Transient Current Investigations in Ion Irradiated Liquid Crystalline Polyurethane

416-423Swift heavy ions (SHI) irradiation of Oxygen (O7+) beam with different ions fluence bring the modifications in the electrical conduction behavior of liquid crystalline Polyurethane (LCPU). The persent investigation carried out under different transientconditions in the operating temperature range of 50-220°C at various selectric fields of 4.35-43.45 kV/cm. The transient currents show thehyperbolic decay character and the decay exponent Δt (one-tenth decay time) dependent on the field and temperature. Theincrease in I0 /Isvalues (where I0 represents the current observe dimmediately after applying the voltage and Ismeans the steady state current) and the mobility variation at high operating temperatures shows the appearance of mesophase. The transient currents originated due to the dipolar nature of carbonyl(C＝O) groups in the main chain of LCPU and the trapping charge carriers

Dielectric spectroscopy of 100 MeV Ag ion irradiated polyetherimide

660-666The dielectric constant (′) and loss factor (Ɛ′′) have been measured in pristine and 100 MeV Ag ion irradiated (fluences: 5.610¹⁰, 1.810¹¹ and 1.810¹² ions/cm2) polyetherimide (PEI) in the temperature region 30-250C at different frequencies ranging from 200 Hz to 5 MHz. There is an overall increase in Ɛ′ in irradiated samples. This shows the dominance of interfacial polarization arising from the large number of radiation induced defect sites and free radicals. However, the increase in Ɛ′ is not directly proportional to the fluence of irradiance. There is a sudden decline in ′ at intermediate fluence (1.810¹¹ions/cm²) which is due to the occurrence of new secondary radiation induced crystalline (SRIC) phase. In the low temperature region 30-100C, the Ɛ′ follows the Kirkwood model. Above 100C, the Ɛ′ is almost temperature independent. The radiation induced free radical cross-linking and formation of free radicals have been held responsible for this behaviour. Various relaxation processes revealed their presence in the form of loss peaks in Ɛ′′-T curves appearing around 40-50C, 120-130C and 180-220C associated to the dipolar nature of ether linkages, carbonyl groups and space charge relaxation processes, respectively

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

790-800<span style="font-size: 15.5pt;mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">Thermally 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 <span style="font-size: 15.5pt;mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">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 <span style="font-size: 15.5pt;mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">affect the true nature of α -peak. A high temperature maxima around 190°C in TSDC spectra of high temperature poled <span style="font-size: 15.5pt;mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">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<span style="font-size:13.0pt;mso-bidi-font-size:6.0pt; font-family:" times="" new="" roman","serif""="">, <span style="font-size:15.5pt; mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">3.13× 1011ions/cm2 <span style="font-size:13.0pt;mso-bidi-font-size:6.0pt;font-family: " times="" new="" roman","serif""="">) <span style="font-size:15.5pt;mso-bidi-font-size: 8.5pt;font-family:" times="" new="" roman","serif""="">show the presence of new energy traps (deep/shallow). The peak magnitudes and peak temperatures for <span style="font-size: 15.5pt;mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman","serif""="">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

FTIR analysis of high energy heavy ion irradiated kapton-H polyimide

563-568FTIR spectroscopy technique has been applied for the analysis of high energy heavy ion irradiated kapton-H polyimide. The kapton-H samples were irradiated with 75 MeV oxygen, 80 MeV nickel and 50 MeV lithium ions at PELLETRON facility, Nuclear Science Centre, New Delhi. A very broad peak in 2500-3500 cm⁻¹ is due to the presence of absorbed water in irradiated samples. The reduction in the intensity of 1702 cm⁻¹ peak in irradiated samples as compared to pristine samples is associated to the demerization of carbonyl groups. The increase in the intensity of this peak with increase in fluence is due to the increase in cross-linked structure causing the reduction in demerization of carbonyl groups. The FTIR spectrum is independent of the nature of ion

Temperature and frequency dependent dielectric constant/loss studies <span style="font-size:14.0pt;line-height:115%;font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";color:black;mso-ansi-language:EN-IN; mso-fareast-language:EN-IN;mso-bidi-language:HI" lang="EN-IN">in 50 M<span style="font-size:14.0pt;line-height:115%;font-family:"Times New Roman"; mso-fareast-font-family:HiddenHorzOCR;color:black;mso-ansi-language:EN-IN; mso-fareast-language:EN-IN;mso-bidi-language:HI" lang="EN-IN">eV <span style="font-size:14.0pt;line-height:115%;font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";color:black;mso-ansi-language:EN-IN; mso-fareast-language:EN-IN;mso-bidi-language:HI" lang="EN-IN">Si⁺ ion irradiated kapton-H film</span></span></span>

455-460The kapton-H polyimide film samples (25 μm thickness) have been irradiated with 50 MeV Si+ ion beam with fluences 2.3×1012 and 1.38×1013 ions/cm2. The dielectric constant/loss for irradiated samples have been measured in the temperature range 30-250 oC for different frequencies 120 Hz, 1kHz,10 kHz and 100 kHz. An increase in the low temperature (30-70oC) low frequency ε' has been ascribed to the increase in water absorption capacity (γ-relaxation) due to high energy ion irradiation. Dielectric loss maximum around 50oC is in conformity with this relaxation . The dielectric constant in temperature range 70-180oC is mainly governed by dipolar relaxation and space charge relaxation due to shallow energy traps. The ε' value for low flux sample is observed to be more than that for high flux sample. It is suggested that though the space charge relaxation tends to increase ε', a major loss in carbonyl groups due to high energy ion irradiation results in a decrease of ε'. In high temperature region (180- 250oC) the interfacial polarization due to creation of new phases by irrad iation increases the ε' value. The maximum in ε"-T curve at 250oC confirms the presence of this relaxation. However, in this temperature region increase in crystallinity of kapton-H results in a decrease of &nbsp;ε'. The dominance of any one determines the nature of ε' -T curve.</span

Multiple relaxation investigations in polyetherimide: Thermally stimulated depolarization current technique

127-133Thermally stimulated depolarization current (TSDC) technique has been used for investigating various dielectric relaxation processes in polyetherimide. The TSD currents in the temperature range 20º-250ºC (in certain cases up to 300ºC) were obtained as functions of polarizing field (Ep; 20-350 kV/cm), polarizing temperature (Tp; 60 º-180ºC), poling time (tp; 0.5-2 h), sample thickness (d; 25-120 µm), heating rate (h; 2º-6ºC/min), and storage time (ts; 0-552 h). The current maxima in the TSDC spectra reveal the presence of two major relaxation processes termed as β- (around 130ºC) and ⍺- (around 190ºC), associated with dipolar relaxation and space-charge relaxation processes, respectively. However, in certain cases, we observe merging of β- and ⍺-relaxation processes to become the ⍺β-relaxation process (140º-180ºC). The observed dependence of the peak temperature Tm on polarizing temperature and poling time indicates a continuous distribution of relaxations. The high Ep/Tp samples also show a relaxation (ρ) around 260ºC associated with charge injection phenomenon. The low temperature region of TSDC spectra (30º-70ºC) shows the presence of a weak relaxation (β′), considered as a satellite of the main dipolar relaxation process. The activation energies for various relaxation processes have been calculated using Bucci plot method

<span style="font-size:14.0pt;line-height: 115%;font-family:"Times New Roman";mso-fareast-font-family:HiddenHorzOCR; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">Thermally <span style="font-size:14.0pt;line-height:115%; font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">stimulated <span style="font-size:14.0pt;line-height: 115%;font-family:"Times New Roman";mso-fareast-font-family:HiddenHorzOCR; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">depolarization current <span style="font-size:14.0pt; line-height:115%;font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">behaviour of 50 M<span style="font-size:14.0pt; line-height:115%;font-family:"Times New Roman";mso-fareast-font-family:HiddenHorzOCR; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">eV <span style="font-size:14.0pt;line-height:115%; font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">Li⁺ ion-irradiated kapton-H polyimide film</span></span></span></span></span></span>

259-262Different dielectric relaxation processes such as dipolar and space charge have been investigated in high-energy ion irradiated kapton-H polyimide using thermally stimulated discharge current (TSDC) technique. Kapton-H samples (12.5μm thickness) are irradiated with Li+ ion (50MeV) at different flux (5×105, 105, 104 ions/cm2) at Nuclear Science Center, New Delhi (PELLETRON Facility). The thermoelectret of irradiated samples are prepared following the usual method for various poling fields and temperatures. The TSD currents are obtained at heating rate of 2oC/min. The peak appearing at low temperature and associated with dipolar polarization is largely affected in irradiated samples. This is mainly due to the dimerization of the carbonyl groups. The high temperature peak which is associated with space charge relaxation becomes more pronounced in irradiated samples. High-energy ion-irradiation provides deep energy trap centers in the form of conjugated bonds due to de-localized electrons. Low temperature tail of TSDC shows many kinks. These kinks are due to creation or new cross- linking dependent sub polar groups and shallow energy traps as a result of high-energy ion - irradiation .</span

Surface chemical etching behaviour of pristine and high energy Li ion irradiated kapton-H polyimide

66-70 High energy heavy ion irradiation effect on surface chemical etching behaviour of kapton-H polyimide has been studied using NaOH (40°C) and NaOCl (55°C) as etchants. The samples have been irradiated with 50 MeV Li ions (fluence 105 ions/cm2 at Pelletron Facility, Nuclear Science Center, New Delhi). The etching behaviour is non-linear in NaOH for both pristine and irradiated samples. There is an enhancement in the etching rate in irradiated samples for both NaOH and NaOCl etchants. The etching mechanism of pristine and irradiated kapton-H polyimide with NaOCl and NaOH has been investigated. In irradiated samples the demerization of carbonyl groups, breaking of imide linkages and increase in crystallinity have been held responsible for the change in the etching behaviour. The bulk activation energy of pristine and irradiated samples for NaOH (0.38 and 0.30 eV) and NaOCl (1.6 and 1.3 eV) has been estimated. High temperature vacuum annealed samples when etched with NaOH show swelling instead of etching, which is due to a unique type of gel formation taking place on the surface. </smarttagtype

Field-induced thermally stimulated currents in poly (p-phenylene sulphide)

595-602<span style="font-size:14.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">Thermally stimulated polarization currents (TSPC) have been investigated in poly p-phenylene sulphide (PPS) in temperature region 30-250°C under various polarization fields, ranging from 3 to 18kV/cm and with different heating rates. The effect of high temperature annealing on TSPC behaviour has also been investigated. The TSPC spectra show the presence of a single peak (P1) around 110°C. This peak has been attributed to a weak polar nature of C-S linkage. A phenomenal rise of several order of magnitudes in the current dominated by conduction current is observed above 170oC. During the successive cooling the current retains its positive polarity and in the 2nd TSPC cycle the peak P1 disappears due to temperature dependence of saturation polarization confirming the polar nature of this peak. The kinks observed in the TSPC spectra of annealed samples and with slow heating rates around 170°C are due to the dipolar relaxation process associated with ether linkage, a cross-linked structure formed due to high temperature annealing. The thermal variation in dielectric constant, deduced from TSPC spectra is in good agreement at low temperature, with the result obtained by other method.</span