Effect of dielectrophoretic force in the self-assembly process of electrosprayed nanoparticles

In this work the effect of the dielectrophoretic force (DEP) in the self-assembly process of nanoparticles electrosprayed onto a substrate, is examined. DEP force is originated by the electric field created by the electrospray gun and by the distortion of the field created by the effective dipole of each nanoparticle. It is also shown that the modulus of this force is large when the distance between particles is few times its diameter, provided the medium is wet and the electric field is not switched off.The directional nature of DEP In this wet phase, is shown to chain nanoparticles aligned with the main electric field direction. Although there is a repulsive force between chains in the orthogonal direction to the field, it is minimum when the beads align with the voids in the nearby chains.DEP is a dominant force in the close distances of nanoparticles compared to double layer, van der Waals, electrophoretic retardation, weight and buoyancy.     

Synthesis of bio-functional nanoparticles from sono-responsive amino acids using high frequency ultrasound

A simple, one-pot high frequency ultrasonication (490 kHz) methodology to convert hydrophobic and amphipathic amino acids into nanostructures was investigated. The approach involved the oxidative coupling of aromatic amino acids (phenylalanine and tryptophan) in aqueous solutions to form high molecular weight dimers and oligomers. The role of cavitation bubble surface and ultrasonic power to trigger the out-of-equilibrium self-assembly of dimers and trimers to spherical and uniform nanostructures with controlled size has been discussed. The synthesized particles exhibited fluorescence in blue, green and red spectral regions and a strong antioxidant activity.     

Thermoelectric properties of pressed bismuth nanoparticles

Theory predicts a substantial increase in the dimensionless figure of merit as the dimensionality and characteristic size of a material are decreased. We explore the use of bismuth nanoparticles pressed into pellets as potential increased efficiency thermoelectric materials. The figure of merit of these pellets is determined by independently measuring the electrical conductivity, thermal conductivity and Seebeck coefficient. The results from the nanoparticle sample are compared to microparticle-based samples. Both sample types show a slight reduction in thermal conductivity relative to bulk bismuth and a Seebeck coefficient near or slightly larger in magnitude than bulk bismuth. These changes are dwarfed by a hundred-fold decrease in the electrical conductivity due to porosity and an oxide layer on the particles. The low conductivity leads to figures of merit at least two orders of magnitude smaller than bulk bismuth. Oxide layer removal and reduced pellet porosity will be required to increase the figure of merit.     

Self-assembly of Polyaniline: Mechanism Study

在水热环境下合成出\掺杂电荷诱导自组装纳米纤维阵列结构的聚苯胺平板,并通过一系列设计实验研究了这种自组装微观结构的形成机理,例如在反应溶液中引入不参与反应、对电荷组装起干扰作用的电解质,以及用计算模拟体系静电能与纳米纤维阵列夹角的相互关系等实验．实验结果发现,由掺杂离子引起的静电相互作用在形成聚苯胺自组装结构的过程中起了重要的作用．     

纳米微粒对低温保护剂溶液结晶性质的影响

为了研究纳米微粒对低温保护剂溶液结晶性质的影响,实验利用差示扫描量热仪(DSC)测量了加入不同粒径、不同质量分数的HA纳米微粒的乙二醇(EG)低温保护剂溶液的成核温度和结晶焓。实验结果表明:纳米微粒加入EG溶液后,成核温度明显升高,并且随着纳米微粒粒径的和质量浓度的增大而升高显著;加入一定质量浓度(>0.2%)的纳米微粒后,同浓度的低温保护剂溶液的结晶焓稳定地升高。成核温度与结晶焓的升高说明,纳米微粒能够促进低温保护剂溶液的结晶。     

NMR波谱技术在两亲分子聚集体研究中的应用

通过近年来NMR技术在两亲分子聚集体研究中的应用实例,特别在弛豫时间、自扩散系数测定、谱线宽度、化学位移等方面取得的研究结果,对确定的两亲分子聚集性质、聚集体结构和聚集体性质的研究进行了较为详细的介绍.主要侧重点在于介绍1HNMR、13CNMR、19FNMR及2H四极分裂谱等技术在两亲分子聚集体结构及结构演变研究中的应用,特别在胶束、囊泡和微乳液结构确定上的应用.     

Structural fluctuations in nanoparticles

Standard methods of thermodynamics are used to investigate fluctuation conditions for individual nanoparticles. This analysis leads to a theorem on fluctuations of nanoparticles in the vicinity of the phase transformation temperature stating that fluctuations are possible only between an equilibrium and a non-equilibrium phase. The basic conditions used to describe fluctuations are well suited to calculate the limits for fluctuations as function of temperature and particle size.     

Raman properties of silicon nanoparticles

The Raman spectra of silicon nanoparticles in the size range between d=3.5– have been studied experimentally. Scattering processes up to second order are being observed. The experimental results are analyzed in the framework of the phonon confinement model. While this model describes qualitatively the observations for first-order scattering processes, it is not applicable for scattering processes of higher order. From the analysis of second-order scattering, we determine a redshift of the TO phonon at the X and L points.     

Influence of surface relaxation on the surface vibrational modes of some ionic crystals

In this paper we evaluate the effects of surface relaxation on the surface vibrational modes of the (001) surfaces of NaCl, NaI and MgO, using bulk shell models which have been modified to allow for distance dependence of the short-range interactions. It is found that these dynamical shell models do not lead to convergent results for the static surface relaxation. In spite of this inconsistency, it is found that surface relaxation gives rise to a new structure of relaxationinduced surface modes, which is common to the three crystals and independent of the details of the relaxation. By using assumed (convergent) relaxation configurations for the MgO (001) surface it is shown that relaxation can account for the high-frequency peak in the surface-excess density of vibrational states of MgO, as found in inelastic neutron scattering experiments on MgO microcrystals. In general, surface relaxation has a profound effect on surface vibrational phenomena, and better shell models will have to be developed to deal with the static and dynamical surface phenomena in a consistent fashion.     

Self-assembly,optical and electrical properties of fork-tailed perylene bisimides

Effect of side-chain length on self-assembly, optical and electrochemical properties of N,N′-di(1-pentylbutyl)perylene-3,4,9,10-tetracarboxylic bisimide and N,N′-di(1-hexylpentyl)perylene-3,4,9,10-tetracarboxylic bisimide has been studied. The photo-physical, thermal and electrochemical properties were studied using UV–Vis and fluorescence, differential scanning calorimetry, and cyclic voltammetry, respectively. The molecules self-assembled as 1D – rods and molecular bundles, self-assembly was studied using SEM, optical and fluorescence microscopic techniques. The results concluded that the compound with short tail exhibits low solubility and self-assembled faster. The photo-physical properties of the compounds were not much affected by varying the alkyl chain length. The compounds geometries were optimized at 6-31G^∗ using DFT and the potentials were correlated with molecular orbitals.     

The crystallization and physical properties of Al-doped ZnO nanoparticles

Un-doped Al (0-9 at.%) nanoparticles and doped ZnO powders were prepared by the sol-gel method. The nanoparticles were heated at 700-800 °C for 1 h in air and then analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectra and photoluminescence (PL). The results of un-doped (ZnO) and Al-doped ZnO (AZO) nanoparticles were also compared to investigate the structural characteristics and physical properties. XRD patterns of AZO powders were similar to those of ZnO powders, indicating that micro-Al ions were substituted for Zn atoms and there were no variations in the structure of the ZnO nanoparticles. From the XRD and SEM data, the grain size of the AZO nanoparticles increased from 34.41 to 40.14 nm when the annealing temperature was increased. The Raman intensity of the AZO nanoparticles (Al = 5 at.%) increased when the annealing temperature was increased. Increasing the degree of crystalline not only reduced the residual stress, but also improved the physical properties of the nanoparticles.     

Structural properties of ionic liquids

Two types of ionic liquids are considered: molten salts and aqueous solutions of strong electrolytes. It is shown that in both cases, modern theoretical methods are capable of making definite predictions about the spatial correlations between the ions themselves and between the ions and water molecules. It is further shown that the technique of neutron diffraction as applied to isotopically enriched samples allows, for the first time, detailed comparisons to be made between theory and experiment. The results of these comparisons are discussed and areas in which the theory is in urgent need of revision are identified.     

Second-harmonic generation at the surface of cubic ionic crystals

The strength of the different source terms in the isotropic Second Harmonic (SH) response of the surface has been measured in different ionic crystals LiF, NaF, GGG(Gadolinium-Gallium-Garnet), and MgF₂, using as excitation beam the fundamental output of a Nd:YAG laser (1.06 m). The azimuthal dependences of the optical second-harmonic generation has also been measured at the LiF(100), LiF(111), GGG(100), and GGG(111) surfaces. No experimental evidence of a bulk contribution to the anisotropic part of the nonlineau polarization has been observed.     

Self-assembly of Ag nanopowder on OTS-patterned glass

Ag ink was spontaneously patterned on glass substrate by using the surface energy difference of a pre-patterned octadecyltrichlorosilane (OTS) layer. Ag ink was confined into the hydrophilic area, where OTS layer was not formed. OTS layer was selectively transferred by micro-contact printing (μCP) method and significantly decreased surface energy. As a result, surface of glass substrate was separated as hydrophobic and hydrophilic with and without OTS layer, respectively. Ag line could be successfully patterned with the width of below 10 μm on the glass. The patterned Ag line was dense and abrupt on the edge and the thickness was about 0.25 μm. Ag film showed good adhesion on a glass substrate after anneal above 200 °C. The minimum resistivity was about 4 μΩ cm.     

聚氨基苯腈自组装膜及其光谱分析

本文用等离子体法合成了聚对氨基苯腈，并用自组装技术将其成功地与聚苯乙烯磺酸钠组装成超薄薄膜，紫外－可见吸收光谱显示自组装过程非常规则。这为制备聚对氨基苯腈薄膜提供了一个新方法。     

Role of adsorption on surface composition of Pd–Cu nanoparticles

Monte-Carlo (MC) simulation is used to study the role of adsorption of hydrogen, oxygen and carbon monoxide (CO) on the surface composition and surface bond geometry of Pd–Cu nanoparticles. For clean particles the surface is found to be enriched in Cu. But in the presence of adsorbed hydrogen and CO there is a segregation reversal from Cu segregation at low coverage to Pd segregation at high coverage. In the presence of adsorbed oxygen, on the contrary, the extent of Cu segregation increases with coverage. For a 586-atom nanoparticle with 50% Pd in the bulk the corner sites are found to be occupied by Cu atoms up to one monolayer adsorption. But, while the occupancy of 7, 8 and 9-coordinated sites by Cu atoms decreases with increase of H and CO coverage, for oxygen adsorption this occupancy increases with coverage. The relevance of such results in catalysis studies is discussed.     

Thermostimulated surface segregation processes in ionic crystals: Potassium chloride

The chemical and phase composition, and cleavage surface morphology and the vapor composition of potassium chloride (KCl) crystals formed as a result of the thermostimulated surface autosegregation (TSAS) are studied by methods of microprobe analysis, high-resolution scanning electron microscopy, optical digital microscopy, and quadrupole mass spectrometry. It is experimentally found that the stoichiometry (K/Cl <1) in the surface layers changes due to a decrease in the potassium surface concentration from 5% in the initial samples to 12% after annealing at a temperature of 1023 K. After annealing at a temperature of 573 K for 5 h at P = 10^?3 Pa, the potassium deficiency increases to 17%. The competing processes resulting in TSAS in potassium chloride are the self-diffusion of potassium to the surface and its subsequent sublimation. During the annealing processes the sublimation of potassium dominates, but at a temperature near fusion, the self-diffusion of potassium to the surface increases. It is concluded that potassium chloride analogous to sodium chloride is a rather stable compound to TSAS. This is an additional argument of the important role of ionic bonds in a decrease in the tendency of chemical compounds to surface autosegregation.     

Optical properties of citrate-stabilized CdS nanoparticles

Citrate-stabilized CdS nanoparticles of size 4 nm are obtained by varying the sulfide:citrate ion concentration in a simple aqueous synthesis method. The optical absorption and photoluminescence properties of the nanoparticles are studied. The size of the crystallites is found to be less affected by sulfide:citrate ratio. At lower concentrations of S²⁻, trap state emission is favoured and at higher concentrations excitonic transition is predominant as shown by optical absorption and photoluminescence spectra. Effective surface capping and optimum concentration of S²⁻ leads to the quenching of surface-defect-related emission. Increase in citrate ion concentration is found to increase the intensity of photoluminescence band arising from trap state emission revealing the role of sulfide:citrate ratio on surface modification of CdS nanocrystals. The nanoparticles are hexagonal as shown by the X-ray diffraction and selected area electron diffraction pattern.