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Gunsik Park - One of the best experts on this subject based on the ideXlab platform.

  • Dielectric Relaxation change of water upon phase transition of a lipid bilayer probed by terahertz Time domain spectroscopy
    Journal of Chemical Physics, 2012
    Co-Authors: Dahye Choi, Heyjin Son, Seonghoon Jung, Jaehun Park, Woongyang Park, Oh Sang Kwon, Gunsik Park
    Abstract:

    We investigate the influence of the 1, 2-ditetradecanoyl-sn-glycero-3-phosphocholine lipid bilayer phases on the water reorientation dynamics with terahertz Time domain spectroscopy. The phase of the lipids was controlled by the temperature in the range of 14–35 °C. During the gel-to-fluid phase transition, the hydration water ratio drastically changed from 0.3 to 0.6. The absorption coefficient of the hydration water increased with the temperature in the gel phase and then decreased in the fluid phase. The Dielectric Relaxation Time of the lipid solution decreased initially but then increased after the phase transition. This indicates that the hydration water reorientation dynamics are restricted by lipids and that this phenomenon is pronounced in a biologically relevant fluid phase.

R J Sengwa - One of the best experts on this subject based on the ideXlab platform.

  • effects of plasticizer and nanofiller on the Dielectric dispersion and Relaxation behaviour of polymer blend based solid polymer electrolytes
    Current Applied Physics, 2015
    Co-Authors: R J Sengwa, Priyanka Dhatarwal, Shobhna Choudhary
    Abstract:

    Abstract Solid polymer electrolytes consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend (50:50 wt/wt%) with lithium triflate (LiCF 3 SO 3 ) as a dopant ionic salt at stoichiometric ratio [EO + (C O)]:Li +  = 9:1, poly(ethylene glycol) (PEG) as plasticizer (10 wt%) and montmorillonite (MMT) clay as nanofiller (3 wt%) have been prepared by solution cast followed by melt–pressing method. The X–ray diffraction study infers that the (PEO–PMMA)–LiCF 3 SO 3 electrolyte is predominantly amorphous, but (PEO–PMMA)–LiCF 3 SO 3 –10 wt% PEG electrolyte has some PEO crystalline cluster, whereas (PEO–PMMA)–LiCF 3 SO 3 –10 wt% PEG–3 wt% MMT electrolyte is an amorphous with intercalated and exfoliated MMT structures. The complex Dielectric function, ac electrical conductivity, electric modulus and impedance spectra of these electrolytes have been investigated over the frequency range 20 Hz to 1 MHz. These spectra have been analysed in terms of the contribution of electrode polarization phenomenon in the low frequency region and the dynamics of cations coordinated polymer chain segments in the high frequency region, and also their variation on the addition of PEG and MMT in the electrolytes. The temperature dependent dc ionic conductivity, Dielectric Relaxation Time and Dielectric strength of the plasticized nanocomposite electrolyte obey the Arrhenius behaviour. The mechanism of ions transportation and the dependence of ionic conductivity on the segmental motion of polymer chain, Dielectric strength, and amorphicity of these electrolytes have been explored. The room temperature ionic conductivity values of the electrolytes are found ∼10 −5  S cm −1 , confirming their use in preparation of all-solid-state ion conducting devices.

  • Dielectric properties of montmorillonite clay filled poly vinyl alcohol poly ethylene oxide blend nanocomposites
    Composites Science and Technology, 2010
    Co-Authors: R J Sengwa, Shobhna Choudhary, Sonu Sankhla
    Abstract:

    Abstract Organic–inorganic nanocomposites of poly(vinyl alcohol) (PVA)–poly(ethylene oxide) (PEO) blend filled with montmorillonite (MMT) nanoclay up to 10 wt.% concentration were synthesized by aqueous solution-cast technique. The complex Dielectric function, electrical conductivity, electric modulus and impedance spectra of the nanocomposites were measured in the frequency range 20 Hz–1 MHz at ambient temperature. A direct correlation was observed between the real part of Dielectric function and the mean Relaxation Time of the polymer chain segmental dynamics, with the exfoliated and intercalated MMT clay structures, and the extent of miscibility between PVA and PEO due to hydrogen bonded bridging through exfoliated MMT clay nanosheets. The large increase of Dielectric Relaxation Time revealed that the dispersed exfoliated nanoscale MMT clay in the polymers blend matrix produces a large hindrance to the polymer chain dynamics. Results confirm that the real part of Dielectric function of the nanocomposites can be tailored by varying amount of MMT clay filler for their use as nanoDielectric materials in the microelectronic technology.

  • Dielectric Relaxation and molecular dynamics in poly vinyl pyrrolidone ethyl alcohol mixtures in pure liquid state and in non polar solvent
    Polymer, 2003
    Co-Authors: R J Sengwa, N M More
    Abstract:

    Abstract Dielectric Relaxation and molecular dynamics in poly(vinyl pyrrolidone)–ethyl alcohol (PVP–E) mixtures with varying concentration in pure state and also in very dilute solutions of benzene were studied for their molecular conformation at 35 °C. Dielectric permittivity e ′ and Dielectric loss e ″ of PVP–E mixtures were measured by a Time domain reflectometry technique in the frequency range 10 MHz to 10 GHz. The value of static Dielectric constant e 0 , Dielectric Relaxation Time τ , and Dielectric free energy of activation Δ F τ has been evaluated by fitting the complex Dielectric data into Debye equation. The variation in e 0 was discussed by considering the volume effect and the structuring effects of the PVP on ethyl alcohol molecules. The formation of cooperative domains between PVP and ethyl alcohol molecules, CD PVP–E and between the ethyl alcohol–ethyl alcohol molecules CD E and their dynamics in the PVP–E mixtures were explored by using the evaluated values of τ and Δ F τ . The PVP–E mixtures of low PVP concentration were also studied in very dilute solutions of benzene at 10.1 GHz. The value of average Relaxation Time τ 0 , distribution parameter α , and Relaxation Time corresponding to the motion of small mulTimer species of alcohol molecules τ 1 and group rotation τ 2 has been determined. It has been observed that in dilute solution of benzene the value of τ 0 and τ 1 increases with the increase in concentration of PVP in PVP–E mixture but the τ 2 value is found independent of the mixture constituent concentration. The entanglement of the CD PVP–E and the increase in the length of CD E in dilute solution of benzene due to dissociation of the complexes between carbonyl and hydroxyl groups has been explored. The value of τ 2 is assigned to the rotation of –OH group about C–O bond in the ethyl alcohol species in dynamic equilibrium with larger steric hindrance due to hydrogen bonding.

B S Murty - One of the best experts on this subject based on the ideXlab platform.

  • influence of bias voltage on Dielectric Relaxation of nanocrystalline anatase tio2 using modulus formalism
    Journal of Applied Physics, 2011
    Co-Authors: T Prakash, S Ramasamy, B S Murty
    Abstract:

    Dielectric Relaxation in sol–gel-derived anatase titanium oxide nanocrystals (6, 9, and 20 nm) has been investigated using impedance spectroscopy in a wide frequency range from 1 Hz to 1 MHz as a function of applied DC bias voltage, ranging from 0 to 4.2 V in a periodic interval of 0.3 V. Under the equilibrium condition, around three order of magnitude variations in the Dielectric Relaxation Time (τ) was observed for the grain size if reduced to 6 nm from 20 nm. An unambiguous evidence for the absence of such a crystallite size effect was experimentally observed in higher biased conditions because of grain boundarySchottky potential barrier height suppression. These experimental results obey the “grain boundary double Schottky barrier model.”

  • Dielectric Relaxation studies of nanocrystalline cualo2 using modulus formalism
    Journal of Applied Physics, 2007
    Co-Authors: T Prakash, S Ramasamy, Padma K Prasad, R Kavitha, B S Murty
    Abstract:

    Transparent semiconductor CuAlO2 in nanodimension was prepared by mechanical alloying of Cu2O and α-Al2O3 powders in toluene medium. The formation of single phase CuAlO2 with an average crystallite size of 45 nm was confirmed by x-ray diffraction analysis. The nanocrystalline nature of CuAlO2 was confirmed by atomic force microscopy. Frequency-dependent Dielectric property measurements and the Relaxation behavior were studied using impedance spectroscopy. Dielectric Relaxation Time estimated from the modulus curves was found to be decreasing with increase in temperature. The existence of stretched exponent parameter β<1 in the present nanocrystalline CuAlO2 implies non-Debye type Relaxation behavior in this material.

Shobhna Choudhary - One of the best experts on this subject based on the ideXlab platform.

  • Effects of different inorganic nanoparticles on the structural, Dielectric and ion transportation properties of polymers blend based nanocomposite solid polymer electrolytes
    Electrochimica Acta, 2017
    Co-Authors: Shobhna Choudhary, Ram Jeewan Sengwa
    Abstract:

    Abstract Nanocomposite solid polymer electrolyte (NSPE) films consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend (50/50 wt%) as host polymer matrix with 20 wt% lithium perchlorate (LiClO 4 ) as dopant salt and 3 wt% inorganic nanoparticles (i.e., Al 2 O 3 , SiO 2 , SnO 2 or ZnO) as filler have been prepared by solution cast method followed by melt-press technique. The X-ray diffraction (XRD) study confirms that the electrolyte films without nanofiller and with Al 2 O 3 and SiO 2 nanofillers have predominantly amorphous structures, whereas the characteristic diffraction peaks of SnO 2 and ZnO crystallites are observed in the respective NSPEs. Fourier transform infra-red (FTIR) spectra of these NSPE films confirm the formation of ion-dipolar coordination between the functional groups of polymers and the lithium ions throughout the material which completely suppressed the crystalline region absorption peaks of the PEO. The metal oxides of the nanoparticles mainly exhibit van der Waals type interaction with the polymers chains and the ions in the NSPE materials. Effects of a lithium salt as a dopant and the nanoparticles as fillers on the crystalline phase and thermal behaviour of PEO–PMMA blend in these electrolyte materials have also been examined by their differential scanning calorimetry (DSC) measurements. Dielectric and electrical dispersion behaviour of the NSPE films have been characterized by employing Dielectric Relaxation spectroscopy (DRS) over the frequency range from 20 Hz to1 MHz and at temperatures 27, 35, 45 and 55 °C. The single Relaxation peak appeared in the Dielectric loss tangent spectra of these electrolytes confirms the ion-dipolar coordinated coupled cooperative chain segmental motion of the PEO and PMMA macromolecules. Lowering in the values of Dielectric polarization strength and ionic conductivity has been observed for all the NSPE films as compared to that of the SPE film without nanofiller. A linear correlation between the crystallite sizes of different nanofillers and the Dielectric permittivity of NSPE materials has been revealed. It is found that the cooperative polymers chain segmental dynamics becomes slower with the dispersion of nanoparticles in the ion-dipolar complexes which causes a decrease of ionic conductivity of the NSPE films. The correlation observed between the Dielectric Relaxation Time and the ionic conductivity confirms that the ions transport occurs by intra- and inter-chain hopping in these PEO–PMMA blend based electrolytes. Temperature dependent values of Relaxation Time and dc ionic conductivity of the electrolyte films obey the Arrhenius relation and their activation energies are found in the range 0.22 eV to 0.40 eV which differ with the types of inorganic nanoparticles dispersed in the NSPEs. The comparative results confirm that the polymers chain segmental dynamics mask the effect of amorphous phase of these materials which contributes in the lithium ions transportation and their mobility. Linear correlation observed between the Dielectric permittivity and ionic conductivity values of these NSPEs suggests that the strength of Dielectric polarization also plays an important role for the ion transportation process in the solid ion-dipolar complexes. The room temperature ionic conductivity values of these NSPE films are found of the order of 10 −5  S cm −1 which confirms their suitability as potential candidates in the design and development of all-solid-state devices including the rechargeable lithium-ion batteries. Finally, these experimental results explain in depth the fundamental issues of nanomaterials science that confront the use of various kind of inorganic nanoparticles in the preparation of NSPEs, and the dependence of their ion transportation process on the amorphous phase, Dielectric permittivity and the cooperative polymers chain segmental motion, especially for the polymers blend based electrolytes.

  • effects of plasticizer and nanofiller on the Dielectric dispersion and Relaxation behaviour of polymer blend based solid polymer electrolytes
    Current Applied Physics, 2015
    Co-Authors: R J Sengwa, Priyanka Dhatarwal, Shobhna Choudhary
    Abstract:

    Abstract Solid polymer electrolytes consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend (50:50 wt/wt%) with lithium triflate (LiCF 3 SO 3 ) as a dopant ionic salt at stoichiometric ratio [EO + (C O)]:Li +  = 9:1, poly(ethylene glycol) (PEG) as plasticizer (10 wt%) and montmorillonite (MMT) clay as nanofiller (3 wt%) have been prepared by solution cast followed by melt–pressing method. The X–ray diffraction study infers that the (PEO–PMMA)–LiCF 3 SO 3 electrolyte is predominantly amorphous, but (PEO–PMMA)–LiCF 3 SO 3 –10 wt% PEG electrolyte has some PEO crystalline cluster, whereas (PEO–PMMA)–LiCF 3 SO 3 –10 wt% PEG–3 wt% MMT electrolyte is an amorphous with intercalated and exfoliated MMT structures. The complex Dielectric function, ac electrical conductivity, electric modulus and impedance spectra of these electrolytes have been investigated over the frequency range 20 Hz to 1 MHz. These spectra have been analysed in terms of the contribution of electrode polarization phenomenon in the low frequency region and the dynamics of cations coordinated polymer chain segments in the high frequency region, and also their variation on the addition of PEG and MMT in the electrolytes. The temperature dependent dc ionic conductivity, Dielectric Relaxation Time and Dielectric strength of the plasticized nanocomposite electrolyte obey the Arrhenius behaviour. The mechanism of ions transportation and the dependence of ionic conductivity on the segmental motion of polymer chain, Dielectric strength, and amorphicity of these electrolytes have been explored. The room temperature ionic conductivity values of the electrolytes are found ∼10 −5  S cm −1 , confirming their use in preparation of all-solid-state ion conducting devices.

  • Dielectric properties of montmorillonite clay filled poly vinyl alcohol poly ethylene oxide blend nanocomposites
    Composites Science and Technology, 2010
    Co-Authors: R J Sengwa, Shobhna Choudhary, Sonu Sankhla
    Abstract:

    Abstract Organic–inorganic nanocomposites of poly(vinyl alcohol) (PVA)–poly(ethylene oxide) (PEO) blend filled with montmorillonite (MMT) nanoclay up to 10 wt.% concentration were synthesized by aqueous solution-cast technique. The complex Dielectric function, electrical conductivity, electric modulus and impedance spectra of the nanocomposites were measured in the frequency range 20 Hz–1 MHz at ambient temperature. A direct correlation was observed between the real part of Dielectric function and the mean Relaxation Time of the polymer chain segmental dynamics, with the exfoliated and intercalated MMT clay structures, and the extent of miscibility between PVA and PEO due to hydrogen bonded bridging through exfoliated MMT clay nanosheets. The large increase of Dielectric Relaxation Time revealed that the dispersed exfoliated nanoscale MMT clay in the polymers blend matrix produces a large hindrance to the polymer chain dynamics. Results confirm that the real part of Dielectric function of the nanocomposites can be tailored by varying amount of MMT clay filler for their use as nanoDielectric materials in the microelectronic technology.

A Ghosh - One of the best experts on this subject based on the ideXlab platform.

  • broadband Dielectric spectroscopy of bmptfsi ionic liquid doped solid state polymer electrolytes coupled ion transport and Dielectric Relaxation mechanism
    Journal of Applied Physics, 2020
    Co-Authors: Prabir Pal, A Ghosh
    Abstract:

    Broadband Dielectric spectroscopy has been used to explore the charge carrier transport and Relaxation mechanisms in different compositions of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide doped poly(methylmethacrylate)-lithium bis(trifluoromethylsulfonyl)imide based solid polymer electrolytes. The free ion diffusivity and number density, which are directly linked with ion transport in ionic liquid based polymer electrolytes, are analyzed following the model of electrode polarization proposed by Macdonald–Trukhan. We have analyzed broadband Dielectric spectra in terms of complex electric modulus formalism using two theoretical approaches such as Havrilliak–Negami and Kohlrausch–Williams–Watts functions. It has been observed that charge carrier diffusivity and Dielectric Relaxation Time are strongly temperature dependent, following Vogel–Tammann–Fulcher behavior. It is also evident from the values of stretched exponent β that the Relaxation behavior is highly non-exponential in these ionic liquid doped polymer electrolytes.