Evaporation-driven assembly of colloidal nanoparticles into clusters: A dissipative particle dynamics study.

In this work we consider a simulation strategy for assembling Janus nanoparticles in oil-in-water emulsion droplets by evaporation based on the dissipative particle dynamics method. Our simple method reproduces all the observed cluster configurations that have been explored experimentally. In addition, the kinetic process of cluster formation is systematically investigated. We observe a structural transition from spherical packings to minimal second-moment configurations via visual inspection and a simple angle parameter. We reveal that the critical volume at which the transition occurs is a cubic function of the number of particles, N. Our approach also allows us to anticipate higher-order clusters, overcoming the limitations of the standard methods in the literature. Similarly to small N values, we find that for each N in the range of 16-39, all final clusters have a unique configuration.

Crystal structure of potassium hydrogen bis-((E)-2-{4-[3-(thio-phen-3-yl)acrylo-yl]phen-oxy}acetate).

The synthesis and spectroscopic data of (E)-2-{4-[3-(thio-phen-3-yl)acrylo-yl]phen-oxy}acetic acid are described. Crystallization from an ethanol-water mixture resulted in the title compound, C30H23KO8S2 or [K(C15H11O4S)(C15H12O4S)] n , containing one mol-ecule of the acid and one mol-ecule of the potassium salt in the asymmetric unit. Both mol-ecules share the H atom between their carboxyl groups and a potassium ion. The C=C bonds display an E configuration. The thio-phene and phenyl rings in the two mol-ecules are inclined by 43.3 (2) and 22.7 (2)°. The potassium ion is octa-hedrally coordinated by six O atoms. This distorted octa-hedron shares on opposite sides two oxygen atoms with inversion-related octa-hedra, resulting in chains of octa-hedra running in the [010] direction, which form ladder-like chains by C-H⋯π inter-actions. A Hirshfeld surface analysis indicates that the highest contributions to the surface contacts arise from inter-actions in which H atoms are involved, with the most important contribution being from H⋯H (31.6 and 31.9% for the two mol-ecules) inter-actions.

Two-Dimensional Clusters of Colloidal Particles Induced by Emulsion Droplet Evaporation.

The minimization principle of the second moment of the mass distribution ( M 2 ) is responsible for the unique structure of three-dimensional clusters by using emulsion droplet evaporation. Herein we study the structure of two-dimensional clusters of colloidal particles bound at the interface of liquid droplets in the plane. We found that, differently from the three-dimensional system, the two-dimensional clusters have multiple degenerate configurations (isomers). An interesting feature of such two-dimensional clusters is that they have the same packings as those belonging to a class of geometric figures known as polyiamonds. In particular, except for the six-particle cluster, many higher order clusters of polyiamond have not been reported previously. Using a simple geometrical approach, based on the number of ways to generate a packing, we calculated the occupation probabilities of distinct isomeric clusters. The level of agreement with the results of metropolis Monte Carlo simulations was good for clusters containing up to nine particles, suggesting that our two-dimensional cluster structures are not a result of the minimization of the second moment. In addition, the structure of these clusters is somewhat insensitive to the range and depth of the interparticle potential, in good agreement with the results in the literature.