Nano-sized Domains Research Articles

Structure and catalytic properties of the most complex intergrown zeolite ITQ-39 determined by electron crystallography

Porous materials such as zeolites contain well-defined pores in molecular dimensions and have important industrial applications in catalysis, sorption and separation. Aluminosilicates with intersecting 10- and 12-ring channels are particularly interesting as selective catalysts. Many porous materials, especially zeolites, form only nanosized powders and some are intergrowths of different structures, making structure determination very challenging. Here, we report the atomic structures of an aluminosilicate zeolite family, ITQ-39, solved from nanocrystals only a few unit cells in size by electron crystallography. ITQ-39 is an intergrowth of three different polymorphs, built from the same layer but with different stacking sequences. ITQ-39 contains stacking faults and twinning with nano-sized domains, being the most complex zeolite ever solved. The unique structure of ITQ-39, with a three-dimensional intersecting pairwise 12-ring and 10-ring pore system, makes it a promising catalyst for converting naphtha into diesel fuel, a process of emerging interest for the petrochemical industry.

Structure and dynamics of nano-sized raft-like domains on the plasma membrane

Cell membranes are constitutively composed of thousands of different lipidic species, whose specific organization leads to functional heterogeneities. In particular, sphingolipids, cholesterol and some proteins associate among them to form stable nanoscale domains involved in recognition, signaling, membrane trafficking, etc. Atomic-detail information in the nanometer/second scale is still elusive to experimental techniques. In this context, molecular simulations on membrane systems have provided useful insights contributing to bridge this gap. Here we present the results of a series of simulations of biomembranes representing non-raft and raft-like nano-sized domains in order to analyze the particular structural and dynamical properties of these domains. Our results indicate that the smallest (5 nm) raft domains are able to preserve their distinctive structural and dynamical features, such as an increased thickness, higher ordering, lower lateral diffusion, and specific lipid-ion interactions. The insertion of a transmembrane protein helix into non-raft, extended raft-like, and raft-like nanodomain environments result in markedly different protein orientations, highlighting the interplay between the lipid-lipid and lipid-protein interactions.

Self-assembly of alkoxysilanized humic substances into multidomain adlayers at the water–solid interface: linking surface morphology to the molecular structure of the adsorbate

Self assembly of natural organic materials (e.g., humic substances) on mineral surfaces leads to the formation of adlayers with physically different domains. However, direct evidence to explain the molecular interactions responsible for the formation of these domains is still missing. Here, we developed alkoxysilanized humic probes capable of self-assembling onto hydroxylated surfaces. Using modified humic substances from vastly differed sources (peat, water, coal) and DNA array glass slides as a flat surrogate for mineral surfaces, we create humic adlayers under aqueous conditions and show them to be homogeneous on the macroscale, but consisted of nanosize domains in coal and water humics and submicron-size domains in peat humics. The surface charge and hydrophilic–lipophilic balance of humic associates were proposed as major molecular drivers of the self-assembly with the former causing the formation of thin adlayers composed of separated nanosize domains (e.g., coal humics) and the latter enhancing the formation of thicker adlayers composed of interconnected domains linked in chains up to the submicron-size (e.g., peat humic materials). To the best of our knowledge, this is the first time alkoxysilanized humic probes were used to examine how humic adsorbates and their molecular structure influences the surface morphology of assembled adlayers. In this fashion, the humic adlayer with molecularly-defined functional elements can be assembled on any hydroxylated surface in situ, at the water–solid interface.

Hybrid thin films derived from UV-curable acrylate-modified waterborne polyurethane and monodispersed colloidal silica

Hybrid thin films containing nano-sized inorganic domains were synthesized from UV-curable acrylate-modified waterborne polyurethane (WPU-AC) and monodispersed colloidal silica with coupling agent. The coupling agent, 3- (trimethoxysilyl)propyl methacrylate (MSMA), was bonded onto colloidal silica first, and then mixed with WPU-AC to form a precursor solution. This precursor was spin coated, dried and UV-cured to generate the hybrid films. The silica con- tent in the hybrid thin films was varied from 0 to 30 wt%. Experimental results showed the aggregation of silica particles in the hybrid films. Thus, the silica domain in the hybrid films was varied from 30 to 50 nm by the different ratios of MSMA- silica to WPU-AC. The prepared hybrid films from the crosslinked WPU-AC/MSMA-silica showed much better thermal stability and mechanical properties than pure WPU-AC.

Phase Separation in Model Membranes Controlled by Hybrid Lipids

Biological membranes are currently considered as a heterogeneous and highly dynamical organization of lipids and proteins. Some of these components phase separate in finite-size domains (known as ‘rafts’) to play a vital role in cellular signaling and transport process. Recent theoretical approaches have suggested that the hybrid lipids (lipids with one saturated and one unsaturated tail) stabilize nano-sized domains by controlling the line tension between ‘gel’ and ‘fluid’ phases [1,2]. Our x-ray scattering experiments on highly oriented multilamellar samples prepared on a hydrophilic surface have exhibited a strong effect of such hybrid lipids on the phase separation behavior in mixtures of saturated and unsaturated lipids. The phase transition temperature is found to decrease dramatically with the added mole percent of the hybrid lipids. Further, the bilayer repeat distance and the amount of phases are found to vary systematically as a function of the added hybrid lipids. This experimental study opens up an opportunity to verify the theoretical ideas about the role of hybrid lipids in forming the ‘raft’ in cellular membranes.[1] R. Brewster, et al., Biophys. J. (2009), 97, 1087-1094.[2] T. Yamamoto et al., Euro. Phys. Lett. (2010), 91, 28002.

Fabrication of Y_2O_3 doped ZrO_2 Nanopowder by Reverse Micelle and Sol-Gel Processing

The preparation of <TEX>$Y_2O_3$</TEX>-doped <TEX>$ZrO_2$</TEX> nanoparticles in Igepal CO-520/cyclohexane reverse micelle solutions is studied here. In this work, we synthesized nanosized <TEX>$Y_2O_3$</TEX>-doped <TEX>$ZrO_2$</TEX> powders in a reverse micelle process using aqueous ammonia as the precipitant. In this way, a hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of a microemulsion consisting of cyclohexane as the oil phase, with poly (oxyethylene) nonylphenylether (Igepal CO-520) as the non-ionic surfactant. The synthesized and calcined powders were characterized by thermogravimetrydifferential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The crystallite size was found to nearly identical with an increase in the water-to-surfactant (R) molar ratio. A FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and the calcined powder. The average particle size and distribution of the synthesized <TEX>$Y_2O_3$</TEX>-doped <TEX>$ZrO_2$</TEX> were below 5 nm and narrow, respectively. The TG-DTA analysis showed that the phase of the <TEX>$Y_2O_3$</TEX>-doped <TEX>$ZrO_2$</TEX> nanoparticles changes from the monoclinic phase to the tetragonal phase at temperatures close to <TEX>$530^{\circ}C$</TEX>. The phase of the synthesized <TEX>$Y_2O_3$</TEX>-doped <TEX>$ZrO_2$</TEX> when heated to <TEX>$600^{\circ}C$</TEX> was tetragonal <TEX>$ZrO_2$</TEX>.

Thermal Conductivity of Highly-Ordered Mesoporous Titania Thin Films from 30 to 320 K

This paper reports the cross-plane thermal conductivity of highly ordered amorphous and crystalline templated mesoporous titania thin films measured by the 3ω method from 30 to 320 K. Both sol–gel and nanocrystal-based films were synthesized by evaporation-induced self-assembly, with average porosity of 30% and 35%, respectively. The pore diameter ranged from 14 to 25 nm. The size of crystalline domains in polycrystalline mesoporous films was 12–13 nm, while the nanocrystals in the nanocrystal-based film were 9 nm in diameter. At high temperatures, the thermal conductivity of amorphous dense and mesoporous films showed similar trends with respect to temperature. This was attributed to the fact that the presence of pores had a purely geometrical effect by reducing the cross-sectional area through which heat can diffuse. By contrast, the thermal conductivity of polycrystalline dense and mesoporous films behaves differently with temperature due to phonon scattering by pores and crystalline nanosize domains. In addition, at low temperatures, the presence of pores caused the thermal conductivity of mesoporous films to be less temperature dependent than their dense counterparts. Despite its crystallinity, the thermal conductivity of the nanocrystal-based film was about 40% less than that of the polycrystalline mesoporous films. This was mainly attributed to its larger porosity, smaller crystal size, and strong phonon scattering at the poorly interconnected nanocrystal boundaries. These results suggest various ways to control the thermal conductivity of mesoporous materials for various applications.

Ferroelectric Domain Structures and Piezoelectric Properties of Pb(Zr,Ti)O&lt;sub&gt;3&lt;/sub&gt; Ceramics

We investigated domain structures in Pb(Zr,Ti)O3(PZT) ceramics whose composition lies on the morphotropic phase boundary (MPB) using transmission electron microscopy (TEM) and evaluated the piezoelectric properties of PZT. We found that monoclinic nanosized domains (nanodomains), which form in tetragonal domains, strongly correlated with the piezoelectric properties of PZT. The degree of formation of nanodomains depends on the grain composition. Thus, controlling the homogeneity of grain composition in the ceramics is crucial for optimizing the piezoelectric properties of PZT.

Unusual dielectric behavior and domain structure in rhombohedral phase of BaTiO3 single crystals

It was noticed long time ago that the dielectric permittivity of BaTiO3 single crystals in the rhombohedral phase varies from observation to observation, but the microstructure mechanism behind this phenomenon remained unclear. We show that the variations in susceptibility can be related to the variable domain structure introduced by different pre-treatments at higher temperatures: Electrical depoling at room temperature leads to nano-sized domains and ultrahigh susceptibility in rhombohedral phase, whereas thermal annealing at 450 °C results in micro-sized domains and relatively lower dielectric permittivity. The influence of the pre-treatments on domains evolution is tentatively rationalized with a stress accommodation mechanism. The ultrahigh dielectric permittivity could be ascribed to the by-produced 180°-domain walls in the ultrafine domain structure.

Intact Nanoparticulate Indomethacin in Fast-Dissolving Carrier Particles by Combined Wet Milling and Aerosol Flow Reactor Methods

Drug development is often hindered by a drug's low dissolution rate. We present a method to increase dissolution rate of a drug powder by producing crystalline nanoparticles that are dispersed in carrier microparticles. Indomethacin crystals of a few hundred nanometers are prepared by media milling using poloxamer 188 as a stabilizer. Nanoparticles are embedded into microparticles with a mannitol matrix and an L-leucine coating layer using an aerosol flow reactor method. Microparticles stabilize the primary nanoparticles in an intact crystalline form and release them when re-dispersed in aqueous medium. Secondary microparticle structure dissolves rapidly, resulting in a fast release and dissolution of indomethacin. In this manner, it is possible to change the surface layer of the particles from the one needed for nanoparticle production to one more suitable for process formulation of pharmaceuticals for, e.g., tablet or pulmonary products. Particle assemblies where nano-sized crystalline drug domains are embedded in solid microparticles are presented. The present work is a promising approach towards a "nanos-in-micros" concept as a tool for pharmaceutical nanoparticle processing.

Transition metal-decorated activated carbon catalysts for dehydrogenation of NaAlH 4

Dehydrogenation of NaAlH 4 can be greatly facilitated by activated carbon catalysts. The catalytic function can be further enhanced by decorating the carbon with Co, Ni, or Cu nanoparticles. The decomposition temperature was lowered by as much as 100 °C using a 3 wt.% Co or Ni-decorated activated carbon, comparable to a Ti-based catalyst, which were the most effective among the metals tested. The catalytic effect is likely due to a combination of hydrogen spillover effect, high contact area between carbon and the hydride, and confinement of the hydride as nano-sized domains in the pores of the carbon matrix. The catalysts were also effective in facilitating rehydrogenation of NaAlH 4 under moderate pressure (75.8 bar H 2) and low temperature (120 °C), when no rehydrogenation would occur without the catalyst. The fact that this new catalyst system is not specific to any hydride offers many potential applications.

Catalytic and reinforcing effects of polyhedral oligomeric silsesquioxane (POSS)-imidazolium modified clay in an anhydride-cured epoxy

In this article, we report novel epoxy-based hybrids prepared via incorporating 1,2-dimethyl-3-(benzyl-heptaisobutyl-POSS) imidazolium chloride (POSS-IMC) and POSS-IMC-modified clay (POSS-MMT) into the resin based on 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (ECHM) and hexahydrophthalic anhydride (HHPA). We demonstrate that both POSS-IMC and POSS-MMT can reduce the cure temperature of the epoxy/anhydride system, and the catalyzing effect involves chemical reactions between POSS-IMC and ECHM/HHPA, which may lead to the attachment of POSS cages at chain ends. The incorporation of the POSS-IMC, free and ionically bonded in clay, gives rise to dissimilar morphologies that affect the thermo–mechanical properties of the hybrids. The ECHM/HHPA/POSS-IMC resin exhibits a slight improvement in glassy modulus as compared with the neat ECHM/HHPA resin, which is attributed to the formation of sub-micron and nano-sized POSS domains that act as physical cross-link points hindering polymer chain motions. The much enhanced reinforcing effect of POSS-MMT is ascribed to the effective stress transfer between the matrix and clay layers that may originate from the strong interactions between the pendent POSS in the network and POSS attached to the clay surfaces. Reduction in coefficient of thermal expansion (CTE) was also found for the hybrids.

Crystallization Behaviour and Nanostructuring in Alkali Niobiosilicate Glasses

23K2O(27Nb2O5(50SiO2((KNS), 13K2O(10Na2O(27Nb2O5(50SiO2 (KNaNS) and 15K2O(12Li2O(27Nb2O5(46SiO2 (KLiNS) transparent glasses were synthesized by melt-quenching technique, and studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) to reveal the effect of the devitrification behaviour on transparent nanostructure. Just above the glass transition temperature Tg in the KNS glass, an unidentified phase was formed, while in KNaNS and KLiNS, mixed-alkali niobate phases with tungsten bronze structure were obtained by bulk crystallization. Heat treatments at Tg performed on the KNS glass resulted in the transparent nanostructure with second order harmonic generation (SHG) activity. Heat treatment for 10 h on KNaNS and KLiNS decreased the first DTA exothermic peaks (at least 24°C), indicating the bulk nucleation, which was confirmed by the DTA in comparison with the powdered as-quenched samples. KNaNS and KLiNS showed similar XRD profiles as the K3Li2Nb5O15 crystal with the five most intense peaks at 22.7, 29.4, 32.3, 46.3 and 52.0 deg. HRTEM micrograph showed clear-cut nano-sized circular domains and spherical nanocrystals dispersed into the amorphous matrix.

ChemInform Abstract: Colloidal Hybrid Nanostructures: A New Type of Functional Materials

AbstractReview: 182 refs.

Dielectric Properties of Barium Titanate Ceramics with Nano-Sized Domain

Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 μm on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 μm on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 μm. The field emission scanning electron microscope (FE-SEM) observations revealed that the 90º domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 μm, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.

Colloidal Hybrid Nanostructures: A New Type of Functional Materials

One key goal of nanocrystal research is the development of experimental methods to selectively control the composition and shape of nanocrystals over a wide range of material combinations. The ability to selectively arrange nanosized domains of metallic, semiconducting, and magnetic materials into a single hybrid nanoparticle offers an intriguing route to engineer nanomaterials with multiple functionalities or the enhanced properties of one domain. In this Review, we focus on recent strategies used to create semiconductor-metal hybrid nanoparticles, present the emergent properties of these multicomponent materials, and discuss their potential applicability in different technologies.

Amphiphilic Asymmetric Comb Copolymer with Pendant Pyrene Groups and PNIPAM Side Chains: Synthesis, Photophysical Properties, and Self-Assembly

An amphiphilic asymmetric comb polymer with pendant pyrene groups and poly(N-isopropylacrylamide) (PNIPAM) side chains was synthesized based on click chemistry and reversible addition-fragmentation chain transfer polymerization. Gel permeation chromatography, FTIR, and (1)H NMR results all indicated successful synthesis of a well-defined comb polymer. The photophysical properties and self-assembly of the polymer in solution were studied by UV-vis spectroscopy, fluorescence technique, and transmission electron microscopy. The intensity ratio of the excimer peak (I(E)) to the monomer peak (I(M)) of the comb polymer in THF was used to monitor the formation of inter- or intramolecular excimers. At low polymer concentration, the value of I(E)/I(M) kept unchanged, indicating the formation of intramolecular excimer; at high polymer concentration, the value increased rapidly with concentration because of the formation of intermolecular excimer. The change of the intensity ratio of the first to the third vibronic band (I(1)/I(3)) on the monomer emission of the comb polymer also proved the association of the pendant pyrene groups in THF at high polymer concentration. In aqueous solution, the comb polymer chains self-assembled into vesicles with pyrene groups in the walls and PNIPAM side chains in the coronae. The value of the critical aggregation concentration of the polymer was determined by fluorescence technique. Temperature exerted a significant effect on the size and morphology of the vesicles. At a temperature above the lower critical solution temperature (LCST) of PNIPAM, PNIPAM brushes in the coronae of vesicles collapsed on the surface of the structures forming nanosized domains, and vesicles with smaller size were obtained. Fluorescence quenching experiments indicated that the collapsed PNIPAM chains protected a part of pyrene groups from being quenched by nitromethane at a temperature above the LCST of PNIPAM.

Laser-assisted three-dimensional atom probe analysis of dopant distribution in Gd-doped CeO2

The grain boundary segregation and the concentration fluctuation of Gd in 25 at.% Gd-doped CeO2 (Gd0.25Ce0.75O1.875) have been directly characterized by a laser-assisted three-dimensional atom probe using an ultraviolent femtosecond pulse laser. Gd was found to be enriched not only at grain boundaries but also in nanosized domains within the grains. Both of these can explain the degradation of the ionic conductivity by the substitution of Gd for Ce in CeO2.

ChemInform Abstract: Ordering Phenomena in Complex Chalcogenides — The Showcase of A2In12Q19 (A: K, Tl, NH4; Q: Se, Te) and Pseudobinary In2Q3.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Boson-fermion duality and metastability in cuprate superconductors

The intrinsic structural metastability in cuprate high T$_c$ materials, evidenced in a checker-board domain structure of the CuO$_2$ planes, locally breaks translational and rotational symmetry. Dynamical charge - deformation fluctuations of such nano-size unidirectional domains, involving Cu-O-Cu molecular bonds, result in resonantly fluctuating diamagnetic pairs embedded in a correlated Fermi liquid. As a consequence, the single-particle spectral properties acquire simultaneously (i) fermionic low energy Bogoliubov branches for propagating Cooper pairs and (ii) bosonic localized glassy structures for tightly bound states of them at high energies. The partial localization of the single-particle excitations results in a fractionation of the Fermi surface as the strength of the exchange coupling between itinerant fermions and partially localized fermion pairs increases upon moving from the nodal to the anti-nodal point. This is also the reason why, upon hole doping, bound fermion pairs predominantly accumulate near the anti-nodal points and ultimately condense in an anisotropic fashion, tracking the gap in the single particle spectrum.