For more than 20 years, our research team (Prof. Dongyuan Zhao’s mesogroup) has been working on the controlled synthesis and application of mesoporous materials. These mesoporous materials containing 2-50 nm pores, which are formed by the assembly of amphiphilic surfactant micelles with precursors, have shown their unique advantages in many fields. With micelles as the mesoporous material assembly unit, precise regulation of mesoporous material structure can be achieved by controlling the micelle assembly process, assembly direction, and assembly interfacial effects. This has been the core of our team's research in recent years, producing a series of delicate mesoporous nanomaterials with various structures.
Water-oil bi-phase emulsion (also known as microemulsion) is a commonly studied system in fields such as catalysis and medicine. In recent years, microemulsions have started to receive special attention in the field of nanomaterials synthesis: the presence of emulsion droplets results in the appearance of many tiny "interfaces" in an otherwise homogeneous solution. Unlike the traditional solid-phase interface of nanomaterials, the dynamic nature of the emulsion droplet interface gives it more variability in the synthesis of nanomaterials and greatly enriches the possibilities of material synthesis. When combined with micelles and the assembly process of mesoporous material, the dynamic emulsion droplets lead to complex interfacial assembly behaviors and versatile mesoporous nanomaterials. However, because of the dynamic property, the synthesis system of emulsion-mediated assembly is complex and poorly controlled, and the related research is very limited.
Figure 1. Mechanism of the emulsion-orientated assembly process. Digital photos of the reaction solution a) before and b) after the addition of TMB. TEM images of the products obtained by directly dropping the reaction mixture on the copper mesh at c) 2 h, d) 4 h and e) 8 h. Schematic illustration of the emulsion-directed oriental assembly approach for the fabrication of the dual-mesoporous Janus MSN&mPDA double-spherical nanoparticles. Scale bar: 200 nm for c and d, 100 nm for e.
In this work, we pioneered an "emulsion-orientated interfacial assembly" strategy to synthesize asymmetric dual-spherical mesoporous nanomaterials with tunable mesopores (Figure 1). In the synthesis, we use the "capillary effect" of mesoporous particles to "anchor" the emulsion droplets to form a stable particle-droplet dual-spherical system, and then use the emulsion droplets to guide the directional assembly of micelles to produce dual-spherical asymmetric mesoporous nanomaterials. Throughout the synthesis, the mesoporous particles, emulsion droplets and micelles are interlinked to achieve a controlled emulsion-orientated interfacial assembly process and precise synthesis results.
Figure 2. Janus double-spherical MSN&mPDA nanoparticles with tunable large mesopores. TEM images of the mesoporous silica nanoparticles with different pore sizes (denoted as MSNx, x = pore diameter in nm), the mesoporous polydopamine nanoparticles with different pore sizes (denoted as mPDAy, y = pore diameter in nm) and dual-mesoporous Janus MSNx&mPDAy nanoparticles with varied mesopore diameter on both sides of the Janus nanoparticles. Scale bar: 50 nm.
Strategies such as modulation of synthesis conditions and direct observation by cryo-electron microscopy have been used to verify the emulsion-induced directed assembly process. By this particular synthesis process, we were able to achieve independent and extensive regulation of the pore size of the two units of the asymmetric dual mesoporous nanomaterials, which was not possible by previous synthesis methods (Figure 2). The discovery of this new synthesis method and the related emulsion-orientated synthesis process have opened up a whole new path for the synthesis of new nanomaterials. Meanwhile, relying on the obtained unique mesoporous silica & mesoporous polydopamine asymmetric nanoparticles, through a series of loading and modification, we have prepared the first single-particle level bionic logic gate with internal signal cascade transmission capability, laying the foundation for the next generation of smart nanomaterials.
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