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Poly-[Rh(1,4-phenylene diisocyanide)+4/2(Cl)-] has a two-dimensional template structure, where Rh atoms are bonded by the -conjugated 1,4-phenylene diisocyanide (pdi) ligands in the x-y plane and through overlapping dz orbitals in the z direction. The more conductive metallic bonds in the z direction create anisotropy in the electrical conductivity. The anisotropy and unique geometry of poly-[Rh(pdi)+4/2(Cl)-] make it a useful test bed for examining the relationship between electrical properties and chemical stability in metal-isocyanide molecular wire systems. The bulk powder of poly-[Rh(pdi)+4/2(Cl)-] is estimated to have a room-temperature bulk conductivity of 3.4 x 10(-11) S x cm(-1), an electrical activation energy of 0.9 eV, and a dielectric constant of 7.5. In this paper, impedance spectroscopy and X-ray powder diffraction were used to show the dependence of the electrical conductivity on the metal-metal bonding of pressed bulk powders of poly-[Rh(pdi)+4/2(Cl)-]. Thermo-gravimetric analysis and X-ray photoelectron spectroscopy were used to demonstrate air sensitivity in the polymer and elucidate the mechanism of oxidative degradation.

The goal of this study was to probe the effect of orientation and alignment of carbon nanotubes (CNTs) embedded in an epoxy polymer matrix under a magnetic field on the mechanical properties of the resulting nanocomposite. We showed that the changes in the mechanical properties of the nanocomposites, i.e. the glass transition temperature, Young’s modulus and elastic and viscous moduli, as a function of the magnetic field strengths used to align the carbon nanotubes, are dependent on the epoxy system used. Moreover, we showed that when CNT alignment actually occurs at high magnetic fields, the properties of the resulting composites are superior to those that were not exposed to a magnetic field.

Hydrous ruthenium oxide (RuO2·xH2O) xerogels were synthesized through the addition of a 1,2-epoxide, propylene oxide, to commercial hydrated ruthenium chloride, “RuCl3·xH2O,” in ethanol. After a blue-black monolithic gel formed in 4 h, the samples were allowed to age for 24 h and were dried in ambient conditions. The dried samples were then characterized by XPS, XRD, DTA and TGA. XPS showed the Ru(3d5/2) peak at a binding energy of 281.7 eV, corresponding to that of hydrous ruthenium oxide. XRD data revealed the synthesized material as amorphous. Heating the sample in inert atmospheres caused the complete reduction of the oxide to the zero-valent state, whereas heating the sample in air resulted in both crystalline anhydrous RuO2 and zero-valent ruthenium, depending on the method of heating. DTA traces showed an endotherm ending at 150 °C, corresponding to the loss of coordinated water, as well as two higher temperature crystallization exotherms when the sample was heated in both inert and oxygen-rich atmospheres. TGA runs also confirmed the complete reduction of the hydrous oxide when heated in nitrogen below 270 °C and the formation of anhydrous ruthenium oxide when heated in air, confirming the XRD results.

The development and characterization of a unique conjugated structure comprised of γ-Fe2O3 nanoparticles (NPs) and PbSe nanocrystal quantum dots (NQDs), bonded via chemical functional groups, are discussed. Compatibility with an aqueous environment was rendered by exchanging the traditional organic surfactants (oleic acid) of the PbSe NQDs and γ-Fe2O3 NPs with 2-aminoethanethiol and polyhedral silsesquioxane hydrate octakis ligands, respectively. Comparison of the transmission electron microscopy (TEM) images of the PbSe NQDs and γ-Fe2O3 NPs capped with either organic or water-soluble ligands highlights the preservation of the morphology and size of both types of nanoclusters upon ligand exchange. Furthermore, the absorbance, photoluminescence (PL), and Fourier transform infrared spectra of the PbSe QDs revealed that the optical properties of the NQDs were retained during the surfactant exchange. High-resolution TEM images of the complete conjugated structure validate the presence of the coupling between ...

We investigate the effect of system properties and adsorption sequence on competitive adsorption of poly(methyl methacrylate) (PMMA) and polystyrene (PS) on narrowly polydispersed cobalt (Co) nanoparticles (D ∼ 27 nm). The adsorbed layer composition is studied using thermo-gravimetric analysis (TGA). We find that adsorbed layers of PS are completely displaced by PMMA when the solvent is a common good solvent. An adsorbed layer of only PMMA is also obtained through competitive adsorption from a common good solvent. However, in a selective solvent that is poor for PS, sequential adsorption leads to the formation of mixed layers.

Synthesis of metal nanoclusters in polymeric media has been shown to yield small clusters with a narrow size distribution. Embedding such clusters in the three-dimensional structures formed by diblock copolymers will allow the development of ordered structures with high optical and magnetic contrast between the different regions. In this paper we investigate the effect of homopolymer and diblock copolymer properties on the cluster size. We find that in homopolymer solutions, the cluster size reaches a minimum at a specific chain molecular weight (MW). In the case of diblock copolymers, the cluster size is set by the MW of the block with the stronger affinity to the metal surface.

The effect of a polymeric medium on the nucleation and growth kinetics of iron oxide (γ-Fe2O3) clusters is studied. We show that the kinetics in both poly(methyl methacrylate) and polystyrene are d...

Aluminum oxide nanoparticles were prepared by the hydrolysis of aluminum oxide alkoxides followed by calcinations, in the presence of surface stabilizing agents, such as Na(AOT) molecules. The size of alumina precursors (bohemite) was 20–30 nm, yielding aluminum oxide particles with an average size of 80 nm after calcinations at 1200 °C. The shape of the α-alumina nanoparticles was mainly spherical and the high temperature inhibited the formation of the hexagonal crystals. The introduction of Na(AOT) during the appropriate processing step, had the effect of controlling the size of the particles, the degree of aggregation and the particles shapes.

The ability to design nanomaterial characteristics requires exact control of particle structure due to the sensitive relationship between the material properties and the particle size and morphology. Borrowing nature's approach where biomineralization is controlled by macromolecules, synthetic polymeric matrices are used to guide the formation of stable, monodisperse iron oxide nanoparticles uniformly distributed in the polymeric matrix. Particle size, size distribution, and morphology are determined by the polymer−particle interactions and are independent of the chain molecular weight: γ-Fe2O3 particles formed in strongly interacting polymeric media are small (∼10−20 nm) and pyramidal in shape, while those formed in weakly interacting media are larger (∼40−60 nm) and spherical. This synthesis method can be easily extended to a variety of inorganic nanoparticle chemistries, thereby enabling exact control over material properties.

A review of the recent work on polymer matrix nanocomposites is presented. This review is not intended to be comprehensive, but provides an overview of the processing techniques and trends in the mechanical behavior and morphology of nanocomposites. A number of composite systems with amorphous and/or crystalline polymer matrices and different nano-sized filler materials are discussed.

Empirical forms of the two-point probability functions for two-phase composites are investigated and alternate forms are introduced which can incorporate both periodicity and randomness. Microstructures of Co-polymer nano-composites have been analyzed and it was discovered that the material did not exhibit randomness and present empirical formulations may not be appropriate for its representation. A modified form of the probability function is introduced that can provide a tool to examine the degree of randomness and periodicity. The results show the potential of these functions in the evaluation of microstructures and acquiring higher order details not available previously.

In this paper, we describe the surface modification of porous polyethylene by the adsorption of polyelectrolyte mutilayers on plasma‐activated polyethylene surfaces. We use the migration rates of deionized water as an effective alternative to contact angle measurements in order to probe the interfacial energy of the modified surface. The newly acquired surface properties that result from the surface modification are monitored with respect to several key chemical and environmental variables. These variables were chosen so that they will reflect some of the common handling procedures in a laboratory or health care environments, such as exposure to solvents of different pH and polarities, and fluctuations of ambient temperature over an extended period, i.e., “shelf‐life” duration. The stability of these surface properties of the modified membranes is a fundamental requirement for their potential use in a variety of applications involving lateral flow and binding media for bio‐assays. In this paper, ...

Hydrophilic and chemically reactive porous media was prepared by adsorbing functional polymers at the surface of sintered polyethylene membranes. Modification of the membrane was accomplished by first exposing the membrane to an oxygen glow discharge gas plasma to render electrostatic charge at the membrane surfaces. A cationic polyelectrolyte was adsorbed from solution to the anionically charged surface to form an adsorbed monolayer. The adsorption of a second anionic polyelectrolyte allowed further modification of the membrane surface with a polyelectrolyte bilayer complex. In this paper we probe the effect of polymer structure on the conformation and stability of the adsorbed polyelectrolyte monolayers and bilayers on the modified polyethylene surface. Using the wicking rate of deionized, distilled water through the porous membrane to gauge the interfacial energy of the modified surface, we show that the wicking rate of the multilayer membrane can be controlled by varying the chemistry of the adsorbing polyelectrolytes and their molecular weights.

The chemical reactivity of metal nanoclusters is determined mainly by their size and their oxidation state. The control of metal particle size is essential in order to manipulate their reactivity and interfacial behavior. Uniformity of size and spatial distribution of the metal nanoclusters is essential in the study of their properties and can be achieved primarily by conducting their synthesis in the presence of stabilizers. These materials, such as surfactants or polymers, adsorb onto the surfaces of growing clusters and create a “shielding effect,” a chemical barrier that prevents the effects of van der Waals interactions between particles, thus inhibiting particle aggregation. Polymers are frequently used as stabilizers for metal clusters because they are transparent, permeable, and nonconductive, and as such, do not interfere with and/or mask the potential optical, electrical, and catalytic properties of these clusters. When the concentration of the polymer in the reaction solution is above its criti...

The stoichiometric hydroformylation reaction has been shown to consist of two variations: conducted in the presence of stoichiometric amounts of HCo(CO) 4 and CO (Type I) or in the presence of Co 2 (CO) 8 and H 2 (Type II). The main difference between these two types of stoichiometric hydroformylation reactions was believed to be the nature of the cobalt carbonyl precursor and the number of steps necessary to the onset of reaction. In both types of reactions, however, the source of the hydrogen in the hydrogenolysis step was considered to be HCo(CO) 4 and not H 2 . In this article, we examine the conventional assumptions regarding the nature and mechanism of the hydrogenolysis step for both types of stoichiometric hydroformylation reactions. This examination stems from inconsistencies observed during the study of the mechanism of the second type of the stoichiometric hydroformylation reaction, which cast some doubt on the identification of HCo(CO) 4 as the hydrogen-donor species, under conditions in which molecular hydrogen is present. The presence of isotope mixtures of H 2 /D 2 in the gas phase during the various steps of the reaction showed that the ratio of H/D isotopes in the hydrocarbon portion of the aldehydic product correlates with the HCo(CO) 4 /DCo(CO) 4 ratio in solution, while the R(CO)H/R(CO)D product ratio correlates with the H 2 /D 2 in the gas phase. Hence, the dominant reaction pathway for the hydrogenolysis step in this type of stoichiometric hydroformylation reaction is the direct reaction of hydrogen or deuterium with the acyl complex intermediate.

Two types of stoichiometric hydroformylation reactions have been described in the literature. One was performed using stoichiometric amounts of HCo(CO) 4 as the cobalt complex, and the second using stoichiometric amounts of Co 2 (CO) 8 at high hydrogen pressure. It has been believed that the second reaction follows the mechanism of the first, once HCo(CO) 4 was formed from Co 2 (CO) 8 and hydrogen. However, there have been some serious discrepancies between the expected mechanism of this reaction and its actual experimental behavior. Using a high pressure–high temperature infrared throughput cell, we have examined in situ whether the second type reaction does indeed proceed as a stoichiometric reaction between HCo(CO) 4 and olefin, and hence, in this case, the role of Co 2 (CO) 8 is merely to activate the hydrogen to form HCo(CO) 4 , or whether there is some other mechanism which is more appropriate to describe the reaction.

The microstructure of an epoxy system oriented in high magnetic fields (15-25 T) has been observed to consist of highly oriented domains at the molecular level along the direction of the applied field. The changes in the microstructure have been characterized as a function of the magnetic-field strength and have been investigated microscopically and with wide-angle X-ray diffraction. The mechanical properties of the epoxy have been examined in light of nanoindentation experiments at different load levels. The basic results of the experimental investigations for the effect of high magnetic fields on the structure and property of the epoxy are presented. Nanoinden- tation testing has revealed large differences in the nanomechanical behavior for ther- momagnetically processed epoxy specimens. The differences can be ascribed to the microstructural changes (reorientation) of the polymer at the molecular level. © 2004

Metallic fragments, or metallomers (similar to the “mer”-based nomenclature for polymers), formed via the decomposition of organometallic complexes, are highly reactive, generating a nucleation and growth process that culminates in the formation of nanocrystals. In the absence of stabilizing molecules, the aggregation process is self-restricting mainly because of the decreasing mobility of the particles and their declining diffusional rates as a function of their increasing size. On the other hand, in the presence of a polymer in the reaction medium, the growing metallic particles are stabilized by the adsorption of the polymer chains onto their surfaces, thus lowering their surface energy and creating a barrier to further aggregation. Studies of the nucleation and aggregation kinetics of metallic particles formed from the decomposition of organometallic precursors have been used to shed light on the mechanism of their formation. In these studies, the rate of decomposition of the precursor organometallic ...

In this paper we present a series of observations on the infrared spectra of DCo(CO) 4 (in comparison with HCo(CO) 4 ) as well as of the l3 CO-exchanged derivatives of HCo(CO) 4 , EtOC(O)CH 2 Co(CO) 4 , EtOC(O)Co(CO) 4 and EtC(O)Co(CO) 4 . Calculated frequencies and intensities for HCo( 12 CO) n ( 13 CO) 4− n based on the C–O factored force field approximation predict data in excellent agreement with that observed experimentally. Splitting of the E band in the complexes R–Co(CO) 4 is shown to depend on reduction of local site symmetry and appears to be greatest for R groups containing a local dipole capable ‘of through-space’ interaction with the three equatorial carbonyls. The analysis of the infrared absorption bands for the l3 CO-substituted compounds sheds light on the nature of bonding and symmetry of these molecules, and the extent of interaction between the organic substituent and the four CO groups in the cobalt tetracarbonyl compound.

We examine experimentally and theoretically the effect of polymer adsorption layers on the stability of metal nanoclusters. We find that, somewhat contrary to expectation in this low volume fractio...

Ionic interactions have been shown to enhance polymer–polymer miscibility in several highly dissimilar blend systems. In some cases, the miscibility is due to proton transfer from an acidic site on one polymer to a basic site on another, which leads to ion–ion interactions. Studies that have focused on the formation of ionomer blends from highly dissimilar materials, such as fluorocarbons and hydrocarbons or aromatics and aliphatics of widely differing glass transitions, have shown that in the absence of ionic interactions, these materials are immiscible. In this study, we have used Fourier transform infrared (FTIR) spectroscopy techniques, both qualitatively and semiquantitatively, to evaluate the extent of the proton-transfer mechanism in the enhancement of miscibility in perfluorinated acid copolymer/poly(ethyl acrylate) blends. The perfluorinated acid copolymer contains sulfonic acid groups, whereas the poly(ethyl acrylate) has been modified by the introduction of various amounts of 4-vinyl pyridine groups as comonomers in the polymer chains. The proton-transfer mechanism in this case consists of the transfer of the proton on the sulfonic acid group to the nitrogen on the pyridine group, forming a pyridinium cation and a sulfonate anion pair. FTIR has been used to distinguish between the pyridine and pyridinium groups through their absorption bands at 1416 and 1642 cm−1, respectively. The relative intensities of these bands, as a function of the molar concentration of the pyridine comonomers in the blend, provides a direct quantitative indication of the extent of proton transfer occurring in the system. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1814–1823, 2003

Blends of sulfonated phenylated polytriphenylene oxide and poly(methyl methacrylate-co-4-vinyl pyridine) were examined by dynamic mechanical, Fourier transform infrared, and NMR techniques. A high degree of miscibility was evident from a single drop in a plot of the storage modulus versus the temperature. The presence of ionic moieties due to proton transfer from sulfonic acid to 4-vinyl pyridine was confirmed by both NMR and IR spectroscopy studies. The coils were found to be close to one another in dimethyl sulfoxide-d6 because the aromatic shielding effect of the phenyl rings of the phenylated polytriphenylene oxide units was observed from the upfield shift of most of the protons of poly(methyl methacrylate) in the NMR spectrum. However, the absence of cross peaks in the nuclear Overhauser and exchange spectroscopy experiments suggested that the intermolecular distance between the chains had to be larger than 4 A. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 728–733, 2003

Nanohybrid functional biomaterials with advanced properties can provide a competitive edge in diverse biomedical applications from diagnosis to therapeutic treatments. This work describes the design of a green functional biomaterial composed of type I collagen reinforced with cellulose nanowhiskers (CNWs) to effectively enhance the rigidity of collagen and to better mimic the morphology and profile features that are characteristic to biological tissues. Careful control of the processing conditions resulted in the successful grafting of CNWs within the collagenous medium and gave rise to the formation of a three-dimensional rigid percolating network; fact which imparted a significant improvement in the system’s mechanical and thermal stability at small amount of nanofiller concentration. Similarly, the initial biocompatibility of the collagen-cellulose nanohybrid composite was probed by in-vitro incubation of human-bone-marrow-derived mesenchymal stem cells (MSCs), which resulted in the invasion and proliferation of MSCs within the hydrogel nanomaterial at day 8 of culture. We believe that the green nanohybrid composite in this study with its unique features could open new perspective design in the self-assembly of functional biomaterials for diverse range of biomedical applications.

The carbonylation of RuCl 3 .3H 2 O in refluxing alcohol represents the entry point to ruthenium organometallic chemistry. The overall carbonylation reaction is composed of three consecutive reactions, each step resulting in a ruthenium carbonyl complex with different Ru/CO ratios. A kinetic analysis of the overall reaction reveals the parameters that are involved in the rates of formation of each compound, and as a result, provides a method for the control of product composition.

The chemical reactivity of metal nanoclusters is largely determined by the size of the particles, and therefore the control of particle size in a given medium has been the topic of several interest...

This paper describes the selective phase separation of cobalt metal nanoclusters within a PS25300-b-PMMA25900 block copolymer. This selective phase separation was achieved due to the different reactivities of the functional groups in the blocks toward the metal fragments. Transmission electron micrographs showed that the cobalt clusters aggregated primarily in the poly(methyl methacrylate) block, while no cobalt nanoclusters were observed in the polystyrene block, thus creating a patterned distribution that coincided with the morphology of the block copolymer. Fourier transform infrared studies demonstrated the development of a reactive adsorption process between cobalt nanoclusters and the poly(methyl methacrylate) block, as evidenced by the appearance of new absorption bands corresponding to the formation of Co(CO)4- and COO- and the shift of C−C−O and C−O combination bands.

The physical and chemical properties of metal nanoparticles differ significantly from those of free metal atoms as well as from the properties of bulk metals, and therefore they may be viewed as a transition regime between the two physical states. Within this nanosize regime, there is a wide fluctuation of properties, particularly chemical reactivity, as a function of the size, geometry, and electronic state of the metal nanoparticles. In recent years, great advancements have been made in the attempts to control and manipulate the growth of metal particles to prespecified dimensions. One of the main synthetic methods utilized in this endeavor, is the capping of the growing clusters with a variety of molecules, e.g., polymers. In this paper we attempt to model such a process and show the relationship between the concentration of the polymer present in the system and the final metal particle size obtained. The theoretical behavior, which we obtained, is compared with experimental results for the cobalt-polystyrene system. The physical and chemical properties of metal nanoclusters differ significantly from those of individual metal atoms, as well as from the properties of bulk metal, 1-5 and hence the size regime of nanoclusters may be viewed as a transition regime between the two physical states. Within the cluster regime, there is a wide fluctuation of properties, particularly chemical reactivity, depending on the size, geometry, electronic state, and packing of the cluster. 6-13 Uniformity of size and spatial distribution of the metal nanoclusters is essential in the study of their properties and can be achieved primarily by conducting their synthesis in the presence of stabilizers. These materials, such as surfactants or polymers, adsorb onto the surfaces of growing clusters and create a “shielding effect”, a chemical barrier that prevents the effects of van der Waals interactions between particles, thus inhibiting the particle aggregation process. 14-23 Polymers are frequently used as stabilizers for metal clusters because they are transparent, permeable, and nonconductive, and as such, do not interfere with and/or mask the potential optical, electrical, and catalytic properties of these clusters. Synthetic routes for the formation of nanoclusters include ultrahigh vacuum techniques (UHV) and “wet” chemical synthesis. The UHV processes, e.g., chemical vapor deposition, have traditionally dominated in the preparation of nanoclusters due to their inherent controllability, but the they lack the flexibility necessary to manipulate a variety of properties within the same system. The chemical synthetic methods, e.g., reduction of metal halides and decomposition of organometallic complexes, are becoming more popular in recent years due to the ability to introduce stabilizing agents and therefore afford limitation of aggregate size. The motivating physical system for this work is the chemical synthesis of nanoscale metal clusters via the thermal decomposition of metal carbonyl complexes in solutions containing either pure solvent or, in addition, polymers, which will result in a more viscous reaction environment. The main factors governing the nucleation and growth of the metal particles during the decomposition process are the metal cluster size, i.e., the number of reactive sites available for chemical reactions, and the mobility of the reactive metal clusters and their ability to diffuse through the solution and collide with each other. Clearly, as particle size grows, the mobility of the particles decreases and a preferred average pseudo-equilibrium size distribution is reached. If the medium in which the thermal decompositions take place is more viscous than a pure solvent, then it is expected that the upper bound on particle mobility will be reached faster, and hence the final average particle size will be smaller. The particular system studied in this work consists of cobalt carbonyl complexes thermally decomposed in the presence of polystyrene (PS). It is important to note that the solvent chosen for the decomposition reactions was toluene, which is a good solvent for polystyrene, and therefore it promoted the solvation of the polymer over a large composition range. Based on this experimental system, we have developed a mathematical model that aims at elucidating the effect of the initial concentration of the polymer present in the reaction solution on the final cobalt particle size obtained via the thermal decomposition mechanism, and correlates the model to our experimental results.

Metallic cluster growth within a reactive polymer matrix is modeled by augmenting coagulation equations to include the influence of side reactions of metal atoms with the polymer matrix: $$\left\{ \begin{gathered} {\kern 1pt} \dot c_j = \frac{1}{2}\,\,\sum\limits_{k\, = \,1}^{j\, - \,1} {\,\,R_{j\, - \,k,\,\,k} c_k c_{j\; - k} - c_j } \,\sum\limits_{k\, = \,1}^x {\,\,R_{jk} } c_k - \delta _{1j} \lambda c_j p,{\text{ }}j = 1,\,2,... \hfill \\ \dot p = - \lambda c_1 p \hfill \\ \end{gathered} \right.$$ where λ > 0 and where c k denotes the concentration of the kth cluster and p denotes the concentration of reactive sites available within the polymer matrix for reaction with metallic atoms. The initial conditions are required to be non-negative and satisfy $$\sum\nolimits_{j\, = \,1}^\infty {\,jc_j } (0) = 1$$ and p(0) = p 0. We assume that $$R_{jk} = [dj^\alpha k^\alpha + (j + k)(j^\alpha + k^\alpha )]/(d + j + k)$$ for 0≤α≤1, which encompasses both bond linking kernels (R jk = j α k α) and surface reaction kernels (R jk = j α + k α). Our analytical and numerical results indicate that the side reactions delay gelation in some cases and inhibit gelation in others. We provide numerical evidence that gelation occurs for the classical coagulation equations (λ = 0) with the bond linking kernel (d → ∞) for 1/2

Design of materials and devices by mimicking the fascinating systems found in nature, have enabled scientists to discover new techniques to treat diseases from diagnosis to therapeutic care. With the recent advances in nanomedicine, the length-scale of this design has further extended down into a nano-sized array. Inspired by the two natural assemblies found in nature; cellulose and collagen; we have designed a new class of green functional material with nano-sized arrangement. The fabricated material composed of collagen hydrogel reinforced by cellulose nanowhiskers in order to effectively enhance the rigidity of collagen and to better mimic the morphology and profile features existed in biological tissues. The biocompatibility of the hydrogel nanocomposite was also investigated by the invasion and proliferation of human bone marrow derived mesenchymal stem cells around the materials at 8 day of culture. We believe that our biomimetically-engineered platform in this study could increase the biomedical applications of fully bio-based systems such as scaffolding in tissue engineering.

Among the most useful methods for the preparation of pure metal powders is the thermolysis of metal carbonyl complexes in hydrocarbon solutions. Zero-valent cobalt particles are obtained by the dec...

In this article, we have developed a simple model that describes the adsorption of polymer chains from a solution having a good solvent onto a reactive surface of varying curvatures. In order to evaluate the impact of particle size on the adsorption process, we have probed the adsorption of poly(methyl methacrylate) (PMMA) on aluminum oxide (Al2O3) surfaces belonging to particles of different sizes. The basic approach assumed that the details of the chemisorption mechanism of PMMA on aluminum oxide surfaces are independent of surface curvature. The combination of the experimental results with the theoretical approach that we have developed show the existence of three different regimes of adsorption of polymer chains onto the surfaces of metal nanoparticles.

Coordination polymers are drawing increasing attention due to their versatility in structure and function, and their potential applications as catalysts. These polymers may be synthesized by using aryldiisocyanides, which when coordinated to a d 6 metal such as Ru(II), act as bridges and give rise to two distinct types of three-dimensional polymeric networks. Polymer A, [Ru(1,4-diisocyanobenzene) 2+ 4/2 (2Cl) 2- ] n has a tetragonal geometry, having, most likely, Ru-Ru stacking interactions in the z direction, while polymer B, [Ru(1,4-diisocyanobenzene) 2+ 6/2 (2Cl) 2- ] n has a cubic geometry, having all the Ru atoms separated by the 1,4-diisocyanobenzene ligands. In the hydrogenation reaction of 1-hexene, polymer A is an efficient but a non-selective catalyst. The hydrogenation reaction is accompanied by isomerization, with trans 2-hexene as the leading isomer, which is hydrogenated as well after all the 1-hexene has been used up. The catalytic reaction proceeds with an induction period which suggests that polymer A in its original structure is not the actual catalyst. Irradiation of the reaction mixture with 350 nm UV light prior and during the catalytic reaction drastically reduces the induction period. This indicates that the energy of irradiation is sufficient to break the Ru-Ru stacking bonds, thus creating electron-deficient Ru sites prior to the addition of the olefin. An in-depth study of the influence of irradiation on the kinetics of the catalytic reaction is presented in this paper.

In recent years, a large emphasis has been placed on the use of renewable resources to less heavily rely on petroleum and to better utilize global energy needs. However, the lack of rigidity of nature’s materials typically limits their mass production for high-tech applications. One promising approach to address this shortcoming is to introduce a composite material reinforced by high purity nanofibers found in nature. Cellulose nanowhiskers (CNWs), the most abundant biopolymer on earth, could integrate a viable nanofibrous porous candidate resulting in superior structural diversity and functional versatility for diverse applications from automotive industry to bioengineering design. Inspired by these fascinating properties, a fully cellulose-based composite was designed using the CNWs reinforcement and their oriented morphology. Comparable to carbon nanotubes or kevlar, CNWs introduced significant strength and directional rigidity to the composite even at 0.2 wt% yet doubled that under magnetic field of only 0.3T. The tendency of CNWs to interconnect with one another confirmed the formation of a three-dimensional rigid percolating network, fact which imparted an excellent mechanical rigidity to the entire structure at such low filler content. Hence, the green nanobiomaterial with an enhanced microstructure performance in this study could potentially increase the biomedical applications of cellulose-based materials.

Surface micro- and nanostructural modifications of dental and orthopedic implants have shown promising in vitro, in vivo and clinical results. Surface wettability has also been suggested to play an important role in osteoblast differentiation and osseointegration. However, the available techniques to measure surface wettability are not reliable on clinically relevant, rough surfaces. Furthermore, how the differentiation state of osteoblast lineage cells impacts their response to micro/nanostructured surfaces, and the role of wettability on this response, remain unclear. In the current study, surface wettability analyses (optical sessile drop analysis, environmental scanning electron microscopic analysis and the Wilhelmy technique) indicated hydrophobic static responses for deposited water droplets on microrough and micro/nanostructured specimens, while hydrophilic responses were observed with dynamic analyses of micro/nanostructured specimens. The maturation and local factor production of human immature osteoblast-like MG63 cells was synergistically influenced by nanostructures superimposed onto microrough titanium (Ti) surfaces. In contrast, human mesenchymal stem cells cultured on micro/nanostructured surfaces in the absence of exogenous soluble factors exhibited less robust osteoblastic differentiation and local factor production compared to cultures on unmodified microroughened Ti. Our results support previous observations using Ti6Al4V surfaces showing that recognition of surface nanostructures and subsequent cell response is dependent on the differentiation state of osteoblast lineage cells. The results also indicate that this effect may be partly modulated by surface wettability. These findings support the conclusion that the successful osseointegration of an implant depends on contributions from osteoblast lineage cells at different stages of osteoblast commitment.

Microtexture and chemistry of implant surfaces are important variables for modulating cellular responses. Surface chemistry and wettability are connected directly. While each of these surface properties can influence cell response, it is difficult to decouple their specific contributions. To address this problem, the aims of this study were to develop a surface wettability gradient with a specific chemistry without altering micron scale roughness and to investigate the role of surface wettability on osteoblast response. Microtextured sandblasted/acid-etched (SLA, Sa = 3.1 μm) titanium disks were treated with oxygen plasma to increase reactive oxygen density on the surface. At 0, 2, 6, 10, and 24 h after removing them from the plasma, the surfaces were coated with chitosan for 30 min, rinsed and dried. Modified SLA surfaces are denoted as SLA/h in air prior to coating. Surface characterization demonstrated that this process yielded differing wettability (SLA0 < SLA2 < SLA10 < SLA24) without modifying the micron scale features of the surface. Cell number was reduced in a wettability-dependent manner, except for the most water-wettable surface, SLA24. There was no difference in alkaline phosphatase activity with differing wettability. Increased wettability yielded increased osteocalcin and osteoprotegerin production, except on the SLA24 surfaces. mRNA for integrins α1, α2, α5, β1, and β3 was sensitive to surface wettability. However, surface wettability did not affect mRNA levels for integrin α3. Silencing β1 increased cell number with reduced osteocalcin and osteoprotegerin in a wettability-dependent manner. Surface wettability as a primary regulator enhanced osteoblast differentiation, but integrin expression and silencing β1 results indicate that surface wettability regulates osteoblast through differential integrin expression profiles than microtexture does. The results may indicate that both microtexture and wettability with a specific chemistry have important regulatory effects on osseointegration. Each property had different effects, which were mediated by different integrin receptors.

The thermal decomposition of Co2(CO)8 to Co4(CO)12 and further to metallic cobait and CO under an inert atmosphere at temperatures

Carbon nanotubes (CNTs) have been the focus of extensive research in recent years due to their exceptional mechanical, thermal, and electrical properties (Treacy et al., 1996; Lourie et al., 1998; Yu et al., 2000; Lukic et al., 2005). As a result of their nanoscale dimensions and high surface area, CNTs could also be considered as efficient templates for the assembly and tethering of nanoparticles on their surface (Grzelczak et al., 2006). The decoration of CNTs with various compounds and various structures could increase their surface functionality and the tunability of their properties, such as their electrical and magnetic characteristics (Korneva et al., 2005; Kuang et al., 2006). Recent reports described the attachment of various inorganic nanoparticles to either the external surface of the CNTs, or to the internal surface of the CNT cavity, through several experimental methods (Han et al., 2004; Qu et al., 2006). In this context, it is important to note that the control of the size of these tethered nanoparticles is of primary importance for the purpose of tailoring the physical and chemical properties of these hierarchical materials. Iron oxide nanoparticles, such as magnetite and maghemite, have been of technological and scientific interest due to their unique electrical and magnetic properties. These nanoparticles can be used in such diverse fields as high-density information storage and electronic devices (Sun et al., 2000; Pu et al., 2005; Yi et al., 2006; Jia et al., 2007; Wan et al., 2007). Maghemite, Fe2O3, is the allotropic form of magnetite, Fe3O4 (Rockenberger et al., 1999; Pileni et al., 2003; Sun et al., 2004). These two iron oxides are crystallographically isomorphous. The main difference is the presence of ferric ions only in -Fe2O3, and both ferrous and ferric ions in Fe3O4. As a result, while the magnetic properties of Fe3O4 are superior, -Fe2O3 is more stable, since the iron cannot be further oxidized under ambient conditions. This renders Fe2O3 nanoparticles easier to work with, especially in the presence of organic solvents and organic ligands, and consequently, they have been widely used for magnetic storage in a variety of fields such as floppy disks and cassette tapes. However, maghemite-CNT nanohybrid materials have not been studied as extensively as magnetite-CNT nanohybrid materials, with the exception of several few examples (Sun et al., 2005; Youn et al., 2009).

Micrometer- and submicrometer-scale surface roughness enhances osteoblast differentiation on titanium (Ti) substrates and increases bone-to-implant contact in vivo. However, the low surface wettability induced by surface roughness can retard initial interactions with the physiological environment. We examined chemical modifications of Ti surfaces [pretreated (PT), R(a) ≤ 0.3 μm; sand blasted/acid etched (SLA), R(a) ≥ 3.0 μm] in order to modify surface hydrophilicity. We designed coating layers of polyelectrolytes that did not alter the surface microstructure but increased surface ionic character, including chitosan (CHI), poly(L-glutamic acid) (PGA), and poly(L-lysine) (PLL). Ti disks were cleaned and sterilized. Surface chemical composition, roughness, wettability, and morphology of surfaces before and after polyelectrolyte coating were examined by X-ray photoelectron spectroscopy (XPS), contact mode profilometry, contact angle measurement, and scanning electron microscopy (SEM). High-resolution XPS spectra data validated the formation of polyelectrolyte layers on top of the Ti surface. The surface coverage of the polyelectrolyte adsorbed on Ti surfaces was evaluated with the pertinent SEM images and XPS peak intensity as a function of polyelectrolyte adsorption time on the Ti surface. PLL was coated in a uniform thin layer on the PT surface. CHI and PGA were coated evenly on PT, albeit in an incomplete monolayer. CHI, PGA, and PLL were coated on the SLA surface with complete coverage. The selected polyelectrolytes enhanced surface wettability without modifying surface roughness. These chemically modified surfaces on implant devices can contribute to the enhancement of osteoblast differentiation.

Scaffolds constitute an essential structural component in tissue engineering of a vascular substitute for small grafts by playing a significant role in integrating the overall tissue constructs. The microstructure and mechanical properties of such scaffolds are important parameters to promote further cellular activities and neo-tissue development. Cellulose nanowhiskers (CNWs), an abundant, biocompatible material, could potentially constitute an acceptable candidate in scaffolding of a tissue-engineered vessel. Inspired by the advantages of cellulose and its derivatives, we have designed a biomaterial comprising CNWs embedded in a matrix of cellulose acetate propionate to fabricate a fully bio-based scaffold. To ensure uniform distribution, CNWs were delicately extracted from a multi-stage process and dispersed in an acetone suspension prior to the composite fabrication. Comparable to carbon nanotubes or kevlar, CNWs impart significant strength and directional rigidity even at 0.2 wt% and almost double that at only 3.0 wt%. To ensure the accuracy of our experimental data and to predict the unusual reinforcing effect of CNWs in a cellulose-based composite, homogenization schemes such as the mean field approach and the percolation technique were also investigated. Based on these comparisons, the tendency of CNWs to interconnect with one another through strong hydrogen bonding confirmed the formation of a three-dimensional rigid percolating network, fact which imparted an excellent mechanical stability to the entire structure at such low filler contents. Hence, our fibrous porous microstructure with improved mechanical properties could introduce a potential scaffold to withstand the physiological pressure and to mimic the profile features of native extracellular matrix in a human vessel. We believe that our nanohybrid design not only could expand the biomedical applications of renewable cellulose-based materials but also could provide a potential scaffold candidate in tissue engineering of small diameter grafts.

Uniform high-quality iron oxide thin films can be formed from the spin coating of iron oxide/hydroxide sol-gels on a silicon substrate. Thermal processing of the films at temperatures of approximately 300 degrees C results in the transformation of films into a ternary layered structure with iron oxide, Fe(2)O(3), at the surface, characterized by Mossbauer spectroscopy, and reduced, metallic iron characterized by depth profiling of the surface by X-ray photoelectron spectroscopy as a function of Ar(+) etching. Imaging of the etched surface by scanning electron microscopy reveals two distinct regions at the interface, nanoparticles that are very iron-rich separated by an unstructured region that is somewhat less iron-rich. The results demonstrate a synthetic protocol for the spontaneous formaton of a ternary layered structure from a simple one-step preparation.

We describe a novel, facile method for the alignment of multi-walled carbon nanotubes (MWNTs) in a magnetic field facilitated by the decoration of the MWNTs with monodisperse γ-Fe2O3 magnetic (maghemite) nanoparticles. The tethering of the nanoparticles was achieved by the attachment of γ-Fe2O3 nanoparticles that were synthesized using a modified sol-gel process, onto the carboxylate-activated MWNTs. Sodium dodecylbenzene sulfonate (NaDDBS) was used to prevent the formation of an iron oxide 3D network. Various characterization methods were employed to confirm the formation of homogeneously-distributed and nearly-monodispersed iron oxide nanoparticles, and show that they were indeed tethered to the walls of the MWNTs. The γ-Fe2O3 nanoparticles imparted magnetic characteristics to the MWNTs, which in turn, were oriented parallel to the direction of an externally-applied magnetic field. This facile alignment of MWNT could promote the enhancement of various properties, e.g. mechanical and electrical properties, of the resulting composites. Moreover, this facile alignment at low magnetic fields, made possible by the magnetization of the carbon nanotubes through the tethering of maghemite nanoparticles, may be applied to a variety of other useful nanofillers, such a glass fibers, clay nanoparticles and cellulose nanowhiskers.

The reaction of Co 2 (CO) 8 with D 2 does not have as product the expected DCo(CO) 4 only but gives rise to a mixture of DCo(CO) 4 and HCo(CO) 4 . This phenomenon, observed also with other metal carbonyl hydrides, was explained by the fact that the reaction-vessel walls were covered by a polymeric layer of water which caused a very fast exchange with the deuterium in DCo(CO) 4 , and hence this was the source of hydrogen in the formation of HCo(CO) 4 . In this present work, we attempt to obtain alkane solutions of DCo(CO) 4 with very high deuteride content in order to study the spectral and chemical properties of this elusive compound. In concentrated solutions of DCo(CO) 4 , having only traces of Co 2 (CO) 8 , an absorption band at 2048 cm −1 was observed, and attributed to a CO stretching fundamental mode of DCo(CO) 4 . This band corresponds to the 2052 cm −1 band found in HCo(CO) 4 . In both cases it can be assigned to the a 1 mode in which the axial and equatorial CO groups stretch out of phase. Another band, the total symmetric v (CO) mode at 2116.3 cm −1 , is only 0.4 cm −1 lower in energy than the corresponding band of HCo(CO) 4 . The extinction coefficients for several significant absorption bands of DCo(CO) 4 were calculated. The high pressure IR spectroscopic analysis, previously applied to calculate cobalt carbonyl concentrations in a three-component system, has proven itself to be quite accurate in the present case as well. Using the quantitative data obtained, the equilibrium constants for the reaction between Co 2 (CO) 8 and D 2 were obtained. Finally, the effect of the presence of H 2 O or D 2 O on H/DCo(CO) 4 mixtures was studied and compared to the exchange with H 2 and D 2 in the gas phase.

Copper (Cu) has been extensively used as an interconnect material for microelectronic devices because of its high electrical and thermal conductivity and excellent electromigration resistance. However, the formation of relatively rough Cu surfaces ( approximately 5 nm roughness) and Cu-oxide layers upon exposure to air still hinders their reliable application in a wide range of fields. In this article, we show the potential values of highly stable and ultrasmooth polycrystalline bare Cu obtained by simple annealing and chemical modification for a wide range of Cu-based electronic devices. The morphological properties and oxidation behavior of annealed Cu surfaces, before and after coating by self-assembled monolayers of terephthalic acid (TPA), were examined upon exposure to ambient air conditions ( approximately 110 days). Thin films of polycrystalline Cu, deposited on top of an adhesion layer of tantalum nitride (TaN) and annealed for 8 h at 580 degrees C under 2 x 10(-7) Torr, provided ultrasmooth Cu surfaces (R(rms) = 0.15-1.1 nm for fresh samples) and had a stable Cu-oxide layer after 65 days ( approximately 3.5 nm). These observations were perceived to be superior to nonannealed polycrystalline Cu samples. Coating fresh (oxide-free) samples of ultrasmooth Cu with TPA molecules created a closely packed monolayer with a standing-up phase configuration and molecular coverage of approximately 90%. The TPA-coated Cu surface has not shown any detectable oxidation during the first 2 weeks of exposure. The protection efficiency of this layer was found to be superior to those reported earlier on polycrystalline Cu surfaces. The oxidation mechanisms of both annealed and nonannealed Cu surfaces are presented and discussed.