Particles with directional interactions are promising building blocks for new functional materials and may serve as models for biological structures 1,2,3 . Mutually attractive nanoparticles that are deformable due to flexible surface groups, for example, may spontaneously order themselves into strings, sheets and large vesicles 4,5,6 . Furthermore, anisotropic colloids with attractive patches can self-assemble into open lattices and colloidal equivalents of molecules and micelles 7,8,9 . However, model systems that combine mutual attraction, anisotropy, and deformability have-to the best of our knowledge-not been realized. Here, we synthesize colloidal particles that combine these three characteristics and obtain selfassembled microcapsules. We propose that mutual attraction and deformability induce directional interactions via colloidal bond hybridization. Our particles contain both mutually attractive and repulsive surface groups that are flexible. Analogous to the simplest chemical bond, where two isotropic orbitals hybridize into the molecular orbital of H 2 , these flexible groups redistribute upon binding. Via colloidal bond hybridization, isotropic spheres self-assemble into planar monolayers, while anisotropic snowman-like particles self-assemble into hollow monolayer microcapsules. A modest change of the building blocks thus results in a significant leap in the complexity of the self-assembled structures. In other words, 1 arXiv:1503.00552v3 [cond-mat.soft] 18 Jul 2016 these relatively simple building blocks self-assemble into dramatically more complex structures than similar particles that are isotropic or non-deformable.For self-assembly of nanoparticles, deformability and mutual attraction have recently been combined by grafting flexible polymers onto the surface of mutually attractive particles. This results in isotropic clusters 10 , and selfassembled strings, sheets, and large vesicles 4,5 . For micrometre-sized colloids, on the other hand, coupling mutual attraction and anisotropy leads to patchy particles. Attractive domains, or patches, have induced self-assembly into open lattices and colloidal equivalents of molecules and micelles 7,8,9 . Here, we combine the three properties mutual attraction, anisotropy and deformability, by synthesizing snowman-like particles that consist of a deformable core and a non-deformable lobe or protrusion. In the first part of this letter, mutual attraction is combined with deformability, resulting in anisotropic or directional interactions as flexible surface groups redistribute upon binding (Fig. 1e). This process is analogous to bond hybridization in quantum chemistry. When two hydrogen atoms bind and form H 2 , for example, the electrons around each atom redistribute, i.e. two isotropic orbitals hybridize into the molecular orbitals of H 2 . Similarly, when mutually attractive, deformable particles bind, flexible surface groups redistribute, resulting in directional interactions. We refer to this effect as colloidal bond hybridization. We observe ...

In this Monte Carlo simulation study we use mesoscopic modeling to show that β-casein, an unstructured milk protein, adsorbs to surfaces not only due to direct electrostatic and hydrophobic interactions but also due to structural rearrangement and charge regulation due to proton uptake and release. β-casein acts as an amphiphilic chameleon, changing properties according to the chemical environment, and binding is observed to both positively and negatively charged surfaces. The binding mechanisms, however, are fundamentally different. A detailed, per-residue-level analysis shows that the adsorption process is controlled by a few very specific regions of the protein and that these change dramatically with pH. Caseins, being the most abundant proteins in milk, are crucial for the properties of fermented dairy products, such as nutrition, texture, and viscosity, but may also influence adhesion to packaging materials. The latter leads to product losses of about 10%, leading to economical and environmental problems.

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.