Naoki Asakawa

Naoki Asakawa
Gunma University | Gundai · Division of Molecular Science

Ph.D.

About

117
Publications
5,723
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Introduction
I am working as PI at Emergent Polymer Science Lab, Gunma University, Japan. I am interested in realization of bio-inspired organic electronics devices using molecular dynamics. Plus, I am also interested in developments and application of noninvasive characterization using magnetic resonance spectroscopy to the devices.
Additional affiliations
August 2019 - present
Gunma University
Position
  • Professor
April 2009 - July 2019
Gunma University
Position
  • Professor (Associate)
October 2006 - March 2009
Osaka University
Position
  • Professor (Associate)

Publications

Publications (117)
Article
Stochastic resonance phenomenon was observed in organic field effect transistor using poly(3-hexylthiophene), which enhances performance of signal transmission with application of noise. The enhancement of correlation coefficient between the input and output signals was low, and the variation of correlation coefficient was not remarkable with respe...
Article
Reported is the observation of dark spin-dependent electrical conduction in a Schottky barrier diode with pentacene (PSBD) using electrically detected magnetic resonance at room temperature. It is suggested that spin-dependent conduction exists in pentacene thin films, which is explored by examining the anisotropic linewidth of the EDMR signal and...
Article
Full-text available
Spin-dependent space-charge-limited carrier conduction in a Schottky barrier diode using polycrystalline p-type π-conjugated molecular pentacene is explored using multiple-frequency electrically detected magnetic resonance (EDMR) spectroscopy with a variable-angle configuration. The measured EDMR spectra are decomposed into two components derived,...
Article
The application of noise to a nonlinear system can have the effect of increasing the signal transmission of the system through the phenomenon of stochastic resonance (SR). This paper presents an analytical characterization of the dependence of the signal transmission performance of an organic field-effect transistor (OFET) on external noise. Simila...
Article
Ferroelectric organic field-effect transistors (FE-OFETs) are fabricated to implement the functions of a neural synapse, including one-directional signal transmission and synaptic plasticity. Stochastic resonance (SR) experiments are conducted with FE-OFETs that use regioregular poly(3-hexylthiophene-2,5-diyl) as the semiconductor layer and poly(vi...
Article
A nuclear magnetic resonance (NMR) fingerprinting method for nanoscale phase-separated block copolymers (BCPs) consisting of hard and soft segments is introduced. The separation of 13C spectra is performed using 1H longitudinal relaxation time in rotating frame (T1ρH)-based ROSY (Relaxation Ordered SpectroscopY) method which uses an inverse Laplace...
Article
Full-text available
StochasticResonance(SR)isaphenomenoninwhichnoiseimprovestheperformanceofa system. With the addition of noise, a weak input signal to a nonlinear system, which may exceed its threshold, is transformed into an output signal. In the other words, noise-driven signal transfer is achieved. SR has been observed in nonlinear response systems, such as biolo...
Article
The results of electrically detected magnetic resonance (EDMR) experiments on organic Schottky barrier diode based on regioregular poly(3-hexylthiophene-2,5-diyl) [P3HT] are presented. The existence of positively charged trapped polarons and bipolaron formation pro- cess with mobile polarons of the same kind are responsible for the EDMR signal. Var...
Article
Stochastic resonance (SR) phenomenon is emerged in organic field effect transistors (OFETs) using $\pi$-conjugated polymer, where application of external noise to the OFET system enhances signal/information processing performance which is often found in biological systems.The channel conductivity of the OFET is slightly increased by spin-coating us...
Article
Pauli spin blockade associated with bipolaron formation from positively charged mobile and trapped polarons in a regioregular poly(3-hexylthiophene-2,5-diyl) (RR-P3HT) Schottky barrier diode is detected using electrically detected magnetic resonance (EDMR) spectroscopy. This is the first experimental observation of bipolaron formation from positive...
Article
A straightforward method for a variable frequency electron spin resonance/electrically detected magnetic resonance (ESR/EDMR) spectroscopy using a C-band microwave cavity equipped with waveguide windows is presented. The method enables us to perform quasi-continuous multiple resonance frequency (MF-ESR/EDMR) experiments for electronic devices. The...
Article
A control and utilizability of spatial fluctuations in polymer capacitors using immiscible bi- nary mixtures are described. The spatial flucuations for the device elements are of particular important for bioinspired multi-elemental network devices that is composed of elements with distributed electric property. Here we first report that spatial dis...
Article
Zeolite materials are used as solid acid catalysts in petrochemical reactions, which typically occur at Brønsted acid sites located at bridging hydroxyl groups (Si–OH–Al). These sites have been investigated spectroscopically, albeit at room temperature; a proper understanding requires that such data be acquired at actual reaction temperatures. The...
Article
A stochastic delay-derivative element (SDDE) using an immiscible polymer binary mixture of poly(L-lactic acid) with poly(ε-caprolactone) is fabricated, which is useful for a basic electronic component in a novel bioinspired signal/information processing device. Noise power spectral density(PSD) that is a Fourier transform of temporal correlation fu...
Conference Paper
Full-text available
We have tried to realize bio-inspired signal/information processing device using immiscible polymer binary mixture of poly(lactic acid)[PLLA] with poly(ε-caprolactone)[PCL]. First, we showed a fundamental properties that mimicked bio-inspired signal/information processing using both analog electric circuits and numerical simulations. Second, nano-t...
Research
Full-text available
This document written in Japanese language describes basic aspect of nuclear magnetic resonance, particularly conerning how to solve Liouville-von Neumann equation.
Article
Full-text available
A design of a bio-inspired signal/information processing device and the fabrication of a stochastic delay-derivative element (SDDE) using an immiscible polymer binary mixture of poly(L-lactic acid) with poly(ε-caprolactone) are described. A functional aspect of bio-inspired signal/information processing using both analogue electric circuits and num...
Article
Full-text available
Stochastic threshold devices using a trap-filling transition (TFT) coupled with molecular dynamics in poly(3-alkylthiophene)s were fabricated as potential key devices for noise-driven bioinspired sensors and information processors. This article deals with variable-temperature direct current conductivity and alternating current impedance measurement...
Article
Full-text available
Stochastic threshold devices using trap-filling transition coupled with molecular dynamics in poly(3-alkyl thiophene)s [P3ATs] were fabricated as potential key devices for noise-driven bio-inspired sensors and information processors. This article deals with variable-temperature direct current conductivity and alternating current impedance measureme...
Article
Proton-exchanged Y zeolite (H–Y zeolite) has two types of bridging hydroxyl groups; one exists in the supercage and the other exists in the sodalitecage. The dynamic property of protons due to these hydroxyl groups was investigated by variable temperature 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR). Proton exchange between two t...
Article
The influence of temperature on the 1H chemical shift due to hydroxyl groups in H+-exchanged any kind of zeolites (ZSM-5 type zeolites including silicalite, mordenite and Y zeolites) was examined by variable temperature 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR) spectroscopy measured from 298 to 673 K. The 1H chemical shifts du...
Article
Two applications of quasi-static magnetic field gradients in nuclear magnetic resonance spectroscopy are discussed. The first application is conformon transport in the quasi-ordered pi-conjugated polymer, poly(4-methylthiazole-2,5-diyl). With the assistance of proton longitudinal relaxation (R-1) dispersion measurements of the powdered polymer samp...
Article
The molecular structure and dynamics of regioregulated poly(3- butylthiophene)(P3BT) and poly(3-hexylthiophene) (P3HT) were investigated using Fourier transfer infrared spectroscopy and high-resolution solid-state 13C nuclear magnetic resonance (NMR). For P3BT, a "twist glass transition", which is the glass transition of the thiophene ring twist in...
Article
Spinel ferrite oxides doping non-magnetic ions show the photo-induced magnetization (PIM) effect at high temperature [1-3]. Such a magnetization enhancement by light irradiation is a unique property in this material. In order effectively to use the PIM effect and precisely to control the magnetism, direct light-emission from light-emitting element...
Article
Stochastically excitable threshold units using functional materials will potentially be among the key devices for the production of noise-driven bio-inspired sensors and information processors with ultra-low energy consumption. In particular, a noise generator and threshold unit will be able to be fabricated utilizing the fluctuations found in mate...
Article
It is reviewed that through the observation of solid-state 13C NMR chemical shift, the main-chain conformation and hydrogen-bonded structure of peptides, polypeptides and proteins in the solid state have been successfully elucidated, and the combination of solid state 13C NMR and chemical shift calculation by quantum chemistry is a powerful means f...
Article
Full-text available
We demonstrated signal transmission using the nonlinearity of VO2 in the manner of stochastic resonance (SR). A correlated insulator state of VO2 changes nonlinearly to a metallic state when an applied bias voltage increases beyond a threshold. The transition of the states between insulator and metal is adaptable to the SR theory. In this study, th...
Article
The molecular structure and dynamics of regioregulated poly(3-hexylthiophene) (P3HT) were investigated using high-resolution solid-state (13)C nuclear magnetic resonance (NMR) and optical absorption spectroscopies. A crystal (C)-plastic crystal (PC) transition induced by the molecular motion of the aliphatic side group was observed for P3HT in the...
Article
A compositional graded film of poly(ε-caprolactone) (PCL) with 4,4'-thiodiphenol (TDP), in the film thickness direction, was fabricated by self-diffusing of TDP in the PCL melt. We found out the self-bending deformation of the gradient film, which bent into a rolled-up shape by itself. The initial shape of the film was flat when the sample was quen...
Article
We study effects of trehalose on the swelling behavior of hydrogel, exemplified here by agarose. Its volume increase on immersion into water is suppressed in the presence of disaeeharides, the extent of which lies in the order, sucrose < maltose < trehalose. Such tendency is attributable to the relatively higher hydration ability of trehalose.
Article
Full-text available
Problems with artificial neural networks originate from their deterministic nature and inevitable prior learnings, resulting in inadequate adaptability against unpredictable, abrupt environmental change. Here we show that a stochastically excitable threshold unit can be utilized by these systems to partially overcome the environmental change. Using...
Article
Full-text available
We have investigated cooperative dynamics of an artificial stochastic resonant system, which is a recurrent ring connection of neuron-like signal transducers (NST) based on stochastic resonance (SR), using electronic circuit experiments. The ring showed quasi-periodic, tunable oscillation driven by only noise. An oscillation coherently amplified by...
Article
Solid-state structures of regioregulated poly(3-hexylthiophene) (P3HT) and poly(3-butylthiophene) (P3BT) were investigated using Fourier transform infrared absorption (FT-IR) spectroscopy. This study revealed that a twist glass transition of thiophene twisting for P3HT exists around 300 K ( T gp). Additionally, the influence of annealing on populat...
Article
Full-text available
Room-temperature-photoinduced magnetization (PIM) was observed in spinel ferrite Al0.2Ru0.8Fe2O4 thin films with a spin-cluster-glass structure. Additionally, the films exhibited significant properties as spintronic materials, showing a low saturation magnetization under 0.6μB/unit cell and good conductivity with a high spin polarized electron leve...
Article
Full-text available
A study was conducted to determine the dynamic structure of regio-regulated head-to-head HH-P4MeTz by differential scanning calorimetry (SDC) and NMR. The study synthesized regio-regulated polyheterocylic through dehalogenative organometallic polycondensation. The study stated that the physical properties showed by HH-P4MeTz differ from other P4RTz...
Article
A mechanism for the generation of the compositional gradient along the long axis for poly(ε-caprolactone) (PCL)/poly(ethylene oxide) (PEO) blend under uniaxial thermal gradient was proposed by observations of the convection of polymer using graphite powder as a visual probe. The convection under the thermal gradient promoted the transfer of PCL int...
Article
Full-text available
Compositionally graded bulk materials of organic polymer blends were prepared by using non-equilibrium self-organization processes with a uniaxial thermal gradient (Bridgman method). The Bridgman method was firstly applied to prepare two kinds of polymeric compositionally graded materials: a polymer/low molecular weight additive system (poly(e-capr...
Article
This chapter reports a selection of recent publications on the application of nuclear shielding, related NMR chemical shifts and NMR lineshapes, which have been published from 1 June 2011 to 31 May 2012. The number of the papers in this field is rapidly increasing, covering practically all magnetically active nuclei. Therefore, a selection of relat...
Article
Full-text available
The molecular structure and dynamics of regioregulated poly(3-butylthiophene) (P3BT), poly(3-hexylthiophene)(P3HT), and poly(3-dodecylthiophene) (P3DDT) were investigated using Fourier transform infrared absorption (FTIR), solid state 13 C nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC) measurements. In the DSC measure...
Article
New five-membered ring π-conjugated polymers composed of 2,2′-bithiophene and 4,4′-dialkyl-2,2′-bithiazole units were prepared. The polymers were soluble in 1,2-dichlorobenzene and showed a UV–vis peak at about 490nm above 120°C. Cooling the solution led to the appearance of new UV–vis peaks at 550 and 600nm, which were considered to originate from...
Article
Poly(epsilon-caprolactone) (PCL)/chitin and PCL/chitosan blend films with compositional gradients were successfully fabricated by a dissolution/diffusion method; that is, repeatedly pouring the PCL/chitin (or PCL/chitosan) blend solutions, with variable composition, onto polysaccharide layers. The compositional gradient structure in the resulting f...
Article
The crystalline structure of biodegradable poly(3-hydroxypropionate) (PHP) has been found to quite depend on the molecular weight (MW) and crystallization conditions. In particular, a new crystal form (the δ-form) has been successfully prepared by casting and optimal melt-crystallizing the low-MW PHP. The overwhelming growth of the δ-form in the ca...
Article
A biodegradable, immiscible poly(butylenes adipate-co-butylenes terephthalate) [P(BA-co-BT)]/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film-thickness direction has been successfully prepared in the presence of a low-molecular-weight compound 4,4′-thiodiphenal (TDP), which is used as a miscibility-enhancing age...
Article
Full-text available
Dynamics of Yamamoto-type poly(p-phenylene)[PPP] was investigated by differential scanning calorimetry(DSC) and proton solid-state NMR relaxation spectroscopy. The DSC chart shows the baseline jump without latent heat at 295K, which is due to the glass transition of the polymer. From the variable temperature proton longitudinal relaxation time(T1)...
Article
Using wide-angle X-ray diffraction, high-resolution solid-state 13C NMR (SNMR), attenuated total reflection infrared (ATR/IR), and Fourier transform infrared (FTIR) spectrometry, we investigated the crystalline structure and morphology of melt-crystallized poly(3-hydroxypropionate)s (PHPs). The melt-crystallization of the β-form crystal and that of...
Article
A new crystal morphology (6 form) of poly(3-hydroxypropionate) (PHP) is found in cast and melt-crystallized PHPs with low molecular weight, in which the PHP chains possibly adopt a 2(1) helix rather than the trans conformation found in the beta or gamma form. The fusion temperature- and the crystallization temperature-dependent polymorphism are res...
Article
This article describes the relationships between not only comonomer-unit compositions but also their distributions and structures as well as properties for bacterial copoly(hydroxyalkanoate)s, including poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxy-propionate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(...
Article
Lattice diffusion and internal local magnetic field gradients in solids are investigated by numerical simulation of nuclear mangetic resonance(NMR) spin echo experiments. The Fourier-spectrum method is employed in order to solve the Bloch-Torrey equation with arbitrary magnetic field gradients in one- and two-dimensional lattice restrictions.
Article
Biodegradable poly(butylene succinate) (PBS)/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film thickness direction was prepared using a method of interdiffusion across the interface between the PBS and PEO layers at a temperature above the melting points of both the component polymers. The miscibility between PBS...
Article
The dynamics of regioregulated poly(4-methylthiazole-2,5-diyl) (HH-P4MeTz) was investigated by solid-state H1,D2 , and C13 NMR spectroscopies, and differential scanning calorimetry (DSC) measurements. DSC, D2 quadrupolar echo NMR, C13 cross-polarization and magic-angle spinning (CPMAS) NMR, and two-dimensional spin-echo CPMAS NMR spectroscopy sugge...
Article
Nuclear magnetic resonance(NMR) spectroscopy under inhomogeneous magnetic field is one of promising nondestructive methods for investigating transport phenomena. In solids the diffusion coefficient can often be small and a local internal MFG, which in some cases heterogeneous and/or anisotropic, can be remained, resulting in the crucial limiting fa...
Article
The dynamics of regioregulated poly(4-methylthiazole-2,5-diyl) [HH-P4MeTz] was investigated by solid-state 1H, 2D, 13C NMR spectroscopies, and differential scanning calorimetry(DSC) measurements. DSC, 2D quadrupolar echo NMR, 13C cross-polarization and magic-angle spinning(CPMAS) NMR, and 2D spin-echo CPMAS NMR spectroscopy suggest existence of a q...
Article
The effect of lignin fine powder, as a new kind of nucleating agent, on the crystallization process of poly(3-hydroxybutyrate) (PHB) was studied. The kinetics of both isothermal and nonisothermal crystallization processes from the melt for both pure PHB and PHB/lignin blend was studied by means of differential scanning calorimetry. Lignin shortened...
Article
Miscibility and hydrogen bonding interaction have been investigated for the binary blends of poly(butylene adipate-co-44 mol % butylene terephthalate)[P(BA-co-BT)] with 4,4'-thiodiphenol (TDP) and poly(ethylene- oxide)(PEO) with TDP; and the ternary blends of P(BA-co-BT)/PEO/TDP by differential scanning calorimetry (DSC) and Fourier transform infra...
Article
The effect of intermolecular hydrogen bonding on the crystallization kinetics and the morphology of poly(ε-caprolactone) (PCL)/4,4‘-thiodiphenol (TDP) blends with TDP content 0−20 wt % has been investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray measurements, and in situ FT-IR. The equilibrium melting point ( ) o...
Article
A novel method for accurate determination of small chemical shielding anisotropy (CSA) of the solid state nuclear magnetic resonance is described. The method is based on the adiabatically ramped spin-locking of transverse magnetization. The equation for the time evolution of the spin dynamics for a system on the presence of chemical shielding and t...
Article
The comonomer-unit compositions and their distribution of as-produced bacterial copolyesters, including poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxy-butyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are described in this paper. Each copolyester sample can...
Article
This paper describes two topics concerned with anisotropic molecular diffusion in a single crystal of stearic acid (SA) and measurements of local magnetic field gradient (MFG) in a powdered film of regio-regulated poly(4-methylthiazole-2,5-diyl)(HH-P4MeTz) by 1H transverse relaxation time measurements with two pulse Hahn-echo (TPHE) and Carr–Purcel...
Article
The miscibility and phase behavior of poly(ethylene oxide) (PEO) blends with poly(3-hydroxybutyrate) (P(3HB)), poly(3-hydroxypropionate) (P(3HP)), and poly(3-hydroxybutyrate-co-3-hydroxypropionate)s (P(3HB-co-3HP)s) have been investigated by differential scanning calorimetry (DSC) and high-resolution solid-state 13C nuclear magnetic resonance (NMR)...
Article
The effects of low molecular weight compounds with hydroxyl groups on the properties of poly(L-lactic acid) (PLLA) were investigated. The specific interaction between PLLA and 4,4′-thiodiphenol (TDP) was investigated by Fourier transform IR spectroscopy. The spectra of the blends suggested that there were interassociated hydrogen bonds between the...
Article
FTIR spectra were obtained for several different states of trehalose including dihydrate crystal, anhydrous form II (designated by Gil, A. M.; Belton, P. S.; Felix V. Spectrochim. Acta 1996, A52, 1649-1659), anhydrate crystal, dried melt, amorphous solid and aqueous solution. From the observation of the symmetric and antisymmetric stretch vibration...
Article
Blend films of poly(L-lactide) (PLLA) and poly(vinyl alcohol) (PVA) were obtained by evaporation of hexafluoroisopropanol solutions of both components. The component interaction, crystallization behavior, and miscibility of these blends were studied by solid-state NMR and other conventional methods, such as Fourier transform infrared (FTIR) spectra...
Article
Bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxypropionate) [P(3HB-co-3HP)] samples were compositionally fractionated using solvent/nonsolvent fractionation techniques. Binary blends between these compositionally fractionated P(3HB-co-3HP) samples, with much narrower comonomer compositional distribution, were prepared, and their thermal...
Article
We propose an integrated MOZYME + DFT method for calculation of the pKa values of ionizable residues in a protein. The method is applied to two protein systems, bacteriorhodopsin (bR) and ribonuclease T1. It is shown that the present method reproduces the experimental pKa values of several targeted residues better than other conventional methods. T...
Article
The crystalline structural changes of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with narrow compositional distribution were investigated. The investigations were performed using differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). The degree of crystallinity obtained by WAXD was observed to be almost cons...
Article
The formation of the inter-associated hydrogen bond between poly(ε-caprolactone) (PCL) and 4,4′-thiodiphenol (TDP) was investigated as a function of composition and temperature by temperature-variable Fourier transform infrared spectroscopy. It was found that the fractions of associated carbonyl groups in PCL/TDP blends increased with the increase...
Article
The specific interactions between several low-molecular-weight diamino compounds and poly(ε-caprolactone) (PCL) have been investigated by FT-IR. It was found that PCL and 3,3′-diaminodiphenylmethane (3,3′-DADPM) interact through strong intermolecular hydrogen bonds in the blend. Thermal and mechanical properties of PCL/3,3′-DADPM blends were invest...
Article
The comonomer compositional distribution and thermal and morphological characteristics were investigated for five bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] samples with 3HV content of 45, 49, 70, 80, and 96 mol %. All these samples were fractionated into many fractions with widely different 3HV content by...
Article
The specific interaction between poly(3-hydroxybutyrate) [P(3HB)] and 4,4′-thiodiphenol (TDP) and between poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and TDP was investigated by Fourier transform infrared (FTIR) spectroscopy. Interassociated hydrogen bonds were found between the polyester chains and the TDP molecules in the binary blends. T...
Article
The solid-phase structure and biodegradability were investigated for a series of binary blends of bacterial poly(3-hydroxybutyrate) with chemosynthetic poly(butylene succinate-co-butylene adipate) (PBSA) and poly(butylene succinate-co-ε-caprolactone) (PBSC) prepared via compression molding of solution cast films. By high-resolution solid-state 13C...