micro-Brownian Motion Research Articles

Sodium Ion-Conducting Electrolytes Based on Chloroaluminate Ionic Liquids and δ-NaCl.

Sodium-containing ionic liquids are very promising candidates as ion-conducting materials in alternative to electrolytes based on lithium chemistry. Here we investigate a series of seven ionic liquids with formula (EMImCl/(AlCl3)1.5)/(δ-NaCl)x (0≤x≤0.74). The salt is comprised of a disordered form of NaCl prepared by metalorganic synthesis, which assures faster dissolution in high concentration. The vibrational investigation carried out by FT-IR spectroscopy in the medium IR region shed light on salt-IL interactions. The ionic conductivity was investigated by Broadband Electric Spectroscopy. The direct current conductivity (σdc) profiles versus the reciprocal temperature exhibited a Vogel-Tamman-Fulcher behavior indicating the assistance of micro-Brownian motions to ionic migration. The value of σdc at 25 °C for x=0.74 was found to be 1.2×10-2 S cm-1. Reversible deposition of Na and Al-containing species take place with high Coulombic efficiency (up to 97 %) and a high Na+ cation transport number (up to 0.95). The understanding of ionic speciation was investigated in comparison with aqueous acid-base systems exploring the benefits and limitations of such analogy. The role of a Grotthuss-type mechanism facilitating the exchange of chlorides between acidic catenated chloroaluminate species in anionic domains of the ILs is considered.

Mechanism of physical hardening on the fracture characteristics of polymer-modified asphalt binder

This article aims to reveal the physical hardening mechanism of polymer-modified asphalt binder (PMA) and accurately assess its impact on the low-temperature fracture properties of asphalt binders. Base asphalt binder (BA), styrene–butadiene–styrene modified asphalt binder (SBSMA), and crumb rubber modified asphalt binder (CRMA) were used as the research objects. Molecular dynamics (MD) simulation and differential scanning calorimetry (DSC) test were used to investigate the physical hardening mechanism of PMA at the microscopic level. The fracture characteristics of PMA under physical hardening were analyzed based on the single-edge notched beam (SENB) test. The results show that under prolonged cold service conditions, the asphalt molecular mobility is weakened, the non-bond energy and the free volume are reduced, and the molecules undergo aggregation state transformation, leading to the physical hardening of asphalt materials. In the process of physical hardening of asphalt molecules in the micro-Brownian motion of the main active force from the aromatic and saturate fractions. Considering the effect of physical hardening, it is recommended that the method used to test the low temperature properties of asphalt binders should ensure a constant temperature for at least 24 h. The crack tolerance (Ct) is recommended as the evaluation index of low-temperature cracking resistance of PMA in cold regions. The Ct of BA, SBSMA, and CRMA are reduced by 52.88 %, 12.04 %, and 35.24 %, respectively, after 24 h of constant low temperature. This indicating that the polymer modifiers can improve the fluidity of asphalt molecules, inhibit molecular aggregation, and reduce the effect of physical hardening on asphalt binders. Thermo-oxidative aging can aggravate the physical hardening phenomenon of asphalt binder, and the higher the degree of thermo-oxidative aging, the more severe the physical hardening of asphalt binder. The related research results provide the theoretical basis and technical support for the accurate design and development of the low-temperature performance of asphalt binders for roads in cold regions.

Thermal softening properties of various wood species within an annual ring

Dynamic mechanical analysis (DMA) measurements of water-saturated earlywood (EW) and latewood (LW) of various wood species in the temperature range from 0 to 100 °C were focused to clarify the differences in thermal softening properties within an annual ring. The following results were obtained. The peak of tanδ caused by micro-Brownian motion of lignin was observed in both EW and LW all species. For softwoods, the peak temperatures of tanδ of EW appeared at higher temperatures than those of LW. For hardwoods, in the other hand, the peak temperatures of tanδ were slightly different between EW and LW in the diffuse-porous wood, whereas the temperatures were almost the same in the ring-porous wood. It was found that the difference in peak temperature of tanδ between EW and LW varied greatly among species. The difference in peak temperature between EW and LW was relatively large for softwoods. In addition, the thermal softening properties both in the radial and tangential directions differed depending on the species, so this suggested that there was anisotropy in the thermal softening properties depending on the species.

Separation of Micro-Brownian Motion and Side-Group Rotational Motion for Poly(N-isopropylacrylamide) in 1,4-Dioxane Studied by Dielectric Relaxation Spectroscopy

Dielectric relaxation of poly(N-isopropylacrylamide) (PNiPAM) was investigated in 1,4-dioxane as a low-polarity solvent at a concentration between 0 and 20 wt %, temperature between 40 and −35 °C, and a frequency range between 40 Hz and 1.8 GHz. Results suggest that relaxation due to the molecular motion of PNiPAM has two components: relaxation of side-group rotational motion at ∼100 MHz and micro-Brownian motion of PNiPAM chain at ∼1 MHz at room temperature. These processes are described by the sum of two Cole–Cole equations. Furthermore, the relaxation times of these processes showed distinct temperature dependences, as confirmed by activation energies obtained from the Arrhenius plot. In addition, asymmetric relaxation was observed in the MHz region of PNiPAM in various solvents comprising two individual relaxations. This could explain some fundamental aspects of PNiPAM solution properties and provide a deeper understanding of the molecular dynamics of PNiPAM.

Oxygen permeability of regenerated cellulose films with different water regains

The effect of water regain on the oxygen permeability coefficient (OP) of regenerated cellulose film was investigated. The OP of the dry film was extremely low, which was classified as a “very high” performance gas barrier; however, the OP increased with increasing water regain, and reached to the OP similar to that of low-density polyethylene film, which was categorized as a “poor” gas barrier. The film thickness increased with increasing water regain, and edge-view small-angle X-ray scattering revealed widening of the space between microcrystals in the thickness direction. Oxygen molecules likely passed through the space between cellulose molecules, which was widened with increasing water regain. The viscoelastic measurements indicated that regenerated cellulose existed in a rubbery state under wet conditions. Overall, the OP of regenerated cellulose was increased because of the widening and micro-Brownian motion of cellulose main chains caused by water.

Synthesis of Supramolecular A8 Bn Miktoarm Star Copolymers by Host-Guest Complexation.

We report a new synthetic method to construct supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers by host-guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size-exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in the bulk. The micro-Brownian motion of the A8 B4 structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.

Combined analysis of microstructures within an annual ring of Douglas fir (Pseudotsuga menziesii) by dynamic mechanical analysis and small angle X-ray scattering

Dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS) measurements of water-saturated wood of Douglas fir (Pseudotsuga menziesii) in the temperature range of 0 ℃ to 100 ℃ were focused to clarify microstructural changes within an annual ring. The following results were obtained. Thermal softening behavior caused by micro-Brownian motion of lignin was observed in both earlywood and latewood. The peaks of tanδ were found at around 95 ℃ for earlywood and at around 90 ℃ for latewood. These results suggested that the structures of lignin in the cell wall were different between earlywood and latewood. SAXS measurements of water-saturated earlywood and latewood in water were performed with precise temperature control. The scattering intensity increased with increasing temperature, indicating that the density of the matrix was reduced at higher temperature. One-dimensional SAXS intensity at the equator, which approximately represents cellulose microfibrils arrangement in the matrix, was intensively analyzed using the WoodSAS model. The result of this model fitting showed that the cellulose microfibril diameter of latewood was higher than that of earlywood. In addition, the value of interfibrillar distance decreased monotonically in the earlywood, while it decreased rapidly in the latewood from 60 ℃ to 90 ℃. The changes in the cellulose microfibril (CMF) diameter and the interfibrillar distance with increasing temperature between earlywood and latewood by SAXS measurement were different. The differences in CMF diameter and inter-fibril distance between earlywood and latewood measured by SAXS also support the hypothesis that lignin structure differs between earlywood and latewood based on the results of DMA measurements.

Modification of the multiphase shape memory composites with functionalized graphene nanoplatelets: enhancement of thermomechanical and interfacial properties

Ameliorating the mechanical and thermomechanical properties of the shape memory polymers (SMPs) make them an important class of materials for new-age applications ranging from aerospace, electronics, and marine. To show the more recent attempts proof-of-concept in designing the SMPs with higher mechanical and thermomechanical properties, herein we had designed the multiscale shape memory hybrid composites (SMHCs) having known composition of functionalized graphene nanoplatelets (fGNPs) through dispersing the fGNPs uniformly using ultrasonication in shape memory epoxy polymer. Subsequently, hybrid composites were prepared through impregnation of carbon fiber in the fGNP ∼ epoxy solution. Mechanical and thermomechanical characterizations were performed to evaluate the effect of the fGNPs within the SMHC. Significant improvement in the mechanical and thermomechanical properties were achieved in the SMHC with amine functionalized fGNP compared with the carboxy functionalized fGNP and non-functionalized epoxy polymer. Compared with the unmodified carbon fiber reinforced polymer composites, SMHC with 0.4 and 0.6 wt% amine fGNP improved by 19.7% and 33.2%, whereas 5.9% and 17.4% by carboxyl fGNP. Morphological study indicated the improvement of wettability of carbon fiber and interfacial bonding between the fiber and matrix. The recovery of the modified polymer composites into the original shape primarily occurred due to the gradual release of internal energy harnessed in the frozen and active phase of the polymer network. Due to the incorporation of nanofillers, the molecular kinetic energy of the reversible active phase increases, which intensifies the micro-Brownian motion. Thereby, the recovery stage was achieved due to the return of the frozen phase to the disoriented entropy condition. The addition of nanoparticles increases the cross-linking, which in turn increases the volume of the frozen phase. Hence, higher volume of frozen phase would hamper the recovery of the samples in its original shape, resulting in the lower shape fixity. However, the shape memory parameters of shape fixity and shape recovery evaluated with the heat activation bending did not degraded significantly and remained ∼95 ± 2% and ∼96 ± 1%, respectively.

Multipoint Lock-and-Key Assembly of Particles with Anisotropic Dents toward Modeling Rigid Macromolecules in a Colloidal Scale.

Multipoint lock-and-key particle assembly, consisting of lock particles with multiple anisotropic dents and rod-shaped particles as key particles, is developed for colloidal modeling application. The lock particles were connected with each other at a key particle as their joint in the presence of depletants, forming rigid colloidal molecules imitating rigid polymers (e.g., polymers containing aromatic rings and intramolecular hydrogen bonds). A single-particle level observation was conducted to visualize the colloidal polymerization of the particle assembly. Motion trajectories of the lock particles observed by optical microscopy indicated that the particle diffusivity was dramatically lowered when the lock particle connected with another one, suggesting that particle diffusion was suppressed by particle assembly formation. Because the kinetic and regioselectivity of colloidal polymerization are assumed to be analogous to those at the atomic scale, the proposed lock-and-key assembly can be a promising colloidal model for atomic-scale polymers associated with their micro-Brownian motion.

The effect of Zn0.95Ni0.05O nanoparticles on the physical properties of polyvinyl chloride

Nanoparticles of Zn0.095Ni0.05O (ZNO) were prepared by the co-precipitation technique and added to polyvinyl chloride (PVC) to get nanocomposite films. X-ray diffraction (XRD) was performed on nano-sized ZNO to test its crystal structure. Field emission-scanning electron microscopy (FE-SEM) was used to check the homogeneity of PVC and the dispersion of ZNO on the surface of the polymer matrix. The crystal size of ZNO is about 40.5 nm. Energy-dispersive X-ray spectroscopy (EDS) revealed the same element compositions of ZNO. The dielectric properties of ZNO/PVC nanocomposite film were analyzed in details within the frequency and temperature ranges of 0.5–1000 kHz, and 303–430 K, respectively. The dielectric permittivity as well as the ac conductivity of pure PVC increased noticeably with adding ZNO nanoparticles. The dependence of both temperature and frequency of the dielectric modulus, M", showed α-relaxation due to the micro-Brownian motion of the main polymeric chains. The UV–vis spectroscopy revealed a pronounced increase in both absorbance and extinction coefficient by adding ZNO to PVC. Different optical parameters were calculated. The outcome results of this work were compared and discussed with similar nanocomposite films.

Relaxation phenomenon and swelling behavior of regenerated cellulose fibers affected by organic solvents

Regenerated cellulose fibers are extremely sensitive to water. In particular, their mechanical properties are greatly affected by water. Recently, it was clarified that the glass transition temperatures of regenerated cellulose over 500 K can be shifted to room temperature, and small-angle X-ray scattering (SAXS) showed the maxima and shoulders on the equator line in the wet state. In this study, glass transition caused by organic solvents was observed, although the peak heights of tangent δ (tan δ) were low, which suggested the regions affected by organic solvents were small. SAXS showed the maxima and shoulders, suggesting that organic solvents decreased the density of the amorphous region, i.e., widened space between cellulose molecules, creating sufficient space for the micro-Brownian motion of cellulose main chains. However, alkanes with molecular weight larger than n-nonane did not show tan δ peaks, which suggests that the solvent is hard to enter between microfibrils.

Dielectric and optical properties of PVA/PAN doped TiO2 NPs

Titanium dioxide nanoparticles (TiO2 NPs) were prepared by sol–gel method. The effect of TiO2 NPs on structure, dielectric and optical properties of PVA/PAN films was reported. The X-ray diffraction (XRD) and high resolution scanning electron microscopy (HR-SEM) it were used to characterize the prepared samples. The XRD result shows the phase formation of TiO2 as anatase, with average crystal size of about 50 nm. PVA/PAN-TiO2 nanocomposite films have an amorphous nature. In addition, the dielectric constant e′, the electric modulus M″ and the ac conductivity (σac) were studied also. It was found that e′ increases with temperature, dielectric relaxation observed by electric modulus M″, which may be associated with Micro-Brownian motion of the main PVA/PAN chains. The ac conductivity supports hopping mechanism for the nanocomposite films. The optical investigations show that, increasing TiO2 content of the samples results in a decrease of the optical band gap accompanied with an increase of the refractive index and electric susceptibility of the nanocomposite films

SiO2 particles effect on the mechanical properties of the starch/PVA blends

The present work studies the mechanical properties of SiO2 μPs, and NPs in St/PVA blends. The samples were prepared by casting method as PVA, St/PVA blends at different concentrations (30, 40, 50, and 60 %). DSC and TGA tests were carried out to the samples evolved. The result showed a single glass transition temperature (Tg) for all St /PVA blends that was attributed to the good miscibility of the blends involved. It was found that (Tg) decrease with starch ratio increase. It was seen that (PVA) of (Tg=105 oC); The glass transition temperature which was decrease with starch ratio that was attributed to glass transition relaxation process due to micro-Brownian motion of the main chain back bond. The endothermic peak at 200 oC was attributed to melting point of (PVA). Thermal properties of PVA; and St /PVA blends at different concentration (30, 40, 50, and 60 %) were evaluated by thermo gravimetric analysis (TGA). The analyses were carried out from 20 to 600 oC at 10 oC)/min heating rate in air oxygen atmosphere. The weight loss stages depended on polymer system. The starch addition causing shifting in the second degradation temperature to the higher temperature; which result in overlapping between the two main degradation steps, these result was attributed to the St/ PVA blend compatibility. The mechanical properties results showed a decrease in ultimate strength with starch ratio increase. The ultimate strength of (PVA) was (47 MPa), whereas the ultimate strength of 60 %St/PVA was (11 MPa) and for 30 %St/PVA was the highest ultimate strength of blends involved (26 MPa). SiO2μPs (753.7 nm), and NPs (263.1 nm) were added at different concentrations (1.5, 2, and 2.5 %). 1.5% SiO2μPs, and NPs of the best ultimate strength (69 MPa), (86 MPa) respectively then it was decreased by SiO2μPs, and NPs increase. Optical microscope of the samples involved was investigated. It was concluded the prepared samples were suggested to be used as packaging materials for agriculture application and its ultimate strength could be controlled by SiO2μPs, and NPs addition.

Electron beam induced modifications in the microstructure of PVA/Li2B4O7 polymer films: Positron annihilation study

The films of 5 wt% Lithium Tetra Borate (Li2B4O7) doped Poly(vinyl alcohol) (PVA) were prepared by solution casting method. The prepared films were irradiated with different doses of 8 MeV electron beam. Fourier Transform Infrared (FTIR) Spectroscopy, UV–Visible Spectroscopy, electrical conductivity measurements and Positron Annihilation Lifetime (PAL) Spectroscopy were used to study the effects of electron radiation on the microstructure and properties of these films. The FTIR results show that the radiation induced chain scission in Li2B4O7 doped PVA, which affects the physical properties of the composite film. The variation of optical parameters for instance optical energy band gap, activation energy were obtained from UV–Visible absorption spectra, which reveals the formation of additional energy levels within the band gap due to the creation of defects and carbonaceous clusters upon irradiation. The conductivity of the sample was found to increase as the electron dose increased. It was found from the PAL study that the free volume size of the polymer increases with electron dose, which facilitates the micro-Brownian motions of the segmental polymer chain backbone. Consequently the motion of Li+ ions within the polymer segment will be speeded up. Accordingly ion transport within the polymer matrix strongly depends on rearrangement of free volume adequate to allow ion transport.

Influence of the structure on the collapse of poly(N-isopropylacrylamide)-based microgels: an insight by quantitative dielectric analysis.

The collapse of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) and poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) microgel suspensions is studied by dielectric spectroscopy in a frequency range from 40 Hz to 110 MHz as a function of temperature. Dielectric measurements show that the structure affects the relaxation behavior of microgels: two relaxations (micro-Brownian motion and interfacial polarization at low frequency and counterion polarization at high frequency) are observed in the SIPN microgel whose charges mainly exist in domains and one relaxation (interfacial polarization) is observed in the copolymer microgel whose charges distribute in the whole network. A dielectric model is proposed to describe the collapsed microgel suspensions, from which some parameters, such as the volume fraction and the permittivity of microgels, were calculated using Hanai's equation. The temperature dependencies of these parameters show that the SIPN microgel has better low-temperature swelling properties and thermal responsiveness. This is caused by different polymer-solvent and electrostatic repulsion interactions in different microgels. Compared with pure PNIPAM, the relationship of volume phase transition temperature (VPTT) is VPTTP(NIPAM-co-AA) > VPTTPNIPAM/PAA SIPN > VPTTPNIPAM, and it is explained from the viewpoint of interaction. Besides, the activation energy data prove that the structure influences the electrical properties of microgels, which is consistent with the results obtained from quantitative dielectric analysis.

Characterization and Optical and Dielectric Properties of Polyvinyl Chloride/Silica Nanocomposites Films

Silica nanoparticles were synthesized by a sol-gel method and mixed with different amounts of polyvinyl chloride (PVC) to get nanocomposite films. The samples were characterized by XRD, HR-TEM, SEM, and FTIR. High resolution transmission electron microscopy (HR-TEM) proved that the average particle size of the nanosilica is 15 nm. The scanning electron microscopy (SEM) showed that the nanosilica was well dispersed on the surface of the PVC films. Fourier Transform Infrared (FTIR) spectra for nanocomposite films intimate a significant change in the intensity of the characteristic peaks of the functional group with addition of nanosilica. The optical band gap was found to decrease with the addition of nanosilica while the refractive index increased. The dielectric constantε′, the dielectric loss modulusM′′, and AC conductivity(σAC)were also studied. It was found thatε′increases with temperature for all samples, clear dielectricα-relaxation observed from dielectric lossM′′around the glass temperature (Tg), and this could be related to micro-Brownian motion of the main PVC chain. The activation energy was calculated, and the AC conductivity could be a hopping one. The results of this work are discussed and compared with previously obtained data.

Anomalous Volume Phase Transition Temperature of Thermosensitive Semi-Interpenetrating Polymer Network Microgel Suspension by Dielectric Spectroscopy.

A new experimental result from dielectric spectroscopy of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) microgel, which undergoes significant volume phase transition, is reported. Two significant dielectric relaxations were observed around 0.1-0.5 MHz and 1-5 MHz, respectively. The high-frequency relaxation is attributed to the migration of counterions tangentially and radially along the domain formed by linear PAA chains (counterion polarization). The temperature dependence of the domain size obtained from this relaxation shows that the SIPN microgel with higher content of PAA has better thermal response and swelling property. The low-frequency relaxation shows two separate mechanisms below and above the volume phase transition temperature (VPTT), which are dominated by different relaxation processes, respectively: micro-Brownian movement of solvated side groups of PNIPAM dominates when T < VPTT, while the interfacial polarization does when T > VPTT. A dielectric model was proposed to describe the collapsed microspheres suspension, from which the electrical parameters of microgel were calculated. The permittivity of microgel shows that a special ordered arrangement of water molecules is formed in microgel with less PAA. Thermodynamic parameters obtained from Eyring equation reveal that the difference in PAA content has a great influence on the thermodynamics of the phase transition process. Besides, it was found that the VPTT of the SIPN microgel was significantly increased compared with pure PNIPAM hydrogel microspheres. The essence of anomalous VPTT revealed by relaxation mechanism is the difference in composition content leading to different hydrophilic/hydrophobic and electrostatic interaction. Determining the reason for anomalous VPTT is of instructive significance to understand the volume phase transition of complex polymer materials.

Measurement of polyethylene pellets near the glass transition temperature to enhance Raman spectral selectivity among samples and improve accuracy for density determination.

A simple and effective strategy for improving the accuracy of the multivariate determination of polyethylene (PE) density using Raman spectroscopy has been demonstrated. This strategy is based on the possibility that varied polymeric structures of the PE samples, especially at a sub-zero temperature range, would enhance their spectral selectivity, thereby potentially improving the multivariate correlation with their pre-determined physical properties such as density. For the evaluation, Raman spectra were collected at regular intervals during continuous increase of the PE temperature from cryogenic to near room temperature. Then, using partial least squares (PLS) regression, calibration models were developed to correlate the Raman spectral features collected at each time period with the reference PE density values. Interestingly, the accuracy was improved when the temperature of the PE pellets was -35 °C, near the glass transition temperature (Tg). To explain the improved accuracy, a two-dimensional (2D) correlation analysis was employed to detail the spectral variation induced by temperature change. Diverse segmental chain motions (so called micro-Brownian motion) predominantly occurring in the amorphous section of the PEs around Tg greatly enhanced the spectral selectivity among PE samples. In addition, minor β-relaxation occurring around this temperature was an additional source of the enhanced spectral selectivity. In parallel, differential scanning calorimetry (DSC) curves of the samples were also examined to check the existence of the phase transitions.

Dielectric relaxations of poly(N-isopropylacrylamide) microgels near the volume phase transition temperature: impact of cross-linking density distribution on the volume phase transition.

Dielectric relaxation behaviors of three types of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels with different cross-linking density distributions were investigated in a frequency range from 40 Hz to 110 MHz at temperatures from 15 °C to 55 °C. After eliminating the electrode polarization at low frequency, two remarkable relaxations were observed, one in the kHz frequency range and the other in the MHz range. The low-frequency relaxation is attributed to the counterion polarization in the whole measuring temperature range, while the relaxation at high-frequency is probably dominated by different polarization mechanisms depending on below or above the volume phase transition temperature (VPTT): it is considered as micro-Brownian motion of side groups of PNIPAM when T < VPTT and interfacial polarization when T > VPTT. The temperature dependence of the dielectric parameters for both the relaxations presents an abrupt change around 32.5 °C, indicating the occurrence of phase transition. Based on the analysis and discussion about the micro-Brownian motion of the side groups, a possible microstructure for the microgels before and after the collapse of PNIPAM was suggested. A dielectric model to describe the collapsing microgel suspension was proposed, from which the electrical and structural parameters of the suspension were calculated. The information on the internal structure and hydration dynamic behavior of microgels was obtained by using the thermodynamic parameters which were calculated based on the Eyring equation. Our results reveal that the spatial distribution of the cross-linking density distribution has almost no effect on the volume phase transition temperature, but markedly affects the swelling capacity of PNIPAM microgels at low temperatures.

α-Fe2O3 /(PVA + PEG) Nanocomposite films; synthesis, optical, and dielectric characterizations

Hematite (α-Fe2O3) nanorods with an average diameter of 40 nm were prepared using a template-free sol–gel method. These nanorods then mixed with polyvinyl alcohol (PVA)/polyethylene glycol (PEG) blend at concentrations of 0.0, 0.5, and 1.0 wt.%. The transmittance percentage (T%) of the films showed a decrease from 80.26 to 33.24 %. The direct optical band gap also decreased from 5.28 to 4.83 eV whereas the refractive index significantly increased with increasing the hematite content. The dielectric measurements were performed in the temperature range 303–413 K and frequency range 30 kHz–3.0 MHz. According to the temperature dependence of the dielectric constant (e’), αa-relaxation peaks observed in all films and assigned to the micro-Brownian motion of the polymer blend chains. The behavior of the ac conductivity, σac (f), of the nanocomposite films indicated that the homogenous distribution of α-Fe2O3 nanorods allows the formation of conductive three-dimensional networks throughout the nanocomposite film. Also, indicated that the correlated barrier hopping is the most suitable conduction mechanism.