On the modelling of the dynamic contact angle

The dynamic contact angle is a value of great significance for characterizing wetting processes. Three strategies have been developed for modelling this value; empirical models, models based on molecular kinetics and models based on flow mechanics.Models based on molecular kinetics start from the fact that the dynamic contact angle appears immediately at the Une of wetting, and that the curvature of the liquid surface can be neglected. Models based on flow mechanics show that near the line of wetting the curvature is very strong. These models require the presence of the static contact angle at the line of wetting and give a model of the dynamic contact angle as the slope of the interface. In the present paper, models based on flow mechanics are extended in two directions. For the case of flow in a tubular capillary, the model represents the effect of the adsorption kinetics of surfactants on the dynamic contact angle, assuming the adsorption to be kinetically controlled. Another model is concerned with the effect of the flow of the third phase on the dynamic contact angle and on the boundaries of dynamic wetting. It is demonstrated that coating under an inert liquid is possible only for small working ranges.Symbols A dimensionless number of adsorption - B dimensionless number of adsorption - c concentration - C curvature - D diffusion coefficient - D _s surface diffusion coefficient - h, H height above the solid surface - K ₁ ,K ₂ rate constants - l length of slippage - p pressure - q mass flow density - r, R radius - R viscosity ratio - R _G gas constant - t time - U, v velocity - , , angle - viscosity - y dimensionless surface concentration - surface concentration - stream function - density - surface tension - _LF liquid-fluid interfacial tension - shearing stress - dimensionless radius - Ca capillary number     

In the heart of a dynamic chromatin

An audacious bet on transforming histone H4 into a real-time sensor probe has been won by the group of Minoru Yoshida, who designed the first FRET probes capable of signaling the occurrence of dynamic site-specific acetylations in live cells.     

Estimation of the dynamic size of fractal aggregates

A model is presented for an aggregation act occurring between two aggregates of any mass and fractal dimension. The kinetics of aggregation is also analyzed, as well as some previous works concerning the structure of fractal aggregates. As a result, a generalized curve is derived describing the normalized dynamic radius of clusters of spherical character as dependent on both the aggregate fractal dimension and the space dimension. It is shown how the curve may be utilized to determine the dynamic size of anisotropic aggregates. The obtained dependence can be used to estimate the dynamic size of fractal aggregates, to evaluate the prefactor in mass–radius relation and to model the aggregation kinetics.     

The state of the art of dynamic coatings

The present review highlights the mechanisms of action and efficiency of three major classes of dynamic coatings so far adopted in capillary electrophoresis: (i) amines to oligo-amines, (ii) neutral synthetic and natural polymers, and (iii) neutral and zwitter-ionic surfactants. Their merits and efficacy have been explored in depth via a novel quantitation technique consisting of eluting, by frontal analysis, any adsorbed proteinaceous material, which can then be correctly quantified as a peak as it moves in front of the detector window. This is achieved by loading sodium dodecyl sulfate (SDS) micelles onto the cathodic side and migrating them electrophoretically into the capillary lumen, where they efficiently sweep any adsorbed polypeptide material. It is found that a common trend, for all quenchers, is linked to a hydrophobicity scale: the more hydrophobic the inhibitor, the better it minimizes potential interactions of macromolecules with the wall. This seems to be true for all the classes of dynamic modifiers tested. Finally, we describe a novel, dynamic to static quencher: it is a quaternary piperazine, bearing a reactive iodine atom at the end of a butyl tail (N(methyl-N-omega-iodo-butyl),N'-methyl piperazine). This molecule first binds to the wall, at alkaline pH values, via ionic and hydrogen bonds. Once docked onto the wall, the reactive tail forms a covalent link with the silica surface, to which it then remains permanently affixed.     

On the dynamic mechanical behavior of nylon 66

Summary The dynamic mechanical properties of nylon 66 films and fibers have been examined, as a function of annealing and drawing, with a Vibron viscoelastometer. It is found that the transition is little affected by annealing treatments, but increase in orientation causes the transition to move to a higher temperature. Experiments, with X-ray diffraction of samples at elevated temperatures, lead to the conclusion that the triclinic to hexagonal phase change does not contribute significantly to the transition. Samples cut parallel and perpendicular to the drawing direction of nylon 66 film, have been used to show that the curves of dynamic tensile modulus versus temperature, for the parallel and perpendicular directions, cross in the neighborhood of the transition. This observation is discussed in relation to the suggestion that the transition is the glass transition in nylon 66.

---

Zusammenfassung Die dynamisch-mechanischen Eigenschaften von Filmen und Fasern aus Nylon 66 wurden als Funktion der Temperung und Verstreckung mit einem Virbon-Viskoelastometer untersucht. Die -Umwandlung wird wenig durch die Temperung beeinflußt, aber erhöhte Orientierung läßt siezu höheren Temperaturen verlagern. Messungen der Röntgenstreuung bei erhöhten Temperaturen führen zu dem Schluß, daß der Übergang triklin/hexagonal nicht wesentlich zu der -Umwandlung beiträgt. Proben aus verstrecktem Nylon-66-Film, parallel und senkrecht zur Streckrichtung geschnitten, zeigen, daß die Kurven des dynamischenE-Moduls gegen die Temperatur für beide Orientierungen sich in der Nachbarschaft der -Umwandlung überkreuzen. Diese Beobachtung wird hinsichtlich der Vermutung diskutiert, daß die -Umwandlung den Glasübergang in Nylon 66 darstellt.

---

---

With 5 figures and 2 tables     

Direct method of calculating the dynamic scattering spectrum

A method of obtaining the scattering spectrum that bypasses the need to solve for the configurational distribution function of the macromolecules is presented. It involves the direct calculation of averages that appear in the structure factor expression. Application of the method to Rouse coils recovers Pecora's classical results. The method is applied to obtain the coherent spectrum of a solution of “encapsulated” dumbbells for which the configurational distribution is not available.     

The origin of the dynamic transition in proteins

Despite extensive efforts in experimental and computational studies, the microscopic understanding of dynamics of biological macromolecules remains a great challenge. It is known that hydrated proteins, DNA and RNA, exhibit a so-called "dynamic transition." It appears as a sharp rise of their mean-squared atomic displacements r2 at temperatures above 200-230 K. Even after a long history of studies, this sudden activation of biomolecular dynamics remains a puzzle and many contradicting models have been proposed. By combining neutron and dielectric spectroscopy data, we were able to follow protein dynamics over an extremely broad frequency range. Our results show that there is no sudden change in the dynamics of the protein at temperatures around approximately 200-230 K. The protein's relaxation time exhibits a smooth temperature variation over the temperature range of 180-300 K. Thus the experimentally observed sharp rise in r2 is just a result of the protein's structural relaxation reaching the limit of the experimental frequency window. The microscopic mechanism of the protein's structural relaxation remains unclear.     

Molecular dynamic study of hydrophilicity of the NaCl molecule

The NaCl molecule is represented as a physical dipole in which the distance between the ions equals that in the crystal lattice of NaCl. The water molecules, initially uniformly distributed in the sphere around the NaCl molecule, in 1 or 2 ps form a hydration shell around the positively charged sodium ion, leaving the negatively charged chloride ion naked. When the number of water molecules around the sodium ion reaches 14, the NaCl(H₂O)₁₄ cluster becomes sensitive only to thermal perturbations that are due to the librational motion of water molecules. It is shown that the dependence of the cluster volume on the number of water molecules in the cluster does not admit simple linear approximation. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 299–309, March–April, 1996. Translated by L. Smolina     

A dynamic model of the decomposition of excited molecules

A conjugate kinetic equation has been considered for the investigation of the dynamics of the decomposition of excited molecules. On the basis of this, an equation has been obtained for the mean lifetime of the molecules. The probability of the transition of energy in the system of oscillators which models the molecule has been calculated in the perturbation theory from the anharmonic linkage of normal vibrations. It has been shown that the energy relationships of the rate constant for the decomposition are close to the analogous relationships in the Kassel-Rosenstock theory, but the absolute magnitudes of the rate constants may differ considerably from the values obtained in the quasi-equilibrium theory.In conclusion, the authors express their sincere gratitude to N. N. Tunitskii for his interest in the work and to A. A. Ovchinnikov for numerous discussions and observations.     

Temperature dependence of the dynamic viscosity of liquid mercury

The dependence of the dynamic viscosity of mercury on temperature is calculated and expressed in terms of the cluster associate model, based on the Boltzmann distribution and with normalization at the melting point. The resulting refined equation for mercury viscosity adequately reflects this dependence over the range of the liquid state, including the critical point.     

Evolution of the dynamic mechanical relaxations during the gel formation

Static and dynamic properties of a polyurethane system at different stages of the gelation process have been investigated. Shear modulus data were collected over a wide frequency range covering both the α-relaxation and the internal modes relaxations. The evolution of the relaxation spectra in relation with the structural transformation occurring during the growth process is analysed within the percolation model.     

On the origin of dynamic instability of molecular systems

The vibronic origin of dynamic instability of molecular systems considered earlier, is here given a more complete and rigorous treatment. It is shown that the nonvibronic contribution to the curvature of the adiabatic potential arising due to nuclear displacements under fixed electronic density distribution, is always positive, and hence the only reason for dynamic instability is the pseudo Jahn-Teller effect. For some examples of special interest (planar equilateral NH₃, planar square CH₄ and linear H ₃ ⁺ ) the molecular excited states, responsible for the instability of the ground state, are revealed by means of ab initio calculations.     

Quantitative analysis of the dynamic behaviour of photochromic systems

The good understanding of a photochromic reaction mechanism requires the establishment of the list of all the transient species and the definition of their connecting processes. The purpose of kinetic studies is the determination of the main photochromic parameters, such as the quantum yields of photoisomerization, rate constants of thermal relaxation and spectra of transient species. These data allow the establishment of structure properties relationships in order to select the best substituents to improve photochromic performances within a given series. In this review, we describe the dynamic behaviour of various photochromic systems during thermal relaxation after irradiation, from the simplest mono-exponential decay to the more complicated multi-exponential dynamics. Then, we analyse the evolution of the long-lived isomers under continuous irradiation. Several pedagogical examples and tricks to perform easy kinetic analysis are given in the appendices.     

Mathematical approach for the dynamic testing technique

In dealing with phenomena which show a linear response such as viscoelastic or dielectric properties, measurements are carried out by observing the relationship between the stimulus applied to the sample and the response from the sample. Since the Fourier analysis technique is effective in obtaining this relationship, two types of circuitries based on Fourier analysis have been created. Both DMA and dielectric measurement were used to evaluate these circuitries. Results were satisfactory, especially with respect to tanδ precision.

---

Zusammenfassung Bei der Arbeit mit Erscheinungen, die wie z.B. viskoelastische oder dielektrische Eigenschaften eine lineare Reaktion zeigen, wurden Messungen durch Beobachtung der Beziehung zwischen der auf die Probe angewendeten Aktion und der von der Probe gezeigten Reaktion durchgeführt. Da die Fourier-Analyse eine effektive Technik zur Ermittlung dieser Beziehung ist, wurden auf der Grundlage der Fourier-Analyse zwei Typen von Schemen geschaffen. Sowohl DMA als auch dielektrische Messungen wurden zur Entwicklung dieser Schemen verwendet. Did Resultate waren zufriedenstellend, insbesondere mit Hinblick auf die Genauigkeit von tanδ.

     

Evaluation of the dynamic properties of polymer latex particles interacting with quartz interface by evanescent wave dynamic light scattering

The diffusion behavior of polymer latex particles in dispersion near the quartz interface has been estimated by evanescent wave dynamic light scattering (EVDLS) technique. The diffusion coefficient of the particles was measured as a function of the distance between the particle and interface. The apparent diffusion coefficient estimated by EVDLS was small for particles near the interface and increased upon increasing the distance from the interface, and then saturated at a certain value which is close to the value expected for free-motion. The range of the distance over which diffusion was affected by interaction with the interface depended on the added salt concentration. This means that the diffusion of the particle is influenced by an electrostatic interaction between the particle and quartz interface in addition to the hydrodynamic effect near the wall. This range was found to be more than 800?nm at 0?M salt condition but about 400?nm at 10^-4 and 10^-3?M salt conditions. Hence it is appropriate to say that the hydrodynamic effect reaches up to 400?nm and the electrostatic effect is longer ranged, more than 800?nm, for the system studied here. The EVDLS technique is a very powerful tool for quantitative estimations of the dynamic behavior of the particle near the interface and for estimation of the range where the wall effect is dominant. EVDLS will give us an answer to the question of “where is the ‘interface’ and where is the ‘bulk’?”.     

Differential dynamic microscopy for the characterization of polymer systems

This review summarizes recent progress in investigating polymer systems by using Differential dynamic microscopy (DDM), a rapidly emerging approach that transforms a commercial microscope by combining real-space information with the powerful capabilities of conventional light scattering analysis. DDM analysis of a single microscope movie gives access to the sample dynamics in a wide range of scattering wave-vectors, enabling contemporary polymer science experiments that would be difficult or impossible with standard light scattering techniques. Examples of application include the characterization of polymer solutions and networks, of polymer based colloidal systems, of biopolymers, and of cellular motility in polymeric fluids. Further applications of DDM to a variety of polymer systems are suggested to be just behind the corner and it is thus likely that DDM will become a tool of choice of the modern experimental polymer scientists.