Dielectric Analyzer Research Articles

Synthesis, characterization, physicochemical and dielectric properties of siloxane, polyimide and their blends

Very low molecular weight polydimethylsiloxane (PDMS) has been synthesized and characterized by using Infrared spectroscopy (IR), nuclear magnetic resonance, thermogravimetric analysis (TGA) and differential scanning calorimetry. Molecular weight distribution of PDMS has been determined by using multiple angle light scattering and size exclusion chromatography while hydrodynamic radii have been determined by quasi elastic light scattering. Electrical properties fo PDMS were determined using broadband dielectric analyzer with variable temperature and frequency. Polyamic acid has been synthesized and characterized. Two polymers were blended at precursor stage and cured following unique time-temperature profile. Both the component in blends are characterized by using IR and TGA. Dielectric properties of both neat polyimide and its blend have been evaluated using broad band dielectric analyzer in variable temperature and frequency range. PDMS was found to dominate the surface characteristics of the blends as determined by scanning electron microscopy and optical microscopy. Possible mechanism of blend formation has been proposed wherein concurrent amicacid catalyzed equilbration and immobilization of siloxane moiety due to charge transfer complexation existing between the two componenets visualized to occur.

Dielectric properties of self‐catalytic interpenetrating polymer network based on modified bismaleimide and cyanate ester resins

AbstractBismaleimide (BMI) resins with good thermal stability, fire resistance, low water absorption, and good retention of mechanical properties at elevated temperatures, especially in hot/wet environments, have attracted more attention in the electronic and aerospace industries. However, their relatively high dielectric constant limits their application in the aforementioned fields. In this work, a new promising approach is presented that consists of the formation of a self‐catalytic thermoset/thermoset interpenetrating polymer network. Interpenetrating polymer networks (IPNs) based on modified BMI resin (BMI/DBA) and cyanate ester (b10) were synthesized via prepolymerization followed by thermal curing. The self‐catalytic curing mechanism of BMI/DBA‐CE IPN resin systems was examined by differential scanning calorimetry. The dielectric properties of the cured BMI/DBA‐CE IPN resin systems were evaluated by a dielectric analyzer and shown in dielectric properties‐temperature‐log frequency three‐dimensional plots. The effect of temperature and frequency on the dielectric constant of the cured BMI/DBA‐CE IPN resin systems is discussed. The composition effect on the dielectric constant of the cured IPN resin systems was analyzed on the basis of Maxwell's equation and rule of mixture. The obtained BMI/DBA‐CE IPN resin systems have the combined advantages of low dielectric constant and loss, high‐temperature resistance, and good processability, which have many applications in the microelectronic and aerospace industries. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1123–1134, 2003

Electrical conductivity and dielectric properties of PMMA/expanded graphite composites

PMMA/expanded graphite (EG) composites were prepared by direct solution blending of PMMA with the expanded graphite filler. Electrical conductivity and dielectric properties of the composites were measured by a four-point probe resistivity determiner and a dielectric analyzer (DEA). Interestingly, only 1 wt.% filler content was required to reach the percolation threshold ( φ) of transition in electrical conductivity from an insulator to a semiconductor using PMMA/EG. The thickness of the interlayer of the expanded graphite was shown to be close to the nanometer scale. The reported filler content was much lower than that required for conventional PMMA/carbon black (8 wt.% carbon) and PMMA/graphite (3.5 wt.% graphite) composites. The improvements in both electrical conductivity and structural integrity were attributed to the difference in filler geometry (aspect ratio and surface area) and the formation of conductive networks in the composites.

Gas transport in modified polysulfones with trimethylsilyl groups: effect of substitution site

Trimethylsilyl (TMS) groups were chemically introduced on to the phenylene group of bisphenol-A polysulfone (PSf) at sites ortho to ether (EM3) or to sulfone (SM3) linkages. Gas permeabilities increased by substitution of TMS and especially oxygen permeability increased from 1.1 barrer for PSf to 4.2 barrer for SM3 and to 7.1 barrer for EM3. Perm-selectivity of oxygen to nitrogen decreased from 5.8 to 5.5 and therefore substitution of TMS on polysulfone resulted in improved gas transport properties. In addition, it was found that EM3 is more effective in enhancing the gas transport properties than SM3. In order to interpret the effect substitution site on gas transport, d-spacing was investigated in terms of interchain packing. Furthermore, the effect of substitution site on chain motion was investigated through dynamic mechanical analyzer (DMA), dielectric analyzer (DEA), and solid-state NMR. DMA and DEA experiments showed that motions of unsubstituted phenylene and sulfonyl linkage are much more hindered in SM3 than in EM3. NMR experiments showed that motion of TMS is more mobile in EM3 than in SM3. These results revealed that chain motions of SM3 are more hindered than those of EM3 and substitution site affects chain motions. Therefore, we can conclude that these changes in chain motion also gas transport in modified polysulfones with silyl side group.

Synthesis and properties of copolyimides containing naphthalene group

Several series of copolyimides were synthesized from various ratios of two diamines with aromatic tetracarboxylic dianhydrides through thermal imidization process to determine the effect of naphthalene ring on the physical properties of polymers. The copolyimides were characterized using inherent viscosity, differential scanning calorimetry (DSC), TGA, DMA, TMA and dielectric analyzer. DSC showed only a T g and exhibited that the copolyimides had a low entropy, amorphous state and formed random polymers. They retained high modulus even at high temperatures by DMA, and had measured coefficients of thermal expansion in the range of 15–57 ppm by TMA. The glass transition temperatures ( T g) of all polymers were found to be 287–321 °C by DSC. Their decomposition temperatures at 10% weight loss in nitrogen atmospheres were above 556 °C. These polymer films had dielectric constants ranging from 2.9 to 3.4 with moisture absorptions of less than 2.65%.

Anisotropic dielectric properties of polyimides consisting of various molar ratios of meta to para diamine with trifluoromethyl group

AbstractA series of copolyimides based on pyromellitic dianhydride (PMDA) with various molar fractions of 4,4′‐(hexafluoro‐isopropylidene)dianiline (4,4′‐6F) and 3,3′‐(hexafluoro‐isopropylidene)dianiline (3,3′‐6F) were synthesized by a two‐step method. The five different composition copolyimides in the fozrm of {(PMDA+3,3′−6F)m/ (PMDA+4,4′−6F)n were mainly characterized using a dielectric analyzer (DEA) by single surface sensor (in‐plane direction) and thin film parallel plate sensor (out‐of‐plane direction) measurements. DSC, TMA, and XRD were also used to study the structure property. The increasing of molar ratio of para diamine in the copolyimide system up to 35% affected glass transition temperature, coefficient of thermal expansion, in‐plane dielectric constant and out‐of‐plane dielectric constant of copolyimides, correspondingly. The in‐plane dielectric constant was higher than that of the out‐of plane constant for our polyimide films. Anisotropy δε of the dielectric constants was 0.14 for CPI(100/o)a, 0.19 for CPI(85/15)a, 0.11 for CPI(75/25)a, and 0.05 for CPI(65/35)a. The difference in curing history also exhibited an effect on solvent diffusion behavior in our polymer system. Polymers cured at a slower curing rate had smaller CTE than that cured at a faster curing rate, as confirmed by X‐ray diffraction results. Polymers with smaller CTEs had larger dielectric constants at a slower curing rate, and vice versa. The experimental results suggested that CPI(65/35) a with smaller dielectric anisotropy could solve the crosstalk problem and provide equal electrical insulation in microelectronic devices. Therefore, a smaller and faster IC device could, it is hoped, be achieved, with smaller spacing between adjacent metal lines.

Interaction mechanism of a novel polymer electrolyte composed of poly(acrylonitrile), lithium triflate, and mineral clay

AbstractThe addition of optimum cetyl pyridium chloride (CPC)–modified montmorillonite (CM) increases the ionic conductivity of poly(acrylonitrile)‐based electrolytes by roughly two orders of magnitude. Specific interactions between the silicate layer, the nitrile group, and the lithium cation were investigated by FTIR, solid‐state NMR, dielectric analyzer, and alternating current impedance. IR and NMR spectra confirm that the negative charges in the silicate layers alter the ionic charge environment of the PAN‐based electrolyte composites, which have the same function as the polar group in PAN. The optimum CM content to achieve the maximum ionic conductivity is 6 phr. However, untreated montmorillonite leads to insignificant polymer intercalation, the negative charges in the silicate layers fail to appreciably disturb the attractive force of the lithium salt, and the resulting conductivity improvement is also less than that of the CM additives. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2407–2419, 2001

In Situ Characterization of Methylsilsesquioxane Curing

This paper focuses on the in situ characterization of methylsilsesquioxane curing. As the final properties of this material depend on the curing process, it is important to investigate the mechanisms operating during its cross‐linking process. Thermal analysis techniques such as dielectric analysis, differential scanning calorimetry, thermomechanical analysis, and thermogravimetric analysis are employed to carry out an in‐depth study on its curing. The curing of methyl‐silsesquioxane is found to be an endothermic process accompanied by weight loss, shrinkage, and reduction in coefficients of thermal expansion and dielectric constant. A two‐stage curing process has also been postulated based on the data collected. The dielectric analyzer provides real‐time molecular relaxation of the dielectric material before, during, and after the curing process.

Glass fibre epoxy composite cure monitoring using parallel plate dielectric analysis in comparison with thermal and mechanical testing techniques

This investigation considers dielectric response using a parallel plate arrangement, as opposed to the commonly used single surface sensor, in an attempt to monitor signal change during composite cure. Parallel plate arrangements provide the possibility of obtaining an average state of cure throughout the composite thickness without necessitating the inclusion of the sensor within the composite structure. To assess the suitability of this sensor arrangement, a Dielectric Analyser (DEA) was used to simulate the cycle conditions of a Resin Transfer Moulding (RTM) process. Arbitrary positions of the DEA analysis output were used to identify the conditions for various states of cure, to which several mouldings were subsequently manufactured and cured using an RTM system. Thermal and mechanical testing techniques were performed on these RTM mouldings in an attempt to determine the suitability of the parallel plate sensors for degree of cure detection and the influence of cure upon the final composite material properties . Results indicated that a correlation does exist between the DEA output using parallel plate sensors and the change in properties of the composite with cure time. This was additionally beneficial in that the optimum cure cycle was identified. Finally parallel plate DEA is discussed as a means not only for optimising cure cycles in the laboratory but as a potential means of process control.

Pervaporation and properties of chitosan-poly(acrylic acid) complex membranes

Polyelectrolyte complex membranes between chitosan as a cationic polyelectrolyte and poly(acrylic acid) as an anionic species were prepared by blending two polymer solutions in different ratio. Characterization of chitosan-poly(acrylic acid) complex membrane was investigated by Fourier transform-infrared (FT-IR), wide angle X-ray diffractometer, dielectric analyzer. Their mechanical properties were studied by universal testing machine. The swelling of polyelectrolyte membranes was studied. Thermal properties of polyelectrolyte membranes from chitosan and poly(acrylic acid) by varying blend ratios showed a shift in transition temperatures of polyelectrolyte complexes. Polyelectrolyte complex membranes from chitosan and poly(acrylic acid) had pH sensitive characteristics as determined by FT-IR studies and swelling behaviors. Pervaporation performances were investigated with various organic mixtures; water-ethanol, water-isopropanol, methanol-methyl t-butyl ether mixtures. An increase of poly(acrylic acid) content in the polyelectrolyte complex membranes affected the swelling behavior and pervaporation performance of water-ethanol mixture. Permeation flux decreased and the water concentration in the permeate was close to 100% upon increasing the feed alcohol concentration.

Studies on the thermotropic liquid crystalline polycarbonates—V. Synthesis and properties of carbonato side chain liquid crystalline polysiloxanes

Two series of spacer-containing carbonato side chain liquid crystalline polysiloxanes were prepared by hydrosilylation of various novel allyl carbonates with poly(hydrogen-methylsiloxane). The thermotropic liquid crystalline properties of synthesized monomers and polymers were investigated by: (1) examination of the melt birefringence and stirred opalescene by a polarizing microscope equipped with a heating stage; (2) characterization of mesophase transitions by a differential scanning calorimeter (DSC); and (3) analysis of dielectric properties, conductivity and phase transition by a dielectric analyzer (DEA). It was found that most of the synthesized polymers with the carbonate groups in the side chains showed excellent mesophase stabilities and low glass transition temperatures. In the meantime, the melting transitions were reduced by introducing longer spacers.

The relationship between structure and deformation behavior of sulfone polymers

AbstractThe deformation of three types of sulfone polymers—polysulfone (PSF), poly(ether sulfone) (PESF), and polyarylsulfone (PASF)—was performed with a mechanical testing system (MTS). The result and samples were studied using a transmission electron microscope (TEM), a dynamic mechanical analyzer (DMA), and a dielectric thermal analyzer (DETA). Stripes on TEM micrographs for small deformations increase with the fracture toughness (GIc). The activation energy (Ea) of the α‐transition was determined from DETA. The results show that both Ea and TEM micrographs can be used to qualitatively estimate the order of GIc of sulfone polymers. An energy model was proposed to explain this phenomenon.

Study of Molecular Dynamics of a Nematic Main Chain Liquid Crystalline Polyester by Dielectric Spectroscopy

Abstract Dielectric spectroscopy was applied to study the molecular dynamics of a nematic main-chain liquid crystalline polyester using a Du Pont Dielectric Analyser. The dielectric measurements covered a frequency range from 0.03 to 100000Hz and a temperature range from -100 to 160°C leading from the transition region up to the isotropic fluid region. Dielectricrelaxation processes α,β,γ and δ were observed and analysed. Apparent activation energies of the processes were calculated.

Studies on the thermal and curing behavior of polyimide blends

AbstractBlends of thermosetting (Thermid MC‐600 and Thermid FA‐700) and thermoplastic (UL‐TEM 1000) polyimide resins with different compositions were prepared. Curing and thermal behavior of the blends were investigated using differential scanning calorimetry and dynamic thermogravimetry in a nitrogen atmosphere. The peak exotherm temperature increased with increasing amount of thermoplastic resin, whereas the heat of polymerization decreased. The electrical characteristics of the blends were also investigated using a dielectric analyzer. Dynamic as well as isothermal scans were recorded. Ionic conductivity, permittivity, and the loss factor were measured as a function of temperature at various frequencies. These results showed the complete curing of the resins having 50% Ultem at 225°C in 1 h, whereas Thermid MC‐600 required a postcuring step to observe fully cured resins. A marginal decrease in thermal stability was observed on blending. © 1994 John Wiley & Sons, Inc.

Evaluation of doped polyethylene oxide as solid electrolyte

A study correlating electrical properties (a.c. conductivity and permittivity) to changes in the polymer morphology of polyethylene oxide (PEO) doped with lithium tetrafluoroborate (LiBF 4) was investigated. A TA Instruments Dielectric Analyzer, DEA 2970, was used to measure electrical properties. The morphological changes were traced via differential scanning calorimetry (DSC), thermogravimetry (TG), and Fourier transform infrared spectroscopy (FTIR). The study showed that the relationship between dopant concentration and morphological changes of the polymer is rather complex. A reduction of crystallinity at low dopant concentration, phase separation involving ion-polymer complexes at high concentration, and formation of neutral ion pairs at very high ion concentration are the proposed mechanisms to explain the conductivity data. The dissociation of ions, changes in viscosity, and their effect on ion mobility were also considered to explain conductivity and permittivity data. The advantages and limitations of the DEA 2970 for measuring the ionic conductivity of polymeric electrolytes are discussed.

Dielectric studies of ferroelectric liquid crystals

The dielectric properties of some ferroelectric alpha-chloroester thiobenzoate liquid crystal materials have been studied using a Du Pont 2970 dielectric analyzer (DETA) in the 0.01 Hz-100 kHz range. These materials exhibit smectic A and chiral smectic C mesophases, as well as additional mesophases in some cases. Transitions involving the chiral smectic C phase are of most interest because this phase has ferroelectric properties. The effect on these transitions of fluorine addition to the alkoxy tail was investigated. The Goldstone mode and soft mode are seen in the frequency dispersion curves of the dielectric loss factor. Very low heating rates of 0.01°C min −1 and small step-wise increments are possible, providing measurements at small temperature increments which permit close observation of the transition regions. DSC measurements and optical microscopy observations were also performed and the three techniques were found to be complementary.

Influence of water on pure sorbitol polymorphism

The behaviour of very pure sorbitol and sorbitol–water mixtures has been examined in relation to water content by both differential scanning calorimetry (d.s.c.) and a new thermal and dielectric analyser operating at microwave frequencies. A new hydrate has been isolated. Four different crystalline forms have been obtained from this hydrate and characterized by d.s.c. and X-ray diffraction. The influence of both temperature and water content on transitions from hydrate to other polymorphs has also been studied. Different types of water interactions have been evidenced from dielectric measurements for sorbitol and glucose, and comparisons of these, according to the physical states of the mixtures and hydrate properties have been made. For both molecules, the influence of water content on dielectric relaxation maximum temperatures has been studied and compared with the viscosity or the entropy. Non-congruency and possible deviation from stoichiometry are suggested for the new sorbitol hydrate. The dielectric properties of mannitol and sorbitol diastereoisomers have been measured at room temperature and compared. The glass transitions of sorbitol and sorbitol solutions have also been investigated down to 170 K by calorimetry measurements. The lowering of Tg with respect to water content is compared with isoviscosity curves.