Usually when we hear about liquids being 3D printed, we’re talking about liquid metal. But aside from 3D printed innovations only visible in water and using a 3D printer to create images with water, good old H2O has not exactly been at the forefront in the 3D printing world…until now. Researchers from the Lawrence Berkeley National Laboratory (Berkeley Lab), managed by the University of California for the US Department of Energy’s Office of Science, recently determined a way to 3D print structures that are made completely of liquid materials.

Tom Russell, a visiting faculty scientist in Berkeley Lab’s Materials Sciences Division, explained, “It’s a new class of material that can reconfigure itself, and it has the potential to be customized into liquid reaction vessels for many uses, from chemical synthesis to ion transport to catalysis.”

The team injects threads of water into silicone oil using a modified 3D printer, actually sculpting liquid tubes inside an additional liquid. Learning how to create liquid tubes inside another liquid, and then figuring out how to automate the process, were crucial advances in getting the method to work properly.

These schematics show the printing of water in oil using a nanoparticle supersoap. Gold nanoparticles in the water combine with polymer ligands in the oil to form an elastic film (nanoparticle supersoap) at the interface, locking the structure in place. [Image: Berkeley Lab]

Russell and Joe Forth, a postdoctoral researcher in the Materials Sciences Division, developed the material, and the findings were published in an article, titled “Reconfigurable Printed Liquids,” in the Advanced Materials journal; co-authors of the paper include Forth, Xubo Liu, Jaffar Hasnain, Anju Toor, Karol Miszta, Shaowei Shi, Phillip L. Geissler, Todd Emrick, Brett A. Helms, and Russell. The research effort was truly collaborative – Liu and Shi are from the Beijing University of Chemical Technology, while Miszta works with the Molecular Foundry at the Berkeley Lab, Geissler is with the University of California, Emrick is from the University of Massachusetts, and Forth, Hasnain, Toor, Helms, and Russell are all with the Berkeley Lab.

The abstract reads, “Liquids lack the spatial order required for advanced functionality. Interfacial assemblies of colloids, however, can be used to shape liquids into complex, 3D objects, simultaneously forming 2D layers with novel magnetic, plasmonic, or structural properties. Fully exploiting all‐liquid systems that are structured by their interfaces would create a new class of biomimetic, reconfigurable, and responsive materials. Here, printed constructs of water in oil are presented. Both form and function are given to the system by the assembly and jamming of nanoparticle surfactants, formed from the interfacial interaction of nanoparticles and amphiphilic polymers that bear complementary functional groups. These yield dissipative constructs that exhibit a compartmentalized response to chemical cues.”

The scientists first determine a method for sheathing tubes of water in a special nanoparticle-derived surfactant, which locks the liquid in place. The surfactant is basically soap, though the team refers to it as a nanoparticle supersoap because it so efficiently keeps the tubes from breaking up into droplets. Gold nanoparticles were dispersed into water, and polymer ligands into oil, to make the supersoap, and while the ligands and nanoparticles want to attach to each other, they also want to stay in their own mediums of water and oil; Helms helped to develop the ligands.

A highly branched, 3D printed liquid structure is imaged over the course of two months. The structure is approximately 5 cm long. Na-fluorescein (2 mg mL-1) was injected into each
end and intersection of the structures one day after printing to clarify structure.

Not long after the water is injected into the oil, dozens of ligands inside will, in practice, attach to individual nanoparticles in the water to form the supersoap. The supersoaps then hit each other vitrify, just like glass, which will stabilize the interface between the water and oil and secure the liquid structures in place.

“This stability means we can stretch water into a tube, and it remains a tube. Or we can shape water into an ellipsoid, and it remains an ellipsoid. We’ve used these nanoparticle supersoaps to print tubes of water that last for several months,” explained Russell.

To automate the process, Forth removed the extruder from an off-the-shelf 3D printer, and replaced it with a liquid-extruding syringe pump and needle.

“We can squeeze liquid from a needle, and place threads of water anywhere we want in three dimensions. We can also ping the material with an external force, which momentarily breaks the supersoap’s stability and changes the shape of the water threads,” Forth said. “The structures are endlessly reconfigurable.”

Generation of more complex 3D printed aqueous structures. (a) Composite
image of two interconnected spirals of opposing chirality (b) A nested structure of a
spiral within a vertical coil shown from two viewpoints. (c) A highly branched structure,
containing Na-fluorescein, 2 mg mL-1, to clarify the image.

Threads of water from 10 microns to 1 millimeter in diameter have been successfully 3D printed with the team’s method, along with several branching and spiraling shapes up to several meters long. Even better, the material is able to conform to its surroundings and change many times.

The research into the team’s 3D printable all-liquid material, which was funded by the DOE’s Office of Science, has many applications, such as chemical synthesis or liquid electronics that power flexible, stretchable devices. Additionally, the scientists believe they could chemically tune the liquid tubes to send molecules flowing through, which could introduce a new method for molecule separation.

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[Source/Images: Berkeley Lab]

 

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