Multicomponent Clusters Research Articles

Assembly of Latex Particles by Using Emulsion Droplets as Templates. 1. Microstructured Hollow Spheres

We describe an emulsion-based technique that allows the assembly of colloid particles into microstructured or multicomponent clusters (“supraparticles”). The particles are gathered, assembled, and fixed together in the restricted, colloid-size 2D or 3D space provided by emulsion droplets. The process is carried out by multiple modification of the colloid interactions within the particle/droplet system“interaction-tailored colloid assembly”. In the first paper of the series we provide a general description of the method. Then we present the data on the assembly of negatively charged (sulfate) or positively charged (amidine) latexes into ordered hollow spherical supraparticles. The following steps are included in the assembly schemes: (1) modification of latex surface charge and properties, so the microspheres are able to adsorb on the droplet surfaces but without homocoagulation; (2) adsorption and structure formation around the emulsion drops (at this stage the interfacial mobility of the particles is of crucial importance); (3) sterical protection of the particle/droplet complexes against coagulation or flocculation; (4) “binding” of particles within the assembled microspheres by strong coagulant; (5) extraction of the supraparticles by dissolving the carrier droplets in the surrounding environment. To characterize the electrostatic interactions throughout the assembly stages, we used electrophoretic mobility measurements. The electrophoretic data are in good qualitative agreement with the interaction-tailored assembly scheme. Clues on the other interactions involved are provided by altering the assembly process and using different modifying agents.

Solvation shells of the proton surrounded by acetonitrile, ethanol, and water molecules

The filling of solvent shells around the proton was investigated by the method of cluster ionization and fragmentation. Hydrogen-bonded clusters of H{sub 2}O, CH{sub 3}CN, C{sub 2}H{sub 5}OH, and mixtures of these molecules were studied. Well-defined first shells corresponding to (CH{sub 3}CN){sub 2}H{sup +}, (CH{sub 3}CN){sub 3}(H{sub 2}O)H{sup +}, and (H{sub 2}O){sub 4}H{sup +} were observed. Most significantly, only one shell was found in clusters of pure CH{sub 3}CN, whereas a structure corresponding to (CH{sub 3}CN){sub n}(H{sub 2}O){sub n-2}H{sup +} was observed up to n = 7 in multicomponent clusters of water and acetonitrile. These results illustrate how results derived from small clusters in high-pressure mass spectrometric experiments may be extended to large clusters.

Precollapse Evolution of Globular Clusters

Density profiles of most globular clusters are well fitted by a King (1966) model. The evolution of a King model in the tidal gravitational field of the Galaxy is first discussed. If the concentration parameter c (= log(rt/rc)) is small enough, the evolution is nearly along the King model sequence and c becomes larger. When c becomes large enough (about 2.1), gravothermal instability sets in. The basic properties of gravothermal instability is next discussed. The stability criterion and its interpretation are given. Globular clusters consist of stars with disparate masses, so that finally the evolution of multi-component clusters is discussed. Acceleration of evolution in multi-component clusters and equipartition of the kinetic energies among components are discussed, and conclusions and future problems are given.

A gas model for multicomponent star clusters: method and comparison with Fokker–Planck theory

On a simule un systeme stellaire multi-masse en integrant numeriquement un ensemble de quatre equations pour chaque composante. Les composantes interagissent par interaction gravitationnelle mutuelle, par transfert d'energie cinetique et par friction dynamique. Les calculs pre-effondrement des systemes a deux composantes sont presentes et compares aux resultats obtenus par integration directe de l'equation fondamentale de Fokker-Planck

Dynamical Evolution of Multi-Component Clusters

Presence of stars with disparate masses causes great differences in the dynamical evolution of star clusters from the evolution of single component clusters. One remarkable effect is acceleration of the evolution. Another effect is destabilization or stabilization. In two-component clusters equipartition at the cluster centre is nearly achieved if Spitzer's (1969) condition is satisfied. In multi-component clusters equipartition at the cluster centre is achieved if either the range of stellar mass is very narrow or the mass spectrum is very steep. Global equipartition is never achieved. Post-collapse evolution of multi-component clusters is discussed briefly and some remained problems are presented.