Dutch College Students Use Gold Nanoparticles to Print Color Change Cup in 3D
Vittorio Saggiomo and his colleagues from Wageningen University in the Netherlands learned about the optical effects and developed a method of printing gold nanoparticles in 3D to create objects with dichroic properties. Material with dichroism can be traced back at least to the Lycurgus cup (possibly accidentally) made in the 4th century. Glass containers show opaque green when illuminated from the front and translucent red when illuminated from the back. This effect is caused by slender gold and silver nanoparticles that reflect light at certain wavelengths while transmitting other wavelengths, although the manufacturers of Lycurgus cups may not know this, but add metal powder to make the glass more glossy.
Researchers began to use an improved version of Turkevich's method to create dichroic solutions, using citrate to reduce gold ions to gold nanoparticles. The solution undergoes several temporary color changes, initially from yellow to blue, then several minutes later, it turns dark black, and finally settles on a dichroic opaque brown/transparent purple.
The experiment pointed out: "Time-dependent studies have shown that the formation of small gold nuclei gathers in time to form nanowire structures associated with the first color change. The second color change, from black to purple, accompanied by enhanced scattering, makes the purple solution brown reflection. While boiling, the gold nanowires fragmented to form nanoparticles with large heads and slender tails, similar to tadpoles. As time goes on, the tail begins to shrink. "
They then injected a solution of dichroic gold nanoparticles into polyvinyl alcohol (PVA), a plastic that is usually used to produce support when it dissolves in water during 3D printing. Extruding plastic into filaments can be used in any standard FDM 3D printer. The 3D parts printed in the material look brown, with light shining in front, but a lamp behind it turns transparent purple.
The effect of Turkevich method is a well studied phenomenon. This is one of the lovely events that physics and chemistry meet. Combining light bending with 3D printing will certainly bring some new attention to the old techniques, especially since only a small amount of gold nanoparticles is needed to achieve the effect. In addition to finding appeal among artists, dichroic plastics can also be used for 3D printing optics and sensors.