Mixture Of Rods Research Articles

The effects of shape and flexibility on bio-engineered fd-virus suspensions

We present a theoretical model to describe binary mixtures of semi-flexible rods, applied here to fd-virus suspensions. We investigate the effects of rod stiffness on both monodisperse and binary systems, studying thick-thin and long-short mixtures. For monodisperse systems, we find that fd-virus particles have to be made extremely stiff to even approach the behavior of rigid rods. For thick-thin mixtures, we find increasingly rich phase behavior as the rods are either made more flexible or if their diameter ratio is increased. For long-short rod mixtures we find that the phase behavior is controlled by the relative stiffness of the rods, with increasing the stiffness of the long rods or decreasing that of the short rods resulting in richer phase behavior. We also calculate the state point dependent effective shape of the rods. The flexible rods studied here always behave as shorter, thicker rigid rods, but with an effective shape that varies widely throughout the phase diagrams, and plays a key role in determining phase behavior.

Physico-chemical characterization of a cellulosic fraction from sugar beet pulp

The residue of sugar beet pulp from which pectin and alkaline soluble polysaccharides have been removed by microwave assisted extraction or conventional heat was treated with sodium monochloroacetate under alkaline pH to convert the residual cellulose present to carboxy methyl cellulose (CMC). Weight average molar masses ranged from about 96 to 220 × 103 Daltons, weight average intrinsic viscosity from 1.9 to 4.1 dL/g and degree of substitution from 1.38 to 0.59. HPSEC with online molar mass detectors and Atomic Force Microscopy revealed that CMC was comprised of aggregated linear moieties in contact with spherical bodies. The linear portion was a mixture of rods and segmented rods. Some of the rods had long branches.

Self-assembly of mixtures of nanorods in binary, phase-separating blends

Aligned nanorod inclusions have the potential to significantly improve both the photovoltaic and mechanical properties of polymeric materials. Establishing facile methods for driving or “corralling” the nanorods to self-assemble into such aligned morphologies could facilitate the fabrication of effective, robust devices. Using a variety of computational methods, we model the self-assembly of a mixture of A-coated and B-coated rods in an AB phase-separating blend. Using dissipative particle dynamics (DPD) simulations, we first show that the steric repulsion between ligands causes the coated rods to preferentially align end-to-end within the minority phase of the binary blend. Using this information, we then utilize a coarse-grained approach, which combines a Cahn–Hilliard (CH) model for the polymer blend with a Brownian dynamics (BD) simulation for the rods, to simulate a larger sample of a rod-filled 30 : 70 AB thin film. We find that just a small volume fraction of B rods in the majority B phase promotes the percolation of A-like rods within A, so that the percolation threshold for the A-rods is significantly lowered. If, however, the number of Bnanorods in the B phase exceeds a particular volume fraction, the B particles inhibit the percolation of the A rods. Thus, there is an optimal volume fraction of Bnanorods that provides the beneficial effects. The output from these morphological studies then serves as the input to the lattice spring model (LSM) for mechanical behavior of the composite. The results reveal that nanorods oriented along the tensile direction contribute to the enhancement of the macroscopic mechanical properties of the material. This multi-scale approach, integrating techniques that cover the microscopic, mesoscopic and macroscopic, provides a valuable means of determining structure–property relationships in nanocomposites and establishing useful guidelines for tailoring the components to yield optimal materials' properties.

Generation of Ag2O Micro-/Nanostructures by Pulsed Excimer Laser Ablation of Ag in Aqueous Solutions of Polysorbate 80

A new route to synthesis of Ag(2)O micro-/nanostructures, including a mixture of cubes, pyramids, triangular plates, pentagonal rods, and bars, has been developed by pulsed excimer laser ablation of bulk silver in water using polysorbate 80 as surfactant. The polysorbate 80 played an important role in the formation of the Ag(2)O structures, and similar structures could be obtained in polysorbates 20 and 40 aqueous solutions. We have proposed a mechanism to explain the formation of Ag(2)O structures. This laser ablation method provides a unique approach to discover and fabricate new Ag(2)O morphologies.

Synthesis of nanocrystalline CdS from cadmium(II) complex of S-benzyl dithiocarbazate as a precursor

The single X-ray crystal structure of the cadmium(II)–S-benzyl dithiocarbazate (SBDTC) complex, [Cd(SBDTC)Cl 2] 2, is reported. The compound has been found to be an effective single-source precursor for the preparation of CdS nanocrystals (NCs) via solvothermal method. CdS NCs including spheres and rods were prepared at a relatively low temperature by thermolysis of the precursor using chelating solvent like ethylene glycol (EG), ethylenediamine (EN), hydrazine hydrate (HH) or in a mixture of EG and EN. The influence of solvent, temperature and reaction time was investigated on the size and morphology of the NCs. Use of EG afforded spherical CdS NCs while EN uniquely yielded rod-shaped NCs, and mixture of spheres and rods are obtained from the mixture of EN and EG with a ratio 0.2 (v/v: EN/EG). UV–visible spectroscopy established pronounced quantum confinement with enhanced band gap and XRD analyses revealed hexagonal crystal phase for so obtained CdS NCs. The NCs were also characterized by transmission electron microscopy (TEM), photoluminescence spectroscopy (PL), energy-dispersive X-ray spectroscopy (EDS) and FTIR. The possible formation mechanism for the anisotropic growth of NCs was also discussed.

Assembly of Colloidal Semiconductor Nanorods in Solution by Depletion Attraction

Arranging anisotropic nanoparticles into ordered assemblies remains a challenging quest requiring innovative and ingenuous approaches. The variety of interactions present in colloidal solutions of nonspherical inorganic nanocrystals can be exploited for this purpose. By tuning depletion attraction forces between hydrophobic colloidal nanorods of semiconductors, dispersed in an organic solvent, these could be assembled into 2D monolayers of close-packed hexagonally ordered arrays directly in solution. Once formed, these layers could be fished onto a substrate, and sheets of vertically standing rods were fabricated, with no additional external bias applied. Alternatively, the assemblies could be isolated and redispersed in polar solvents, yielding suspensions of micrometer-sized sheets which could be chemically treated directly in solution. Depletion attraction forces were also effective in the shape-selective separation of nanorods from binary mixtures of rods and spheres. The reported procedures have the potential to enable powerful and cost-effective fabrication approaches to materials and devices based on self-organized anisotropic nanoparticles.

Synthesis of miktoarm star amphiphilic block copolymers via combination of NMRP and ATRP and investigation on self‐assembly behaviors

AbstractThe novel trifunctional initiator, 1‐(4‐methyleneoxy‐2,2,6,6‐tetramethylpip‐eridinoxyl)‐3,5‐bi(bromomethyl)‐2,4,6‐trimethylbenzene (TEMPO‐2Br), was successfully synthesized and used to prepare the miktoarm star amphiphilic poly(styrene)‐(poly(N‐isopropylacrylamide))2 (PS(PNIPAAM)2) via combination of atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMRP) techniques. Furthermore, the star amphiphilic block copolymer, poly (styrene)‐(poly(N‐isopropylacrylamide‐b‐4‐vinylpyridine))2 (PS(PNIPAAM‐b‐P4VP)2), was also prepared using PS(PNIPAAM)2 as the macroinitiator and 4‐vinylpyridine as the second monomer by ATRP method. The obtained polymers were well‐defined with narrow molecular weight distributions (Mw/Mn ≤ 1.29). Meanwhile, the self‐assembly behaviors of the miktoarm amphiphilic block copolymers, PS(PNIPAAM)2 and PS(PNIPAAM‐b‐P4VP)2, were also investigated. Interestingly, the aggregate morphology changed from sphere‐shaped micelles (4.7 < pH < 3.0) to a mixture of spheres and rods (1.0 < pH < 3.0), and rod‐shaped nanorods formed when pH value was below 1.0. The LCST of PS(PNIPAAM)2 (pH = 7) was about 31 °C and the LCST of PS(PNIPAAM‐b‐P4VP)2 was about 35 °C (pH = 3). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6304–6315, 2009

Structure, Dynamics, and Hydration of a Collagen Model Polypeptide, (l-Prolyl-l-ProlylGlycyl)10, in Aqueous Media: a Chemical Equilibrium Analysis of Triple Helix-to-Single Coil Transition

The structure, dynamics, and hydration behavior of a collagen model polypeptide, (L-prolyl-L-prolylglycyl)(10) (PPG10), were investigated in pure water and dilute acetic acid over a wide temperature range using broadband dielectric relaxation (DR) techniques that spanned frequencies from 1 kHz to 20 GHz. All samples showed pronounced dielectric dispersion with two major relaxation processes around 3 MHz and 20 GHz. Because DR measurements sensitively probe dipoles and their dynamics, the structures and ionization states of the carboxy and amino termini of aqueous PPG10 were precisely determined from the relaxation times and strengths in the 3 MHz frequency range. In solution, PPG10 formed mixtures of monodisperse rods as triple helices with lengths and diameters of 8.6 and 1.5 nm, respectively, and monomeric random coils with radii of approximately 1.4 nm. Ionization of the C-terminus was suppressed by the addition of acetic acid in both states. The fraction of random coils (f(coil)) was found to be a function of temperature (T) and the concentration of PPG10 (c). At low temperatures, small f(coil) values were found, which increased with temperature to reach f(coil) = 1 at approximately 60 degrees C, irrespective of c. This phenomenon, well-known as a triple helix-to-single coil transition, is discussed on the basis of the chemical reaction, (PPG10)(3) <==> 3PPG10, with an equilibrium constant of K = 3(c/55.6)(2)f(coil)(3)(1 - f(coil))(-1). The standard enthalpy change evaluated from Arrhenius plots (ln K versus T(-1)) was found to change dramatically at the same transition temperature that was previously determined by using optical rotation experiments. The other major DR process, observed at approximately 20 GHz, was assigned to free and hydrated water molecules and used to determine the average hydration number (m) per PPG10. The m values for the triple helix and random coil state at 25 degrees C were evaluated to be m(th) = 60-70 and m(coil) = 250-270. The m(th) value was in reasonable agreement with the number of hydrated water molecules in crystals of (PPG10)(3) residing in the first and second hydration shells around the amino acid residues. This agreement suggests that the structure of the triple helix in crystals is very similar to that in aqueous solution, including the location of hydrated water molecules.

Investigation of subsurface deformations associated with model tunnels in a granular mass

The study presented in this paper focuses on the subsurface settlement profiles above shallow and deep model tunnels in a granular mass simulated by aluminium rods. In order to provide theoretical deformation patterns during the development of the volume loss due to the tunnel excavation, CRISP is used for the finite element analysis. Comparison is then made for the three laboratory model tunnel tests using close range photogrammetry to measure the displacement data within a multi-sized rod mixture. FEA based on the displacement-controlled model tunnel boundary is shown to be in good agreement with the physical model data. In addition, it is found that the most values of K obtained from both the FEA and the model test are placed between Dyer et al. [Dyer, M.R., Hutchinson, M.T., Evans, N., 1996. Sudden valley sewer: a case history. In: Mair, R.J., Taylor, R.N. (Eds.), International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground. Balkema, London, pp. 671–676] and Moh et al. [Moh, Z.-C., Ju, D.H., Hwang, R.N., 1996. Ground movements around tunnels in soft ground. In: Mair, R.J., Taylor, R.N. (Eds.), International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground. Balkema, London, pp. 725–730] field observation data.

Induction of B 1 phase in binary mixtures of rod- and bent-shaped mesomorphic compounds

The miscibility of a rod-shaped (R) and a bent-shaped (BC) compound forming an induced B 1 phase is reported. B 1 phase is not present in both R and BC in the entire phase sequence. R exhibits partially bilayered smectic A d phase with cholesteric and TGB while BC shows a B 2 phase. It is interesting to show that the B 2 phase is totally diminished in low composition (weight%) of BC, B 1 phase is induced at lower temperature range (~90–135 °C). A dielectric study is also incorporated to confirm the induction of B 1 phase in the binary mixture.

Mesoporous silica–magnetite nanocomposites: Fabrication, characterisation and applications in biosciences

Template assisted fabrication of magnetic mesoporous silica–magnetite nanocomposites and their performance in binding and elution of Salmon sperm DNA has been reported. The effect of reaction pH (10–2) during the fabrication of nanocomposites has been studied. All materials fabricated at various pH were characterised by XRD, TEM, FT-IR, nitrogen adsorption and magnetic susceptibility measurements. Fabrication at neutral pH (7) in the presence of a cationic surfactant (cetyl trimethyl ammonium bromide; CTAB) produced core–shell nanocomposites of quasi spherical and rod shaped morphologies with mesoporous (pore size ∼3.5 nm) silica shell and rhombic magnetite core. Fabrication at alkaline pH (10) produced monolithic mesoporous silica composites with embedded magnetite nanoparticles. Fabrication at acidic pH (4 and 2) produced a biphasic mixture of rhombic magnetite and amorphous silica rods. A similar fabrication at acidic pH (2) in the absence of CTAB produced a biphasic mixture of rhombic magnetite and spherical silica nanoparticles. All materials exhibited a high value of Salmon sperm DNA binding at physiological pH whereas elution value of DNA was observed to be dependent on the extent of silica coating on magnetite nanoparticles.

Morphological control of CuPc and its application in organic solar cells

We have prepared organic photovoltaic (OPV) cells possessing an ideal bulk heterojunction (BHJ)structure using the self-assembly of copper phthalocyanine (CuPc) as the donor material and fullerene(C60) as the acceptor. The variable self-assembly behavior of CuPc on a diverse range of substrates(surface energies) allowed us to control the morphology of the interface and the degree ofcarrier transportation within the active layer. We observed rod-like CuPc structures onindium–tin oxide (ITO), poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate)(PEDOT:PSS) and Au substrates. Accordingly, the interfaces and continuing transportpath between CuPc and fullerene domains could be greatly improved due to the idealBHJ structure. In this paper, we discuss the mechanisms of producing CuPcrod-like films on ITO, PEDOT:PSS and Au. The OPV cell performance wasgreatly enhanced when a mixture of horizontal and vertical CuPc rods was presenton the PEDOT:PSS surfaces, i.e. the power conversion efficiency was 50 timesgreater than that of the corresponding device featuring a planar CuPc structure.

Purification of High Aspect Ratio Gold Nanorods: Complete Removal of Platelets

Because physical and chemical properties of nanostructures strongly depend on their shape, it is of great importance to find either synthetic or separation techniques that can produce objects of a particular shape in a pure state. This manuscript describes a solution to a long standing problem of separating 2D platelets from 1D nanorods. The key aspect of our approach relies on the partial dissolution of faceted platelets with Au(III)/CTAB complex that transforms them into smaller nanodisks. Because of the reduction in size, the 2D structures become fully soluble in water and can be separated from the nanorods that undergo slow precipitation. In addition, the isolated nanodisks can be converted back into initial faceted platelets upon treatment with Au(I)/ascorbic acid mixture. As a result of these simple procedures, a seemingly inseparable mixture of rods, platelets, and spheres is converted into nearly pure individual components.

Gross and cytological characteristics of normal feline anal-sac secretions.

This study was conducted to characterize the gross and cytological characteristics of secretions from normal feline anal sacs. Thirty cats with no recent history of anal-sac disease were selected consecutively and their anal sacs manually expressed. The color, cell counts, or presence of solid portions of the secretions in the youngest cats (<1 year old) were not significantly different from the rest. Young cats (<1 year old) tended to more often have watery secretions. The secretions contained 13 (median) epithelial cells per 600x magnification microscopic field, basophilic background debris, and a mixture of Gram-positive cocci (83 per field; median), Gram-negative cocci (38 per field; median), and Gram-negative rods (1.8 per field; median). Most secretions had occasional neutrophils, and a minority of cats had occasional yeasts in their secretion. Erythrocytes were found only rarely. Extreme heterogeneity existed in gross color, consistency, and amount of solid material. Hence, these latter parameters would not be valid indicators of anal-sac disease.

Discussion of proposed mechanisms of thermal conductivity enhancement in nanofluids

Based upon Green–Kubo linear response theory, we use the exact expression for the heat flux vector of the base fluid plus nanoparticle system to estimate the contribution of nanoparticle Brownian motion to thermal conductivity. We find that its contribution is too small to account for abnormally high reported values. The possibility of convection caused by Brownian particles is also found to be unlikely. We have estimated the mean free path and the transition speed of phonons in nanofluid through density functional theory. We found a layer structure can form around the nanoparticles and the structure does not further induce fluid–fluid phase transition in the bulk fluid. By analyzing the compressibility of the fluid, we have also investigated the sound speed in the nanofluid. For the models of an asymmetric hard sphere mixture representing the single spherical nanoparticles and a mixture of rods and hard spheres representing aggregates, both suspended in the fluid, we found that for the very low volume fraction cases, the compressibility changes little. This shows that the speed of phonon transition does not change due to the addition of nanoparticles of either type. Our results indicate that, besides the enhancement due to the high thermal conductivity of nanoparticles themselves, fluid molecules make no evident contribution to the enhancement of thermal conductivity attributable to the presence of the nanoparticles at volume fractions less than 5%.

Isotropic–isotropic phase separation in mixtures of rods and spheres: Some aspects of Monte Carlo simulation in the grand canonical ensemble

In this article we consider mixtures of non-adsorbing polymers and rod-like colloids in the isotropic phase, which upon the addition of polymers show an effective attraction via depletion forces. Above a certain concentration, the depletant causes phase separation of the mixture. We performed Monte Carlo simulations to estimate the phase boundaries of isotropic–isotropic coexistence. To determine the phase boundaries we simulated in the grand canonical ensemble using successive umbrella sampling [J. Chem. Phys. 120 (2004) 10925]. The location of the critical point was estimated by a finite size scaling analysis. In order to equilibrate the system efficiently, we used a cluster move in which rods and spheres were exchanged.

Morphological controlled synthesis and catalytic activities of gold nanocrystals

In this paper, we report a convenient and efficient procedure for controlling the morphologies of gold nanocrystals via varying the molecular structure of polyols. The gold nanostructures, from nanoplate to mixtures of rod, plate, and sphere, and nanosphere, can be synthesized quantitatively with 1,3-propylene glycol, 1,2-propylene glycol, and glycerol, respectively. On the basis of the results, we speculate that polyols with diverse position and number of OH group play an important role in determining the geometric structures and morphologies of the final products. It may be due to the specific interaction between OH groups and Au 3+ ions, which affect selective growth of various planes of gold nanocrystals. In addition, the catalytic activity of the obtained different shaped gold nanocrystals for hydrogen production from formaldehyde solution at room temperature has also been investigated. The gold nanoplates exhibit higher catalytic activities than spherical gold nanoparticles and the mixtures of rod, plate, and sphere.

Isotropic-to-nematic nucleation in suspensions of colloidal rods.

Using computer simulations, we study the isotropic-to-nematic nucleation in a fluid of colloidal hard rods as well as in a mixture of colloidal rods and non-adsorbing polymer. In order to follow the transformation of the system from the isotropic to the nematic phase, we use a new cluster criterion that enables us to distinguish the nematic clusters from the isotropic fluid phase. Applying this criterion in Monte Carlo simulations, we find two different regimes depending on the supersaturation. At low supersaturation we find nucleation and growth, while at higher supersaturation spinodal decomposition is observed. We determine the height of the nucleation barrier, and we study the structure as well as the shape of the nematic clusters. We discuss our simulation results in the light of classical nucleation theory.

Size and shape separation of gold nanoparticles with preparative gel electrophoresis

We employed agarose gel preparative electrophoresis to separate gold nanoparticles based on size, shape, and charge. The separating technique was first demonstrated by size separation of 5 nm, 15 nm, and 20 nm spherical gold nanoclusters; and further evidenced through the purification of crude 15 ± 2.7 nm nanoclusters to nanoclusters that were 15 ± 0.4 nm. The ability to separate gold nanoparticles by shape was also shown by the purification of a mixture of gold spheres, plates, and long rods.

An internal Mg–Li alloy composite process for the fabrication ofMgB2 wire

This paper proposes a composite process for the fabrication ofMgB2 wire utilizing the excellent room temperature workability of Mg–Li alloy (LA141) as one ofthe promising processes for scale-up production. The starting composite is a Fe sheath tubewith a coaxial internal Mg–Li alloy rod and powder mixture of B and nano-SiC filling thespace between the inner wall of the Fe tube and the Mg–Li alloy rod. The composite can bedeformed uniformly into the final wire with large cross-sectional area reduction and nointermediate annealing. During the subsequent heat treatment, Mg and Li in the liquidstate infiltrate into the B layer and react with B forming a reacted layer along the innerwall of the Fe tube and a hole at the centre. The reacted layer is composed of aMgB2 matrix composed of equi-axed grains with sub-micron size. Li is little incorporated into theMgB2 phaseand does not degrade the superconducting properties. The superconducting transition temperatureTc is 38 K and the transport critical current densityJc(core) for thecore is 3 × 104 A cm−2 at 4.2 K and 4 T.