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We report the (spontaneous) formation of colloidal strings, Bernal spiral-like, and tubular clusters comprising spherical, isotropically functionalized colloidal particles in an aqueous environment. The formation of colloidal strings and Bernal spiral-like clusters is guided by an interplay between short-ranged hydrophobic attraction and relatively longer-ranged electrostatic repulsion acting between the colloids. When a dispersion of these colloids is densified via centrifugation, well-defined tubular aggregates were observed. [ABSTRACT FROM AUTHOR]

We report the first example of reversible encapsulation of micron-sized particles by oppositely charged submicron smaller colloids. The reversibility of this encapsulation process is regulated by pH-responsive poly(acrylic acid) (PAA) present in solution. The competitive adsorption between the small colloids and the poly(acrylic acid) on the surface of the large colloids plays a key role in the encapsulation behavior of the system. pH offers an experimental knob to tune the electrostatic interactions between the two oppositely charged particle species via regulation of the charge density of the poly(acrylic acid). This results in an increased surface coverage of the large colloids by the smaller colloids when decreasing pH. Furthermore, the poly(acrylic acid) also acts as a steric barrier limiting the strength of the attractive forces between the oppositely charged particle species, thereby enabling detachment of the smaller colloids. Finally, based on the pH tunability of the encapsulation behavior and the ability of the small colloids to detach, reversible encapsulation is achieved by cycling pH in the presence of the PAA polyelectrolytes. The role of polyelectrolytes revealed in this work provides a new and facile strategy to control heteroaggregation behavior between oppositely charged colloids, paving the way to prepare sophisticated hierarchical assemblies. [ABSTRACT FROM AUTHOR]

Wereport a versatile emulsion-based synthesis for the preparationof nanometer-sized dumbbell-shaped particles that contain two chemicallydifferent patches. One patch consists of solely polystyrene and istherefore chemically inert toward most chemical reactions. The otherpatch contains reactive surface chlorine groups. To achieve this,we prepared seed particles with a chlorinated surface that were transformedinto dumbbell-shaped particles by introducing a liquid styrene protrusionon the surface, which was polymerized to form a solid, anisotropiccolloidal particle. The chlorinated layer on the seed particles providesboth sufficient hydrophilicity to set a finite contact angle betweenthe liquid protrusion and the seed particle and a chemical handlefor further site-specific modification of the reactive patch. Thechlorine groups can be easily converted to other functionalities,making these particles an ideal platform for the preparation of colloidswith complex (surface) properties. As an example, it was shown thatthis patch could participate in copper-catalyzed Huisgen 1,3-dipolarcycloaddition reactions after conversion of the chlorines to azides.This very robust form of click chemistry allows us to decorate thereactive patch with a wide variety of molecules. [ABSTRACT FROM AUTHOR]