A challenging goal in many research fields is the ability to create novel structures using tailor made building blocks that self-assemble under certain condition. During the last decades, large emphasis has been placed on the design of anisotropic particles, so-called Janus particles, which could potentially lead to the formation of a wide variety of ordered structures through self-assembly. In this work, we show how naturally available Janus tri-block particles can be used to create thermo-responsive gels. The Janus tri-block particles exist of “cube-like” nanoparticles (existing of zein, a class of proteins found in maize), in which a hydrophilic interior is accompanied by two parallel hydrophobic patches. When dispersed in a rather hydrophilic environment, these nanoparticles are allowed to aggregate by hydrophobic interactions forming a liquid dispersion. However, the orientation of the assembly can be controlled, leading to the formation of a gel, even at low zein concentrations. This oriented assembly behavior is induced by the addition of hydrophobic particles (in the form of oil droplets). These particles acts as nucleation sites for further aggregation, and chain-like formation of these “cube-like” particles is observed. The formation of these chains or ribbons leads to a space spanning network, in which the hydrophobic sites of the particles are connected. The formation of these chains is a result of the interplay of hydrophobic interaction between the particles, and hydrophilic interactions with the surrounding hydrophilic medium. As the hydrophobicity and the accompanying interactions can be modified by temperature, these gels show thermo-responsive behavior. Increasing the temperature shows that the assembly of the particles is diminished and the gel returns into its liquid state displaying a certain “melting” temperature. This temperature is dependent on the hydrophobicity of the nuclei, and the polarity of the solvent. The interplay between these parameters can be used to tune the strength of the gels and its breakdown behavior, and may lead to new applications in the food, pharma, cosmetic, and organic electronics industry.
Dr. Elke Scholten elke.scholten@wur.nl
