Size effect of X-shaped carbon nanotube junctions

Systematic calculations have been performed for X-shaped junctions formed between two crossed identical carbon nanotubes (armchair or zigzag tubes) with diameters ranging from 3.92 Å to 9.49 Å using an empirical potential method. The formation energy of X junctions is found to be a function of the diameter of the tubes. The formation temperature is dependent on the curvature of tubes. The calculations show that it is energetically favorable to form X junctions by the direct heating method if the tube diameter is less than 0.85 nm.     

Impedance analysis of a phosphatidylcholine-phosphatidylethanolamine system in bilayer lipid membranes

Electrochemical impedance spectroscopy was used for the study of two-component lipid membranes. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were to be investigated, because of their presence in biological membranes. Capacitance values of pure components are 0.62 and 0.32 μF cm⁻², respectively. The 1:1 complex was formed during formation of the PC-PE lipid membrane. Formation of the complex can explain the deviation from the additivity rule. This equilibrium was described by mathematical equations and was further verified experimentally. Adequate equations let us calculate such parameters as: capacitance of the complex molecule, area occupied by the complex molecule as well as the stability constant of the complex.     

A molecular dynamics study of an archaeal tetraether lipid membrane: Comparison with a dipalmitoylphosphatidylcholine lipid bilayer

Molecular dynamics simulations of an archaeal membrane made up of bipolar tetraether lipids and a dipalmitoylphosphatidylcholine (DPPC) lipid membrane were performed and compared for the first time. The simulated archaeal membrane consists of a pure monolayer of asymmetrical lipids, analogous to the main polar lipid [MPL; Swain, M., Brisson, J.-R., Sprott, G.D., Cooper, F.P., and Patel, G.B., (1997) Identification of β-1-Gulose as the Sugar moiety of the Main Polar Lipid of Thermoplasma acidophilum, Biochim. Biophys. Acta 1345, 56–64] found in T. acidophilum, an extremophile archaeal organism. This simulated membrane lipid contains two cyclopentane rings located on one of the two aliphatic chains of the lipid. The archaeal membrane is simulated at 62°C, slightly above the optimal growth temperature of T. acidophilum. We compared the organization of this tetraether lipid monolayer with a DPPC bilayer simulated at 50°C, both of them being modeled in a partially hydrated state. Our results assess the singularity of the tetrather lipid organization, in particular the influence of the spanning structure on the molecular ordering within the archaeal membrane.     

The dual effect of oxidation on lipid bilayer structure

Sphingomyelin membranes were prepared with different levels of oxidative damage caused bytert-butyl hydroperoxide (TBH). Temperature-induced changes in membrane hydrocarbon chain packing (phase transitions) were monitored using infrared spectroscopy. Lipid phase transition characteristics were evaluated from thermodynamic parameters fitted to the experimental transition curve data. At temperatures below the lipid phase transition T_c, hydrocarbon chains pack in an ordered state whereas above the T_c the hydrocarbonchains pack in a disordered state. Compared to the non-oxidized control, the packing of the hydrocarbon chains of mildly oxidized sphingomyelin (<10 nmol TBH/mg lipid) was no different at all temperatures below the T_c, and was more ordered above the T_c. The hydrocarbon chains of strongly oxidized sphingomyelin (>10nmol TBH/mg lipid) were more disordered at temperatures above and below the T_c compared to the control samples. These results suggest that lipid oxidation has a dual effect on lipid order. A more ordered or disordered state may result depending on the degree of oxidation and the state of lipid order prior to oxidation. These results could be important for explaining the structural changes in oxidized membranes high in sphingomyelin such as those found in the ocular lens and liver plasma membranes.     

A theoretical investigation of the mechanical stability of single-walled carbon nanotube 3-D junctions

The deformation behavior of five types of X-junctions made from ultrathin single-walled carbon nanotubes (SWCNTs) was investigated using molecular dynamics (MD) simulation. Three deformation modes were observed in the X-junctions under uni-axial or bi-axial tensile stresses. If the junction is strong, as is the case with certain (3,3)-(3,3) junctions, then the bonds break at individual nanotubes, rather than at the junction region, and the original bonding structures around the junctions remain. However, for some (3,3)-(3,3) junctions and X-junctions formed by (5,0)-(5,0) nanotubes, the bonds at the junction region break and are reconstructed, which results in the transformation of a 3-D junction into a 2-D type. Either one neck or two necks may be nucleated near the junction. The use of random seed numbers in MD simulations plays an important role in the outcome of the deformation process due to the small number of carbon atoms involved in the junction regions.     

Impedance analysis of phosphatidylcholine-cholesterol system in bilayer lipid membranes

Electrochemical impedance spectroscopy was used for the study of two-component lipid membranes. Phosphatidylcholine (lecithin, PC) and cholesterol (Ch) were chosen for the study because they are present in biological membranes and they fulfil essential functions in lively organisms. The theory of equilibrium between components of the membranes has been developed in order to obtain the parameters describing the PCCh complex. The equilibrium between the PC, Ch and PCCh complex on the basis of derived equations was considered and forming the 1:1 complex was proved. The following parameters of the complex were determined: capacitance (C₃), conductance , area occupied by complex molecule (A₃) as well as stability constant of the complex (K).     

Dye-sensitized solar cells based on a nanoparticle/nanotube bilayer structure and their equivalent circuit analysis

Dye-sensitized solar cells (DSSCs) were prepared by capitalizing on a TiO(2) bilayer structure composed of P-25 nanoparticles and freestanding crystalline nanotube arrays as photoanodes. After being subjected to sequential TiCl(4) treatment and O(2) plasma exposure, the bilayer photoanode was sensitized with N719 dye. DSSCs based on a 20 μm TiO(2) nanoparticle film solely and a bilayer of 13 μm TiO(2) nanoparticles and 7 μm TiO(2) nanotubes exhibited the highest power conversion efficiency, PCE, of 8.02% and 7.00%, respectively, compared to the devices made of different TiO(2) thicknesses. On the basis of J-V parameter analysis acquired by equivalent circuit model simulation, in comparison to P-25 nanoparticles, charge transport in nanotubes was found to be facilitated due to the presence of advantageous nanotubular structures, while photocurrent was reduced owing to their small surface area, which in turn resulted in low dye loading, as well as the lack of cooperative effect of anatase and rutile phases.     

A study on the interaction between ibuprofen and bilayer lipid membrane

Ibuprofen is a well-known nonsteroidal anti-inflammatory drug, which can interact with lipid membranes. In this paper, the interaction of ibuprofen with bilayer lipid membrane was studied by UV-vis spectroscopy, cyclic voltammetry and AC impedance spectroscopy. UV-vis spectroscopy data indicated directly that ibuprofen could interact with lipid vesicles. In electrochemical experiments, ibuprofen displayed a biphasic behavior on bilayer lipid membrane supported on a glassy carbon electrode. It could stabilize the lipid membrane in low concentration, while it induced defects formation, even removed off bilayer lipid membrane from the surface of the electrode with increasing concentration. The mechanism about the interaction between ibuprofen and supported bilayer lipid membrane was discussed.     

An analysis of the factors affecting strengthening in carbon nanotube reinforced aluminum composites

Tensile strength data of Al/CNT composites from the literature is analyzed to understand the effects of CNT dispersion, processing technique, degree of deformation and CNT–matrix interface on the elastic modulus, strength and toughness of composites. Strengthening can be divided in three regimes which show decreasing strengthening effect with an increasing CNT content. The strengthening is highest for CNT content less than 2 vol.%. The applicability of the micromechanics models in predicting the strength and elastic modulus of CNT reinforced metal matrix composites is also analyzed. The rule of mixtures is effective in predicting the elastic modulus of the Al/CNT composites for low CNT content (<2 vol.%) whereas Halpin–Tsai and combined Voigt–Reuss models are better at intermediate CNT content (2–5 vol.%). Effect of degree of deformation such as extrusion ratio during processing on the load transfer to CNT and resulting strengthening is also discussed. Tensile data on Cu/CNT and Mg/CNT composites is compared with Al/CNT to show that strengthening is not effective when there is no chemical interaction between metal matrix and CNT. The analysis presented here would be very helpful in the future design of high strength CNT/metal matrix composites.     

Observation of self-spreading lipid bilayer on hydrophilic surface with a periodic array of metallic nano-gate

We have fabricated micro-channel with a periodic array of nano-gate with a width of 500 and 100 nm by electron beam lithography. The effect of nano-gates on the self-spreading of egg-PC bilayer doped with dye-labeled lipid TR-DHPE was investigated using fluorescence microscope. Compared with the control channel without the nano-gate, the self-spreading velocity was suppressed due to the presence of nano-gate. The quantitative analysis of the spreading behavior suggests that the self-spreading bilayer was compressed during passing through the gate. This structural deformation imposed an energetic barrier for the self-spreading, leading to reduction of the spreading velocity. Furthermore, the number of TR-DHPE molecule in the spreading bilayer was apparently decreased during spreading in the gate channels. This phenomenon was also closely related to the possible structural deformation at the gate. Formation of higher lipid density state at the gate region induced by the compression was thought to be responsible to the reduced penetration ability of bulky TR-DHPE molecules into the nano-gates, which resulted in the gradual decrease in TR-DHPE concentration in the spreading bilayer.     

Relating carbon nanotube growth parameters to the size and composition of nanocatalysts

A gas-phase approach to studying carbon nanotube (CNT) nucleation and growth from nanoparticle catalysts has been developed. Dimensionally- and compositionally-tuned metal particles with mean diameters between 2 and 5 nm and standard deviations less than 15% are initially synthesized from metallocene vapors in an atmospheric-pressure microplasma. The nanocatalysts are continuously fed with acetylene and hydrogen into a flow furnace reactor to grow CNTs. Kinetic studies are performed by in situ aerosol size classification of the nanotubes to relate the CNT length and thus, the growth rate in our thermal process to the catalyst size and composition. We find that reducing the catalyst size results in an increase in the growth rate while varying the catalyst composition affects the growth rate, activation energy, and the onset temperature for CNT growth.     

Conductance modulation of charged lipid bilayer using electrolyte-gated graphene-field effect transistor

Graphene is an attention-grabbing material in electronics, physics, chemistry, and even biology because of its unique properties such as high surface-area-to-volume ratio. Also, the ability of graphene-based materials to continuously tune charge carriers from holes to electrons makes them promising for biological applications, especially in lipid bilayer-based sensors. Furthermore, changes in charged lipid membrane properties can be electrically detected by a graphene-based electrolyte-gated graphene field effect transistor (GFET). In this paper, a monolayer graphene-based GFET with a focus on the conductance variation caused by membrane electric charges and thickness is studied. Monolayer graphene conductance as an electrical detection platform is suggested for neutral, negative, and positive electric-charged membrane. The electric charge and thickness of the lipid bilayer (Q_LP and L_LP) as a function of carrier density are proposed, and the control parameters are defined. Finally, the proposed analytical model is compared with experimental data which indicates good overall agreement.     

Growth mechanism of Y-junctions and related carbon nanotube junctions synthesized by Au-catalyzed chemical vapor deposition

Y-junctions and related carbon nanotube (CNT) junctions were synthesized by Au-catalyzed chemical vapor deposition. The catalyst was prepared by evaporating a 10-nm-thick Al₂O₃ film and a 1-nm-thick Au film on a Si substrate. Based on thorough investigations under a high-resolution transmission electron microscope, the CNT junctions were proved to be formed by a unified catalyst-merging mechanism. Different merging processes resulted in different morphologies, such as Y-shaped, T-shaped, multi-leveled, multi-terminal and L-shaped CNT junctions.     

Concentration and time dependant behavior of chlorpromazine interaction with supported bilayer lipid membrane

The interaction of chlorpromazine (CPZ) with supported bilayer lipid (dipalmitoyphosphatidylcholine) membrane (s-BLM) on the glassy carbon electrode (GCE) was investigated using cyclic voltammetry and ac impedance spectroscopy. The experimental data, based on the voltammetric response of Ru(NH₃)₆³⁺ associated with the oxidation of CPZ on the electrode, indicated that the interaction of CPZ with s-BLM was concentration and time dependant. The interaction between them could be divided into three stages by the concentration of CPZ: low, middle and high concentration. At the first stage, s-BLM was not affected by CPZ and the interaction was only a penetration of a small quantity of CPZ molecule into s-BLM. At the second stage, the defects formed in s-BLM due to the penetration of more CPZ molecule into s-BLM. At the last stage, a high CPZ:lipid ratio reached in s-BLM, resulting in the solubilization of s-BLM. The interaction time had different effect at three stages.     

Structural stability of a coaxial carbon nanotube inside a boron–nitride nanotube

The structural stability of a coaxial carbon nanotube inside a boron–nitride nanotube (C@BNNT) is investigated by molecular dynamics simulation. The geometric structures of armchair C(5,5)@BN(n,n) and zigzag C(9,0)@BN(m,0) nanotubes (n = 8–15; m = 15–22) are optimized by the density functional theory method using the DMol3 code. A comparison of the variation in the tube radius and analyses of the bind energy and radial distribution function show that the best BN(n,n) nanotubes for coupling with C(5,5) to form C(5,5)@BN(n,n) are BN(10,10), and the best BN(m,0) nanotubes for coupling with C(9,0) to form C(9,0)@BN(m,0) are BN(17,0) and BN(18,0). The optimal interwall distances between the inner C tube and the outer BN tube are about 0.35 nm for armchair and from 0.33 to 0.36 nm for zigzag nanotubes, respectively. The armchair C@BNNTs achieve a more stable combination structure than the zigzag case. Analyses of their energy and deformation electron density reveal that the interwall interaction between the inner carbon nanotube and outer boron–nitride nanotube is a van der Waals interaction.     

乳液聚合中乳胶粒粒径大小及分布的影响因素

在乳液聚合中,乳胶粒的大小及分布对乳液的性能及其应用有很大的影响,同时也反映了乳液聚合反应进行的过程。本文综述了影响乳胶粒粒径大小及分布的各种因素,如聚合工艺、乳化剂、单体种类、聚合温度、引发剂等,并介绍了不同粒径乳液的性能及其应用。     

Glassy carbon electrode modified with a bilayer of multi-walled carbon nanotube and polypyrrole doped with new coccine: Application to the sensitive electrochemical determination of Sumatriptan

A promising electrochemical sensor was developed based on a layer by layer process by electro-polymerization of pyrrole in the presence of new coccine (NC) as dopant anion on the surface of the multi-walled carbon nanotubes (MWCNTs) pre-coated glassy carbon electrode (GCE). The modified electrode was used as a new and sensitive electrochemical sensor for voltammetric determination of sumatriptan (SUM). The electrochemical behavior of SUM was investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results showed a remarkable increase (∼12 times) in the anodic peak current of SUM in comparison to the bare GCE. The effect of experimental variables such as, drop size of the casted MWCNTs suspension, pH of the supporting electrolyte, accumulation conditions and the number of cycles in the electro-polymerization process on the electrode response was investigated. Under the optimum conditions, the modified electrode showed a wide linear dynamic range of 0.02–10.0 μmol L⁻¹ with a detection limit of 6 nmol L⁻¹ for the voltammetric determination of SUM. The prepared electrode showed high sensitivity, stability and good reproducibility in response to SUM. This sensor was successfully applied for the accurate determination of trace amounts of SUM in pharmaceutical and clinical preparations.