Tatsuhiko Nakano
Thermo Electron
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Featured researches published by Tatsuhiko Nakano.
Applied Spectroscopy | 1993
Tatsuhiko Nakano; Toru Yokoyama; Hirokazu Toriumi
This paper describes the advances in step-scan FT-IR time-resolved spectroscopy (TRS) and its application to the study of liquid crystal reorientation dynamics. The most important advantage of step-scan interferometry lies in the fact that the optical retardation of the interferometer is held constant during the sampling of interferogram elements, and consequently the spectral multiplexing is decoupled from the time dependence of data collection. This feature of step-scan interferometry allows us to perform both time-domain (one-dimensional time-resolved spectroscopy: 1D TRS) and frequency-domain (two-dimensional frequency correlation spectroscopy: 2D IR) dynamic experiments without the need to deconvolute the time dependence of the sample response from that of the data collection process. The design of the step-scan FT-IR spectrometer used in this study (Bio-Rad FTS60A/896), the experimental setup for 1D and 2D TRS measurements, and the results of a performance test are detailed. The FT-IR TRS techniques applied to the dynamic analysis of liquid crystals have revealed new information that enables us to penetrate into detailed sub-molecular mechanisms of the electrically induced liquid crystal reorientation. The results include the following: (1) 1D FT-IR TRS with microsecond time resolution has been able to follow the real-time transition dynamics of each individual functional group in the molecule; (2) 2D FT-IR TRS, capable of analyzing spatial and temporal correlations between reorientational motions of different sub-molecular segments, has shown that a flexible chain appended to a rigid core of the liquid crystalline molecule undergoes a fast local motion in addition to the rotational relaxation motion of the entire molecule; and (3) 2D frequency correlation analyses have been able to isolate a hidden absorption band and have suggested a possible assignment of this new band. It is emphasized that all these results have been obtained by taking the advantage of time-resolved spectroscopy that provides both temporal and spectral information simultaneously. The results presented in this paper should illustrate the potential applicability of FT-IR TRS to the study of a wide variety of time-dependent phenomena.
Applied Spectroscopy | 1993
Tatsuhiko Nakano; Shigeru Shimada; Rieko Saitoh; Isao Noda
Transient two-dimensional infrared (2D IR) correlation spectroscopy coupled with real-time Fourier transform infrared (RT FT-IR) measurement was used to analyze the reaction processes of photopolymerization systems. Unlike the previously developed 2D IR methods based on sinusoidally varying IR signals, a newly developed 2D correlation formalism applicable to transient spectroscopic signals having an arbitrary waveform was used. By this method, features associated with spectral intensity changes and peak shifts arising from polymerization reactions were clearly observed.
Applied Spectroscopy | 2000
Masashi Sonoyama; Tatsuhiko Nakano
Recently developed dynamic step-scan FT-IR spectroscopy combined with software-based digital signal processing (DSP) was applied for infrared rheo-optical measurements of isotactic polypropylene and regenerated Bombyx mori silk fibroin film undergoing sinusoidal mechanical strain. Comparative measurements of dynamic infrared spectra of polypropylene film using the DSP-based method and two lock-in amplifiers (LIAs) indicated that a high signal-to-noise ratio (SNR) advantage is attained by the DSP method compared with the LIA method. With the DSP technique, dynamic spectra of Bombyx mori silk fibroin film with high SNR were successfully recorded in the whole mid-infrared region in only 30 min. The dynamic spectra revealed that stress-induced dynamic reorientation in fibroin film is mainly localized in the segment with β-sheet conformation and is almost synchronous with the applied mechanical strain. Two-dimensional (2D) correlation analyses of the dynamic spectra showed that (1) the broad amide I band is resolved into three components whose positions are dependent on secondary structures, (2) the dynamic behavior of tyrosine residues was extracted by separation of the feature due to its aromatic side chains from the broad envelope of the amide I band in the 2D asynchronous map, and (3) the dynamic behavior of the amide A and B modes is the same as that of the amide II mode, when the mechanical strain is applied to fibroin film.
Journal of Electroanalytical Chemistry | 1997
Masatochi Osawa; Katsumasa Yoshii; Yu-ichi Hibino; Tatsuhiko Nakano; Isao Noda
Abstract Three advanced IR spectroscopy techniques, surface-enhanced IR absorption spectroscopy (SEIRAS), step-scan Fourier-transform interferometry, and two-dimensional (2D) IR correlation analysis, have been applied to the study of electrochemical reactions. A combined use of SEIRAS and step-scan interferometry enables time-resolved spectral monitoring of electrochemical reactions with time-resolutions ranging from microseconds to milliseconds. 2D-IR correlation analysis highlights the dynamic information obscured in the time-resolved spectra. The basic concept of 2D-IR is somewhat analogous to that of 2D-NMR, and synchronous and asynchronous obscured in spectra defined by two independent wavenumbers are generated by a correlation analysis of dynamic fluctuation of IR signals induced by a potential modulation. The synchronous and asynchronous spectra characterize the coherence and incoherence respectively of dynamic fluctuations of IR signals at two different wavenumbers. Bands arising from different transient species are clearly differentiated by their characteristic time-dependent behavior. The temporal relationship between the intensity fluctuations of different bands also becomes clear. From these data, deep insights into reaction processes are gained. The utilities of 2D-IR are demonstrated for the one-electron reduction of hyptylviologen at a silver electrode surface.
Applied Spectroscopy | 2006
Yuji Nishikawa; Tatsuhiko Nakano; Isao Noda
Attenuated total reflection (ATR) based dynamic compression modulation two-dimensional (2D) correlation studies of uniaxially drawn polyethylene terephthalate) (PET) films have been performed in combination with spectral simulation analysis by density functional theory (DFT). The dynamic 2D infrared (IR) correlation spectra in the region of the CCO stretching mode vibrations show four distinct correlation peaks located around 1290, 1265, 1248, and 1234 cm−1. These bands can be clearly assigned to the combination bands or coupling modes of the CH in-plane bend of the benzene ring or the CH2 deformation of the ethylene glycol unit, as well as CCO stretching vibrations, which are gauche conformers characteristic bands, by DFT analysis. The sequential analysis of 2D correlation data shows that, upon applying the dynamic compression, the response of the side chain regions (ester groups) occurs first, followed by that of the backbone regions (benzene rings). The ATR based dynamic compression modulation 2D correlation spectroscopy in combination with DFT analysis can be a powerful tool for various polymer characterizations.
Applied Spectroscopy | 2007
Yuji Nishikawa; Tatsuhiko Nakano; Isao Noda
Attenuated total reflection (ATR)-based dynamic compression modulation two-dimensional (2D) correlation study of poly(p-phenylene biphenyltetracarboximide) film is carried out in combination with spectral simulation analysis by density functional theory (DFT). The dynamic 2D infrared (IR) correlation spectra in the region of imide I (C=O stretching mode) show three distinct correlation peaks located around 1777, 1725, and 1708 cm−1. The band at 1708 cm−1 is the lower wavenumber shift component of 1777 or 1735 cm−1 peaks and is attributed to the results from intermolecular interactions, according to the DFT analysis. The 1708 cm−1 band also shows the largest dynamic response, suggesting that these intermolecular interactions may enhance the dynamic response. The dynamic 2D IR correlation spectra in the region of imide II (C–N–C axial stretching mode) vibrations also show three correlation peaks located around 1335, 1355, and 1370 cm−1, although the imide II band is shown to consist substantially of one component by the DFT analysis. These multiple peaks may be attributed to the compression-induced wavenumber shift of the band in the backbone structures. The sequential analysis of 2D correlation data show that, upon applying the dynamic compression, the response of the backbone regions (imide II) occurs first, followed by that of the side-chain regions (imide I, C=O).
Applied Spectroscopy | 2004
Yuji Nishikawa; Tatsuhiko Nakano; Hiroshi Miyauchi; Koichi Nishikida; Eric Y. Jiang
Dynamic compression modulation attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopic methods have been developed in this paper for characterizing polymer films. To obtain dynamic compression polarized ATR spectra, internal reflection element (IRE) secure assemblies made of tungsten carbide with very high hardness (Knoop hardness of >1000 kgf/mm2) have been designed. These assemblies are mounted on the Harrick Seagull® ATR attachment and measured by step-scan FT-IR spectroscopy. The effect of static compression, air gaps, and refractive index changes were examined. Experimental and simulated results showed that the effect of air gaps between the sample and IRE and refractive index changes of the sample and IRE are negligible at values larger than a static torque of 40 cN m and good signal-to-noise ratios (SNR) and reproducible data can be obtained. Uniaxially and biaxially drawn poly(ethylene terephthalate) films were measured by the presented method. Both bipolar and unipolar bands were observed in the dynamic in-phase ATR spectra, which can be associated with their micro-structural environmental changes. This technique shows promise in evaluating various polymer film materials, including biaxially oriented films, multilayer coated film surfaces, and molecular interactions between polymer–polymer and polymer–additives at the film surface.
Applied Spectroscopy | 2012
Yuji Nishikawa; Tatsuhiko Nakano; Isao Noda
An improved time-resolved soft-pulse dynamic compression attenuated total reflection (ATR) step-scan Fourier transform rheo-optical system has been developed. This system was used to observe reversible dynamic responses of poly(ethyleneterephthalate) (PET) and poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) films. In the case of PET, reversible nonlinear dynamic responses were observed in the C=O stretching vibration. The nonlinear responses decreased with decreasing compressive strain from 0.045 to 0.018. For the C–O stretching bands associated with the backbone structure of the PET, the nonlinear responses were very small. Characteristic burst-like reversible nonlinear dynamic responses can be seen in the in-phase and out-of-phase C=O stretching vibrations of cyclic imides, and phenyl ring deformation bands in the PDA parts of the BPDA-PDA. The results suggest the presence of inter-molecular interaction between C=O of cyclic imides and the phenyl ring groups of the PDA parts. The present method shows promise for characterizing a wide variety of polymeric materials, including polymer alloys, blends, composites, and copolymers and semicrystalline polymers.
Applied Spectroscopy | 2009
Yuji Nishikawa; Tatsuhiko Nakano; Isao Noda
A time-resolved soft-pulse dynamic compression attenuated total reflection (ATR) step-scan Fourier transform rheo-optical system has been developed. This system was used to observe different viscoelastic properties of polyethyleneterephthalate (PET) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx). Resonance features were observed in the dynamic compression ATR spectrum of PHBHx with 625 Hz soft-pulse frequency. In contrast, the dynamic compression ATR spectrum of PET showed no resonance features. The resonance feature of PHBHx was found at 1723 cm−1, which corresponds to the structural or morphological reorganization of a less ordered (Type II) crystalline form under compressive perturbation. The time-resolved evolution of infrared (IR) spectra was effectively analyzed by conventional generalized two-dimensional (2D) correlation analysis. The 2D-IR results indicate that the dynamic response of the well-ordered Type I crystalline state (1289 and 1261 cm−1) is faster than that of the Type II (1723, 1277, and 1228 cm−1). The present method shows promise for characterizing a wide variety of viscoelastic materials, including polymer alloys, blends, composites, and copolymers, and semicrystalline polymers.
Applied Spectroscopy | 2008
Yuji Nishikawa; Tatsuhiko Nakano; Isao Noda
An impulse-induced attenuated total reflection (ATR) based dynamic compression step-scan time-resolved Fourier transform rheo-optical system has been developed. This system was used to observe different viscoelastic properties of poly(ethylene terephthalate) (PET), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx), and carbon-black-filled polyester-polyamide blend. In the case of PET, almost no viscoelastic response extending beyond 15 ms was observed in the dynamic absorbance difference time domain spectrum. In contrast, PHBHx showed apparently different viscoelastic responses in the dynamic absorbance difference spectrum, especially in the C=O stretching band region. A long relaxation tail of the 1723 cm−1 band lasting about 2.7 milliseconds was clearly seen. The tail corresponds to the structural or morphological reorganization of a less ordered crystalline form (Type II) under compressive perturbation. The carbon-black-filled polyester–polyamide blend film also shows different viscoelastic response tails. In this case, the amide C=O stretching vibration band does not show distinct viscoelastic responses, suggesting that the polyamide component does not contribute much to the viscoelastic properties. The present method shows promise for characterizing a wide variety of viscoelastic materials, including polymer alloys, blends, composites, copolymers, and semicrystalline polymers.