Effects of soluble surfactants on the Langmuir monolayers compressibility: A comparative study using interfacial isotherms and fluorescence microscopy

Langmuir monolayer isotherms and fluorescence microscopy (FM) techniques have been used to study the effect of two soluble surfactants on the methyl octadecanoate monolayer's compressibility at the air/water interface. The combination of these two techniques allows one to bridge the mechanical and morphological properties of the monolayer at different surfactant subphase concentrations. Our results show that the presence of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) affects the monolayer elasticity differently. In addition, the outcome of this study emphasizes the role of the cationic and anionic surfactants on the monolayer compressibility. In fact, their effect was found to be primly depending on the monolayer thermodynamic situation. The isotherms of the monolayers at different surfactant concentrations underneath the monolayer preserve the characteristics behavior of the monolayer as imaged by FM. The calculated monolayer compressibility shows two different trends depending on the monolayer pressure and the surfactant type. A decreasing compressibility as a function of SDS concentration was found at pressure π = 5 mN/m, while no noticeable effect was found due to DTAB. At π = 10 mN/m both surfactants convert the monolayer from rigid to soft monolayer. Such characteristic behavior of the monolayer has been confirmed by FM.     

Preparation and electrochemical characterization of lithium cobalt oxide nanoparticles by modified sol–gel method

Uniformly distributed nanoparticles of LiCoO₂ have been synthesized through the simple sol–gel method in presence of neutral surfactant (Tween-80). The powders were characterized by X-ray diffractometry, transmission electron microscopy and electrochemical method including charge–discharge cycling performance. The powder calcined at a temperature of 900 °C for 5 h shows pure phase layered LiCoO₂. The results show that the particle size is reduced in presence of surfactant as compared to normal sol–gel method. Also, the sample prepared in presence of surfactant and calcined at 900 °C for 5 h shows the highest initial discharge capacity (106 mAh g^?1) with good cycling stability as compared to the sample prepared without surfactant which shows the specific discharge capacity of 50 mAh g^?1.     

The glass to NZP crystal transformation in a mixed alkali germano-phosphate glass matrix

A mixed alkali germano-phosphate glass composition (Li_0.5Na_0.5Ge₂(PO₄)₃) has been prepared and characterized. The crystallization mechanism of a NZP-type phase, the nucleation rate and the non-isothermal kinetic parameters have been studied by differential thermal analysis (DTA).The plot of the DTA peak height versus the glass particle size has shown a great tendency for surface crystallization. The nucleation rate type curves have given a maximum at 465 ± 2 °C and confirmed that nucleation was instantaneous at this temperature. Furthermore, the average value of the Avrami exponent (5.4 ± 0.4) has revealed a tri-dimensional growth controlled by the development of the glass–crystal interface with a decreasing nucleation rate in the temperature range explored. From non-isothermal experiments, the apparent activation energy for the overall crystallization phenomenon has been founded in the range 260–273 kJ/mol whereas the activation energy for crystal growth was 488 ± 6 kJ/mol.     

Anionic surfactant-assisted hydrothermal synthesis of high-aspect-ratio ZnO nanowires and their photoluminescence property

ZnO nanowires with high-aspect-ratio of up to ca. 600 were synthesized in a quaternary reverse microemulsion containing sodium dodecyl sulfate (SDS) / water / heptane / n-hexane via a hydrothermal method. SDS, as an anionic surfactant, plays an important role in the formation of morphologies. Subsequently, we studied lots of key influencing factors including the molar ratio (w) value of NaOH to Zn(OAc)₂, the reaction temperature, and the instance without the quaternary reverse microemulsion. The selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) reveal the single-crystal nature of the ZnO nanowires. The morphologies and crystalline structure of the as-obtained products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD), respectively. Through this route, we can obtain a mass of products and the method is both convenient and reproducible. Finally, we measured the photoluminescence (PL) spectra and found that the ZnO nanowires exhibited green-orange emission at 525 nm and short ultraviolet emission at 380 nm and the ZnO nanomaterials with different aspect ratio (length to diameter) (L / D) showed PL intensity disciplinary change. Aiming at this phenomenon, we propose a reasonable mechanism to explain the PL spectra of the ZnO nanomaterials in detail.     

Microstructure and photoluminescent properties of Sr2SiO4:Eu3+ phosphors with various NH4Cl flux concentrations

In this paper, effect of NH₄Cl flux concentrations (0, 1, 2, 3 and 4 wt%) on the crystal structure, morphology and photoluminescent properties of Sr₂SiO₄:Eu³⁺ phosphors synthesized by a microwave sintering at 1200 °C for 1 h was investigated and discussed. X-ray powder diffraction analysis showed the crystal structure was not affected and the pure Sr₂SiO₄ phase was formed without second phase or phases of starting materials when adding with the NH₄Cl flux. The SEM images indicated that increase of the NH₄Cl flux enlarged the particle size of the phosphor particles. The photo-luminescence results showed the addition of 1 wt% NH₄Cl flux much improved the emission intensity at λ_em of 617 nm as the excitation spectrum at λ_ex of 395 nm. The decay times of Sr₂SiO₄:Eu³⁺ phosphors with different NH₄Cl flux concentrations were obtained around 2.47–2.52 ms.     

Voltammetric behaviour of nitroxazepine in solubilized system and biological fluids

This study reports the development and validation of sensitive and selective assay method for the determination of the antidepressant drug in solubilized system and biological fluids. Solubilized system of different surfactants including cationic, anionic and non-ionic influences the electrochemical response of drug. Addition of cationic surfactant cetrimide to the solution containing drug enhances the peak current signal while anionic and non-ionic showed an opposite effect. The current signal due to reduction process was function of concentration of nitroxazepine, pH, type of surfactant and preconcentration time at the electrode surface. The reduction process is irreversible and adsorption controlled at HMDE. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for niroxazepine hydrochloride determination. The proposed SWCAdSV and DPCAdSV methods are linear over the concentration range 2.0 × 10^-7– 5.0 × 10^-9 mol/L and 6.1 × 10^-7– 1.0 × 10^-8 mol/L with detection limit of 1.62 × 10^-10 mo/L and 1.4 × 10^-9 mo/L respectively. The method shows good sensitivity, selectivity, accuracy and precision that makes it very suitable for determination of nitroxazepine in pharmaceutical formulation and biological fluids.     

Substrate pre-treatment and initial growth: Strategies towards high-quality III-nitride growth on sapphire by molecular beam epitaxy

Sapphire substrates annealed at 1200 °C in N₂ : O₂ (3 : 1) developed terrace-and-step morphology, ideal for III-nitride growth by molecular beam epitaxy. In situ treatment of sapphire substrates, using Ga deposition and desorption prior to growth, is shown to be negative for GaN growth. Nitridation transforms the sapphire substrate surface to a lateral structure similar to AlN (mismatch < 2.5%). The surface lattice parameters after nitridation did not depend on the substrate temperature. AlN nucleation layer growth conditions have been optimized for growth of GaN. Ideal Al / N flux ratio was found to be 0.6 for a 9 nm thick nucleation layer.     

Size-controlled synthesis of Rod-like α-FeOOH nanostructure

One-dimensional goethite (α-FeOOH) nanorods were successfully fabricated by a hydrothermal route without any template. Experimental results reveal that concentrations of Fe^3 + and ethylenediaminetetraacetic disodium salt (Na₂EDTA) affect the phase composition and size of the as-synthesized products. The size of the rod-like α-FeOOH increased when the concentration of Na₂EDTA was increased, where Na₂EDTA acts as a nucleation inhibitor. α-Fe₂O₃ nanoparticles were produced when the concentration of Fe^3 + was increased from 0.02 to 0.08 and 0.40 M. A possible formation mechanism was proposed based on the results of the time dependent experiments. Different electrolytes and surfactants can affect the size and the aspect ratio of the as-prepared nanorod-like α-FeOOH. Na₂SO₄ induced the decreasing of the size of the as-prepared sample. KCl and PVP affected the aspect ratio of the nanorods.     

Nucleation and crystallization behaviors of nano-crystalline lithium–mica glass–ceramic prepared via sol–gel method

The paper investigates the effects of nucleation and crystallization treatments on nano-crystalline lithium–mica glass–ceramics, taking the composition LiMg₃AlSi_3(1+x)O_10+6xF₂ (x = 0.5) and 8 mass% MgF₂ synthesized by sol–gel technique. Here, X-ray diffraction, thermal analysis and transmission electron microscopy were used to assess the structural evolutions of as-synthesized nano-crystalline lithium–mica glass–ceramics. It was found that MgF₂ crystals perform as nuclei centers for the mica crystallization hence; a large quantity of mica crystallites obtained following the nucleation process at 400 °C for 12 h. For both the un-nucleated and nucleated samples, the crystallization activation energy was measured as 400.2 and 229.6 kJ mol^?1, respectively. Consequently, the calculated Avrami exponents demonstrated that the growth mechanism of mica crystallites, while applying appropriate nucleation treatment, changes from needle-like to three-dimensional growth.     

X-ray powder diffraction,vibration and thermal studies of [A0.92(NH4)0.08]2TeCl4Br2 with A = Cs,Rb: Influence of mixed cationic and anionic substitutions

The crystal structures of [A_0.92(NH₄)_0.08]₂TeCl₄Br₂ with A = Cs, Rb have been determined using X-ray powder diffraction techniques. The two compounds crystallize in the tetragonal space group P4/mnc, with the unit cell parameters: a = 7.452(1) Å, c = 10.544(3) Å, Z = 2 and a = 7.315(2) Å, c = 10.354(4) Å, Z = 2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH₄⁺/Rb⁺/Cs⁺ and octahedral TeCl₄Br₂^2? anions. The stability of these structure is by ionic and hydrogen bonding contacts: A?Cl, A?Br and N–H?Cl, N–H?Br. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780 K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213 K by DSC experiment. This transition was confirmed by dielectric measurements.     

Low temperature synthesis of nanocrystalline calcium aluminate compounds with surfactant-assisted precipitation method

Nanocrystalline calcium aluminates with different CaO:Al₂O₃ and surfactant/metal ion molar ratios were prepared by wet chemical synthesis method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG–PPG–PEG, MW:5800) as surfactant. X-ray diffraction (XRD) and N₂ adsorption–desorption results showed that the increase in CaO:Al₂O₃ ratio decreased the specific surface area and increased the particle sizes of prepared samples while the surfactant/metal ion molar ratios were kept constant. These analyses also declared that for the sample with CaO:Al₂O₃ = 1:2 (CA2) addition of polymeric surfactant increased the specific surface area and decreased the crystallite size. Scanning electron microscopy (SEM) results confirmed that size of particles for CaO:Al₂O₃ = 1:6 (CA6) sample are smaller than CA2. Transmission electron microscopy (TEM) revealed no particular particle shape for the CA2 sample but it showed the high degree of crystallinity and single phase for the prepared sample at 1100 °C.     

Fabrication of WO3 nanofibers by high voltage electrospinning

Mixtures of 0.1, 0.3, and 0.5 mmol ammonium metatungstate hydrate (AMH), and poly (vinyl alcohol) (PVA) were electrospun by a + 20 kV direct voltage to synthesize fibers. Those of 0.5 mmol AMH were further calcined to have PVA removed and crystalline degree improved. At 500 °C and 2 h calcination, WO₃ nanofibers, including two main stretching modes, 3.24 eV direct energy gap, and 378 nm wavelength violet emission were detected. A possible formation mechanism of WO₃ nanofibers was proposed according to the experimental results.     

The influence of preparation conditions on ZrO2 nanoparticles with different PEG–PPG–PEG surfactants by statistical experimental design

In this study mesoporous Zirconia powder with high surface area was prepared by using PEG–PPG–PEG new block copolymer as the non-ionic surfactant. The preparation conditions were optimized by Taguchi method of experimental design and Minitab Software to synthesize high surface area tetragonal-ZrO₂ nanoparticles. The BET surface area of powders was 114–175 m²/gr and the particles size calculated by Deby–Sherrer equation was 5–9 nm. pH = 11, aging time 38 h, Zr molarity 0.03, Surfactant/Zr mole ratio 0.04 and molecular weight 8400 were the best conditions to manufacture ZrO₂ with higher surface area. The sample prepared under optimized conditions was compared to that synthesized by PEG surfactant. XRD patterns of two ZrO₂ samples, hysteresis loop, pore size distribution, BET surface area and SEM results are similar.     

Surfactant-assisted hydrothermal synthesis and characterization of WS2 nanorods

WS₂ nanorods with diameters of about 20–100 nm and lengths of about 0.1–2 μm were successfully synthesized by a simple hydrothermal method with the help of the surfactant Cetyltrimethylammonium Bromide (CTAB). As-prepared WS₂ samples are characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Moreover, the influence of surfactant CTAB on the formation of WS₂ nanorods was investigated. A possible three-step growth mechanism of WS₂ nanorods, in which initial nucleation, self-assembly (oriented aggregation), and subsequent crystal growth (Ostwald ripening) is involved, is proposed to explain the formation of WS₂ nanorods on the basis of observations of a time-dependent morphology evolution process.     

Experimental investigation of the size effects of SiO2 nano-particles on the mechanical properties of binary blended concrete

In the current study, the size effects of SiO₂ nano-particles on compressive, flexural and tensile strength of binary blended concrete were investigated. SiO₂ nano-particles with two different sizes of 15 and 80 nm have been used as a partial cement replacement by 0.5, 1.0, 1.5 and 2.0 wt.%. It was concluded that concrete specimens containing SiO₂ particles with average diameter of 15 nm were harder than those containing 80 nm of SiO₂ particles at the initial days of curing. But this condition was altered at 90 days of curing. Also from the viewpoint of free energy, it can be concluded that the C–S–H gel formation around the particles with average diameter of 15 nm was more at the primary days of curing. This can be as a result of more nucleation sites that causes acceleration in early age strength. On the other hand, the growth probability of C–S–H gel around the 80 nm particles was more at 90 days of moist curing. This is due to the fact that the nucleus of strengthening gel could simply reach to the critical volume of nucleation that causes increase in the strength.     

Effect of surfactants on preparation of nanoscale α-Al2O3 powders by oil-in-water microemulsion

The nanoscale α-Al₂O₃ powders have been synthesized by the O/W microemulsion system using cyclohexane as the oil phase, ultrapure water as the water phase, OP-10 and alcohol as the surfactant and co-surfactant. It has been found that the nature of surfactants played an important role to regulate the size and morphologies of the α-Al₂O₃ nanoparticles. Three different nonionic surfactants (OP-10, Triton X-100 and Tween-80) have been used for the preparation of microemulsions. The microemulsions were characterized by Zeta Potential Analyzer. The results showed that the OP-10 system possesses wide and stable microemulsion phase regions. The synthesized α- Al₂O₃ powders have been comprehensively characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD). The powders calcined at 900–1150 °C showed the presence of alumina phase with crystal structure, The SEM images showed that the powders was an average diameter of 30–100 nm.     

Synthesis of spherical NiO nanoparticles through a novel biosurfactant mediated emulsion technique

Spherical nickel oxide nanoparticles were synthesized by microemulsion technique using rhamnolipids as the surfactant along with n-heptane and water. Nickel hydroxide (Ni(OH)₂) particles were first formed which were then calcined to obtain nickel oxide (NiO) particles. Scanning Electron Microscopy (SEM) studies revealed that the synthesized nickel hydroxide particles were spherical in shape with stacked lamellar sheets. Nickel hydroxide was converted to nickel oxide by calcinations at 600 °C for 3 h and was confirmed by X-ray Diffraction (XRD) analysis. Transmission Electron Microscopy (TEM) showed that the nickel oxide particles were crystalline and of uniform size. The effect of pH on particle size was investigated and it was found that the particle size decreased from 86 ± 8 nm at pH 11.6 to 47 ± 5 nm at pH 12.5. A novel method using rhamnolipid biosurfactant for microemulsion synthesis has been demonstrated which offers an eco-friendly alternative to conventional microemulsion technique based on organic surfactants.     

Zero-valent iron nanoparticles preparation

Zero-valent iron nanoparticles were synthesized by hydrogenating [Fe[N(Si(CH₃)₃)₂]₂] at room temperature and a pressure of 3 atm. To monitor the reaction, a stainless steel pressure reactor lined with PTFE and mechanically stirred was designed. This design allowed the extraction of samples at different times, minimizing the perturbation in the system. In this way, the shape and the diameter of the nanoparticles produced during the reaction were also monitored. The results showed the production of zero-valent iron nanoparticles that were approximately 5 nm in diameter arranged in agglomerates. The agglomerates grew to 900 nm when the reaction time increased up to 12 h; however, the diameter of the individual nanoparticles remained almost the same. During the reaction, some byproducts constituted by amino species acted as surfactants; therefore, no other surfactants were necessary.     

Effect of three types of surfactants on fabrication of Cu-coated graphite powders

Cu-coated graphite powders were fabricated by electrodeposition using a device that we developed in our lab. The effect of different type surfactants on the dispersion and stability of graphite particles in a copper sulfate electrolyte was investigated by UV–Vis spectrophotometry. The electrochemical behavior of the stainless steel cathode plate and graphite particles were examined by linear sweep voltammetry. It shows that surfactants improved dispersion and stability of graphite particles in electrolyte, produced different electrochemical polarization behaviors on graphite surface and cathodic stainless plate, respectively. In the presence of surfactants, copper was apt to be deposited on graphite particle surface. The optimum surfactant content in electrolyte is 150 mg dm^?3 for all of three types of surfactants. Hexadecyltrimethyl ammonium bromide (CTAB) is the most effective surfactant for improving the quality of copper coated graphite powders among the three type surfactants.     

Synthesis and characterization of Co/SiO2 as catalyst catalyze hydrogen generation

Novel composites of porous SiO₂-LP and SiO₂-HP supports are synthesized by the silica–polyethylene glycol monooleyl ether surfactant self-assembly method to obtain a large surface area. Cobalt is immobilized in the supports by incipient wetness impregnation. A stable and active Co/SiO₂ catalyst is examined using FE-SEM, BET and XRD. Further, the catalyst is tested for catalytic hydrolysis of alkaline sodium borohydride (NaBH₄) solution: the rate of hydrogen generation is found to increase with increasing cobalt loading of the Co/SiO₂ catalyst. The hydrogen generation rates increase dramatically when the temperature is increased from 17 to 40 °C. The highest hydrogen generation rates of Co/SiO₂ catalyst are obtained at 2513 mL min^? 1 g^? 1 in 20 mL of 5 wt.% NaBH₄ solution containing 5 wt.% NaOH at 40 °C.