Effect of Surface Charge on a Microsphere on the Stability of a Nanoparticle Suspension

A stable suspension of nanoparticles is generally achieved by modifying the surface properties of the nanoparticles using a surfactant. This is to create a surface charge on the nanoparticles which prevents them from forming aggregates. This phenomenon is very sensitive to changes in the local environment. Conventional optical tweezers though capable of trapping sub-micrometer particles are not known to trap single nanoparticles. However, the stability and dynamics of a suspension of nanoparticles can be probed through the changes in the fluctuations of an optically trapped microsphere that has been added to the suspension. Adding microspheres to the nanoparticle suspension can affect the stability depending on the surface charges the microparticles themselves have. The study reports here on the variation of the dynamics of suspended nanoparticles, which have a positive surface charge, when silica microspheres, which are negatively surface charged, are added to the suspension. With the addition of silica beads, there is agglomeration of the nanoparticles. The dynamics of these agglomerated structures are then probed by measuring the Brownian fluctuations of an optically trapped silica bead. These results are in sharp contrast to those of earlier studies carried out with suspensions of identical nanoparticles but with negative surface charge.     

Effect of the thickness of the Pt film coated on a counter electrode on the performance of a dye-sensitized solar cell

The effects of the thickness and morphology of a Pt film coated on a counter electrode on the performance of a dye-sensitized solar cell (DSC) were investigated. Deposition of a Pt film ranging in thickness from 2 to 415 nm gradually decreases the sheet resistance of the counter electrode. No significant difference in the charge-transfer resistance at the electrolyte|counter electrode interface was observed for a Pt film thickness ranging from 25 to 415 nm. A high energy conversion efficiency of approximately 5% can be obtained for DSCs based on a counter electrode with a very thin Pt film of 2 nm, as well as with a 415-nm thick Pt film. These results are important for reducing production costs by reducing the required amount of expensive platinum.     

Influence of the electric field on a bio-mimetic film supported on a gold electrode

A model biological membrane was formed by fusion of mixed cholesterol and DMPC (dimyristoylphosphatidylcholine) phospholipid vesicles onto a gold-coated quartz support. The gold surface was charged and the influence of the charge at the solid support on the structure and integrity of the phospholipid bilayer was investigated using the specular reflection of neutrons and electrochemical measurements. When the surface charge density is close to zero, the lipid vesicles fuse directly on the surface to form a bilayer with a small number of defects and hence low water content. When the support's surface is negatively charged the film swells and incorporates water due to the field driven poration of the membrane. When the charge density is more negative then -8 microC cm(-2) the bilayer is detached from the metal surface. However, it remains in close proximity to the metal electrode, suspended on a thin cushion of water. The film thicknesses, calculated from neutron reflectivity, have allowed us to determine the tilt angle of the lipid molecules as a function of the support's charge density. The lipid molecules are tilted 55 degrees from the surface normal at zero charge density but become significantly more perpendicular (30 degrees tilt angle) at charge densities more negative than -8 microC cm(-2). The tilt angle measurements are in very good agreement with previous IR studies. This paper describes the highlights of a more in-depth study which is fully described in [1].     

Impact of a pressure drop on a monolithic capillary column on the efficiency and separation ability of the column

The impact of inlet and outlet column pressures on column separation properties was investigated for monolithic capillary column in gas chromatography. It was demonstrated that the classical Van Deemter equation does not allow us to make a clear choice of the optimal separation conditions. More relevant data can be obtained from the dependence of the height equivalent to a theoretical plate (HETP) on the inlet and outlet column pressures. The dependence ensures that the minimum HETP value can be achieved at high values of inlet and outlet column pressures, but the ratio of the pressures must approach 1. The efficiency of the column under these optimal conditions can exceed by 25–35% the column efficiency under the optimal conditions found using the classical Van Deemter plot. It was shown that a decrease in inlet and outlet column pressures even at a relative pressure close to 1 leads to an increase in HETP and the loss of column separation ability.     

Influence of the electric field on a particle in a space with a disclination

We consider a quantum particle in a space with a linear topological defect, i.e., disclination. The effect of the uniform electric field in this space, on the particle, is shown to cause a translation of the wave function. In addition, the electric field is not found to be affected by the defect. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Effect of the inclusion of a cyclic fragment in the chromophore on the properties of a spiropyran-merocyanine system

The corresponding merocyanines, which do not display a tendency to form spiropyran structures, are formed in the condensation of 1,3,3-trimethyl-2-methyleneindoline with 5-methyl-2-furoylacetaldehyde, 2-formylcyclohexanone, or 2-formyl-1-tetralone. Spiran compounds in which the spiropyran—merocyanine equilibrium is shifted markedly to favor the closed form are formed when 4a,9-dimethyl-2,3,4,4a-tetrahydrocarbazone — the cyclic analog of the Fischer base — is used in the reaction with salicylaldehydes and benzoylacetaldehydes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1210, September, 1982.     

Impregnation of a porous material with a PCM on a cotton fabric and the effect of vacuum on thermo-regulating textiles

The purpose of this study was the preparation of a form-stable composite phase change material (PCM) by incorporation of n-nonadecane within the expanded dolomite (ED). In this investigation, two approaches called impregnation treatment with vacuuming and impregnation by magnetic stirrer were used. This method was first proposed for textile thermal protection. In this method, n-nonadecane was applied as the phase change material and ED as the supporting in order to prepare and construct the composite PCM. Composite properties were determined by Fourier transformation infrared spectroscope and scanning electronic microscope (SEM) techniques and the heat transfer measurement and differential scanning calorimeter (DSC) were used to determine the thermal properties of composite on fabrics. Also, moisture transfer properties were measured. The SEM results showed that the n-nonadecane was well absorbed in the porous network of the ED. DSC analysis and heat transfer also indicated that fabric temperature range for the amount of coated PCM depends on its area; further, by adding composite to the fabric surface, thermal transfer could be reduced. The maximum percentages of n-nonadecane within ED in the composite PCM1 and PCM2 were measured to be about 90 and 70 mass%, respectively. Thus, the composite PCM1 can be considered as a form-stable composite change phase materials.     

一种核糖核酸酶构象稳定性的研究

Aspergillus niger SA-13-20核糖核酸酶是从突变株A.niger SA-13-20分泌的胞外酶中分离出的一种新的核糖核酸酶。采用紫外光谱、荧光光谱和红外光谱研究了A.niger SA-13-20核糖核酸酶在不同pH值条件下的构象稳定性。紫外光谱和荧光光谱结果均表明该酶蛋白在酸性和弱碱性pH值下构象较稳定,当pH值高于9.6时构象不稳定;红外光谱结合去卷积和曲线拟合技术对蛋白质酰胺Ⅰ带的测定和处理结果表明,在室温下,pH 5.0时该酶蛋白二级结构中α-螺旋、β-折叠、转角和无规结构所占的成分分别为13.28%、42.30%、26.48%和17.95%。测得该酶的热解链温度Tm、解链熵变ΔSm及解链焓变ΔHm分别为70.1℃、644 J.mol-1.K-1及22.1 kJ.mol-1,表明该酶属于耐热能力较强的核糖核酸酶。研究结果有助于揭示该酶结构与功能的关系,推动其在科研和生产等方面的应用。     

On the solidification of a supercooled liquid droplet lying on a surface

We model the solidification and subsequent cooling of a supercooled liquid droplet that is lying on a cold solid substrate after impact. It is assumed that solidification occurs for a given fixed droplet shape. The shapes used by the model are a sphere, truncated spheres, and an experimentally registered droplet shape. The freezing process is conduction-dominant and is modeled as a one-phase Stefan problem. This moving boundary problem is reformulated with the enthalpy method and then solved numerically with an implicit finite-difference technique. The numerical results for the simple case of a spherical droplet touching a surface are similar to those of a freely freezing spherical droplet and are well confirmed by the 1D asymptotic analytical model of Feuillebois et al. (J. Colloid Interface Sci. 169 (1995) 90). A freezing water droplet is considered as an example. The numerical results for full freezing time, subsequent cooling time, and last freezing point coordinate for the various droplets shapes are fitted by analytical functions depending on supercooling, thermal resistance of the target surface (expressed by Biot number), and spreading parameter. These functions are proposed for direct application, thus avoiding the need to solve the full freezing and cooling problem.     

Controlling the self-assembly of a deoxiguaninosine on mica

We report a tapping mode scanning force microscopy investigation on the growth from solutions of a lipophilic deoxiguanosine derivative on the basal plane of a muscovite mica surface. By varying the chemical composition of the substrate surface it is possible to drive the self-assembly towards either layered thin films, which are very likely to consist of guanosine quartets, or nanoribbons, comprising hydrogen bonded networks. Both these two architectures, which are peculiar to the guanine base itself, are of notable importance for the fabrication of molecular nanowires. Moreover, the first arrangement provides evidence that the guanosine is able to behave as ionophore, thus, suggesting its utilization in the development of solid-state ion selective sensors.     

Influence of a valent environment on the hypervalent bond of a silicon atom

X-ray structural study of two (O-Si)-chelate (lactamo-N-methyl)dichlorosilanes and two (O-Si)-chelate (lactamo-N-methyl)trichlorosilanes with the hypervalent O-Si-Cl bond has been carried out. Introduction of more electronegative substituents into equatorial positions of the trigonal-bipyramidal valent environment of a silicon atom increases the hypervalent bond rigidity. It has been concluded that the influence of nonspecific (including electrostatic) intermolecular interactions on geometric parameters of the hypervalent fragment is insignificant.For Communication 2, see Ref. 1.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Deceased in August, 1995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1774–1779, September, 1995.This work was carried out with financial support of the Russian Foundation for Basic Research (Project Nos. 93-03-4855 and 94-03-08338) and the International Science Foundation (Grant No. MO4 000).     

Comments on the characteristic polynomial of a graph

Several unique advantages of the Le Verrier–Fadeev–Frame method for the characteristic polynomials of graphs over the method proposed by Zivkovi? recently based on the Givens–Householder method are described. It is shown that the Givens–Householder method proposed by Zivkovi?, by itself fails for directed graphs, signed graphs, and complex nonhermetian graphs requiring extensive modifications to the Householder algorithm through the double + random shift QR procedure requiring more computations than claimed. Furthermore, the QR procedure does not always converge and requires random shifts. To the contrary, it is shown that the Le Verrier–Fadeev–Frame method does not require any such modifications or random shifts and takes less total CPU times when both algorithms are run using vector processors. Hence it is demonstrated that the Le Verrier–Frame algorithm is efficient and superior in its universal and direct applicability to all graphs requiring no further modifications (directed, signed, and complex).     

Self-assembly of a tripodal pseudorotaxane on the surface of a titanium dioxide nanoparticle

This paper describes the self-assembly of a heterosupramolecular system consisting of a tripodal viologen, adsorbed at the surface of a titanium dioxide nanoparticle, that threads a crown ether to form a pseudorotaxane. The viologen, a 1,1'-disubstituted-4,4'-bipyridinium salt with a rigid tripodal anchor group, has been synthesized. This viologen is adsorbed at the surface of a titanium dioxide nanoparticle in solution. As intended, this tripodal viologen is both oriented normal to and displaced from the surface of the nanoparticle and threads a crown ether to form the heterosupramolecular complex. The threading of the crown ether by the tripodal viologen to form the above pseudorotaxane complex at the surface of a titanium dioxide nanoparticle has been studied by (1)H NMR, optical absorption spectroscopy, and cyclic voltammetry.     

Spectroscopic Investigation of the Structure of a Protein Adsorbed on a Hydrophobic Latex

Spectroscopic methods provide a powerful tool for investigating the structural properties of immobilized proteins. For that purpose, there was a strong need for a hydrophobic particle that allows determination of the adsorbed protein conformation by fluorescence and circular dichroism. Among the various hydrophobic suspensions that are available, perfluoro-alkoxy fluoro carbon Teflon latex satisfies the requirements of low light absorption and scattering. As an example, preliminary results of structural changes of a proteolytic enzyme dissolved in aqueous solution and in the adsorbed state are given.     

Effect of the Nature of the Dopant on the Response of a Sensor Array Based on Polyaniline

The effect of the nature of the dopant on the response of a sensor array based on films of polyaniline (PAn) under the influence of the vapor of various organic solvents was studied. It was established that the main factors determining the magnitude of the response of PAn films are the morphology of the films and the accepting power of the analyte molecules (in the case of "standard" acid dopants) and also the possibility of additional donor–acceptor interaction between the analyte molecules and the dopant (in the case of heteropoly acid dopants). It was shown that with heteropoly acids as dopants of PAn it is possible to increase substantially the selectivity of the response of the sensor array.     

Salt effects on the adsorption of a pesticide on modified bentonites

Adsorption of the herbicide linuron on organo-bentonites was measured in the presence of several salts. The bentonites had been modified by cation exchange with hexadecylpyridinium and hexadecyl tributylphosphonium ions. The organo-bentonites adsorbed distinctly higher amounts of linuron than calcium bentonite and desorption was also reduced. The binding coefficient K (derived from the Freundlich adsorption isotherm) was several times higher than for calcium bentonite. The adsorption isotherms of linuron on the organo-bentonites from salt-free aqueous solutions were of S-type but of J-type from saline water. In the presence of many salts, the amount of linuron adsorbed decreased with increasing salt concentration. These salts reduced the linuron adsorption (at a salt concentration of 20 g/L) in the order NaClO₄ KClO₄ < NaCl < NaBr < RbCl < CsCl. Only NaI, CsBr, and CsI increased the adsorption of linuron in comparison to salt-free solutions. Desorption of linuron was also reduced in saline (NaCl) solutions. The salt effect may have environmental importance in developing environmentally friendly formulations of herbicides with reduced mobility in soil and enhanced ground water protection.     

四氨基铜酞菁(CuTAPc)在金电极上成膜过程的研究

采用循环伏安法和石英晶体微天平(EQCM)技术对四氨基铜酞菁(CuTAPc)在金电极上的聚合成膜过程进行了研究．讨论了扫描速度、溶刺、支持电解质及单体浓度对其成膜过程的影响．同时考察了该聚合膜分别在非水溶液和水溶液中的氧化还原行为及稳定性．其中借助EQCM重点讨论了在这些过程中溶液中的离子在膜中传输的机理。