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5 research outputs found

Thermally stimulated depolarization current studies in pristine and 100 MeV Ni-ion irradiated PET/0.3PHB polymer liquid crystal

Author: Quamara J K
Sridharbabu Y
Publication venue: NISCAIR-CSIR, India
Publication date: 01/10/2003
Field of study

790-800Thermally stimulated depolarization current (TSDC) characteristics of PET/0.3PHB polymer liquid crystal, a copolymer of polyethylene terephthalate and p-hydroxybenzoic acid, have been studied as a function of the polarizing field (38.5- 192.3 kV /em), polarizing temperature (80-220 °C), heating rate (2-6 °C/min), storage time (0-960 h) and electrode material (Au, AI,Cr). The TSDC spectra in general comprise of three maxima namely β, β' and α with their respective location around 35, 122 and 155 °C. The β-peak has been attributed to the dipolar orientation relaxation of PET rich phase. The α-peak has been ascribed to the space charge relaxation. A major contribution towards a-relaxation comes from PHB-rich phase and the cold crystallization of PET-rich phase. The presence of a rigid amorphous phase (γ-relaxation) appears to affect the true nature of α -peak. A high temperature maxima around 190°C in TSDC spectra of high temperature poled samples is due to melting (δ- relaxation). The β'-peak is ascribed to the extremely fast reacting dipoles of PHB and PET phase. The TSDC spectra of PET/0.3PHB samples irradiated with 100 MeV Ni-ion beam (Fluence: 3.39×1010,8.93× 1010, 3.13× 1011ions/cm2 ) show the presence of new energy traps (deep/shallow). The peak magnitudes and peak temperatures for β- as well as α- peak increase with fluence. The appearance of new polar groups due to radiation induced cross- linked structure is also possible in the irradiated PET/0.3PHB sample. </span

NOPR

Dielectric constant/loss behaviour of 11.6 MeV/n U238 ion irradiated poly (p-hydroxy benzoic acid-co-ethylene terephthalate) liquid crystal polymer

Author: Prabhavathi T
Quamara J K
Sridharbabu Y
Publication venue: NISCAIR-CSIR, India
Publication date: 01/09/2002
Field of study

633-636Polymer liquid crystal, a copolymer or polyethylene terephthalate (PET) and poly hydroxy henzoic acid (PHB) whence referred as PET/x PHB where x represents the molar concentration or PHB, for x=0.3 and 0.7 or 165 µm nominal thickness were irradiated with 11.6 MeV /n U238 -ion at DRAMSTADT (Germany) with fluence 1×106 ions/cm2 .The dielectric constant/loss measurements for these polymer liquid crystal samples were measured in the temperature range 20-220°C by using Keithley's precision LCZ meter for frequencies 120Hz, 1 kHz, 10kHz and 100kHz. An increase in the dielectric constant at low temperature (20-60 °C) mainly ascribed to α-relaxation, which depends upon the molar concentration of PHB. This peak has been attributed to the polar nature or both PET and PHB. The α-relaxation is followed by suppression in dielectric constant or PET/0.3PHB and sharp increase in dielectric constant of -PET/0.7PHB from which one can understand that, due to irradiation, the PET rich phase has been affected drastically. The decrease in the dielectric constant at higher temperatures is due to the increase in crystallinity as annealing-like effects are also induced due to irradiation by energetic heavy ions. The peak in the dielectric loss (0.3 PHB) curve ascribed to the space charge relaxation processes, which is in accordance with the thermally-stimulated polarization current behaviour. A continuous decrease in the dielectric loss curve (0.7PHB) ascribed to the m-transition that is in conformity with the investigations on internal friction. </span

NOPR

Dielectric relaxation studies of 100 MeV Ni58 ion irradiated kapton-H polyimide film

Author: Prabhavathi T
Quamara J K
Sridharbabu Y
Publication venue: NISCAIR-CSIR, India
Publication date: 01/09/2002
Field of study

654-659Kapton -H polyimide samples of thickness 12.5µm have been irradiated with 100 MeV Ni58 ion beam with fluences 6.295 ×1011 and 2.57 × 1012 ions/cm2 .The dielectric constant/loss investigations have been measured from 30 to 240°C for different frequencies ranging from 100Hz to 3 MHz. The nature of Ɛ'-T curve in low temperature region (30-70°C) is mainly governed by γ-relaxation. The dielectric loss peak at 60°C is in conformity with this relaxation. The dielectric constant in the temperature range 70-180°C is mainly governed by dipolar and space charge relaxations. The new energy trap due to the formation or free radicals by high-energy ion irradiation, contributes significantly towards space charge relaxation. In this temperature region,Ɛ' or high flux irradiated samples is more than low flux irradiated samples. In high temperature region (180-240°C) the increase in Ɛ ' with temperature is mainly due to interfacial polarization, which arises due to formation or new phases by irradiation. The loss maximumin Ɛ "- T curve at 240°C confirms the presence or this relaxation. </span

NOPR

Electrical conduction behaviour of pristine and 100 MeV Ni ion irradiated PET/0.8PHB polymer liquid crystals

Author: Goyal Geetika
Quamara J K
Sharma Anu
Sridharbabu Y
Publication venue: 'CSIRO Publishing'
Publication date: 01/11/2007
Field of study

910-919Electrical conduction behaviour of pristine and 100 MeV Ni ion irradiated terephthalate (PET)/0.8 poly(p-hydroxy-benzoic acid) (PHB) polymer liquid crystals has been investigated in transient and steady state conditions at different electric fields (13-104.3 kV/cm) and temperatures (40-250ºC). The various mechanisms responsible for charge transport phenomena can be thoroughly investigated by studying temperature and field dependent conduction behaviour. The origin of transient currents in polymers has been ascribed to number of mechanisms. The dipolar relaxation seems to be the major contributor to these currents at lower temperatures. The temporal decay of current may be due to trapping of charge carriers and/or due to the reduction of electric field owing to the formation of Schottky layers in the vicinity of the electrodes. The high temperature relaxations do not contribute much to the transient behaviour. The transient currents in ion irradiated samples are mainly governed by cross-link structures and free radical formation in addition to the δ-transition. Poole-Frenkel and Schottky conduction mechanisms appear to operate at high and low temperature regions, respectively, for both pristine and irradiated samples

NOPR

Evaluation of the thermal decomposition of blends prepared with poly(3-hydroxybutyrate) (PHB) and recyclable ethylene poly-terephthalate (RPET)

Author: A ElMejjatti
A Masek
A Nadia
A Nakkabi
AF Santos
AK Galwey
AK Mohanty
AP Sirocic
B Mihai
C Ioakeimidis
CY Liang
CZ Costa
DS Dias
DS Dias
DS Dias
EV Paula
GQ Zhang
H Liu
JL Souza
JR MacCallun
M Urbanová
MBC Vitorino
ME Brown
MG Kulkarini
MS Rabello
N Vogelsanger
O Ahumada
P Budrugeac
R Mingtao
S Moinuddin
S Yoshida
SD Mancini
SG Hong
SH El-Taweel
SV Levchik
XG Li
Y Sridharbabu
YH Bang
YL Pak
ZS Czégény
Publication venue: 'Springer Science and Business Media LLC'
Publication date
Field of study

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