Self-Assembly of TiO2 Nanofiber-Based Microcapsules by Spontaneously Evolved Multiple Emulsions.

We demonstrate hierarchical nest/crust-like colloidosomes composed of interlocked titanium dioxide (TiO2) nanofibers using spontaneously evolved n-butanol/water/ n-butanol (B/W/B) emulsions. We find two mechanisms to produce colloidosomes from B/W/B droplets due to their mutual solubility and dewetting discrepancy. Porous TiO2 colloidal capsules with loosely intertwined nanofibers were obtained after the dewetting of nanofiber-coated B/W/B droplets, while crustlike TiO2 colloidosomes with a thin shell and large hollow interior are developed from amphiphilic polymer-stabilized B/W/B droplets. We further investigate the effect of experimental parameters, including the initial droplet size, the nanofiber concentration, and the water/butanol ratios in butanol phases, on the droplet-to-colloidosome evolution and resultant morphology of colloidosomes. Our simple and versatile approach for fabricating TiO2 colloidosomes can be extended to a range of irregular colloidal particles, and the products have great potential to act as host systems in electrochemical catalysis, photothermal therapy, or filtration materials.

Spreading-induced dewetting for monolayer colloidosomes with responsive permeability.

Herein, we present a spreading-induced dewetting approach of Pickering emulsion droplets for fabricating monolayer colloidosomes. The dewetting of the water-in-oil-in-water (W/O/W) double emulsion droplets is triggered by the quick spreading and wetting of the fluorinated oil phase on the water/air surface. By combining this colloidosome formation mechanism with thermo-responsive copolymer that adsorbs or desorbs at the surface of the colloidosome shell, we fabricated smart monolayer colloidosomes using a microfluidic-templated approach. These colloidosomes are highly monodisperse and possess a well-defined shell microstructure, tunable permeability, biocompatibility, mechanical stability, and high encapsulation efficiency. These attributes will pave the way for effective encapsulation, transport, and release of a range of active ingredients, especially the biologically active materials.

Droplet Breakup in Expansion-contraction Microchannels.

We investigate the influences of expansion-contraction microchannels on droplet breakup in capillary microfluidic devices. With variations in channel dimension, local shear stresses at the injection nozzle and focusing orifice vary, significantly impacting flow behavior including droplet breakup locations and breakup modes. We observe transition of droplet breakup location from focusing orifice to injection nozzle, and three distinct types of recently-reported tip-multi-breaking modes. By balancing local shear stresses and interfacial tension effects, we determine the critical condition for breakup location transition, and characterize the tip-multi-breaking mode quantitatively. In addition, we identify the mechanism responsible for the periodic oscillation of inner fluid tip in tip-multi-breaking mode. Our results offer fundamental understanding of two-phase flow behaviors in expansion-contraction microstructures, and would benefit droplet generation, manipulation and design of microfluidic devices.