Reconfigurable droplet networks

Abstract

Droplet networks stabilized by lipid interfacial bilayers or colloidal particles have been extensively investigated in recent years and are of great interest for compartmentalized reactions and biological functions. However, current design strategies are disadvantaged by complex preparations and limited droplet size. Here, by using the assembly and jamming of cucurbit[8]uril surfactants at the oil-water interface, we show a novel means of preparing droplet networks that are multi-responsive, reconfigurable, and internally connected over macroscopic distances. Openings between the droplets enable the exchange of matter, affording a platform for chemical reactions and material synthesis. Our work requires only a manual compression to construct complex patterns of droplet networks, underscoring the simplicity of this strategy and the range of potential applications.

Fig. 1. Background introduction and our strategy for preparing droplet networks.

Schematics showing the formation of (a) droplet networks by DIB technique and (b) interpenetrating droplet networks by CB[8] surfactants.

Fig. 2. The formation, assembly, and jamming of CB[8] surfactants at the oil-water interface.

a Time evolution of IFT for water & toluene, CMC-MV²⁺⊂CB[8] & toluene, water & Azo-PLLA, and CMC-MV²⁺⊂CB[8] & Azo-PLLA. b Schematic representation of a. c Morphology evolution of the pendent droplet with wrinkles on the surface. d A series of snapshots showing the shape evolution of a pendent droplet in an extraction–reinjection process. From a–d: [CMC-MV²⁺] = 0.5 mg mL⁻¹, [CB[8]] = 0.25 mg mL⁻¹, [Azo-PLLA] = 0.5 mg mL⁻¹. e Storage and loss dilatational moduli of CB[8] surfactant-based interfacial assemblies; [CMC-MV²⁺] = 0.3 mg mL⁻¹, [CB[8]] = 0.15 mg mL⁻¹, [Azo-PLLA] = 0.5 mg mL⁻¹, ω = 0.01–1 Hz. f AFM height image of the 2D film transferred from the interface and (g) line cut analysis of the film edge on the silicon substrate; [CMC-MV²⁺] = 0.5 mg mL⁻¹, [CB[8]] = 0.25 mg mL⁻¹, [Azo-PLLA] = 0.5 mg mL⁻¹.

Fig. 3. Multiple responsiveness of CB[8] surfactants.

a Schematics showing the assembly and disassembly of CB[8] surfactants at the oil-water interface. b Morphology evolution of the pendent droplet under UV light or visible light. c Time evolution of IFT in a redox process. d Snapshots of droplet’s morphology upon compression in a redox process. e Equilibrium IFT and surface coverage with the introduction of AdH in the aqueous phase. f Snapshots of droplet’s morphology upon compression at different concentrations of AdH. [CMC-MV²⁺] = 0.5 mg mL⁻¹, [CB[8]] = 0.25 mg mL⁻¹, [Azo-PLLA] = 0.5 mg mL⁻¹.

Fig. 4. Interpenetrating droplet networks stablized by CB[8] surfactants.

Optical images showing the process of contact and squeeze of two droplets (a) in different direction and (b) at different assembly time; In all above cases, the partial fusion behavior of two droplets can be observed; [CMC-MV²⁺] = 0.5 mg mL⁻¹, [CB[8]] = 0.25 mg mL⁻¹, [Azo-PLLA] = 0.5 mg mL⁻¹. c The effect of concentrations of CMC-MV²⁺, CB[8] and Azo-PLLA ([CMC-MV²⁺]: [CB[8]] = 2: 1) on arresting the coalescence of droplets (hollow symbols: complete fusion; solid symbols: partial fusion). d Optical images showing the partial fusion of droplets by using different CB[8] surfactant systems; [CMC-MV²⁺] = 0.5 mg mL⁻¹, [PEI-MV²⁺] = 0.5 mg mL⁻¹, [HA-MV²⁺] = 0.5 mg mL⁻¹, [CB[8]] = 0.25 mg mL⁻¹, [Azo-PLLA] = 0.5 mg mL⁻¹, [Nt-PLLA] = 0.5 mg mL⁻¹, [Py-PLLA] = 0.5 mg mL⁻¹. e Schematics showing polymer networks at the oil-water interface. f The diffusion of dye within the droplet pair; [Amaranth] = 0.5 mg mL⁻¹. g The mixture of primary colors within the droplet networks and the destruction of the droplet networks by adding reductant or competitive guest; [Sodium fluorescein] = 0.5 mg mL⁻¹, [Amaranth] = 0.5 mg mL⁻¹, [Nile blue A] = 0.5 mg mL⁻¹, [Na₂S₂O₄] = 2.0 mg mL⁻¹, [AdH] = 2.0 mg mL⁻¹. h Optical images of the formation-separation-reformation of droplet network for several times.

Fig. 5. Microreactors based on droplet networks.

a, b Schematics and optical images showing the chromogenic reaction for Fe³⁺ + 3SCN⁻ = Fe(SCN)₃ within the droplet networks. c, d Schematics and optical images showing the synthesis of ZIF-67 within the droplet networks. e, f Schematics and optical images showing the cascade enzymatic reaction within the droplet networks. [CMC-MV²⁺] = 1.0 mg mL⁻¹, [CB[8]] = 0.5 mg mL⁻¹, [Azo-PLLA] = 1.0 mg mL⁻¹, [Fe³⁺] = 0.1 mg mL⁻¹, [SCN⁻] = 0.3 mg mL⁻¹, [Co²⁺] = 0.1 mg mL⁻¹, [2-MI] = 0.5 mg mL⁻¹, [Glucose] = 0.1 mg mL⁻¹, [GOD] = 0.01 mg mL⁻¹, [HRP] = 0.01 mg mL⁻¹, [OPDA] = 0.1 mg mL⁻¹.

Fig. 6. Complex patterns of droplet networks.

a, b Schematics and optical images showing Tetris composed of droplet networks. c Optical images showing the transmission of a dye solution within the linear droplet network channel; [Amaranth] = 1.0 mg mL⁻¹. d Schematic showing the “Y” type of droplet network channels. e Optical images showing the transmission of three different kind of dye solutions within the “Y” type of droplet network channels; [Amaranth] = 1.0 mg mL⁻¹, [Nile blue A] = 1.0 mg mL⁻¹, [Sodium fluorescein] = 1.0 mg mL⁻¹.