In addition to being one of the most coveted precious metals available, gold is known to have several applications in electronics and scientific research. In the past, researchers have used gold nanoparticle-based electronic skin to detect breast cancer. As part of a recent project, a team of scientists at ETH Zurich has developed a type of gold foam that is as light as air and, actually floats on cappuccino. Composed of up to 98-parts air, this three-dimensional mesh contains a lot of pores and even looks like real gold. What is more, it is also available in other colors, primarily dark red.
Like conventional gold, the aerogel possesses a bright metallic shine. Unlike the former, however, it is soft and indeed quite malleable to be shaped by hand. Apart from air, the material contains four-fifths of actual gold and another one-fifth of milk protein fibrils. According to the researchers, this amounts to a purity of around 20 carats. Speaking about the research, recently published in the Advanced Materials journal, Raffaele Mezzenga, a professor of Food and Soft Materials, says:
The so-called aerogel is a thousand times lighter than conventional gold alloys. It is lighter than water and almost as light as air.
To produce the foam, the researchers first heated milk proteins to create minute protein fibers, known as amyloid fibrils. By placing the fibers in a solution of gold salt, the team caused them to interlace into a complex three-dimensional lattice-like structure. Subsequently, the salt crystallized into tiny particles, which in turn got implanted into the fibril network. When drying the resultant gel-like substance, the scientists had to opt for a gentler and more labor-intensive procedure, based on the use of carbon dioxide.
This is because regular air drying is harsh, and would likely damage the delicate foam structure. As Gustav Nyström, a postdoctoral scholar in Mezzenga’s team and the study’s first author, explains, the optical properties of gold (as in color and luster) depend greatly on the size and shape of its constituent particles. Therefore, by changing the reaction conditions of the process, the researchers were also able to produce smaller nanoparticles, which in turn impart a dark red color to the foam.
According to Mezzenga, the new material could be used as a substitute for conventional gold alloys, in scientific research and experiments. Thanks to its impressive properties, including extremely light weight, porosity and smaller material requirement, the substance has several advantages, and can actually be used in watches and jewelry. Furthermore, its highly porous surface could make certain chemical reactions much more efficient. One major application pertains to the production of advanced pressure sensors. Mezzenga adds:
At normal atmospheric pressure the individual gold particles in the material do not touch, and the gold aerogel does not conduct electricity. But when the pressure is increased, the material gets compressed and the particles begin to touch, making the material conductive.
Source: ETH Zurich