Liquid Printing in Nanochitin Suspensions: Interfacial Nanoparticle Assembly Toward Volumetric Elements, Organic Electronics and Core-Shell Filaments

Abstract

A nanoparticle-nanoparticle assembly is introduced using electrostatic complexation to precisely control volumetric structuring at the water/alcohol interface. In this system, an aqueous graphene oxide (GO) ink interacts electrostatically with partially deacetylated chitin nanofibers (mChNF), modified with benzophenone and dispersed in 1-butanol, which serves as the external phase. Upon extrusion of the GO ink, a jammed interfacial network forms, stabilizing the printed patterns within the external suspension, which provides suitable viscoelasticity for support-free printing. This approach is further extended to inks incorporating metal-organic frameworks or cellulose nanoparticles, demonstrating the advantages of mChNF as a stabilizer. Additionally, by incorporating a conductive polymer, the inks can be tailored for programmable and conductive patterning, opening new opportunities in liquid electronics and reconfigurable systems. Finally, GO inks containing an anionic polyelectrolyte (sodium alginate) undergo osmosis-driven solidification, facilitating the demolding of high-fidelity 3D structures formed by the printed threads of struts. These structures exhibit coreshell morphologies and high mechanical strength (∼175 MPa at 4% strain). Overall, this liquid-in-liquid fabrication approach, enabled by the integration of mChNF in the external phase, unlocks new possibilities for the design of versatile and multifunctional materials.

Keywords: core–shell filaments; high‐resolution extrusion; liquid‐in‐liquid printing; nanoparticle interfacial assembly; partially miscible interfaces.

Figure 1

Photos showing the jetting of 1 mg mL⁻¹ GO aqueous suspension into a) hexane, b) 1‐butanol, and c) 1‐butanol containing 1 mg mL⁻¹ mChNF. Scale bare = 2.8 cm. The photos of liquid filaments after shaking are shown at the bottom of the images. Schematic illustrations of GO‐mChNF nanoparticle‐nanoparticle formation in the 1‐butanol external phase d) and the interaction of chitin nanofibers with GO at the interface e). Contraction of an aqueous GO pendant drop in f) hexane, g) 1‐butanol, h) 1‐butanol with 1 mg mL⁻¹ mChNF, and j) an aqueous GO at pH≈2 (below the pKa of carboxylic acid) pendant drop in 1‐butanol with 1 mg mL⁻¹ mChNF.

Figure 2

a) Flow curves showing the shear‐thinning behavior of mChNF/1‐butanol with varying mChNF concentrations (1–10 mg mL⁻¹). b) Storage (G′) and loss (G″) moduli as a function of angular frequency for mChNF/1‐butanol at different concentrations. c) Photos of 10 mg mL⁻¹ GO aqueous ink printing into mChNF/1‐butanol with mChNF concentrations of (I) 1, (II) 2, and (III) 5 mg mL⁻¹, demonstrating that higher mChNF concentrations (5 mg mL⁻¹) stabilize the printed structures, Scale bars = 1 cm. (d) GO ink printed into 5 mg mL⁻¹ mChNF/1‐butanol, shown from a side view (I) and top view (II), demonstrating the role of external phase viscoelasticity in maintaining structural integrity in volumetric designs. Scale bars = 2 cm.

Figure 3

a,b) Liquid‐in‐liquid printing of a 10 mg mL⁻¹ GO aqueous suspension using a 27‐gauge needle into a mChNF/1‐butanol external phase with 5 mg mL⁻¹ mChNF. c) Polarized optical microscopy image of a liquid thread printed with a 27‐gauge needle. Width variation of printed samples using d) 27‐gauge and e) 16‐gauge needles, with GO and mChNF external phase concentrations of 10 and 5 mg mL⁻¹, respectively. Structures printed with f) GO/MOF303, g) GO/CNC, h) GO/CNF, and i) GO/PEDOT, each with a 10 mg mL⁻¹ ink concentration (50% GO, 50% listed material). Scale bars in (a–c) = 1.9, 1.6, and 0.5 cm; (f–i) = 3.4 cm.

Figure 4

Demonstration of an all‐liquid electric switch using GO/PEDOT:PSS printed conductive pathways in mChNF external phase. a) The circuit in the ON state, where the LED is illuminated, indicates current flow through the conductive path. b) The circuit in the OFF state, where a disconnection in the printed path stops the current, turning off the LED. c) Sensor data showing the connection and disconnection process. d) Printed structure functioning as a switch through movement of the printed liquid. e) Repairability sequence: (I) circuit ON, (II) disconnection causing LED to turn OFF, (III) repair by injecting conductive ink, and (IV) circuit reactivated, demonstrating the switch's repeatability and repairability. Scale bars in (a), (a,b), (d), and (e) = 1, 0.5, and 1.2 cm, respectively.

Figure 5

a) Schematic illustration of the interactions between GO/sodium alginate in an aqueous suspension that is extruded in mChNF/1‐butanol. b) Optical microscopy images showing water removal and solidification of GO/sodium alginate filaments at 1 and 15 min post‐printing (Scale bar = 0.5 cm). c) Solidified GO/sodium alginate filaments removed from the external phase (Scale bar = 5.1 cm), d) dried at RT while retaining shape (220 µm diameter, Scale bar = 3.5 cm), and e) demonstrating mechanical robustness by supporting a 25‐g load without structural failure (Scale bar = 2.3 cm). f) Volumetric liquid‐in‐liquid printing of cylindrical shape and demolding of printed structure. g) Volumetric printing of rectangular shape and h) de‐molded of solidified structure (Scale bars in (f–h) = 1 cm).

Figure 6

SEM images illustrating the morphology of GO/sodium alginate filament shells a–d), with mChNF pinned at the interface due to GO‐mChNF assembly and jamming. The filament core exhibits a distinct morphology from the shell. e) High‐resolution CT scans confirm a core–shell configuration, with a compact, dense shell surrounding a less dense core. f) GIWAXS and GISAXS data for the filament. Scale bars in (a), (b–d), and (c) = 100 µm, 300 nm, and 4 µm, respectively.