Structurally Anisotropic Janus Particles with Tunable Amphiphilicity via Polymerization of Dynamic Complex Emulsions.

Bradley D Frank,Markus Antonietti,Lukas Zeininger

doi:10.1021/acs.macromol.0c02152

Bradley D Frank, Markus Antonietti + Show 1 more

Open Access

https://doi.org/10.1021/acs.macromol.0c02152

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Abstract

A facile one-step approach for the synthesis of physically and chemically anisotropic polymer particles with tunable size, shape, composition, wettability, and functionality is reported. Specifically, dynamically reconfigurable oil-in-water Janus emulsions containing photocurable hydrocarbon or fluorocarbon acrylate monomers as one of the droplet phases are used as structural templates to polymerize them into precision Janus particles with highly uniform anomalous morphologies including (hemi-) spheres, lenses, and bowls. During polymerization, each interface is exposed to a different chemical environment, yielding particles with an intrinsic Janus character that can be amplified via side-selective postfunctionalization. The fabrication method allows to start with various common emulsification techniques, thus generating particles in the range of 200 nm –150 μm, also at a technical scale. The anisotropic shape combined with the asymmetric wettability profile of the produced particles promotes their directed self-assembly into colloidal clusters as well as their directional alignment at fluid interfaces. We foresee the application of such Janus particles in technical emulsions or oil recovery, for the manufacturing of programmed self-assembled architectures, and for the engineering of microstructured interfaces.

Highlights

All polymer particles synthesized by this method display an intrinsic Janus character as each interface is exposed to a different chemical environment during polymerization
To ascertain the presence of the anticipated polarity contrast on the surfaces of the particles, we investigated their behavior at fluid interfaces
A straightforward one-step approach for the fabrication of chemically and physically anisotropic polymer particles is developed, wherein Janus emulsions act as particle molds allowing a fine-tuning of the shape, size, composition, and wettability profile of the final particles

Summary

INTRODUCTION

Polymer particles with two distinct faces of differing chemistries, so-called Janus particles, represent a unique collection of functional colloidal materials featuring anisotropic wettability, chemistry, and optical, electric, and magnetic properties.[1,2] Due to their amphiphilicity and directionality within a single hybrid particle, Janus particles have attracted considerable attention in a diverse set of applications, including as powerful solid surfactants to mediate stability in multiphasic fluid mixtures and influence the packing dynamics at the interfaces,[3−7] as motile particles with directional propulsion profiles,[8,9] colloidal building blocks for selfassembled structure formation,[10−12] for imaging,[13,14] or as transducers in sensing applications.[15−17] Because the properties and functions of Janus particles are closely related to their geometry and composition, a variety of fabrication methods have been developed to meet specific application-oriented requirements.[18]. Besides single-phase emulsion droplets, the use of complex emulsion droplets such as multiple, multilayered, and Janus emulsions gives rise to a large structural diversity, which can be polymerized to produce anisotropic particles.[32−35] As a result, microfluidic techniques, in particular, have evolved as a powerful tool for the generation of monodisperse micrometer-sized anisotropic particles, as these approaches allow for the creative design of numerous geometrically complex and intricate objects.[36,37] As a drawback, microfluidic approaches typically require multiple fabrication steps, are limited to the higher micrometer size range, and depend on hard or soft lithographic techniques for the fabrication of highly sophisti-. Dynamic control of these droplet templates allows the creation of intricate particle shapes such as (hemi-) spheres, lenses, and bowls in high uniformity across a sample, with size ranges and distributions solely controlled by the emulsification method (Figure 1)

RESULTS AND DISCUSSION

CONCLUSIONS

■ REFERENCES