Designer Engineered Materials
This stretchable, deformable patch-like structure houses an antennae designed to turn throat vibrations into a decipherable electric signal. The patch was manufactured using a direct-ink writing process, one of four additive manufacturing approaches being developed at Lawrence Livermore.
Cheng Zhu of Lawrence Livermore patterns a 3D micro battery structure with a direct ink writing system. Commercial additive manufacturing systems can at best fabricate single-material structures at resolutions of about 100 micrometers, compared with approaches being taken at Lawrence Livermore that can incorporate several materials into structures with feature sizes in the micrometer and even sub-micrometer range.
Airborne optical assemblies can be exposed to large temperature variations when fielded, which adversely affects alignment and focus of optical components. Lawrence Livermore is using a novel micro-stereolithography additive manufacturing approach to fabricate microlattice structures that counter this thermal expansion.
To counter thermal expansion, Livermore researchers are designing 3D microstructures, like the single cell and lattice in this illustration. Instead of expanding when heated, materials comprised of microstructures like this contract.
A purple catalyst-bearing droplet is suspended within a second clear droplet, using a microfluidic flow focusing technique. The clear fluid is designed to harden into a shell once cured with ultraviolet light, a design feature that makes it possible to turn these double emulsions into carbon capture micro-capsules.
While the clear shells of these micro-capsules have hardened with exposure to ultraviolet light, they have been designed to allow the catalyst-bearing purple fluid inside to absorb carbon dioxide from the air. As the capsules absorb carbon dioxide, they turn yellow to provide a visual cue that they are nearing saturation.
Engineering properties only previously theorized
Ever wonder why on hot days a door sticks in its jamb? The answer is thermal expansion, and it's one of the many material properties being designed into – or out of – a class of new materials at Lawrence Livermore National Laboratory.
Livermore materials scientists and engineers Chris Spadaccini, Joshua Kuntz, and Eric Duoss are developing a novel set of additive manufacturing techniques to fabricate materials with combinations of density, strength and thermal expansion properties that do not exist in nature.
Collaborating with partners at the University of Illinois, Harvard University, and MIT, the Livermore team is testing the boundaries of four additive micro-manufacturing techniques to fabricate three-dimensional (3D) microstructures with micrometer resolutions: Direct-ink writing, micro-stereolithography, electrophoretic deposition and microfluidic flow focusing.
Some materials designed with new additive manufacturing techniques exhibit high stiffness and low density, occupying a previously unpopulated area of the Ashby material selection chart for Young's modulus (stiffness) versus density. The octet truss structure recently fabricated by Livermore researchers is a stretch-dominated lattice.
"By controlling the architecture of a microstructure, we can create materials with previously unobtainable properties in the bulk form."
Chris Spadaccini
Designing new properties into materials
A material's properties and overall performance are determined by its chemical composition, crystalline state, and underlying microstructure – how the constituent elements within the material are arranged relative to one another.
"By controlling the architecture of a microstructure, we can create materials with previously unobtainable properties in the bulk form," says Spadaccini, who leads the effort.
These characteristics have forced scientists to accept certain trade-offs when choosing a material for a specific application. British materials engineer M. F. Ashby developed charts that provide selection guidance by categorizing materials such as metals, ceramics, polymers, and foams based on their properties in bulk form. An example chart comparing a material's stiffness (Young's modulus) with its density illustrates how the two properties are coupled, or linked, so that typically the denser a material is, the stiffer it is.
The collaborators are combining sophisticated computer modeling with these techniques, in projects funded by the Laboratory Directed Research and Development Program and the Defense Advanced Research Projects Agency, to develop a modeling capability that can design and predict the properties of micro-architected materials.
"Our goal is to use these techniques to effectively alter the chemical composition and crystalline state of materials at their microstructural level so we can control their properties and performance," says Kuntz, who leads the team's work on electrophoretic deposition.
Direct-ink writing
This animation shows a conductive ink "written" directly onto a semi-spherical substrate, in this case a glass dome.
Direct-ink writing is capable of creating micro- and macro-scale structures with extreme precision.
| How it works | Inks are deposited through one or more nozzles onto various substrates, creating a component layer by layer with a continuous filament. The patterns it generates range from simple, one-dimensional wires to complex, 3D structures. The nozzles are attached to print heads, which are mounted to a computer-controlled translation stage. Filament diameter is determined by nozzle size, print speed, and rates of ink flow and solidification. The time required to build a final part is determined by the distance from the nozzle to the substrate and by print speed. |
| Characteristics | Direct-ink writing is capable of creating micro- and macro-scale structures with extreme precision. It works well with a variety of materials, but does not offer the same 3D capability as projection micro-stereolithography. This approach also is capable of building void space within components during fabrication. The finest feature size obtained with this technology is approximately 200 nanometers — smaller than the features produced with projection microstereolithography. Recently, the team constructed two direct ink-writing platforms that can travel 30 centimeters at up to 10 centimeters per second while maintaining micrometer and submicrometer resolution. |
| Applications | This technique is being used to engineer embedded sensors, polymer lattice ordered foams, unique radio frequency components, and stretchable conductive inks. |
Micro-stereolithography
This animation shows the fabrication of an octet truss microlattice using micro-stereolithography.
Micro-stereolithography can reliably create structures in three dimensions at high speeds.
| How it works | Two-dimensional images are projected on a digital photomask made from a micromirror or liquid crystal on a silicon chip. An ultraviolet light-emitting diode illuminates the miniature display, which reflects light and an image of the component to be fabricated through a series of reduction optics onto a photopolymer liquid resin. As the resin cures, it hardens into the shape of the image. The substrate holding the resin is then lowered using a motion-controlled stage, and the next 2D slice is processed. |
| Characteristics | Micro-stereolithography can reliably create structures in three dimensions at high speeds in both macro and micro scales. But it is, so far, compatible with only a few materials. This approach is capable of building void space within components during fabrication. The quality of the component depends on the light uniformity and optical resolution. |
| Applications | This novel technique is being used to engineer materials with ultra-high stiffness for their weight for aerospace applications, as well as zero- and negative-thermal-expansion materials for precision alignment of optics deployed in environments with large temperature variations. |
Electrophoretic deposition
This animation shows how nanoparticles within a solution are drawn to the 2D pattern of an electrode pattern.
Electrophoretic deposition can incorporate multiple materials into one structure with extreme precision.
| How it works | An electric field is applied in a 2-dimensional pattern to a liquid medium that contains suspended colloidal nanoparticles. The induced surface charge causes the particles within the liquid to travel parallel to the electric field, attracting the suspended particles to collect along the pattern on the substrate electrode. The pattern is then altered to build additional layers and complex 3D components. The process is similar to the technique used for creating protective or performance-enhancing coatings, but using electrophoretic deposition to achieve 3D geometries is a novel concept. |
| Characteristics | Electrophoretic deposition can incorporate multiple materials into one structure with extreme precision. It also carries the potential for large-scale production, but it does not offer the same 3D capability as projection micro-stereolithography. To create void space with this approach, excess material must be designed into the fabricated component and later burned out. The team has built 2D structures with resolutions smaller than 7 micrometers and horizontal gradients of about 1 micrometer. |
| Applications | This novel technique is being used to manufacture layered structures for superlight armor, as well as transparent ceramics for optics. |
