Rod-like Nanoparticles Research Articles

Elastic Moduli of Cellulose Nanoparticle-Reinforced Composites: A Micromechanical Model

A model for the elastic coefficients of fiber-reinforced materials is applied toward the analysis of the tensile and shear moduli of nanocomposites reinforced by rod-like cellulose nanoparticles. Our formalism integrates results from percolation theory with micromechanical and effective medium approaches. Polydispersity in the fiber length distribution and anisotropies in the stiffness coefficients of cellulose nanoparticles are taken into account explicitly. Results from calculations employing our model display reasonable agreement with experimental measurements of the moduli as functions of the filler volume fraction for several cellulose nanoparticle-reinforced thermoplastic-based composites.

Crystallization Control of CaCO3 by Ionic Liquids in Aqueous Solution

In this paper, the calcium carbonate (CaCO3) crystallization controlled by imidazolium based ionic liquids (ILs) was investigated. 1-Dodecyl-3-methylimidazolium bromide ([C12mim]Br) and 1-butyl-3-methylimidazolium bromide ([C4mim]Br) were chosen as crystal growth template. Rodlike and dendritelike aragonite nanoparticles were obtained easily in the presence of [C12mim]Br and [C4mim]Br, respectively. The morphology changes of the as-prepared CaCO3 crystals from classical calcite rhombohedron to unusual dendritelike and rodlike aragonite nanoparticles were studied by using scanning electron microscopy and transition electron microscopy. The phase change of the obtained crystals was confirmed by using X-ray diffraction. It was shown that the higher reaction temperature favors the production of aragonite, and the optimal pH for pure aragonite phase is 11. Mineralization of CaCO3 controlled by ILs is a simple, novel, and environmentally friendly strategy for aragonite nanoparticles synthesis.

Development of Langmuir−Schaeffer Cellulose Nanocrystal Monolayers and Their Interfacial Behaviors

Model cellulose surfaces based on cellulose nanocrystals (CNs) were prepared by the Langmuir-Schaeffer technique. Cellulose nanocrystals were obtained by acid hydrolysis of different natural fibers, producing rodlike nanoparticles with differences in charge density, aspect ratio, and crystallinity. Dioctadecyldimethylammonium bromide (DODA-Br) cationic surfactant was used to create CN-DODA complexes that allowed transfer of the CNs from the air/liquid interface in an aqueous suspension to hydrophobic solid substrates. Langmuir-Schaeffer horizontal deposition at various surface pressures was employed to carry out such particle transfer that resulted in CN monolayers coating the substrate. The morphology and chemical composition of the CN films were characterized by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Also, their swelling behavior and stability after treatment with aqueous and alkaline solutions were studied using quartz crystal microgravimetry (QCM). Overall, it is concluded that the Langmuir-Schaeffer method can be used to produce single coating layers of CNs that were shown to be smooth, stable, and strongly attached to the solid support. The packing density of the films was controlled by selecting the right combination of surface pressure during transfer to the solid substrate and the amount of CNs available relative to the cationic charges at the interface.

Synthesis and magnetic properties of single-crystalline BaFe12O19 nanoparticles

Abstract Rod-like and platelet-like nanoparticles of simple-crystalline barium hexaferrite (BaFe12O19) have been synthesized by the molten salt method. Both particle size and morphology change with the reaction temperature and time. The easy magnetization direction (0 0 l) of the BaFe12O19 nanoparticles has been observed directly by performing X-ray diffraction on powders aligned at 0.5 T magnetic field. The magnetic properties of the BaFe12O19 magnet were investigated with various sintering temperatures. The maximum values of saturation magnetization (σs=65.8 emu/g), remanent magnetization (σr=56 emu/g) and coercivity field (Hic=5251 Oe) of the aligned samples occurred at the sintering temperatures of 1100 °C. These results indicate that BaFe12O19 nanoparticles synthesized by the molten salt method should enable detailed investigation of the size-dependent evolution of magnetism, microwave absorption, and realization of a nanodevice of magnetic media.

Effects of Magnesium Hydroxide Containing Copper Compound on the Properties of Polypropylene Composites

Rod-like morphological magnesium hydroxide nanoparticles were synthesized via coprecipitation with copper ions. Flame retardant composites were prepared by these particles and polypropylene. The microstructure, flame retardation, mechanical property, thermal oxidative degradation behavior and mechanism of these composites were discussed. The results demonstrated that these composites containing copper compound increased the flame retardation, but decreased the initial oxidative decomposition temperatures and mechanical properties. Thermogravimetric and infrared analysis showed that the decomposition procedure was divided into three stages. In addition, the degradation kinetics was analyzed by Flynn-Wall-Ozawa method, and it showed that polypropylene composites containing copper compound exhibited a different decomposition mechanism.

Long-term Transgene Expression in the Central Nervous System Using DNA Nanoparticles

This study demonstrates proof of concept for delivery and expression of compacted plasmid DNA in the central nervous system. Plasmid DNA was compacted with polyethylene glycol substituted lysine 30-mer peptides, forming rod-like nanoparticles with diameters between 8 and 11 nm. Here we show that an intracerebral injection of compacted DNA can transfect both neurons and glia, and can produce transgene expression in the striatum for up to 8 weeks, which was at least 100-fold greater than intracerebral injections of naked DNA plasmids. Bioluminescent imaging (BLI) of injected animals at the 11th postinjection week revealed significantly higher transgene activity in animals receiving compacted DNA plasmids when compared to animals receiving naked DNA. There was minimal evidence of brain inflammation. Intrastriatal injections of a compacted plasmid encoding for glial cell line-derived neurotrophic factor (pGDNF) resulted in a significant overexpression of GDNF protein in the striatum 1-3 weeks after injection.

Rheological behaviour of nanofluids containing tube / rod-like nanoparticles

Experiments are carried out on the rheological behaviour of ethylene glycol (EG) based titanate nanotubes (TNT) nanofluids containing 0.5, 1.0, 2.0, 4.0 and 8.0 wt.% TNT at 20–60 °C. The results show a very strong shear thinning behaviour of the TNT nanofluids and big influences of particle concentration and temperature on the zero shear viscosity (ZSV) and high shear viscosity (HSV), for which the conventional form of Brenner & Condiff Equation fails to predict. Theoretical analyses show that these experimentally observed phenomena can be well interpreted by the conventional colloid theory if particle shape and aggregation effects are taken into account and different relative importance of the Brownian diffusion and convection at different shear rates. It is suggested that nanofluids containing tube / rod-like nanoparticles with effective aspect ratio ( r a) and effective volume fraction ( φ a) can be classified into dilute nanofluids with 0 < φ a < 1/ r a 2, semi-dilute nanofluids with 1/ r a 2 < φ a < 1/ r a, s emi-concentrated and concentrated nanofluids with 1/ r a < φ a.

Shape Control of Silver Nanoparticles by Stepwise Citrate Reduction

Growth of silver nanoparticles by the citrate reduction of silver nitrate under the range of pH from 5.7 to 11.1 was investigated systematically and quantitatively. Reduction of the silver precursor (Ag+) was promoted with increased pH, attributed to the higher activity of the citrate reductant under high pH value. Under high pH, the product was composed of both spherical and rod-like silver nanoparticles as a result of the fast reduction rate of the precursor. Under low pH, the product was mainly dominated by triangle or polygon silver nanoparticles due to the slow reduction rate of the precursor. The product that is dominated by spherical silver nanoparticles cannot be acquired by the one-step citrate reduction method in the range of pH investigated, indicating the poor balance between the nucleation and growth processes in the reactions. On the basis of the results of quantitative analyses, a stepwise reduction method, in which the nucleation and growth processes were carried out at high and low pH, respectively, was proposed for the syntheses of spherical silver nanoparticles.

Optically active helical polyurethane@attapulgite composites: Effect of optical purity of S-1,1′-binaphthyl-2,2′-diol on infrared emissivity

Helical polyurethane@attapulgite (HPU@ATT) composites were prepared after the surface modification of the rod-like attapulgite (ATT). HPU@ATT composites based on S-1,1′-binaphthyl-2,2′-diol (S-BINOL) with different optical purity (O.P.) were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified ATT without destroying the original crystalline structure of ATT. The rod-like nanoparticles were confirmed by transmission electron microscopy (TEM). Infrared emissivity values of HPU@ATT composites have been investigated, and the results indicate that the optical purity of monomer plays a very important role in the infrared emissivity for HPU@ATT owing to the effect of helical conformation and interchain hydrogen bonds. Along with the increased optical purity of S-BINOL, the infrared emissivity of HPU@ATT is reduced evidently. Infrared emissivity value of HPU@ATT based on S-BINOL with 100% optical purity is the lowest one (0.431).

Dye-Adsorption-Induced Gelation of Suspensions of Spherical and Rodlike Zinc Oxide Nanoparticles in Organic Solvents

The adsorption of amphiphilic Ru(II) complex Z907 onto the surface of ZnO nanospheres and nanorods causes the gelation of organic solvents, such as THF and acetone. The gels are thermally stable at very low concentration (nanoparticle volume fraction phi = 0.009) but mechanically fragile, with the behavior being dependent on the nature of the solvent, nanoparticle concentration, and the Z907/ZnO mole/weight ratio. Rheological experiments confirmed that the solid component built up a network to give a viscoelastic gel-phase material with a weak value of storage modulus G'. However, TEM and SEM experiments did not give evidence that nanoparticle long-range ordering occurred under the experimental conditions investigated. Moreover, time-dependent SAXS measurements pointed to a decrease in the nanoparticle aggregate size upon gelation. All together, the data obtained might be rationalized in terms of the aggregate-to-aggregate transition in solution, with the primitive large aggregates giving rise to smaller ones upon reaction with Z907. The resulting smaller hybrid aggregates could be the active species that act as self-assembling components in the gelation process. Given the interesting electronic and photonic properties of zinc oxide nanoparticles, such hybrid organic-inorganic gels could open new directions in materials science, low-cost electronics, and photovoltaics.

Solid lipid nanoparticles and nanoemulsions containing ceramides: Preparation and physicochemical characterization

Nanoemulsions (NEs) and solid lipid nanoparticles (SLNs) are widely used colloidal carriers for bioactive compounds. They are used in therapeutic, diagnostic, and cosmetic formulations. Ceramides are main components of the stratum corneum and are essential for the efficient barrier function. Their very high lipophilicity renders them difficult to incorporate in an acceptable formulation. The aim of this work was to investigate the possibility of using the benefits of nanotechnology in the efficient topical delivery of ceramides formulated as NEs or SLNs. The physicochemical characteristics of such carriers incorporating ceramides were investigated and their stability over time was assessed. Their morphology was examined under a scanning electron microscope and the interactions of their components were studied by differential scanning calorimetry. The results showed that the nanoemulsions can incorporate a high percentage (48.4% of total lipids by weight) of ceramides giving more homogeneous particle distributions of spherical-shaped nanoparticles and they maintained their characteristics over time. On the contrary, SLNs’ incorporation of ceramide higher than 10.8% of total lipids by weight led to the formation of rod-like nanoparticles deteriorating the homogeneity of the particle distribution, as depicted on the high polydispersity indexes of the corresponding formulations. The results demonstrate that NEs may be the more suitable carrier, compared to SLNs.

Preparation and characterization of homogeneous chitosan–polylactic acid/hydroxyapatite nanocomposite for bone tissue engineering and evaluation of its mechanical properties

Homogeneous nanocomposites composed of hydroxyapatite and chitosan in the presence of polylactic acid were synthesized by a novel in situ precipitation method. The morphological and compositional properties of composites were investigated. Hydroxyapatite nanoparticles in a special rod-like shape with a diameter of about 50 nm and a length of about 300 nm were distributed homogeneously within the chitosan–polylactic acid matrix. The interaction between the organic matrix and the inorganic crystallite and the formation mechanism of the rod-like nanoparticles were also studied. The results suggested that the formation of the special rod-like nanoparticles could be controlled by a multiple-order template effect. High-resolution images showed that the rod-like inorganic particles were composed of randomly orientated subparticles about 10 nm in diameter. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The data indicated that the addition of polylactic acid can make homogeneous composites scaffold resist significantly higher stress. The elastic modulus of the composites was also improved by the addition of polylactic acid, which can make them more beneficial for surgical applications.

Nanocrystalline hydroxyapatite powders by a chitosan–polymer complex solution route: Synthesis and characterization

Nanocrystalline hydroxyapatite (HAp) powders were successfully synthesized by a simple method using chitosan–polymer complex solution. To obtain HAp nanopowders, the prepared precursor was calcined in air at 400–800 °C for 2 h. The phase composition of the calcined samples was studied by X-ray diffraction (XRD) technique. The XRD results confirmed the formation of HAp phase with a small trace of monotite phase. With increasing calcination temperature, the crystallinity of the HAp increased, showing the hexagonal structure of HAp with the lattice parameter a in a range of 0.94030–0.94308 nm and c of 0.68817–0.68948 nm. The particle sizes of the powder were found to be 55.02–73.36 nm as evaluated by the XRD line broadening method. The chemical composition of the calcined powders was characterized by FTIR spectroscopy. The peaks of the phosphate carbonate and hydroxyl vibration modes were observed in the FTIR spectra for all the calcined powders. TEM investigation revealed that the prepared HAP samples consisted of rod-like nanoparticles having the particle size in the range of 100–300 nm. The corresponding selected-area electron diffraction (SAED) analysis further confirmed the formation of hexagonal structure of HAp.

The Cotton-Mouton effect in ferrofluids containing rod-like magnetite particles

Ferrofluids with rod-like nano-sized magnetite particles were prepared by precipitation from aqueous solutions of ferrous hydroxide and aging them in the presence of a magnetic field. We studied the Couton-Mouton effect measuring the azimuthally distribution of the transmitted light intensity and obtained that its magnetic field dependence differs considerably for ferrofluids containing rod-like and spherical magnetic nanoparticles, respectively. After switching off the magnetizing field, the relaxation of the birefringence was observed, measured and analysed.

Comparison of Plasmonic Sensing between Polymer- and Silica-coated Gold Nanorods

Gold nanorods (AuNRs), rod-like gold nanoparticles, show strong plasmon bands in the near-infrared region, based on the longitudinal oscillation mode of surface plasmons. In this research, we have coated AuNRs with silica or poly (sodium 4-styrenesulfonate) (PSS) in order to evaluate the effects of surface modifications as a sensing probe material of AuNR. Multilayered assemblies of the PSS-coated AuNRs have been successfully fabricated on the glass substrate by electrostatic layer-by-layer adsorption, and their plasmonic band profiles have been analyzed as a function of refractive index. The profiles showed satisfactory linear responses with the refractive indices. The effect of the thickness of silica layer on the shift of plasmon band with refractive index of the surrounding media has been investigated, along with, the effect of silica coating on the thermal stability of AuNR. The thermal stability of the silica-coated AuNR has also been investigated. The two types of the above-described coating approaches have been compared.

Shape control synthesis of spheroid and rod-like silver nanostructures in organic–inorganic sol–gel composite

The synthesis of a variety of spheroid and rod-like silver nanoparticles in hybrid organic–inorganic sol–gel composite films was examined. The sol–gel matrix used in this work involves urethane terminated silica network which acts as a stabilizing and coupling agent and can complex with silver atoms through its secondary amine functionality and form stable colloid dispersions. The parameters determining the particles size and shape are the starting concentrations of silver ions, the coordination and reduction abilities of the solvent and the reaction kinetics and temperature. In this work the reduction process of silver ion was performed by DMF in sol–gel polyurethane precursor solution at two reaction temperatures: (a) 40 ∘C and (b) reflux at boiling temperature. The effects of concentration and temperature of solution on the morphology and uniformity of silver nanorods were investigated by UV–VIS spectroscopy, SEM and TEM. Spheroid nanoparticles size was as 10–12 nm. Electron diffraction shows that all nanoparticles have a silver face-centered cubic crystal lattice. The silver nanoparticles obtained in composite films exhibit a strong characteristic extinction peak, due to surface plasmon resonance occurring nearly 420–440 nm.

Synthesis of Pd/α-Fe 2O 3 nanocomposites for catalytic CO oxidation

Iron oxide and metal doped iron oxide nanocomposites have found attractive and versatile applications in many research areas such as catalysts, sensors, and biomedicine. This work reports a surfactant-free hydrolysis approach for the synthesis of hematite (α-Fe 2O 3) and Pd doped α-Fe 2O 3 nanoparticles with low-temperature catalytic activity. By this method, iron oxide rod-like nanoparticles were achieved by hydrolysis of ferric chloride salt with dilute HCl at a temperature of 100 °C. The Pd/iron oxide nanocomposites were obtained by adding citric acid into a mixture of iron oxide nanoparticles and palladium precursor (Pd(CH 3CN) 2Cl 2) under a reflux heating at 90 °C for 2 h. This method is featured as no use of any surfactants and templates, and no requirement of high-temperature thermal decomposition that are usually required for shape/size control in polar or nonpolar solvents. More importantly, it was found that the Pd/α-Fe 2O 3 nanocomposites exhibited high low-temperature catalytic activity in carbon monoxide (CO) oxidation.

Preparation, Characterization and Infrared Emissivity Study of Attapulgite@helical Polyurethane Composites

Attapulgite@helical polyurethane composites (ATT@HPU and ATT@PU) were prepared after the surface modification of the attapulgite nano-fibrillar clay (ATT). ATT@HPU and ATT@PU were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified ATT without destroying the original crystalline structure of ATT. The rod-like fibrous nanoparticles were confirmed by scanning electron microscope (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HTEM). The infrared emissivity of ATT@HPU and ATT@PU was also investigated. The results indicate that the singlehanded helical conformation is favored to the reduction of infrared emissivity due to the more regular structure and ordered stereo structures.

Simulation Model of Concentrated Colloidal Rod-Like Nanoparticles

A simulation model of concentrated colloidal rod-like nanoparticles is developed. As the governing equation of motion of a nanoparticle, the Langevine equation with external force is used. The external force includes capillary force, contact force, electrostatic force, van der Waals force, and elastic force which occurs inside an elastic rod. Numerical simulations are performed for the system of concentrated colloidal rod-like nanoparticles, which experiences solvent evaporation with a constant rate. Consequently, some structures of self-organized rod-like nanoparticles are obtained for the specified aspect ratios. The time evolution of the system is quantitatively analyzed by using the orientational order parameter and the non-dimensional boundary area. Moreover the two quantities are found to resolve the structures obtained in the simulation.

Electrospun PVA/HAp nanocomposite nanofibers: biomimetics of mineralized hard tissues at a lower level of complexity

Based on the biomimetic approaches the present work describes a straightforward technique to mimic not only the architecture (the morphology) but also the chemistry (the composition) of the lowest level of the hierarchical organization of bone. This technique uses an electrospinning (ES) process with polyvinyl alcohol (PVA) and hydroxyapatite (HAp) nanoparticles. To determine morphology, crystalline structures and thermal properties of the resulting electrospun fibers with the pure PVA and PVA/HAp nanocomposite (NC) before electrospinning various techniques were employed, including transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In addition, FT-IR spectroscopy was carried out to analyze the complex structural changes upon undergoing electrospinning as well as interactions between HAp and PVA. The morphological and crystallographic investigations revealed that the rod-like HAp nanoparticles exhibit a nanoporous morphology and are embedded within the electrospun fibers. A large number of HAp nanorods are preferentially oriented parallel to the longitudinal direction of the electrospun PVA fibers, which closely resemble the naturally mineralized hard tissues of bones. Due to abundant OH groups present in PVA and HAp nanorods, they strongly interact via hydrogen bonding within the electrospun PVA/HAp NC fibers, which results in improved thermal properties. The unique physiochemical features of the electrospun PVA/HAp NC nanofibers prepared by the ES process will open up a wide variety of future applications related to hard tissue replacement and regeneration (bone and dentin), not limited to coating implants.