When it comes to 3D printing, the sky is the limit. As 3D printing technology continues to advance, applications can be as far reaching as airplane and automobile parts to medical devices and even anatomically correct, biocompatible models. Although 3D printing technology is developing at a rapid pace, the technology itself is not new. It emerged in the 1980s as a means of creating rapid prototypes. In recent years the applications for 3D printed models have evolved with the available hardware, software, and printable materials. Evolving technology, paired with the creative and innovative minds of scientists, engineers, and physicians, has been the launching pad for developments within 3D printing technology specific to healthcare. One way 3D printing technology is poised to create better patient outcomes is in creating an anatomically and patient-specific models to aid in surgery and medical procedures. With the capability to 3D ...
A new material inspired by the structure of natural gemstones has many properties its earthy counterparts do not.
Opals, which are among the most vividly colored materials in nature, obtain their colors from the reflection of light. Based on this property, the polymer opal, created by researchers from the Fraunhofer Institute for Structural Durability and System Reliability and University of Cambridge, is a flexible, colorful material that will not fade over time and that changes color when stretched.
Natural Opals
Opals form in nature when water evaporates, leaving behind tiny silica spheres. These deposits are suspended in the earth and are ordered so that the spheres diffract the visible light, which cause the beautiful, intense colors in the gems. In polymer opals, silica is replaced by nanoparticles with a rubbery outer shell.
The researchers explain:
Gemstone opals achieve their structure by the regular stacking of perfectly round glass spheres. Polymer opals also consist of ordered spheres. Using clever chemistry similar to that used in the production of latex paints, a mass of nearly identical spheres for polymer opals are synthesised with a hard central core of crosslinked polystyrene, bonded to a soft outer shell of polyethylene acrylate that has the consistency of chewing gum.
Synthetic Opals
Although synthetic opals were first made in the 1970s, they are typically brittle and, add the researchers, aren’t suited for mass market applications.
To make these new synthetic opals, the researchers expose the spheres to high temperatures, which causes them to self-assemble into a 3D crystal with structural color. Structural color refers to a color in both nature and synthetics created by diffraction. This includes peacock feathers, butterfly wings, or photonic crystals.
At these temperatures, the soft outer shells deform while the central core material becomes ordered. This regular pattern diffracts lights. In other words: the internal structure produces the color; the outer shell provides it with its elastic properties.
The precise color of the polymer opal is based on the nanoparticle size. There are small (171 nm), medium (191 nm), and large (266 nm) particles that produce blue, green, and red opals.
Changing Colors
Polymer opals can temporarily change color by deforming — that is, stretching or twisting — the material. Such deformation causes the color to change based on the space between particles changing. This change alters the wavelength at which the material reflects light. Stretching, for example, causes a green sample opal to become blue when stretched; a blue sample becomes green when compressed. These color shifts can be temporary. This property could be ideal for use in strain sensors. Such color changes should be able to show the level of stress an item attached to the material is undergoing.
Possible Applications
The colorfast nature of this material would be attractive in fabrics, as the polymer opal material could replace toxic dyes. Additionally, the color wouldn’t fade or run.
Another possible application: an alternative to holograms used in paper currency to prevent counterfeiting. The color-changing properties are difficult, but inexpensive to reproduce.
The researchers add:
A real advance is that we can make these photonic crystals by standard plastic manufacturing techniques. They are flexible, making them some of the most durable opalescent materials available, and they are suited for mass production and incorporation into consumer items.
The researchers are working to commercialize the material; however, the polymer opals are already being used in creative ways. London-based designer Rainbow Winters included fabrics based on the material at a fashion show in Paris. They also have applications in both security and sensing applications.
Among the future research they are exploring includes producing a single sheet in which there are different colors on different areas of the sheet rather than a single, uniform color.
Jeremy Baumberg, professor of nanophotonics in the University of Cambridge, department of physics, concludes:
The crucial thing is that by assembling things in the right way you get the function you want. […] It’s such a good example of nanotechnology — we take a transparent material, we cut it up in the right form, we stack it in the right way and we get completely new function.
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