Synthesis,characterization, and interactions of single-walled carbon nanotubes modified with doxorubicin with Langmuir–Blodgett biomimetic membranes

The synthesis, characterization, and the influence of single-walled carbon nanotubes (SWCNTs) modified with an anticancer drug doxorubicin (DOx) on the properties of model biological membrane as well as the comparison of the two modes of modification has been presented. The drug was covalently attached to the nanotubes either preferentially on the sides or at the ends of the nanotubes by the formation of hydrazone bond. The efficiency of the modification was proved by the results of FTIR, Raman, and thermogravimetric analysis. In order to characterize the influence of SWCNT-DOx conjugates on model biological membranes, Langmuir technique has been employed. The mixed monolayers composed of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE) and SWCNT-DOx with different weight ratio have been prepared. It has been shown that changes in the isotherm characteristics depend on the SWCNTs content. While smaller amounts of SWCNTs do not exert significant differences, the introduction of the prevailing content of the nanotubes increases area per molecule and decreases the maximum value of compression modulus, leading to more fluid monolayer. However, upon increasing the surface pressure, the aggregation of carbon nanotubes within the thiolipid matrix has been observed. Mixed layers of DPPTE/SWCNT-DOx were also transferred onto gold electrodes by means of LB method. Cyclic voltammetry showed that SWCNT-DOx conjugates remain adsorbed at the electrode surface and are stable in time. Additionally, higher values of peak current and DOx surface concentration obtained for side modification prove that side modification allows for more efficient conjugation of the drug to carbon nanotubes.

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Ordering and growth of Langmuir–Blodgett films: X-ray scattering studies

The interplay of ordering, confinement and growth in ultrathin films gives rise to various interesting phenomena not observed in bulk materials. The nature of ordering and interfacial morphology present in these films, in turn, depends on their growth mechanism. Well-ordered metal–organic films, deposited using an enigmatic Langmuir–Blodgett (LB) technique, are not only ideal systems for understanding the interplay between growth and structure of ultrathin films but also for studying chemical reactions and phase transitions in confined geometries. Studies on these LB films also enhance our understanding of the fundamental interactions of amphiphilic molecules important for biological systems. Advent of grazing incidence X-ray scattering techniques has enabled us to probe the interfacial structure of these multilayer films at very high resolution and as a result has improved our knowledge about the mechanism of growth processes and about physical/chemical properties of ultrathin films. In this review we will focus our attention on recent results obtained using these X-ray scattering techniques to understand the mechanism of growth leading to formation of remarkably well-ordered LB films after giving a brief outline of these scattering techniques. In addition, we also review recent results on growth and structure of nanoparticles formed by suitable chemical processes within the ordered matrix of LB films. Finally, we will discuss the work done on melting of LB films and its implications in our understanding of melting process in lower dimensions. In all these studies, especially those on as-deposited LB films results of atomic force microscopy measurements have provided important complementary morphological information.     

Structural and surface morphological studies of long chain fatty acid thin films deposited by Langmuir–Blodgett technique

In the present work we aim to study the structural and surface morphological characteristics of divalent cation (cadmium ion, Cd²⁺) induced thin mono- to multilayer films of fatty acids such as arachidic acid and stearic acid prepared by the Langmuir–Blodgett (LB) technique. These ultra thin films of various numbers of layers were studied by X-ray diffraction (XRD), X-ray reflectivity (XRR) and Atomic Force Microscopy (AFM). In this specific Y-type deposition, it was found that as the individual layer thickness increases, the corresponding layer by layer interfacial electron density of the thin films decreases. Since the fatty acid chain tries to maintain its minimum value of cross-sectional area, tilting occurs with respect to its nearest neighbor. The tilt angle calculated for 9 layers of cadmium arachidate (CdA₂) and cadmium stearate (CdSt₂) are 18° and 19.5°, respectively. An asymmetric air gap of thickness ∼3 Å was also seen between the tail parts of 2 molecular chains. The RMS roughness and average height factors calculated through AFM studies show non-uniform surface morphology of both CdA₂ and CdSt₂, although the calculated topographic variations were found to have more irregularity in case of CdSt₂ than in case of CdA₂.     

Structure of Lennard–Jones nanowires encapsulated by carbon nanotubes

Molecular dynamics simulations have been performed to investigate the structures of Lennard–Jones(LJ) nanowires(NWs) encapsulated in carbon nanotubes(CNTs). We find that the structures of NWs in a small CNT only adopt multi-shell motifs, while the structures of NWs in a larger CNT tend to adopt various motifs. Among these structures, three of them have not been reported previously. The phase boundaries among these structures are obtained regarding filling fractions, as well as the interaction between NWs and CNTs.     

Atomic composition and stability of Langmuir–Blodgett monolayers based on siloxane dimer of quaterthiophene on the surface of polycrystalline gold

Physics of the Solid State - Atomic composition of monolayers based on siloxane dimer of quaterthiophene deposited by Langmuir–Blodgett technique on a silicon dioxide surface partially...     

Altering the catalytic activity of thin metal catalyst films for controlled growth of chemical vapor deposited vertically aligned carbon nanotube arrays

The growth rate and terminal length of vertically aligned carbon nanotube arrays (VANTAs) grown by chemical vapor deposition have been dramatically improved through pulsed KrF excimer laser pretreatments of multilayer metal catalyst films. Silicon wafers coated with Al, Mo, and Fe layers were laser processed in air with single laser shots of varying fluence through circular apertures, then heated to ∼750°C and exposed to acetylene and ferrocene containing gas mixtures typically used to grow vertically aligned nanotube arrays. In situ videography was used to record the growth kinetics of the nanotube arrays in both patterned and unpatterned regions to understand the changes in catalytic activity, growth rates, and termination of growth. The height of the patterned regions varied with fluence, with the most successful treatment resulting in 1.4 cm tall posts of nanotubes embedded in a 0.4 cm tall nanotube carpet. High-resolution transmission electron microscopy images from the nanotubes in the posts revealed fewer walls, smaller diameters, and a much narrower distribution of diameters compared to the nanotubes grown in the carpet. This information, along with data obtained from weighing the material from each region, suggests that pulsed laser processing can also significantly increase the areal density of VANTAs. Research sponsored by the Division of Materials Sciences and Engineering, U.S. Department of Energy.     

Determination of band gaps of self-assembled carbon nanotube films using Tauc/Davis–Mott model

The band gaps of self-assembled single-walled carbon nanotube (SWNT) films have been determined through curve fitting using the semi-empirical Tauc and Davis–Mott model, based on the measurement of optical absorption at the visible and near infrared range. This study provides a practicable option for the determination of band gaps for ultra-thin SWNT films or multi-walled carbon nanotube films whose vHs peaks cannot be well resolved in absorption spectra.     

Structural and compositional mapping of a phase-separated Langmuir–Blodgett monolayer by X-ray photoelectron emission microscopy

The structure and composition of phase-separated Langmuir–Blodgett monolayer films comprised of mixtures of arachidic acid (C₁₉H₃₉COOH) and perfluorotetradecanoic acid (C₁₃F₂₇COOH) were characterized using a combination of X-ray photoelectron emission microscopy (X-PEEM), secondary electron emission microscopy (SEEM) and atomic force microscopy (AFM). X-PEEM provides high lateral spatial resolution and is directly sensitive to the elemental and chemical (functional group) composition of these ultrathin films through the chemical sensitivity of NEXAFS spectroscopy; AFM provides high-resolution imaging, both in terms of lateral and vertical (height) film topography. SEEM provides additional structural and electronic information through work function and electron scattering effects. The combination is used for chemical mapping of the phase-separated domains in the monolayer film. Our results directly confirm previous AFM measurements that suggested that the discontinuous domains are enriched in arachidic acid, whereas the surrounding continuous domain is a mixture of both arachidic acid and perfluorotetradecanoic acid.     

Effects of N2 and glow discharge on growth behaviours of carbon nanotubes prepared by the hot filament chemical vapour deposition method

Carbon nanotubes (CNTs) are prepared by the hot filament chemical vapour deposition method using CH4 and H2 as reaction gases, and the growth behaviours are investigated by scanning electron microscopy and transmission electron microscopy. The results indicate that the CNTs prepared in the absence of N2 or glow discharge are bent; however, they are in an aligned state after introducing N2 into the chamber or forming glow discharge under a negative biased voltage. The results also indicate that the CNTs are of a bamboo-like structure when N2 is intruded as a reaction gas and the alignment degree of the CNTs grown under glow discharge is higher than that grown in N2. This illustrates that the nitric environment and glow discharge play important roles in the growth of CNTs. Combining with the theory related to alloy thermodynamics and collisions, we have analysed the growth mechanism of the CNTs in nitric environment and glow discharge.     

Decreasing the electromagnetic observability of carbon fiber polymer–matrix composites by using epoxy-coated carbon fibers

The electromagnetic observability of epoxy–matrix composites containing continuous carbon fibers was decreased by using epoxy-coated carbon fibers. The attenuation of electromagnetic waves at 1.0–1.5 GHz upon reflection was increased from 1.3 to 1.7 dB, while the attenuation upon transmission was decreased from 30 to 24 dB. The effect is attributed to the decreased transverse electrical conductivity of the composite due to the epoxy coating. The epoxy coating caused the tensile strength and modulus of the composite to decrease by about 10%, while the elongation at break was not affected.     

Enhancement of the electrical properties of carbon nanotubes with Ar–N2 plasma treatment

Optical emission spectroscopy and Langmuir probe are used to investigate the low pressure inductively coupled Ar–N₂ plasmas as function of rf power, filling pressure and Ar content in N₂ discharge. It is observed that the active species generation, dissociation fraction and electron temperature significantly depends on discharge parameters and may be used to optimize the plasma reactor. Mixture of SWCNTs and MWCNTs are treated for different treatment time (0–120 min) at optimum discharge conditions. Changes induced in the elemental composition, surface morphology, crystallographic structure, and structural disorder in the plasma irradiated CNTs are analyzed by EDX, FTIR, SEM, XRD and Raman spectroscopy, respectively. Ar–N₂ mixture plasma treatment of CNTs lead to a significant increase in the electrical conductivity, modify the microstructure and induce structural disorder and cause a transition of crystalline phase from well crystalline to an amorphous structure.     

Degradation of methylparaben by sonocatalysis using a Co–Fe magnetic carbon xerogel

The degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.2 mg/L and initial pH values between 3 and 10 in ultrapure water (UPW). Matrix effects were studied in bottled water (BW) and secondary treated wastewater (WW), as well as in UPW spiked with bicarbonate, chloride or humic acid. The pseudo–first order kinetics of MP degradation increase with power and catalyst loading and decrease with MP concentration and matrix complexity; moreover, the reaction is also favored at near–neutral conditions and in the presence of dissolved oxygen. The contribution of the catalyst is synergistic to the sonochemical degradation of MP and the extent of synergy is quantified to be >45%. This effect was ascribed to the ability of CX/CoFe to catalyze the dissociation of hydrogen peroxide, formed through water sonolysis, to hydroxyl radicals. Experiments in UPW spiked with an excess of tert-butanol (radical scavenger), sodium dodecyl sulfate or sodium acetate (surfactants) led to substantially decreased rates (i.e. by about 8 times), thus implying that the liquid bulk and the gas-liquid interface are major reaction sites. The stability of CX/CoFe was shown by performing reusability cycles employing magnetic separation of the catalyst after the treatment stage. It was found that the CX/CoFe catalyst can be reused in up to four successive cycles without noteworthy variation of the overall performance of the sonocatalytic process.     

Study on single domain growth of Ag-doped Sm–Ba–Cu–O bulk using cold seeding technique

Attempts to prepare single grain SmBCO/Ag using NdBa₂Cu₃O_7?δ (Nd123) cold seeding technique have been performed. As silver decreases the melting temperature of SmBa₂Cu₃O_7?δ (Sm123) to approximately 1028 °C, it becomes possible to texture SmBCO/Ag samples with the Nd123 cold seeding technique, and very well textured mono-domain crystals with 15 mm on a side have been successfully obtained. However, the growth rate of SmBCO/Ag system is severely reduced compared with Ag free sample. A series of samples quenched at various lower limit temperatures of slow-cooling process were fabricated to investigate the single domain growth of SmBCO/Ag system. It is found that mono-domain growth exhibits a suppressed tendency within the slow-cooling temperature window considered, and then is hindered significantly by the spontaneous nucleation. The transversal slides of these samples show that large amount of entrapped gas did not escape from the samples during the dwell time at the maximum superheating temperature. During the slow-cooling process, the entrapped gas continued to move towards the edges of the samples, coalesced with each other and very large pores several millimeters in size were formed, which finally were released from the sample. The SEM analysis reveals that the coarsening of Sm₂BaCuO₅ (Sm211) precipitates has occurred during the growth of mono-domain. Large Sm211 cause decreased ability to supply samarium for the growth of Sm123 crystal, resulting in a gradual decrease in the growth rate.     

Effect of heat and time-period on the growth of ZnO nanorods by sol–gel technique

Sol–gel routes to metal oxide nanoparticles in organic solvents under exclusion of water have become a versatile alternative to aqueous methods. We focus on the preparation of well-aligned ZnO nanorod arrays using non-aqueous sol–gel synthesis route, where ZnO nanorods arrays have been grown on glass substrates. This work provides a systematic study of controlled morphology and crystallinity of ZnO nanorod arrays. The investigation demonstrates that the synthesis process conditions of ZnO thin film have strong influences on the morphology and crystallinity of the ZnO nanorod arrays grown thereon, where non-aqueous process offers the possibility of better understanding and controlling the reaction pathways on the molecular level, enabling the synthesis of nanomaterials with high crystallinity and well-defined, uniform particle morphologies. Here the annealing temperature plays an important role on the growth of nanostructures of the ZnO grains and nanorod arrays. The scanning electron microscopy (SEM) image shows that the growth of ZnO nanorod arrays are high-quality single crystals growing along the c-axis perpendicular to the substrates. A detailed analysis of the growth characteristics of ZnO nanostructures as functions of growth time is also reported.     

The use of calcination in exposing the entrapped Fe particles from multi-walled carbon nanotubes grown by chemical vapour deposition

Multi-walled carbon nanotubes (MWCNTs) were synthesized a by chemical vapour deposition method. The effect of calcination at temperatures ranging from 300 to 550°C in exposing the metal nanoparticles within the nanotube bundles was studied. The degree of degradation of the structural integrity of the MWCNTs during the thermal process was studied by Raman spectroscopy, X-ray diffraction analysis, field-emission scanning electron microscopy, and transmission electron microscopy. The thermal behaviour of the as-prepared and calcined samples was investigated by thermogravimetric analysis. Calcination in air, at 400°C for 1 h, was found to be an efficient and simple method to extract metallic impurities from the amorphous carbon shells with minimal damage to the tube walls and lengths. The nanotubes were observed to be damaged at temperatures higher than 450°C.     

Effect of sputtered Cu film’s diffusion barrier on the growth and field emission properties of carbon nanotubes by chemical vapor deposition

Growth of carbon nanotube (CNT) films with good field emission properties on glass is very important for low cost field emission display (FED) applications. In addition to Ni, Co and Fe, Cu can be a good catalyst for CNT growth on glass, but due to diffusion into SiO₂ it is difficult to control the CNTs density and uniformity. In this paper, four metal barrier layers (W, Ni, Cr, Ti) were deposited by dc magnetron sputtering on glass to reduce the Cu diffusion. As-grown CNT films showed various morphologies with the use of different barrier metals. CNTs with uniform distribution and better crystallinity can be synthesized only on Ti/Cu and W/Cu. Voltage current measurements indicate that better field emission properties of CNT films can be obtained on titanium and tungsten barriered Cu, while chromium and nickel are not suitable barrier candidates for copper in CNT-FED applications because of the reduced emission performance. PACS 81.05.Uw; 61.46.Fg; 85.45.Db; 66.30.-h     

Aggregate stability and magnetic characteristics of colloidal Fe m O n –SiO2 particles obtained by sol–gel method

Physics of the Solid State - Composite Fe m O n –SiO2 particles have been obtained by precipitation of iron oxide from aqueous solution with the addition of tetraethoxysilane. The shapes and...