The European and Singapore based researchers are excited about a new finding relating to spider silk and are discussing how the finding could lead to new ways to manipulate sound and heat, similar to the way that semiconductors work.
Semiconductors are key to modern electronics, being found in chips and transistors. Most semiconductors contain silicon and they function to conduct electricity under some conditions but not others. This makes them efficient media for the control of electrical currents.
Understanding how semiconductors work has been illuminated in recent years by advances in quantum mechanics. Essentially the movement of electrons is at the heart of the process. Researchers have now found that spider silk has a similar characteristic for transmitting particles. In this case the transmission is of phonons, which are quasiparticles of sound. While phonons relate to sound, they play a major role in many of the physical properties of condensed matter, including thermal conductivity and electrical conductivity.
The Rice University study has revealed spider silk to have a phonon band gap. Through this, it is possible to block phonon waves in certain frequencies. This is very much like an electronic band gap in a semiconductor which allows electrons to flow or to be blocked (a band gap is an energy range in a solid where no electron states can exist.) Phonons move like waves or vibrations. With the spider web, the researchers have termed this a “hypersonic phononic band gap in a biological material.”
Exactly why this gap appears in silk and the exact biological purpose it serves is unclear; although there is probably a connection with how a spider senses vibrations in the web structure when an insect becomes entangled within it. Different insects probably generate different sounds, and these will be distinct from a leaf or other inedible matter for the spider that might become entrapped within the web. By tuning into specific sounds and vibrations a spider can assess whether the item captured in the web is suitable prey or otherwise. Insights into the sonic signals of spider webs have come from the use of advanced techniques like laser vibrometry and ballistic impact.
What the researchers are running with is how this concept can be used with the development of electronics. Lead scientist Professor Edwin Thomas thinks the concept can be applied to different polymers, by replicating the crystalline microstructure of spider silk and provide enhanced sound or thermal insulation.
Phonons can also be manipulated. The waves scatter in different ways and it should be possible for different materials to have different phonic signatures. To examine this further, the research group conducted studies whereby they undertook light scattering experiments to test silk placed under varying degrees of stress. The method used for this is called Brillouin scattering. This technique refers to the interaction of light and material waves within a medium. Through this, the researchers found the pattern of the waves was location and heat dependent.
For example it was found that when silk was “super contracted,” the speed of phonons dropped by 15 percent; at the same time the bandwidth of frequencies blocked increased by 31 percent. Whereas, if the silk was altered differently the velocity increased by 27 percent, and the bandwidth decreased by 33 percent.
The consequences of this discovery are to try and replicate the effect in newly-fashioned materials in fiber form, which can be integrated into new electronic systems. An example polymer to try this with would be nylon (and this could lead into improvements with wearable electronics.)
The new research has been published in the journal Nature Materials. The study is headed “Nonlinear control of high-frequency phonons in spider silk.”
This article is part of Digital Journal’s regular Essential Science columns. Each week we explore a topical and important scientific issue. Last week we looked at how spider webs are inspiring research into next generation electronics. The week before we examined a new warning about cancer risks relating to drinking alcohol.
