Piezoelectric PVDF-TrFE nanocomposite mats filled with BaTiO3 nanofibers: The effect of poling conditions

BaTiO₃ nanofibers (BT NFs), prepared by electrospinning, were used as a filler for electrospun poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) nanocomposite mats. The phase structure and the effect of poling conditions on the piezoelectric properties of PVDF-TrFE/BT nanocomposites were investigated. The results showed an improved degree of crystallinity (78.6%) and a high β-crystal phase (up to 98.3%) in all electrospun samples, independent of the nanofiber content. The two-step poling method, applying electric fields of opposite polarity, led to significantly improved piezoelectric constants d₃₃ (−31.7 pC N⁻¹), strongly dependent on the added BaTiO₃ nanofibers. The inclusion of piezoelectric ceramic nanofibers into a polymer matrix, easily carried out by means of electrospinning, followed by an ad hoc optimized poling treatment, allowed to develop flexible materials with enhanced piezoelectric properties, potentially exploitable in innovative conversion systems used in wearable and sensing devices.     

Tuning of Magnetic Anisotropy in Hexairon(III) Rings by Host–Guest Interactions: An Investigation by High-Field Torque Magnetometry

Full chemical control of magnetic anisotropy in hexairon(III ) rings can be achieved by varying the size of the guest alkali metal ion. Dramatically different anisotropies characterize the Li^I and Na^I complexes of [Fe₆(OMe)₁₂(L)₆] (L=1,3-propanedione derivatives; a schematic representation of the Li^I complex is shown), as revealed by high-field torque magnetometry—Iron: (g), oxygen: ○, carbon: ○, Li⁺: ⊕.     

Coupling reaction of polyisoprenyllithium with 1,2-dibromoethane

The coupling reaction of polyisoprenyllithium with 1,2-dibromoethane (DBE) gives a multimodal molecular weight distribution (MWD). Species with molecular weights three and four times (P₃, P₄) higher than the base polymer (P) are present beside the main expected one with double molecular weight (P₂). The relative abundancies of P₁, P₂, P₃, and P₄ depend on the experimental conditions. Gas-phase chromatographic analysis carried out during the coupling reaction show the presence of ethylene whose formation is related to a lithium–bromine exchange reaction competing with direct alkylation. The lithium–bromine exchange reaction is more effective at T < 80°C and results in the formation of allyl bromide-terminated polyisoprene, while direct alkylation is effective at T > 100°C and yields alkyl bromide chain ends. The allylic and alkylic bromides react differently with the remaining polyisoprenyllithium: the former adds only to polyisoprenyllithium yielding P₂, while the later also yields P₃ and P₄ through radical reactions. © 1997 John Wiley & Sons, Inc.     

Performance and characteristics of a trace gas analyzer for the determination of volatile organic compounds in air

An instrument has been developed and tested for the continuous measurement of volatile organic compounds (VOC) in air. The system consists of a gas chromatograph equipped with a dedicated sampling device that allows the sample to be transferred to a cooled microtrap via sampling loops (10, 100, 250 ml) or via a direct pump transfer to the trap. The microtrap is placed in the chromatographic oven just below a modified split-splitless injector, allowing direct liquid injection for calibration of the system; the injector is in communication with the sampling valve equipped with the loop and the sampling pump. The system allows 24-hour sampling and analysis of a large number of VOC (up to 25 individual hydrocarbons ranging from C2 C9) and also polar volatile organic compounds PVOC. Thanks to the particular trap geometry, a minimum consumption of liquid nitrogen (between 150 300 ml) is needed for each analytical run and no water managing system is normally required for humid air samples.     

Enzyme‐mediated catalytic asymmetric oxidations

Enantiomerically pure sulfoxides are excellent chiral auxiliares for asymmetric synthesis and in the preparation of several enantiopure biologically active compounds. We have explored biocatalytic approaches based on the use of heme peroxidases and flavin monooxygenases such as chloroperoxidase and cyclohexanone monooxygenase respectively. By using isolated enzymes or whole‐cell biotransformations, we have prepared alkyl aryl sulfoxides, 1,3‐dithioacetal‐1‐oxides, dialkyl sulfoxides, and thiosulfinates in high enantiomeric excess. An active site model of cyclohexanone monooxygenase has been proposed in order to explain and to predict the absolute configuration of the product. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:467–473, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10074     

Chemical Functionalization of Nanodiamonds: Opportunities and Challenges Ahead

Nanodiamond(ND)‐based technologies are flourishing in a wide variety of fields spanning from electronics and optics to biomedicine. NDs are considered a family of nanomaterials with an sp³ carbon core and a variety of sizes, shapes, and surfaces. They show interesting physicochemical properties such as hardness, stiffness, and chemical stability. Additionally, they can undergo ad‐hoc core and surface functionalization, which tailors them for the desired applications. Noteworthy, the properties of NDs and their surface chemistry are highly dependent on the synthetic method used to prepare them. In this Minireview, we describe the preparation of NDs from the materials‐chemistry viewpoint. The different methodologies of synthesis, purification, and surface functionalization as well as biomedical applications are critically discussed. New synthetic approaches as well as limits and obstacles of NDs are presented and analyzed.     

A study of the Fermi-Pasta-Ulam problem in dimension two

Continuing the previous work on the same subject, we study here different two-dimensional Fermi-Pasta-Ulam (FPU)-like models, namely, planar models with a triangular cell, molecular-type potential and different boundary conditions, and perform on them both traditional FPU-like numerical experiments, i.e., experiments in which energy is initially concentrated on a small subset of normal modes, and other experiments, in which we test the time scale for the decay of a large fluctuation when all modes are excited almost to the same extent. For each experiment, we observe the behavior of the different two-dimensional systems and also make an accurate comparison with the behavior of a one-dimensional model with an identical potential. We assume the thermodynamic point of view and try to understand the behavior of the system for large n (the number of degrees of freedom) at fixed specific energy epsilon=En. As a result, it turns out that: (i) The difference between dimension one and two, if n is large, is substantial. In particular (making reference to FPU-like initial conditions) the "one-dimensional scenario," in which the dynamics is dominated for a long time scale by a weakly chaotic metastable situation, in dimension two is absent; moreover in dimension two, for large n, the time scale for energy sharing among normal modes is drastically shorter than in dimension one. (ii) The boundary conditions in dimension two play a relevant role. Indeed, models with fixed or open boundary conditions give fast equipartition, on a rather short time scale of order epsilon(-1), while a periodic model gives longer equilibrium times (although much shorter than in dimension one).     

Monitoring of Pollutants Content in Bottled and Tap Drinking Water in Italy

The concentration levels of thirteen organic pollutants and selected heavy metals were investigated in 40 plastics bottled and tap water samples. Some of the selected contaminants have an ascertained or suspected endocrine disrupting activity, such as Bisphenol A (BPA) and its analogs, and Bis 2-ethylhexyl phthalate (DEHP), which are used by industries as plasticizers. The most frequently detected pollutants were Bisphenol AF (BPAF) (detection frequency (DF) = 67.5%, mean 387.21 ng L⁻¹), DEHP (DF = 62.5%, mean 46.19 µg L⁻¹) and BPA (DF = 60.0%, mean 458.57 ng L⁻¹), with higher concentration levels found in tap waters. Furthermore, a possible level of exposure to thirteen pollutants via drinking water intake was calculated. Our findings show that, even though the occurrence of contaminants and heavy metals in drinking waters does not pose an immediate, acute health risk for the population, their levels should be constantly monitored and “hard-wired” into everyday practice. Indeed, the health impact to the continuous and simultaneous intake of a huge variety of xenobiotics from various sources by humans is complex and still not fully understood.