Simultaneous direct measurement of the electrocaloric and dielectric dynamics of ferroelectrics with microsecond temporal resolution.

A contactless technique for direct time-resolved measurements of the full dynamics of the adiabatic temperature change in electrocaloric materials is introduced. The infrared radiation emitted by the electrocaloric sample is sensitively detected with µs time resolution and mK temperature resolution. We present time-resolved measurements of the electrocaloric effect up to kHz frequencies of the driving electric field and down to small field strengths. The simultaneous recording of transients for applied electric field and induced polarization gives a comprehensive view of the correlation of electrocaloric and ferroelectric properties. The technique can further be applied to the continuous measurement of fatigue for >106 electric field cycles.

Poly(vinyl alcohol) freeze casts with nano-additives as potential thermal insulators.

Freeze-casting consists of freezing a liquid suspension (aqueous or other), followed by sublimation of the solidified state to the gas state under reduced pressure, and subsequent sintering of the remaining scaffold to consolidate and densify the struts and walls. The structure is very porous with the pores being a replica of the solvent crystals. The technique is rather versatile and the use of a liquid solvent (water most of the time) as a pore forming agent is a strong asset. Freeze-casting has also been developed as a near net shape forming route yielding dense ceramics. In this work we report on porous composite materials synthesized via the ice templating method. Poly(vinyl alcohol) (PVA) is used as matrix and nano-silica (SiO2), nanoclay (NC) and microfibrillated cellulose (MFC) are used as fillers to improve the mechanical stability of the PVA scaffold. We show our results on the porosity and mechanical stability and consider these porous nanocomposites as potential insulation materials with low thermal conductivity and superior mechanical properties.

Evolution of poled state in P(VDF-TrFE)/(Pb,Ba)(Zr,Ti)O3 composites probed by temperature dependent Piezoresponse and Kelvin Probe Force Microscopy.

Polarized states of polymer/inorganic inclusion P(VDF-TrFE)-(Pb,Ba)(Zr,Ti)O3 composites are studied at the nanoscale using both piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM). It has been shown that inorganic inclusions can be visualized using KPFM due to a discontinuity of the surface potential and polarization at the interface between the inclusions and the polymer matrix. The temperature evolution of the PFM and KPFM signal profiles is investigated. Softening of the polymer matrix on approaching the Curie temperature limits application of the contact PFM method. However non-contact KPFM can be used to probe evolution of the polarization at the phase transition. Mechanisms of the KPFM contrast formation are discussed.

Temperature Effect on the Stability of the Polarized State Created by Local Electric Fields in Strontium Barium Niobate Single Crystals.

The stability of ferroelectric domain patterns at the nanoscale has been a topic of much interest for many years. We investigated the relaxation of the polarized state created by application of a local electric field using a conductive tip of a scanning probe microscope for the model uniaxial relaxor system SrxBa1-xNb2O6 (SBN) in its pure and Ce-doped form. The temporal relaxation of the induced PFM contrast was measured at various temperatures. The average value of the induced contrast decreases during heating for all investigated crystals. Below the freezing temperature the induced state remains stable after an initial relaxation. Above the freezing temperature the induced state is unstable and gradually decays with time. The stability of the induced state is strongly affected by the measuring conditions, so continuous scanning results in a faster decay of the poled domain. The obtained effects are attributed to a decrease of the induced polarization and backswitching of the polarized area under the action of the depolarization field.

Nanoscale mapping of heterogeneity of the polarization reversal in lead-free relaxor-ferroelectric ceramic composites.

Relaxor/ferroelectric ceramic/ceramic composites have shown to be promising in generating large electromechanical strain at moderate electric fields. Nonetheless, the mechanisms of polarization and strain coupling between grains of different nature in the composites remain unclear. To rationalize the coupling mechanisms we performed advanced piezoresponse force microscopy (PFM) studies of 0.92BNT-0.06BT-0.02KNN/0.93BNT-0.07BT (ergodic/non-ergodic relaxor) composites. PFM is able to distinguish grains of different phases by characteristic domain patterns. Polarization switching has been probed locally, on a sub-grain scale. k-Means clustering analysis applied to arrays of local hysteresis loops reveals variations of polarization switching characteristics between the ergodic and non-ergodic relaxor grains. We report a different set of switching parameters for grains in the composites as opposed to the pure phase samples. Our results confirm ceramic/ceramic composites to be a viable approach to tailor the piezoelectric properties and optimize the macroscopic electromechanical characteristics.

Doping of inorganic materials in microreactors - preparation of Zn doped Fe3O4 nanoparticles.

Microreactor systems are now used more and more for the continuous production of metal nanoparticles and metal oxide nanoparticles owing to the controllability of the particle size, an important property in many applications. Here, for the first time, we used microreactors to prepare metal oxide nanoparticles with controlled and varying metal stoichiometry. We prepared and characterised Zn-substituted Fe3O4 nanoparticles with linear increase of Zn content (ZnxFe3-xO4 with 0 ≤ x ≤ 0.48), which causes linear increases in properties such as the saturation magnetization, relative to pure Fe3O4. The methodology is simple and low cost and has great potential to be adapted to the targeted doping of a vast array of other inorganic materials, allowing greater control on the chemical stoichiometry for nanoparticles prepared in microreactors.

Mössbauer study of temperature-dependent cycloidal ordering in BiFeO3 nanoparticles.

To study the effects of different temperatures and particle sizes on the anharmonic cycloidal spin structure in BiFeO3 nanoparticles, Mössbauer spectroscopy was applied to three sets of particles with different mean diameters in the range of 54 nm to 1.6 µm at temperatures between 4.2 and 800 K. The paramagnetic transition showed a distinct broadening upon decreasing particle size with Néel temperatures decreasing from 652 to 631 K. The anharmonicity of the long-range cycloidal structure, calculated from experimental Mössbauer spectra, is revealed to decrease upon rising temperature, starting at 150-200 K and reaching the harmonic state at about 400 K.

New derivatives of aryl-propionic acid. Synthesis and biological evaluation.

AIM: To design new derivatives of aryl-propionic acid with potential antibacterial and antioxidant activity. MATERIAL AND METHODS: New hydrazone of ibuprofen (2-(4-isobutylphenyl)propionic acid) have been synthesized by reaction of ethyl ester of ibuprofen with hydrazine hydrate and then condensation of corresponding hydrazide with various aromatic aldehydes. RESULTS: The synthesized compounds were screened for their antibacterial activity against Gram positive (Staphylococcus aureus ATCC 25923, Sarcinalutea ATCC 9341, Bacillus cereus ATCC 14579, Bacillus subtilis) and Gram negative bacterial strains (Escherichia coli ATCC 25922). Some of them were found to have good antibacterial activity. The antioxidant activity of these compounds was also tested using the total antiox idant capacity test. CONCLUSIONS: The chemical modulations performed on ibuprofen structure have a good influence on the biological activity of the synthesized compounds.

New hydrazones with pyrazolone structure: synthesis, characterization and biological evaluation.

AIM: To design new hydrazones with pyrazolone structure with improved biological properties. MATERIAL AND METHODS: New hydrazones of antipyrine have been prepared by reaction of 4-aminophenazone (4-aminoantipyrine) with chloracetylchoride and hydrazine hydrate and then condensation with various aromatic aldehydes. RESULTS: The synthesized compounds were screened for their antibacterial activity against Gram positive (Staphylococcus aureus ATCC 25923, Sarcinalutea ATCC 9341, Bacillus cereus ATCC 14579, Bacillus subtilis) and Gram negative bacterial strains (Escherichia coli ATCC 25922) and pathogenic yeasts (Candida albicans ATCC 10231, Candida sake, Candidaglabrata). Some of them were found to have good antibacterial and antifungal activity. The antioxidant activity of these compounds was also evaluated using the total antioxidant capacity test. CONCLUSIONS: The chemical modulations performed on antipyrine structure have a good influence on the biological activity of the synthesized compounds.

Effect of particle size on ferroelectric and magnetic properties of BiFeO3 nanopowders.

The ferroelectric and magnetic behaviour of multiferroic BiFeO3 nanoparticles has been studied using piezoresponse force microscopy (PFM), Mössbauer spectroscopy and SQUID magnetometry. The results of the PFM studies indicate a decay of the spontaneous polarization with decreasing particle size. Nevertheless, particles with diameter ∼50 nm still manifest ferroelectric behaviour. At the same time these particles are weakly ferromagnetic. The Mössbauer spectroscopy studies prove that the weak ferromagnetic state is due to non-compensated surface spins rather than distortions of the cycloidal spin structure characteristic for bulk BiFeO3.

[Synthesis and characterization of some new rutin and 7-aminocephalosporanic acid derivatives]. / Sinteza si caracterizarea unor noi derivati ai rutozidului cu acid 7-amino-cefalosporanic.

UNLABELLED: Many studies show that flavonoids have a numerous biological properties, antimicrobial effects included. It is also known that rutin is able to increase the antibacterial activity of other compounds. MATERIAL AND METHODS: Starting from these facts, we synthesised some water soluble rutin derivatives treating rutin with 1, 3-dichloro-2-propanol, 1-bromo-3-chloro-propane, 2-dibromethane, and dibrommethane, and than with 7-amino-cephalosporanic acid. The antimicrobial activity of the new compounds was determined by disc diffusion method. RESULTS: Molecular formula, weight, yield, melting points and solubility of the new derivatives have been determined. Elemental analysis and spectral analysis (UV and IR) confirmed the structure of new compounds. CONCLUSIONS. These derivatives are water-soluble and have a good antimicrobial activity, both on Gram-positive and Gram-negative bacteria, comparable with that of tetracycline.

[Flexor tendons involvement in gout. A case report and review of literature]. / L'atteinte des tendons fléchisseurs dans la maladie goutteuse. A propos d'un cas et revue de la littérature.

We present a case of synovial and flexor tendons gouty involvement associated to the flexion contracture of a single digit. The case was treated surgically by tenosynovectomy and resection of the flexor superficialis tendon followed by arthrolysis of the proximal interphalangeal joint. This rare etiology of flexion contracture must be taken into account in every patient with a history of gout and tendon pathology.

[Research concerning rutin semisynthetic derivatives. Synthesis, physico-chemical and microbiological characterisation of some new rutin-isoniazid derivatives]. / Cercetari in seria derivatilor de semisinteza ai rutozidului. Sinteza si caracterizarea fizico-chimica si microbiologica a unor noi compusi ai rutozidului cu izoniazida.

UNLABELLED: Isoniazid is one of the most used antituberculosis drugs, but its toxicity is high. In this study, four derivatives of rutin and isoniazid were prepared and their antibacterial and antimycotic activities were investigated. METHOD: Synthesis of these compounds started through reaction of rutin with fresh prepared sodium methoxide, subsequently treating with 1, 3-dichloro-2-propanol, 1-brom-3-chloropropane, 1, 2-dibrom-ethane or dibrommethane and finally, stirring with isoniazid, to afford crystalline, yellow, water soluble powders. RESULTS: The four compounds were marginally active against Staphylococcus aureus and Staphylococcus saprophyticus and were inactive against Escherichia coli. CONCLUSION: We synthesised four new derivatives of rutin and isoniazid; melting points, solubility, yields characterised these compounds, and their structure was confirmed by C, H, N elemental analysis and UV spectra. The compounds showed a modest antibacterial activity. We think that the toxicity of the new derivatives will be lower that of isoniazid toxicity. The next steps in our research will be the toxicological study and antituberculosis assay.

[Synthesis and physico-chemical characterisation of some new derivatives of rutoside and clofibric acid]. / Sinteza si caracterizarea fizico-chimica a unor noi compusi ai rutozidului cu acidul clofibric.

Fibrates are drugs with efficacy in reducing blood cholesterol levels and especially, triglyceride plasma levels. Unfortunately, fibrates have a poor water-solubility and showed some adverse reactions at long treatment. The objective of this study was to obtain some new clofibric acid derivatives with rutin; some of these compounds contain a guanidine moiety, known as effective at cardiovascular level. All the compounds are soluble in water.

[Research concerning rutin semisynthetic derivatives, synthesis and pharmaco-toxicological properties of some new morpholine and piperidine derivatives]. / Cercetari în seria derivatilor de semisinteza ai rutozidului. Sinteza si proprietatile farmaco-toxicologice ale unor noi derivati morfolinici si piperidinici.

In order to continue the research of the rutin semisynthetic derivatives we obtained some new morpholine and piperidine derivatives. Melting points, solubility, yield, C, H, N elemental analysis and UV spectra characterised all of these compounds. The toxicity was established by intraperitoneal administration at mice; the values of LD50 are between 743.75 and 856.25 mg/kg (medium toxicity). Pharmacological assays included the following parameters: leukocytes formula, NBT test, and serum complement activity. The new derivatives of rutin have a very good solubility in water, a pH closed to physiological value and immunosuppressive activity: peripheric blood PMN and lymphocytes are decreased; fagocytic capacity of peripheric blood PMN is also decreased; serum complement activity is not changed.

[Vanadium derivatives--a new source of antidiabetic drugs]. / Derivatii de vanadiu--o noua sursa de medicamente antidiabetice.

Vanadium, a transitional element belonging to Vb group is wide-spread both in vegetal and animal world. Although known by more a hundred years ago only in 1985 its hypoglycaemic properties were established. Recent research shown that the hypoglycaemic properties and the toxicity are influenced both by vanadium valence state and organic moiety that is binding it.

[The production of nitro esters active at the level of the cardiovascular system]. / Cercetari privind obtinerea unor nitroesteri activi la nivelul aparatului cardiovascular.

In order to obtain new compounds with cardiovascular activity, some esters of nitric acid with ethanolamine were synthesised, using some aromatic acids, acexamic acid, the natural methylxanthines-theophylline and theobromine. The melting points, yields and solubility of the new compounds were determined, and the chemical structures were confirmed by elemental analysis C, H, N, and by spectral analysis in KBr.