFT), ring opening polymerization (ROP), and click chemistry. First, an innovative azide-functionalized xanthate mediated chain transfer agent (CTA) [S-(3-azidopropyl propanamide)-(O-butyl xanthate)] was synthesized and used for vinyl acetate (VAc) polymerization through RAFT. Then, azide-terminated poly(vinyl acetate) (azide-PVAc) was converted to the corresponding azide-terminated poly(vinyl alcohol) (azide-PVA) through hydrolysis. Alkyne-terminated poly (L-lactide) (alkyne-PLLA) was synthesized via ROP using a bifunctional initiator, having an alkyne and a hydroxyl group. Finally, azide-PVA and alkyne-PLLA were coupled by 1,3 cycloaddition click reaction to get PVA-b-PLLA. Synthesized azide-PVAc, azide-PVA, alkyne-PLLA and PVA-b-PLLA were characterized by size exclusion chromatography and H-1 NMR spectroscopy. The self-assembly of PVA-b-PLLA in water was investigated by transmission electron microscope, atomic force microscopy, dynamic light scattering and H-1 NMR spectroscopy. Spherical micelles in water were clearly observed. The critical micelle concentration of PVA-b-PLLA in water was determined by fluorescence spectroscopy, and it was decreased with increasing the molecular weight of PLLA block. PVA-b-PLLA exhibited low cytotoxicity which could be used in biomedical application. (C) 2016 Elsevier Ltd. All rights reserved.1142sciescopu

    Improvement of power conversion efficiency of P3HT:CdSe hybrid solar cells by enhanced interconnection of CdSe nanorods via decomposable selenourea

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    We introduce a novel method to improve the device performance of P3HT: CdSe hybrid solar cells by using selenourea (SeU) for ligand exchange. SeU induces interconnection of CdSe nanorods in the nanoscale range without severe aggregation. The power conversion efficiency of the devices with SeU is improved from 1.71% to 2.63% due to efficient charge transport through interconnected CdSe nanorods.N

    Improvement of power conversion efficiency of P3HT:CdSe hybrid solar cells by enhanced interconnection of CdSe nanorods via decomposable selenourea

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    We introduce a novel method to improve the device performance of P3HT: CdSe hybrid solar cells by using selenourea (SeU) for ligand exchange. SeU induces interconnection of CdSe nanorods in the nanoscale range without severe aggregation. The power conversion efficiency of the devices with SeU is improved from 1.71% to 2.63% due to efficient charge transport through interconnected CdSe nanorods.X111111sciescopu

    Air-stable inverted structure of hybrid solar cells using a cesium-doped ZnO electron transport layer prepared by a sol-gel process

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    We have developed an air-stable inverted structure of poly(3-hexylthiophene) (P3HT) : cadmium selenide (CdSe) hybrid solar cells using a cesium-doped ZnO (ZnO:Cs) electron transport layer. The ZnO:Cs layer was simply prepared at low temperature by the sol-gel process using a ZnO solution containing cesium carbonate (Cs2CO3). With increasing Cs-doping concentration, the conduction band edge of ZnO is decreased, as confirmed by scanning Kelvin probe microscopy. The energy level of ZnO: Cs is effective for electron transport from CdSe. Consequently, the power conversion efficiency (PCE) of the inverted P3HT : CdSe hybrid solar cells using the ZnO: Cs electron transport layer is 1.14%, which is significantly improved over that (0.43%) of another device without Cs. X-ray photoelectron spectroscopy analysis revealed that the amount of CdSe on the substrate (or the bottom surface) is larger compared with the air (or top) surface regardless of the P3HT : CdSe weight ratio. The vertically inhomogeneous distribution of CdSe in the hybrid solar cells gives better charge transport from CdSe to ZnO:Cs in the inverted structure of the device compared with that in the normal structure. As a result, the inverted hybrid solar cell consisting of 1 : 4 (wt/wt) P3HT : CdSe shows the best efficiency, while the best efficiency of a normal hybrid solar cell is achieved at 1 : 9 (wt/wt) P3HT : CdSe.N
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