Determination of the surface tension of surfactant solutions applying the method of Lecomte du Noüy (ring tensiometer)

Summary Starting from a comparative assessment of the outstanding works on the ring method (du Noüy) for the determination of the surface tension of liquids and its solutions it is shown that the application of this method to surfactant solutions can lead to substantial errors if one follows conventional conditions. These errors are mainly connected with so far unknown phenomena occurring during the raising of the ring and concerning the influence of the hydrophilic vessel wall above the solution level and the stretching of the solution surface. This is demonstrated quantitatively with surfactant solutions of different kind and concentration. These effects can be explained theoretically very simply by introducing certain assumptions on the behaviour of a surfactant adsorption layer on the inner vessel wall. Conditions leading to the elimination of these errors are given, thus enabling the application of the ring method to the determination of the surface tension of surfactant solutions.With 10 figures and 3 tables     

Semi-wet growth and characterization of multi-functional nano-engineered mixed metal oxides for industrial application

This review paper covers the low temperature wet growth of nano-engineered particles of ZnO-based mixed metal oxides, their growth mechanism, and characterization using X-ray diffraction, SEM, TEM and IR, UV–visible, and XPS spectral techniques. Main focus of this article is centered on low temperature semi-wet methods of synthesis that are suitable for large scale production of zinc oxide-based systems mixed with iron oxide, copper oxide, nickel oxide and cobalt oxide. These mixed metal oxides have broad industrial applications as catalyst, semiconductors, adsorbents, superconductors, electro-ceramics, and antifungal agents in addition to extensive applications in medicines. This paper discusses the low-cost and environment friendly synthesis of these mixed metal oxides, measurement of properties and applicability of these materials systems.     

Spherically symmetric inhomogeneous dust collapse in higher dimensional space-time and cosmic censorship hypothesis

We consider a collapsing spherically symmetric inhomogeneous dust cloud in higher dimensional space-time. We show that the central singularity of collapse can be a strong curvature or a weak curvature naked singularity depending on the initial density distribution.     

Synaptic depression and short-term habituation are located in the sensory part of the mammalian startle pathway

Background  

Short-term habituation of the startle response represents an elementary form of learning in mammals. The underlying mechanism is located within the primary startle pathway, presumably at sensory synapses on giant neurons in the caudal pontine reticular nucleus (PnC). Short trains of action potentials in sensory afferent fibers induce depression of synaptic responses in PnC giant neurons, a phenomenon that has been proposed to be the cellular correlate for short-term habituation. We address here the question whether both this synaptic depression and the short-term habituation of the startle response are localized at the presynaptic terminals of sensory afferents. If this is confirmed, it would imply that these processes take place prior to multimodal signal integration, rather than occurring at postsynaptic sites on PnC giant neurons that directly drive motor neurons.     

Determination of Surface Dilational Viscosity Using the Oscillating Bubble Method

A new version of the oscillating bubble method enables us to determine the dilational modulus of fluid surfaces in the frequency range 1 Hz相似文献   

Estimation of trace elements in some medicinal plants used in anti‐cancer drugs by PIXE

A trace elemental analysis was carried out in various parts of 12 anticancer medicinal plants, using the PIXE (particle‐induced X‐ray emission) technique. A 3‐MeV proton beam was used to excite the samples, and spectra were recorded using a Si (Li) detector. Data analysis was done using the GUPIX software. The elements Cl, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, Br and Sr were identified, and their concentrations estimated. The results of the present study provide justification for the usage of these medicinal plants in the development of anticancer drugs. Copyright © 2012 John Wiley & Sons, Ltd.     

The role of surface viscoelasticity in slide coating processes

In the slide hopper coating process for simultaneously applying multiple layers of coating liquids to a moving web, surfactants must be added to the photographic emulsion to ensure a stable position of the liquid bridge formed between the lower edge of the slide hopper and the moving web. In slide coating of gelatin solutions without an added surfactant, the liquid bridge becomes instable and begins to oscillate if critical coating conditions are reached. The addition of anionic surfactants stabilizes the liquid bridge against oscillations. The action of the added surfactants is a result of their interaction with gelatin. The degree of binding can be used as a measure of the interaction. The binding of anionic and cationic surfactants to gelatin was investigated using a surfactant-selective electrode. The binding isotherms of the surfactants to an alkali-processed bone gelatin were determined and compared with the surface dilational properties of the gelatin/surfactant adsorption layers. The comparison of surface rheological data obtained by the oscillating bubble method with the results of coating experiments demonstrates that the viscoelastic properties of gelatin/anionic surfactant adsorption layers are of essential importance to the stabilization of the liquid bridge against oscillations. Pure elastic adsorption layers are not able to stabilize the liquid bridge. The mechanism of the stabilizing action is discussed. Received: 30 October 2000/Revised: 12 February 2001/Accepted: 14 February 2001     

On the awarding of the Russian Federation State Prizes of 1995 for young scientists for outstanding works in the field of science and engineering

Information

On the awarding of the Russian Federation State Prizes of 1995 for young scientists for outstanding works in the field of science and engineering     

Oscillating bubble SHG on surface elastic and surface viscoelastic systems: new insights in the dynamics of adsorption layers

Surface rheology governs a great variety of interfacial phenomena such as foams or emulsions and plays a dominant role in several technological processes such as high-speed coating. Its major difference with bulk rheology resides in the high compressibility of the surface phase, which is the direct consequence of the molecular exchange between adsorbed and dissolved species. In analogy to bulk rheology, a complex surface dilational modulus, epsilon, which captures surface tension changes upon defined area changes of the surface layer, can be defined. The module epsilon is complex, and the molecular interpretation of the dissipative process that gives rise to the imaginary part of the module is subject to some controversy. In this contribution, we used the oscillating bubble technique to study the surface dilational modulus in the mid-frequency range. The dynamic state of the surface layer was monitored by a pressure sensor and by surface second-harmonic generation (SHG). The pressure sensor measures the real and imaginary part of the modulus while SHG monitors independently the surface composition under dynamic conditions. The experiment allows the assessment of the contribution of the compositional term to the surface dilational modulus epsilon. Two aqueous surfactant solutions have been characterized: a surface elastic and a surface viscoelastic solution. The elastic surface layer can be described within the framework of the extended Lucassen-van den Tempel Hansen model. The change in surface concentration is in phase with the relative area change of the surface layer, which is in strong contrast with the results obtained from the surface viscoelastic solution. Here, surface tension, area change, and surface composition are phase-shifted, providing evidence for a nonequilibrium state within the surface phase. The data are used to assess existing surface rheology models.