Method for determining resin cure kinetics with low-frequency Raman spectroscopy.

Characterizing resin extent of cure kinetics is critical to understanding the structure-property-processing relationships of polymers. The disorder band present in the low-frequency region of the Raman spectrum is directly related to conformational entropy and the modulus of amorphous materials, both of which change as the resin polymerizes. Normalizing the disorder band to its shoulder (∼85 cm-1) provides structural conversion kinetics, which we can directly correlate to chemical conversion kinetics for methacrylate and epoxy-amine based resin systems. In addition to fitting both the structural and chemical conversion data to a phenomenological kinetic rate equation, we also demonstrate a relationship between the chemical and structural kinetics which appears to relate to the softness of the material. Lastly, we use the method to investigate a methacrylate/epoxy interpenetrating polymer network resin system. We find that the structural and chemical conversions occur simultaneously during the formation of the primary (methacrylate) network, but there is a lag between the two during the formation of the secondary (epoxy-amine) network.

Investigation of Photoelectrocatalytic and Magnetic Properties of Sr2YbRu1-xTaxO6 (x = 0, 0.25, 0.5, 0.75, and 1).

We report the effect of substitution of Ru by Ta in Sr2YbRuO6 on its magnetic and photoelectrocatalytic properties. The powder X-ray diffraction data, was satisfactorily refined in the monoclinic space group, P21/n. The DC magnetization studies indicated that Sr2YbRuO6 shows antiferromagnetic interaction through Yb-O-Ru orbital ordering, with the highest Weiss temperature, among Sr2YbRu1-xTaxO6 (x = 0, 0.25, 0.5, and 0.75) which have values of -148, -125, -118, and -102 K, respectively. The difference in observed and theoretical magnetic moments was found to increase as x increases. It was also observed that with the increase of Ta concentration in Sr2YbRu1-xTaxO6, the band gap increased almost linearly, from 1.78(1) eV (x = 0) to 2.08(1) (x = 0.75), and thereafter a sharp increase 2.65(1) eV (x = 1) was observed, with the lowering of energy level of valence band, along with disruption in orbital ordering as x increases. The photoelectrocatalytic oxygen evolution reaction (OER) studies carried out on the series yield a maximum photocurrent density of 17 µA/cm2 and photoresponse current of 5.5 µA/cm2 at 0.8 V at an onset potential at 0.29 V vs Ag/AgCl for Sr2YbRuO6. The XPS analysis showed Ta and Ru to be in +5/+4 oxidation states, with the highest concentration of Ru4+ ion observed for Sr2YbRuO6. The presence of oxygen vacancies was confirmed by XPS as well as EPR studies.

High Nuclearity Assemblies and One-Dimensional (1D) Coordination Polymers Based on Lanthanide-Copper 15-Metallacrown-5 Complexes (LnIII = Pr, Nd, Sm, Eu).

Complexes {[LnCu5(GlyHA)5(m-bdc)(H2O)4-x]2[LnCu5(GlyHA)5(SO4)(m-bdc)(H2O)4]2}·(30 + 2x)H2O (where GlyHA2- = glycinehydroxamate, m-bdc2- = m-phthalate; Ln = Pr and x = 0.21 for compound 1, or Ln = Sm and x = 0.24 for 3) and one-dimensional (1D) coordination polymers {[NdCu5(GlyHA)5(H2O)5(m-bdc)]nn[NdCu5(GlyHA)5(H2O)4(µ-CO3)(m-bdc)]}·13nH2O (2) and {[EuCu5(GlyHA)5(H2O)3](m-bdc)2[EuCu5(GlyHA)5(m-bdc)(H2O)3]}n·17nH2O (4) were obtained starting from the 15-metallacrown-5 complexes {[LnCu5(GlyHA)5(SO4)(H2O)6.5]}2(SO4)·6H2O (Ln = Pr, Nd, Sm, Eu) by the partial or complete metathesis of sulfate anions with m-phthalate. Compounds 1 and 3 contain unprecedented quadruple-decker neutral metallacrown assemblies, where the [LnCu5(GlyHA)5]3+ cations are linked by m-phthalate dianions. In contrast, in complexes 2 and 4, these components assemble into 1D chains of coordination polymers, the adjacent {[NdCu5(GlyHA)5(H2O)5(m-bdc)]+}n 1D chains in 2 being separated by discrete [NdCu5(GlyHA)5(H2O)4(µ-CO3)(m-bdc)]}- complex anions. The crystal lattices of 2 and 4 contain voids filled by solvent molecules. Desolvated 4 is able to absorb up to 0.12 cm3/g of methanol vapor or 0.04 cm3/g of ethanol at 293 K. The isotherm for methanol absorption by compound 4 is consistent with a possible "gate opening" mechanism upon interaction with this substrate. The χMT vs T data for complexes 1-4 and their simpler starting materials {[LnCu5(GlyHA)5(SO4)(H2O)6.5]}2(SO4)·6H2O (Ln(III) = Pr, Nd, Sm, Eu) were fitted using an additive model, which takes into account exchange interactions between lanthanide(III) and copper(II) ions in the metallamacrocycles via a molecular field model. The exchange interactions between adjacent Cu(II) ions in metallacrown fragments were found to fall in the range of -47 < JCu-Cu < -63 cm-1. These complexes are the first examples of a Ln(III)-Cu(II) 15-metallacrowns-5 (Ln(III) = Pr, Nd, Sm, Eu), for which values of exchange parameters have now been reported.

Silver Oxide Coatings with High Silver-Ion Elution Rates and Characterization of Bactericidal Activity.

This paper reports the synthesis and characterization of silver oxide films for use as bactericidal coatings. Synthesis parameters, dissolution/elution rate, and bactericidal efficacy are reported. Synthesis conditions were developed to create AgO, Ag2O, or mixtures of AgO and Ag2O on surfaces by reactive magnetron sputtering. The coatings demonstrate strong adhesion to many substrate materials and impede the growth of all bacterial strains tested. The coatings are effective in killing Escherichia coli and Staphylococcus aureus, demonstrating a clear zone-of-inhibition against bacteria growing on solid media and the ability to rapidly inhibit bacterial growth in planktonic culture. Additionally, the coatings exhibit very high elution of silver ions under conditions that mimic dynamic fluid flow ranging between 0.003 and 0.07 ppm/min depending on the media conditions. The elution of silver ions from the AgO/Ag2O surfaces was directly impacted by the complexity of the elution media, with a reduction in elution rate when examined in complex cell culture media. Both E. coli and S. aureus were shown to bind ~1 ppm Ag⁺/mL culture. The elution of Ag⁺ resulted in no increases in mammalian cell apoptosis after 24 h exposure compared to control, but apoptotic cells increased to ~35% by 48 and 72 h of exposure. Taken together, the AgO/Ag2O coatings described are effective in eliciting antibacterial activity and have potential for application on a wide variety of surfaces and devices.

Simultaneous Large Optical and Piezoelectric Effects Induced by Domain Reconfiguration Related to Ferroelectric Phase Transitions.

Electrical switching of ferroelectric domains and subsequent domain wall motion promotes strong piezoelectric activity, however, light scatters at refractive index discontinuities such as those found at domain wall boundaries. Thus, simultaneously achieving large piezoelectric effect and high optical transmissivity is generally deemed infeasible. Here, it is demonstrated that the ferroelectric domains in perovskite Pb(In1/2 Nb1/2 )O3 -Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 domain-engineered crystals can be manipulated by electrical field and mechanical stress to reversibly and repeatably, with small hysteresis, transform the opaque polydomain structure into a highly transparent monodomain state. This control of optical properties can be achieved at very low electric fields (less than 1.5 kV cm-1 ) and is accompanied by a large (>10 000 pm V-1 ) piezoelectric coefficient that is superior to linear state-of-the-art materials by a factor of three or more. The coexistence of tunable optical transmissivity and high piezoelectricity paves the way for a new class of photonic devices.

Miniemulsion synthesis of metal-oxo cluster containing copolymer nanobeads.

Hybrid nanobeads containing either a manganese-oxo or manganese-iron-oxo cluster have been prepared via the miniemulsion polymerization technique. Two new ligand substituted oxo clusters, Mn(12)O(12)(VBA)(16)(H(2)O)(4) and Mn(8)Fe(4)O(12)(VBA)(16)(H(2)O)(4) (where VBA = 4-vinylbenzoate), have been prepared and characterized. Polymerization of the functionalized metal-oxo clusters with styrene under miniemulsion conditions produced monodispersed polymer nanoparticles as small as ~60 nm in diameter. The metal-oxo polymer nanobeads were fully characterized in terms of synthetic parameters, composition, structure, and magnetic properties.

Development of a microemulsion-based process for synthesis of cobalt (Co) and cobalt oxide (Co3O4) nanoparticles from submicrometer rods of cobalt oxalate.

Rod-shaped nanostructures of cobalt oxalate dihydrate were synthesized at room temperature by the microemulsion (reverse micellar) route. These rods are highly uniform in length and can be modified with temperature (from approximately 6.5 microm at 50 degrees C to approximately 2.5 microm at 150 degrees C) while keeping the diameter nearly constant (200-250 nm). Thermal decomposition of these rods in a controlled atmosphere (air and H(2)) leads to nanoparticles of Co(3)O(4) and Co, respectively, while in a helium atmosphere a mixture of Co and CoO nanoparticles is obtained. Co(3)O(4) nanoparticles (approximately 35 nm) were slightly agglomerated, while Co nanoparticles were monodispersed and highly uniform (approximately 25 nm). The oxalate rods and Co(3)O(4) nanoparticles show an antiferromagnetic ordering at 54 and 35 K, respectively.

Nanorods of copper and nickel oxalates synthesized by the reverse micellar route.

Nanorods of nickel and copper oxalate have been synthesized by the reverse micellar route. Powder X-ray diffraction studies and thermo gravimetric analysis confirms the formation of monophasic NiC2O4 x 2H2O and CuC2O4 x H2O. Transmission electron microscopy shows that the as prepared nanorods of nickel and copper have diameter of 250 nm and 130 nm while the length is of the order of 2.5 microm and 480 nm respectively. The aspect ratio of the nanorods could be modified by changing the solvent. The nickel oxalate nanorods appear very smooth with uniform length while the copper oxalate nanorods appear to be corrugated. Nickel oxalate dihydrate nanorods show an antiferromagnetic transition at T(N) = 34 K while the copper based nanorods show temperature independent paramagnetism.

Multiferroic operation of dynamic memory based on heterostructured cantilevers.

Multiferroic heterostructures consisting of Pb(Zr0·52Ti0·48)O3 and Fe0.7Ga0.3 thin films are integrated on microfabricated Si cantilevers, and they are operated in a non-linear regime. Enhanced mechanical coupling at the multiferroic interface and tunability of the resonant frequency are used to devise bistable dynamic states that can be reversibly switched by both DC magnetic and electric fields.

Thickness-dependent crossover from charge- to strain-mediated magnetoelectric coupling in ferromagnetic/piezoelectric oxide heterostructures.

Magnetoelectric oxide heterostructures are proposed active layers for spintronic memory and logic devices, where information is conveyed through spin transport in the solid state. Incomplete theories of the coupling between local strain, charge, and magnetic order have limited their deployment into new information and communication technologies. In this study, we report direct, local measurements of strain- and charge-mediated magnetization changes in the La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 system using spatially resolved characterization techniques in both real and reciprocal space. Polarized neutron reflectometry reveals a graded magnetization that results from both local structural distortions and interfacial screening of bound surface charge from the adjacent ferroelectric. Density functional theory calculations support the experimental observation that strain locally suppresses the magnetization through a change in the Mn-eg orbital polarization. We suggest that this local coupling and magnetization suppression may be tuned by controlling the manganite and ferroelectric layer thicknesses, with direct implications for device applications.

Novel borothermal process for the synthesis of nanocrystalline oxides and borides of niobium.

A new process has been developed for the synthesis of nanocrystalline niobium oxide and niobium diboride using an amorphous niobium precursor obtained via the solvothermal route. On varying the ratio of niobium precursor to boron and the reaction conditions, pure phases of nanostructured niobium oxides (Nb(2)O(5), NbO(2)), niobium diboride (NbB(2)) and core-shell nanostructures of NbB(2)@Nb(2)O(5) could be obtained at normal pressure and low temperature of 1300 °C compared to a temperature of 1650 °C normally used. The above borothermal process involves the in situ generation of B(2)O(2) to yield either oxide or diboride. The niobium oxides and borides have been characterized in detail by XRD, HRTEM and EDX studies. The core-shell structure has been investigated by XPS depth profiling, EFTEM and EELS (especially to characterize the presence of boron and the shell thickness). The niobium diboride nanorods (with high aspect ratio) show a superconducting transition with the T(c) of 6.4 K. In the core-shell of NbB(2)@Nb(2)O(5), the superconductivity of NbB(2) is masked by the niobium oxide shell and hence no superconductivity was observed. The above methodology has the benefits of realizing both oxides and borides of niobium in nanocrystalline form, in high purity and at much lower temperatures.

Controlling the size and morphology of anisotropic nanostructures of nickel borate using microemulsions and their magnetic properties.

Anisotropic nanostructures of nickel borate with controlled size and morphology have been synthesized by a precursor-mediated route. The nickel boron precursor has been synthesized using microemulsions using Tergitol as a surfactant. Microemulsions with various co-surfactants (1-butanol, 1-hexanol and 1-octanol) have been used to obtain uniform nanorods (dia 3-5 nm, length 25 nm) and nanospindles (dia 30 nm, length 400 nm). A higher chain length of the co-surfactant (octanol) leads to more uniform rods rather than spindles (butanol). These nanorods show antiferromagnetic behavior with the Néel temperature ranging from 44 to 47 K. Though there is no marked variation in Neel temperature, the magnetic moment increases drastically with the anisotropy of nanorods (thinner rods).

Microemulsion-mediated synthesis of cobalt (pure fcc and hexagonal phases) and cobalt-nickel alloy nanoparticles.

By choosing appropriate microemulsion systems, hexagonal cobalt (Co) and cobalt-nickel (1:1) alloy nanoparticles have been obtained with cetyltrimethylammonium bromide as a cationic surfactant at 500 degrees C. This method thus stabilizes the hcp cobalt even at sizes (<10 nm) at which normally fcc cobalt is predicted to be stable. On annealing the hcp cobalt nanoparticles in H(2) at 700 degrees C we could transform them to fcc cobalt nanoparticles. Microscopy studies show the formation of spherical nanoparticles of hexagonal and cubic forms of cobalt and Co-Ni (1:1) alloy nanoparticles with the average size of 4, 8 and 20 nm, respectively. Electrochemical studies show that the catalytic property towards oxygen evolution is dependent on the applied voltage. At low voltage (less than 0.65 V) the Co (hexagonal) nanoparticles are superior to the alloy (Co-Ni) nanoparticles while above this voltage the alloy nanoparticles are more efficient catalysts. The nanoparticles of cobalt (hcp and fcc) and alloy (Co-Ni) nanoparticles show ferromagnetism. The saturation magnetization of Co-Ni nanoparticles is reduced compared to the bulk possibly due to surface oxidation.