Foam, which is used in industries ranging from packaging and aerospace to infrastructure and sports, can be 3D printed, which can provide better durability and long-term mechanical performance than foam products made with conventional methods of manufacturing. Last year, researchers from Rice University figured out how to manufacture strong, lightweight graphene material in bulk by producing graphene foam, and have now developed a simple new method for making conductive 3D objects, using graphene foam, that can be shaped for a variety of applications.

This technique is a continuation of the university’s innovative work from 2014, which resulted in the first production of laser-induced graphene, or LIG, which can be made at room temperature in macroscale patterns. A laser is used to heat sheets of inexpensive polyimide plastic – it burns halfway through, turning the top layer into flakes of interconnected 2D carbon that continue to stay attached to the bottom half.

According to James Tour, a chemist at Rice, while the team was able to create LIG on food and wood, 3D objects made of pure graphene were not practical at the time.

a-b: LIG/PDMS composite. c-d: LIGF/PDMS composite. By SEM, all voids inside the LIG foam appear filled with PDMS.

“Now we have built a prototype machine that lets us make graphene foam into 3D objects through automated successive layering and laser exposure. This truly brings graphene into the third dimension without furnaces or the need for metal catalysts, and our process is easily scaled,” explained Tour.

Making 3D LIG foam through an automated process.  [Image: Tour Group]

The 3D solids created with the new method may feel squishy and insubstantial, but actually introduce new possibilities for flexible electronic sensor and energy storage applications. The technique is based on laminated object manufacturing, which involves assembling layers of a material and cutting them into a desired shape with a laser cutter.

The researchers recently published a paper on their work, titled “Laminated Object Manufacturing of 3D-Printed Laser-Induced Graphene Foams,” in the journal Advanced Materials. The research was supported by the Vietnam Education Foundation and the Air Force Office of Scientific Research.

The abstract reads, “Laser‐induced graphene (LIG), a graphene structure synthesized by a one‐step process through laser treatment of commercial polyimide (PI) film in an ambient atmosphere, has been shown to be a versatile material in applications ranging from energy storage to water treatment. However, the process as developed produces only a 2D product on the PI substrate. Here, a 3D LIG foam printing process is developed on the basis of laminated object manufacturing, a widely used additive‐manufacturing technique. A subtractive laser‐milling process to yield further refinements to the 3D structures is also developed and shown here. By combining both techniques, various 3D graphene objects are printed. The LIG foams show good electrical conductivity and mechanical strength, as well as viability in various energy storage and flexible electronic sensor applications.”

The bottom LIG layer stays attached to the polyimide base, while another layer is coated with ethylene glycol and placed facedown on the first layer. Then, the polyimide top is burned into graphene, and the process is repeated until a 3D block has been created. The ethylene glycol binder is evaporated on a hot plate, while any polyimide that’s left is removed in a furnace, which leaves a spongy, pristine carbon block.

Rice University scientists have layered LIG and built a prototype that shapes the resulting 3D blocks into sophisticated shapes. [Image: Tour Group]

After stacking up to five layers of foam, the team milled this block into a variety of complex shapes using a custom-built fiber lasing system on a modified 3D printer. They developed proof of concept lithium-ion capacitors, which used 3D LIG as cathodes and anodes. The cathode’s gravimetric capacity exceeded the average of other carbon materials, and the anode’s 354 milliamp hours per gram capacity was close to graphite’s theoretical limit. Better still, after nearly 1,000 charge-discharge cycles, the full test cells still retained roughly 70% of their capacity.

Tour said, “This is excellent performance in these new-generation lithium-ion capacitors, which capture the best properties of lithium-ion batteries and capacitor hybrids.”

Rice graduate student Duy Xuan Luong suspends a 3D block of LIG atop two willows.

In order to make a stronger conductive material that was still flexible, without changing the shape of the original foam, the researchers infused a block of 3D LIG with liquid polydimethylsiloxane through its 20- to 30-nanometer pores. Using this material, they were able to successfully create a flexible sensor that could accurately record a volunteer’s pulse from their wrist.

In addition, the team also explained that if they were able to calibrate the device even further, they would be able to use it to “extract blood pressure from the pulse waveform.”

Co-authors of the paper include Rice graduate student Duy Xuan Luong, Rice alumnus Ajay K. Subramanian; Rice graduate student Gladys A. Lopez Silva; former postdoc researcher Jongwon Yoon; Rice undergraduate student Savannah Cofer; Rice graduate students Kaichun Yang, Peter Samora Owuor, Tuo Wang, and Zhe Wang; Jun Lou, a professor of materials science and nanoengineering; chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and professor of chemistry Pulickel M. Ajayan; and Tour.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below. 

[Source: Rice University]

 

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