A Surfactant-Free and Shape-Controlled Synthesis of Nonspherical Janus Particles with Thermally Tunable Amphiphilicity

Abstract

A surfactant-free approach is proposed to synthesize nonspherical Janus particles with temperature-dependent wettability on hydrophobic surfaces. Sub-micrometer-sized particles comprising poly(styrene-co-divinylbenzene) core and a thermally responsive poly(N-isopropylacrylamide-co-methacrylic acid) shell are first synthesized to stabilize styrene droplets in water, producing a Pickering emulsion. Upon heating to 80 °C and subsequent addition of initiators to the aqueous phase, styrene droplets are polymerized and combine with the core-shell particles to construct dumbbell-shaped nonspherical particles. The shape of the nonspherical particles is controllable by adjusting the equilibrium time of the Pickering emulsion at 80 °C, which is conducted prior to polymerization. The mechanism of formation is discussed in more detail. Since molecular surfactants or stabilizers are not used during the synthesis, the present nonspherical particles well exhibit their own temperature-dependent amphiphilic characteristics. The aqueous dispersion containing the dumbbell-shaped particles alters its wettability on hydrophobic polymer surfaces according to temperature changes, demonstrating its temperature-dependent amphiphilicity change.

Switchable CO2-Responsive Janus Nanoparticle for Lipase Catalysis in Pickering Emulsion

“…In biphasic reaction systems, lipase and substrates can come into more efficient contact at the oil–water interface, enhancing the catalytic activity of the enzyme for effective catalysis. , Pickering emulsion is a specific type of biphasic emulsion that offers significant advantages in catalytic reactions. , It not only provides a large interfacial area, reducing the diffusion distance of substrate molecules and minimizing mass transfer resistance, but also, in comparison to traditional emulsions, features a layer of densely packed solid particles at the oil–water interface. − This greatly enhances emulsion stability, making it an ideal system for enzyme-catalyzed interfacial reactions . Among the particles capable of forming Pickering emulsions, Janus particles, with their hydrophilic characteristics on one side and hydrophobic characteristics on the other side, offer unique advantages in stabilizing Pickering emulsions. − By modulating the hydrophilicity and hydrophobicity of Janus particles, the surface morphology and reaction conditions of Pickering emulsions can be precisely controlled, enabling efficient catalysis. , …”