micro-Brownian Motion Research Articles

Synthesis and controlling the optical and dielectric properties of CMC/PVA blend via γ-rays irradiation

Carboxymethyl cellulose (CMC)/Polyvinyl alcohol (PVA) blend films were prepared by solution casting method. Then, these films were irradiated with γ-rays from a Co-60 source at doses over the range 0–70kGy to investigate the modifications induced in the optical and dielectric properties. The dielectric constant (ε′) was measured in the temperature range 303–408K and in the frequency range 10kHz–1MHz. The indirect optical band gap was found to increase within the dose range 0–10kGy, and to decrease at the higher doses. The refractive index values, however, showed a reversed behavior. The highest transmittance percentage was obtained at 10kGy dose. According to the frequency and temperature dependence of ε′, α- relaxation peaks were observed in all samples and assigned to the micro-Brownian motion of the blend chains. The values of ɛ′ showed a decrease in the dose range 0–10kGy and an increase in the dose range 10–70kGy. The ac conductivity σac (T) showed an Arrhenius type behavior separated into two distinct regions. The results of the present system are compared with those of similar materials.

Controlling the dielectric and optical properties of PVA/PEG polymer blend via e-beam irradiation

Polyvinyl alcohol (PVA)/polyethylene glycol (PEG) blend films were prepared by the solution casting method. The films were irradiated using 1.5 MeV of the electron beam at varying doses over the range 0–70 kGy to investigate the modifications induced in the dielectric and optical properties. The dielectric constant (e′) and dielectric loss (e″) were measured in the temperature range 308–408 K and in the frequency range 30 kHz - 3 MHz. According to the frequency and temperature dependence of e′; an α- relaxation peaks were observed in all samples and assigned to the micro-Brownian motion of the polymer blend chains. Both e′ and e″ showed a decrease with 5 and 10 kGy doses and an increase in the dose rang 10–70 kGy. The temperature dependence of the ac conductivity (σ ac (T)) shows an Arrhenius type behavior separated into three distinct regions. The frequency dependence of the ac conductivity (σ ac (f)) indicates that the correlated barrier hopping (CBH) is the most suitable mechanism for conduction. Also, the influence of e-beam irradiation on the absorption coefficient (α), the indirect optical band gap (E g ) and the refractive index (n) of PVA/PEG copolymer films were investigated. The results of the present system are compared with those of similar materials.

Dielectric relaxation and optical properties of polyvinyl chloride/lead monoxide nanocomposites

Sol–gel synthesized lead monoxide (PbO) nanoparticles were mixed with polyvinyl chloride (PVC). The dielectric characteristics of PVC/PbO nancomposite films were studied in the temperature range 303–408 K and frequency range 30 kHz–3 MHz. There is a sharp increase in the dielectric constant (e′), after the glass transition temperature. According to the temperature and frequency dependence of the dielectric loss modulus (M″), the observed αa-relaxation peak is due to the micro-Brownian motion of the polymer main chains. The behavior of σac (f) for the composite films indicate that the homogenous distribution of PbO nanoparticles allows the formation of conductive three-dimensional networks throughout the nanocomposite films which assisting the charge carriers to hop from conducting clusters to neighbors. The influences of PbO content on the direct optical band gap and the refractive index of the films are also discussed and compared with those of previous studies of PVC composites. POLYM. COMPOS., 34:2031–2039, 2013. © 2013 Society of Plastics Engineers

Dynamic Mechanical Properties of Trimethylborate (TMB) Modified Poplar Wood by Sol-Gel Process

To develop novel wood preservation technique trimethylborate(TMB) and boric dioxide were used by sol-gel process to modify poplar (Populus euramevicana cv.‘I-214'.) wood. The temperature variations of the storage modulus and the loss tangent along the grain for two kinds of chemically modified poplar woods were measured at 2Hz over a temperature range of -50 to 200°C. The storage modulus of modified woods were observed slight increases over the temperature range tested by introduction of bulky side chains and the tanδ remarkably reduced due to boric acid bridges between the hydroxyl groups which restricted the micro-Brownian motion of the main chains. In TMB treatment, peak width at half height of tanδ broadened significantly, indicating remarked cross-linking effect in polycondensation with wood cellulose.

Miscibility Behavior of Poly Ethylene Glycol or Poly Ethylene Succinate/Chlorinated Poly Vinyl Chloride Blends Studied by Dielectric Relaxation Spectroscopy

The miscibility of chlorinated poly vinyl chloride (CPVC) and poly ethylene glycol (PEG) or poly ethylene succinate (PES) had been investigated using dielectric relaxation spectroscopy (DRS) over frequency and temperature ranges; 10 kHz - 4 MHz and 300 - 450 K, respectively. Three relaxation processes namely ρ-, α’-, and α-relaxation processes were observed for tan(δ) and the electric modulus M" of pure components and blends. The first one was attributed to the space charge polarization or the Maxwell-Wagner polarization. The second one was related to the amorphous regions located between the lamellar crystal stacks. The third one was due to the micro-Brownian motion of CPVC main chains. This process was found to be dependent in respect of temperature and frequency. The molecular dynamics of α-relaxation process were influenced by blending, i.e., the dielectric strength (De), the peak broadness, and the peak maximum of tan(δ) were found to be compositional dependent. Electric modulus analysis reveals that there is a role of electrode polarization for the dielectric relaxation.

Influence of Cr2O3 nanoparticles on the physical properties of polyvinyl alcohol

Nano-sized chromium oxide (Cr2O3) was synthesized by sol-gel method and mixed with polyvinyl alcohol (PVA) to produce nanocomposite films. Scanning electron microscopy (SEM) was used to observe the morphology and dispersion of Cr2O3 on the surface of the PVA films. X-ray diffraction (XRD) was performed on nano-sized Cr2O3, pure PVA, and Cr2O3/PVA composites. Based on the results of both XRD and high-resolution transmission electron microscopy (HR-TEM), the average particle size of the Cr2O3 was ≈ 46 nm. Differential scanning calorimetry (DSC) showed that the thermal stability and degree of crystallinity of the PVA were reinforced by the addition of Cr2O3 nanoparticles. The absorbance and extinction coefficients of the composites were studied in the UV-vis range and compared with those of pure PVA. The optical energy band gap, Eg, was calculated. Dielectric constant, ε′, dielectric loss modulus, M″, and ac conductivity, σac, of all samples were measured within temperature and frequency ranges of 300–468 K and 10 kHz-2 MHz, respectively. According to the frequency and temperature dependence of the dielectric loss modulus, M″, the observed α-relaxation peak was due to the micro-Brownian motion of the polymer main chains. The behavior of σac(f) for the composite films indicated that the conduction mechanism was correlated barrier hopping (CBH). The results of this work were discussed and compared with those of previous studies of PVA composites.

Dielectric relaxation and alternating current conductivity of lanthanum, gadolinium, and erbium-polyvinyl alcohol doped films.

Fourier transform infrared (FTIR) spectrum dielectric constant, ε', loss tangent, tan(δ), electric modulus, M*, and ac conductivity, σ(ac), of pure polyvinyl alcohol (PVA) as well as La-, Gd-, and Er-PVA doped samples have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 300-450 K and 1 kHz-4 MHz, respectively. FTIR measurements reveal that La(3+), Gd(3+), and Er(3+) ions form complex configuration within PVA structure. Two relaxation processes, namely, ρ and α were observed in pure PVA sample. The first process is due to the interfacial or Maxwell-Wagner-Sillers polarization. The second one is related to the micro-Brownian motion of the main chains. For doped PVA samples, α-relaxation process splits into α(a) and α(c). This splitting is due to the segmental motion in the amorphous (α(a)) and crystalline (α(c)) phases of PVA matrix. Electric modulus analysis was discussed to understand the mechanism of the electrical transport process. The behavior of ac conductivity for all PVA samples indicates that the conduction mechanism is correlated barrier hopping.

Effect of plastic deformation on the character of micro-brownian motions in glassy poly(methyl methacrylate)

Glassy PMMA samples are plastically deformed at room temperature in the uniaxial compression regime to residual strains of e res = 25%. Dielectric spectra of the initial and deformed samples are recorded via the method of broadband dielectric spectroscopy in the frequency range f = (5 × 10−4) − 107 Hz. The results are compared with the dynamic mechanical spectra of samples deformed under the same conditions. Dielectric and mechanical spectra are noticeably distorted by deformation. As a result, dielectric permittivity ɛ′ increases, shear modulus G′ decreases, and the intensity of dielectric β losses slightly increases, while dielectric and mechanical α losses increase appreciably. In addition, the “anomaly” of total dielectric Δɛtot and total mechanical ΔG tot dispersions (Δɛtot = ɛ0 − ɛ∞ ≈ Δɛα + Δɛβ and ΔG tot = G 0 − G ∞ ≈ ΔG α + ΔG β) occurs, that is, the polymer is transformed from the state with Δɛα ≪ Δɛβ and ΔG α Δɛβ and ΔG α > ΔG β. The described phenomenon is related to a strong gain in α dielectric and mechanical losses in the deformed material. It is found that α losses increase owing to an anelastic deformation component arising during glass loading. This component is responsible for an increase in the internal energy of the glass during its anelastic deformation. Possible causes of the observed effects are discussed.

Dielectric and Electric Modulus Behavior of Chlorinated Poly(Vinyl Chloride) Stabilized with Phenyl Maleimide

Dielectric constant, e', dielectric loss factor, e, electric modulus, M, and ac conductivity, σac, of pure CPVC and that stabilized with 10 wt% of phenyl maleimide, PM, have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 310 K - 450 K and 1 kHz- 4 MHz, respectively. The incorporation of 10 wt% of PM as stabilizer for CPVC leads to reduce its Tg from 405K to 378K at 10 kHz. PM molecules within CPVC structure reduce the double bond, stabilizer effect, and cause the widely spacing between CPVC main chains, plasticizer effect. Three dielectric relaxation processes namely ρ, α', and α were observed for pure CPVC. The first process was explained based on space charge formation or Maxwell-Wagner-Sillers, MWS, polarization. The second one is due to the segmental motion of the branching of CPVC. The third process occurs around the glass-rubber temperature, Tg, and is related to the micro-Brownian motion of the main polymer chain. Electric modulus and ac conductivity reveal that the conduction mechanism of CPVC is follow the correlated barrier hopping, CBH, while stabilized sample exhibits a quantum mechanical tunneling, QMT, type conduction.

Dielectric relaxation and alternating current conductivity of polyvinylidene fluoride doped with lanthanum chloride

X-ray diffraction (XRD), dielectric constant (ɛ′), dielectric loss factor (ɛ″), and ac conductivity (σac) of pure and LaCl3-doped polyvinylidene fluoride (PVDF) have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 140–450 K and 0.1−1000 kHz, respectively. XRD results reveal that pure and LaCl3-PVDF samples are in the α-phase. The incorporation of La3+ ions within the PVDF polymer matrix forms complexes which reduce the order structure of PVDF. Three relaxation processes, namely; ρ, αa, and αc were observed for pure PVDF. The first relaxation can be explained based on space charge formation or Maxwell-Wagner polarization. The second one occurs around the glass transition temperature, Tg, and is related to the micro-Brownian motion of the main polymer chain. It becomes broad and shifted to higher temperatures with the doping of LaCl3. The third process appears below the melting temperature of PVDF and can be attributed to molecular motions of the main polymer chain. The behavior of the ac conductivity shows that the conduction mechanism of pure, 5 wt. % and 10 wt. % of LaCl3-doped PVDF samples is follows the correlated barrier hopping (CBH) model, while 3 wt. % of LaCl3-doped PVDF exhibits a small polaron tunneling (SPT) conduction.

Investigation of the mobility in poly(vinylidene fluoride) ferroelectric films with different structures

The molecular mobility in two isotropic poly(vinylidene fluoride) samples crystallized in the α phase from the melt with different crystallinities and lattice perfections has been investigated by broadband dielectric spectroscopy. It has been revealed that the local-mobility parameters are insensitive to structural features. The average relaxation times of micro-Brownian motion in the disordered phase are found to be identical in the samples under consideration, which can be associated with the localization of the mobility in the interphase layer at the crystal-amorphous phase interface. The motion in the crystal (α c transition) has been described using the soliton mechanism of relaxation. It has been found that, as should be expected, the average relaxation time increases with an increase in the longitudinal crystal size; however, in this case, a strict quantitative correlation is absent. According to the small-angle X-ray scattering data, this is caused by different microstructures of interlamellar amorphous regions. It has been demonstrated that the samples with a higher degree of crystallinity are characterized by a larger difference in the electron densities of the crystalline and amorphous phases and a larger size of the amorphous layer. It has been assumed that an increase in the concentration of chemical defects in the interlamellar layers with a simultaneous increase in their length is responsible for the increased probability of attenuation of the solitary wave (conformational defect) in its passage between neighboring lamellar crystals.

Electrical conduction and dielectric relaxation in polyethylene terephthalate succinate

AbstractElectrical conduction and complex permittivity are examined in polyethylene terephthalate succinate, focusing on their relations to dielectric relaxation processes. Both the real and imaginary parts of the complex permittivity, namely, the dielectric constant ε′r and the dielectric loss factor ε′′r, increase with a decrease in frequency, especially at high temperatures. They are both ascribed to the transport of ionic mobile carriers. Namely, the carrier transport forms a conduction current that should contribute to ε′′r. On this occasion, if charge exchange does not occur at the two electrodes, heterocharge layers should be formed before the electrodes. This should increase the charge density on the electrodes, thus contributing to ε′r. In addition to the increase in ε′r and ε′′r due to mobile ions, two relaxation processes, one due to micro‐Brownian motion of dipoles and the other due to orientation and magnitude change of the dipole moment induced by two end groups in the polymer main chain, are observed. Corresponding to these two relaxation processes, two thermally stimulated discharge current (TSDC) peaks appear. The two TSDC peaks as well as the increments in ε′r and ε′′r become larger when the crystallinity of the sample decreases. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 1–8, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20956

The effect of lignin on the bending properties and fixation by cooling of wood

To clarify the effects of lignin on the fixation of bending deformation by cooling, cooling set for delignified woods with various lignin residues were investigated to compare with mechanical and dynamic viscoelastic properties. Bending tests showed that steep reductions occurred in the modulus of elasticity and modulus of rupture with delignification during the initial stage of delignification. The dynamic viscoelastic measurements revealed that the peak temperature of tan δ due to micro-Brownian motion of lignin was reduced with delignification, and the peak disappeared in the temperature range of 5°–100°C for the specimens that had lost more than 21% of their weight. On the other hand, no clear change in residual set was found in the range of 0%–15% of weight loss in spite of a marked reduction in lignin content. Subsequently, set decreased steeply for the specimens delignified beyond 15% of weight loss. It was suggested that cooling set is not determined solely by lignin content but is influenced by changes in the quality of lignin due to delignification. Lignin quality affects the balance of the elastic potential to recover from deformation and its viscosity, which is an indication of resistance against flow.

Single-Molecule Imaging of a Micro-Brownian Motion of a Chiral Helical π-Conjugated Polymer as a Molecular Spring Driven by Thermal Fluctuations

Abstract We observed a micro-Brownian motion of single molecules of a chiral helical π-conjugated polymer as a molecular spring on mica substrate under n-octylbenzene at room temperature using high-speed (rapid scan) AFM. The average velocity at the chain end of the polymer was 67 nm s−1 at the observation point. The analytical result shows that the mean square displacement in a single polymer chain is proportional to the time and, hence, complies with Einstein’s law of Brownian motion. The diffusion constant (D) is measured to be 8.2×10−15 m2 s−1 at the solid/liquid interface.

Dynamic viscoelastic behavior of wood under drying conditions

In this study heartwood from a Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantation was treated using a high-temperature drying (HTD) method at 115°C, a low-temperature drying (LTD) method at 65°C, and freeze vacuum drying (FVD), respectively. The dynamic viscoelastic properties of dried wood specimens were investigated. The measurements were carried out at a temperature range of −120 to 250°C at four different frequencies (1, 2, 5, and 10 Hz) using dynamic mechanical analysis (DMA). We have drawn the following conclusions: 1) the storage modulus E′ and loss modulus E″ are the highest for HTD wood and the lowest for FVD wood; 2) three relaxation processes were detected in HTD and LTD wood, attributed to the micro-Brownian motion of cell wall polymers in the non-crystalline region, the oscillations of the torso of cell wall polymers, and the motions of the methyl groups of cell wall polymers in the non-crystalline region in a decreasing order of temperatures at which they occurred; and 3) in FVD wood, four relaxation processes were observed. A newly added relaxation is attributed to the micro-Brownian motions of lignin molecules. This study suggests that both the HTD and the LTD methods restrict the micro-Brownian motion of lignin molecules somewhat by the cross-linking of chains due to their heating history.

Characteristics of bamboo tissue in relation to cooling set

To clarify the effects of tissue and structure of bamboo on its bending properties and set by cooling (bent at 90°C and cooled to 20°C with bending), the effects of set in bast-fiber-rich (Bfib) and parenchyma-cell-rich (Bpar) specimens were investigated with regard to their dynamic viscoelastic properties, chemical composition, and recovery from deformation with time. The results are summarized as follows: (1) while no clear effect of the proportion of parenchyma cells and bast fibers on residual set immediately after cooling was found, the relative recovery from the deformation with time for Bfib was larger than that for Bpar. (2) Slightly higher lignin content and a-cellulose were seen in Bfib than in Bpar. (3) The peak temperature of loss modulus (E″) found for Bpar, which was attributable to micro-Brownian motion of lignin, was obviously lower than that for Bfib. This was considered to be due to differences in the degree of condensation of lignin or higher-order structure. From these results, it was deduced that the bastfiber-rich specimen, which showed a higher peak temperature regarding thermal softening of lignin allowing the induction of insufficient thermal-softening in the range of 20° to 90°C, caused a larger recovery from deformation with time.

Specifics of structural transformations in poly(vinylidene fluoride)-based ferroelectric polymers in high electric fields

The behavior of polymorphic transformations in the solid phase under the action of strong electric fields in crystallizable ferroelectric polymers based on PVDF was analyzed. The occurrence of two transitions, α → αp and α → β, was revealed by means of IR spectroscopy in homopolymer films crystallized as a mixture of the nonpolar α phase and the polar β phase. If such films were crystallized into the ferroelectric β phase, the action of the field reduced to the processes of reorientation of chain segments in the all-trans (planar zigzag) conformation. Reversible and irreversible changes in the crystallinity are possible in this case. A shift in the frequency of some skeletal-vibration bands indicates a change in the mechanical stress on atomic bonds. For vinylidene fluoride copolymers in polar crystals, the field can initiate molecular rearrangements, which lead to an increase in the interchain density of chain packing in the lattice. It was assumed that the delayed kinetics of field-induced solid-state transformations is controlled by two factors. On the one hand, the nucleation of the new phase follows the fluctuation mechanism of appearance of conformation defects of the kink-link type in the initial crystal. An important role is played in such processes by the dynamics of amorphous-phase tie chains bordering the crystals, when a decrease in their activation energy in micro-Brownian motion processes increases the probability of a conformational defect appearing in the crystal. On the other hand, the role of space charge (including the charge due to carrier injection from the electrode metal) in the formation of a local electric field is substantial. Allowance for both factors may provide a qualitative explanation of the specifics of the kinetics of these structural transformations in an electric field.

ポリエチレンテレフタレートサクシネートにおける電気伝導と誘電緩和

Electrical conduction and complex permittivity are examined in polyethylene terephthalate succinate, focusing on their relations to dielectric relaxation processes. Both the real and imaginary parts of complex permittivity, namely dielectric constant er' and dielectric loss factor er'', increase with a decrease in frequency, especially at high temperatures. They are both ascribed to the transport of ionic mobile carriers. Namely, the carrier transport forms conduction current that should contribute to er''. On this occasion, if charge exchange does not occur at the two electrodes, heterocharge layers should be formed before the electrodes. This should increase the charge density on the electrodes, thus contributing to er'. In addition to the increase in er' and er'' due to mobile ions, two relaxation processes, one due to micro-Brownian motion of dipoles and the other due to orientation and magnitude change of the dipole moment induced by two end groups in the polymer main chain, are observed. Corresponding to these two relaxation processes, two thermally stimulated discharge current (TSDC) peaks appear. The two TSDC peaks as well as the increment in er' and er'' become larger when the crystallinity of the sample decreases.

Single Molecular Imaging of a micro-Brownian Motion and a Bond Scission of a Supramolecular Chiral π-Conjugated Polymer as a Molecular Bearing Driven by Thermal Fluctuations

Abstract The micro-Brownian motion of a single polymer chain was directly measured by high-speed (rapid-scan) AFM on a mica substrate under an aqueous solution at room temperature. The diffusion constant was 1.3×10−14 m2/s, which is a basic property of a molecular bearing at a solid–liquid interface. The molecule was a micrometer-long supramolecular chain in which π-conjugated polyrotaxane was coupled by a π–π interaction. Bond scission of this supramolecular chain was directly observed, and the dynamic folding behavior of a single polymer chain was also imaged.

Effect of Crystallinity on Electrical Conduction Characteristics of Poly(L-lactic acid)

The crystallinity of poly(L-lactic acid) was changed by thermal annealing and its effects on electrical conduction characteristics were studied. Low-crystallinity samples have a higher conductivity and a higher remaining charge quantity than high-crystallinity samples. The sample shows two thermally stimulated current (TSC) peaks at around Tg and about 20 °C higher than Tg when its crystallinity is low, while it shows only the former TSC peak when its crystallinity is high. The TSC peak at around Tg is attributable to the micro-Brownian motion that enables the orientation of dipoles in a direction perpendicular to the polymer main chain, whereas the high-temperature peak is attributable to the orientation and magnitude change of the end-to-end vector in the polymer main chain.