Fig. 1

MNLP technique to engineer two-dimensional natural liquid foam for structuring materials. a Schematic of the microfluidic device in 3D view. The PDMS frame having microposts is covered with the through-hole PUA membrane. b Cross-sectional side view of the device. Liquid filled in the device (sky-blue) can be evaporated through the microholes. c Comparison between generation/dry processes of engineered 2D liquid foam (top, red) and natural 2D liquid foam (bottom, blue). Uniform pattern of liquid films in fourfold junctions are possible in the engineered form, being produced against Plateau’s law and without Ostwald ripening. The blue region is the liquid. The black-bold lines are liquid–air interfaces. The white circles in the blue region and within the black-bold lines are microposts and membrane holes, respectively, as indicated with red arrows. In the natural foam, green liquid films are in the T1 transition, and blue arrows describe the T2 transition. d SEM images of structured solid materials, in consequence of assembly process during evaporation of the engineered foam. The schematic of A–A′ cross-sectional side view depicts the principle of the MNLP process. The scale bars in top and those in bottom are 20 and 1 µm, respectively