Fig.1 Regulation of meso-scale structures of emulsion droplets during their trans-interfacial transfer process. (a) Schematic illustration of the trans-interfacial transfer process of an emulsion droplet[21]. (b) Schematic illustration of the trans-interfacial transfer of aqueous droplets (W1) from continuous oil phase (O1) to continuous water phase (W2), and the aggregation meso-scale structures of amphiphilic molecules at the droplet interface[21]

Fig.2 Regulation of meso-scale structures of emulsion droplets during their coalescence process. Packing structures of fluorescent PNIPAM nanoparticles on the equator (a) and the top (b) of a droplet at different temperatures[17]. (c) Packing structural change of fluorescent PNIPAM nanoparticles at droplet interface during the temperature-triggered coalescence process[17]. (d) Schematic illustration showing the metal-microneedle-induced coalescence of emulsion droplets in T-junction microchannels[18]. High-speed snapshots showing the metal-microneedle-induced coalescence between two single emulsion droplets (e), and between one single emulsion droplet and one double emulsion droplet (f)[18]

Fig.3 Regulation of meso-scale structures of emulsion droplets during their wetting-induced engulfment and dewetting-induced evolution processes. (a) Schematic illustration showing the formation of double emulsion droplets from selective wetting-induced engulfment between single emulsion droplets[20]. High-speed snapshots showing the formation process of single-core double emulsion droplets (b), multi-core double emulsion droplets (c), and triple emulsion droplets (d) via wetting-induced engulfment[20]. (e) Schematic illustration showing the dewetting-induced evolution from spherical core-shell double emulsion droplets to non-spherical acorn-like emulsion droplet[22]

Fig.4 Regulation of the meso-scale structures of microparticles via trans-interfacial mass transfer and self-assembly. Schematic illustrations showing the synthesis of solid (a) and hollow (b) PAH/PSS polyelectrolyte microparticles from W/W emulsion templates via controllable trans-interfacial mass transfer and self-assembly[23]. (c) Schematic illustrations showing the synthesis of solid Au-nanoparticle/PSS microparticles from W/W emulsion templates via controllable trans-interfacial mass transfer and self-assembly[37]. (d) SEM image of the solid nanoparticle/PSS microparticle[37]. (e) Optical microscopic snapshots showing the fabrication process of Au-nanoparticle/PSS microparticle[37]

Fig.5 Regulation of the meso-scale structures of hollow microparticles via trans-interfacial mass transfer and reaction. (a) Schematic illustrations showing the synthesis of hollow chitosan microparticles from W/O emulsion templates via trans-interfacial mass transfer and crosslinking reaction[25]. (b) — (d) Confocal laser scanning microscope images of hollow chitosan microparticles with different structures from regulation of trans-interfacial mass transfer and reaction[25]

Fig.6 Regulation of the meso-scale structures of porous microparticles via trans-interfacial mass transfer and reaction. (a) — (d) Schematic illustrations showing the synthesis of bubble-propelled porous microparticles via creation of water nanodroplets in emulsion droplets as pore-forming templates induced by trans-interfacial mass transfer[41]. (e) Schematic illustrations showing the bubble-propelled porous microparticles for efficient degradation of organic pollutants in water based on coupling mass-transfer intensification of bubble-propelled motion and photo-catalytic degradation of ZIF-8@ZnO[41]

Fig.7 Regulation of the meso-scale structures of hierarchical porous microparticles via trans-interfacial mass transfer and reaction. (a) Schematic illustrations showing the synthesis of hierarchical porous microparticles from W/O/W double emulsions via trans-interfacial mass transfer and reaction[39]. SEM images of bubble-propelled hierarchical porous microparticles[40] (b), and hierarchical porous microparticles integrated with MIL-88A nanoparticles (c)[42]