PVDF/BaTiO3 composite foams with high content of β phase by thermally induced phase separation (TIPS)

Poly(vinylidene fluoride) (PVDF) displays ferroelectric, piezoelectric and pyroelectric behavior and it is widely used in high-tech applications including sensors, transducers, energy harvesting devices and actuators. The crystallization of this polymer into highly polar β phase is desirable but is hard to achieve without applying specific thermo-mechanical treatments. Indeed, fabrication processes directly affect PVDF molecular chain conformation, inducing distinct polymorphs. In this paper, we present the fabrication of PVDF/BaTiO3 composite foams by thermally induced phase separation method (TIPS). Different compositions are tested and characterized. The crystallinity, and in particular the development of electroactive β crystal phase is monitored by FTIR, DSC and XRD measurements. Dielectric properties are also evaluated. It turns out that TIPS is a straightforward method that clearly promotes the spontaneous growth of the β phase in PVDF and its composite foams, without the need to apply additional treatments, and also significantly improves the degree of crystallinity. BaTiO3 content gives additional value to the development of β phase and total crystallinity of the systems. The low permittivity values (between 2 and 3), combined with the cellular morphology makes these materials suitable as lightweight components of microelectronic circuits

Thermal investigation of acetochlor adsorption on inorganic- and organic-modified montmorillonite

Results presented in this paper are pioneering attempt toward better understanding of the thermal stability of acetochlor sorption in inorganic and organic montmorillonites. Changes in surface properties of acetochlor adsorbed on montmorillonites and montmorillonites modified with hexadecyltrimethylammonium bromide have been investigated by thermogravimetry, derivative thermogravimetry and infrared spectroscopy. The mass loss, as a result of the heating treatment, indicates release of free water, transformation of hydrophilic to hydrophobic surface, the release of acetochlor sorbed on the montmorillonite, the release of acetochlor sorbed on the montmorillonite and dehydroxylation of the structural OH units

Microhardness Evolution in Relation to the Crystalline Microstructure of Aluminum Alloy AA3004

Equal-channel angular pressing (ECAP) was used as a technique for severe plastic deformation (SPD) on Al alloy AA3004. This technique produced fully dense materials of refined grain structure to sub-micrometer dimensions and advanced mechanical properties. The ECAP processing of samples was conducted as 1 to 4 passes through the die at room temperature. We present the results of the studied homogeneity evolution with the ECAP treatment. Furthermore, a Scanning Electron Microscope (SEM) was used for examination of the microstructure changes in samples undergone from 1 to 4 passes. The microhardness-HV increased upon each ECAP pass. The resulting micro-hardness evolution was attributed to crystalline microstructure modifications, such as the d-spacing (studied by X-ray Diffraction-XRD) depending on the number of ECAP pressings. The microcrystalline changes (grain refining evaluated from the Scanning Electron Microscopy - SEM images) were found to be related to the HV, following the Hall-Petch equation

Comparison of structural, textural and thermal characteristics of pure and acid treated bentonites from Aleksinac and Petrovac (Serbia)

Bentonite samples collected from vicinity of Petrovac and Aleksinac were treated with different sulfuric acid molarities. Acid attack dissolved the octahedral sheets by interlayer and edge attack. The effects of the H(2)SO(4) acid caused an exchange of Al(3+), Fe(3+) and Mg(2+) with H. ions leading to a modification of the smectite crystalline structure. The Mg and Fe substitution in the octahedral sheets promoted the dispersion of corresponding layers and formation of amorphous silicon. The activated bentonites, after the treatment of sulfuric acid, exhibited a lower cation-exchange capacity (CEC)and significant increase of specific surface area from 6 to 387 m(2) g(-1) (bentonite from Petrovac) and from 11 to 306 m(2) g(-1) (bentonite from Aleksinac). The acid reaction caused a splitting of particles within the octahedral sheet which led to an increase in specific surface area and decrease in CEC in both bentonites. (C) 2011 Elsevier B.V. All rights reserved

Near-infrared spectroscopy study for determination of adsorbed acetochlor in the organic and inorganic bentonites

NIR spectroscopy is used to determine acetochlor herbicide adsorption on Na-montmorillonite (NaP) and organically modified montmorillonite (NaOM). Both montmorillonites NIR spectra shows bands at 7061 and 6791 cm(-1). Organo-montmorillonite is characterised by two emphasized bands at 5871 and 5667 cm(-1) that are attributed to the fundamental overtones of the mid-IR bands at 2916 and 2850 cm(-1). Bands at 6017 and 6013 cm(-1) are attributed to acetochlor adsorbed to organo-montmorillonite and Na-montmorillonite, which is confirmed by X-ray powder diffraction (XRPD). Greater quantity of acetochlor is adsorbed to organo-clays compared to non-modified montmorillonite. Acetochlor poses high risk to environmental contamination. Organo-clays are the most useful for removing acetochlor from water and soil

NIR and MIR spectroscopic characteristics of hydrophilic and hydrophobic bentonite treated with sulphuric acid

Near-infrared (NIR) and mid-infrared (MIR) spectroscopy are irreplaceable methods for characterization of bentonites. The paper presents work on bentonites modified with inorganic Na+ and organic HDTMA(+) (hexaclecyltrimethylammonium) cations and treated by 1.5, 3, 4.5 and 6M H2SO4. The characterization was based on the assignment of the stretching (nu) and bending (delta) vibrations observed in the MIR region and the first overtone [2 nu(R-H)] and combination [nu(R-H)+delta(R-H)] modes of R-H groups (R=O, C) in the NIR region. NIR spectrum shows the characteristic OH and CH bonds for organomontmorillonite. The effect of larger alkylammonium cations on the vibrations of Si-O and OH bonds in montmorillonite layers is observed. A few key-bands in the NIR region show the change of water in the interlayer montmorillonite. The intensities of the overtone (7080 and 6840cm(-1)) and combination (5242cm(-1)) bands of H2O have considerably decreased as a result of hydrophobic character of the NaOM. Spectra of acid-treated samples show a gradual decrease in the intensities of the OH overtone (near 7100-7000cm(-1)) and combination bands (4600-4300cm(-1)) reflecting a fewer number of octahedral atoms. This paper also points out that ATR technique and the 2nd derivative spectrum enables much precise band assignment

NIR and MIR spectroscopic characteristics of hydrophilic and hydrophobic bentonite treated with sulphuric acid

Near-infrared (NIR) and mid-infrared (MIR) spectroscopy are irreplaceable methods for characterization of bentonites. The paper presents work on bentonites modified with inorganic Na+ and organic HDTMA(+) (hexaclecyltrimethylammonium) cations and treated by 1.5, 3, 4.5 and 6M H2SO4. The characterization was based on the assignment of the stretching (nu) and bending (delta) vibrations observed in the MIR region and the first overtone [2 nu(R-H)] and combination [nu(R-H)+delta(R-H)] modes of R-H groups (R=O, C) in the NIR region. NIR spectrum shows the characteristic OH and CH bonds for organomontmorillonite. The effect of larger alkylammonium cations on the vibrations of Si-O and OH bonds in montmorillonite layers is observed. A few key-bands in the NIR region show the change of water in the interlayer montmorillonite. The intensities of the overtone (7080 and 6840cm(-1)) and combination (5242cm(-1)) bands of H2O have considerably decreased as a result of hydrophobic character of the NaOM. Spectra of acid-treated samples show a gradual decrease in the intensities of the OH overtone (near 7100-7000cm(-1)) and combination bands (4600-4300cm(-1)) reflecting a fewer number of octahedral atoms. This paper also points out that ATR technique and the 2nd derivative spectrum enables much precise band assignment

Adsorption of Acetochlor Herbicide on Inorganic- and Organic-Modified Bentonite Monitored by Mid-Infrared Spectroscopy and Batch Adsorption

The results of sorption of acetochlor herbicide with different concentrations (1-15 mu g/mL) in inorganic- and organic-modified bentonite are presented. Acetochlor sorption in both bentonite types was studied by attenuated total reflectance spectroscopy in the mid-infrared region and by batch equilibrium method. Infrared spectroscopy results suggest that the interaction of acetochlor with inorganic (or organic) bentonite takes place by mechanism involving the carbonyl stretching vibration and phenyl ring in the acetochlor molecule. The increase of the acetochlor concentration results in red shift of both corresponding band wavenumbers. Batch adsorption study pointed out more expressed sorption of acetochlor in organic bentonite

Vibrational spectra of (M3MS3)-M-I-S-III type synthetic minerals (M-I = Tl or Ag and M-III = As or Sb)

The vibrational (Raman and far infrared) spectra of four (M3MS3)-M-I-S-III type synthetic minerals (proustite, Ag3AsS3; ellisite, Tl3AsS3; pyrargyrite, Ag3SbS3; stibioellisite, Tl3SbS3) in the region from 600 to 100 cm(-1) (Raman) and 600 to 20cm(-1) (far infrared) were investigated. Their infrared and Raman spectra were compared with corresponding vibrational spectra of natural orpiment, As2S3, and stibnite, Sb2S3. In general, rather expressed similarity between the Raman spectra of the (M3AsS3)-As-I type synthetic minerals, and particularly between the (M3SbS3)-Sb-I type synthetic minerals (M-I = Ag or Tl) was observed. This is, most probably, due to the presence of the (MS3)-S-III pyramids (M-III = As or Sb) as main structural units in all minerals. The observed similarity between the Raman spectra of the (M3AsS3)-As-I type minerals and the corresponding spectrum of orpiment, As2S3 (also built up of (MS3)-S-III pyramids), justifies the treatment of those pyramids as a main vibrational units. The agreement between the Raman spectra of (M3SbS3)-Sb-I type minerals, on the one hand, and the Raman spectrum of stibnite, Sb2S3, on the other hand, is even much more pronounced. It was found, however, that the bands in the infrared spectra in the studied (M3MS3)-M-I-S-III type minerals, besides the sensitivity to the M-III atom (As or Sb), are significantly influenced by the nature of the M-I atom (Ag or Tl). This is most probably related to the different extent of the covalent character of the Ag-S bonds compared to the Tl-S bonds. (C) 2003 Published by Elsevier B.V

Piezoelectric properties of PVDF-TrFE/BaTiO3 composite foams with different contents of TrFE units

Piezoelectric (PE) materials play an important role in the emerging field of micro and wearable electronics. Achieving high PE response is a key feature for their use in energy harvesting and sensing systems. In this study, highly porous lightweight composite foams composed of PVDF-TrFE (70/30 and 80/20 mol%) and different BaTiO3 content (5, 10, and 20 wt%) are prepared by thermally induced phase separation method. The PE foams were structurally and thermally examined by using Fourier-transform infrared spectroscopy, x-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis analyses. All composite foams were characterized by high β-phase content, while the addition of ceramic particles resulted in higher crystallinity and thermal stability of the investigated foams. Two distinct poling methods were employed due to the different molar compositions of the copolymers. The PE response was measured by the PE strain coefficient (d33) and the output current (Ip). The composite foams based on PVDF-TrFE 70/30 mol% copolymer, having two well-separated Curie temperatures for the organic and inorganic phases, can be polarized to achieve the contribution of both components to the PE performance, reaching the highest value of −28.3 pC N−1 and 130 nA at 10 Hz for the composite with 20 wt% BaTiO3