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Tuesday, July 26, 2016

Hooked on Phononics: Spider Silk Sound and Heat

      New discoveries about spider silk could inspire new materials to manipulate heat and sound in the same way semiconducting circuits manipulate electrons, according to scientists at Rice University.

      A paper published yesterday in Nature Materials looks at the microscopic structure of spider silk and reveals unique characteristics in the way it transmits phonons, quasiparticles of sound.

      A phonon (cool moving graphic at this link) is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids. It represents an excited state in the quantum mechanical quantization of the modes of vibrations of elastic structures of interacting particles.

     The research shows for the first time that spider silk has a phonon band gap. That means it can block phonon waves in certain frequencies in the same way an electronic band gap -- the basic property of semiconducting materials -- allows some electrons to pass and stops others.

     The researchers wrote that their observation is the first discovery of a "hypersonic phononic band gap in a biological material."

      How the spider uses this property remains to be understood, but there are clear implications for materials, according to materials scientist and Rice Engineering Dean Edwin Thomas, who co-authored the paper. He suggested that the crystalline microstructure of spider silk might be replicated in other polymers. That could enable tunable, dynamic metamaterials like phonon waveguides and novel sound or thermal insulation, since heat propagates through solids via phonons.

     "Phonons are mechanical waves," Thomas said, "and if a material has regions of different elastic modulus and density, then the waves sense that and do what waves do: They scatter. The details of the scattering depend on the arrangement and mechanical couplings of the different regions within the material that they're scattering from."

       Spiders are adept at sending and reading vibrations in a web, using them to locate defects and to know when "food" comes calling. Accordingly, the silk has the ability to transmit a wide range of sounds that scientists think the spider can interpret in various ways. But the researchers found silk also has the ability to dampen some sound.

      "(Spider) silk has a lot of different, interesting microstructures, and our group found we could control the position of the band gap by changing the strain in the silk fiber," Thomas said. "There's a range of frequencies that are not allowed to propagate. If you broadcast sound at a particular frequency, it won't go into the material."

     Thomas and other researchers decided to take a more detailed look at dragline silk, shown below in a SEM, which spiders use to construct a web's outer rim and spokes and as a lifeline. (A spider suspended in midair is clinging to a dragline.) Though silk has been studied for thousands of years, it has only recently been analyzed for its acoustic properties.

      "Silk is a hierarchical structure comprised of a protein, which folds into sheets and forms crystals. These hard protein crystals are interconnected by softer, amorphous chains," Thomas said. Stretching or relaxing the interconnecting chains changes the silk's acoustic properties by adjusting the mechanical coupling between the crystals.

       "Right now, we don't know how to do any of this in other macromolecular fiber materials," Thomas said. "There's been a fair amount of investigation on synthetic polymers like nylon, but nobody's ever found a band gap."

Have you ever found a band gap?!

Zoë and her "Camp English" group in Ethiopia this summer:


  1. Drag line? So many ways to jest there. Suggestions welcome.

    1. Have I ever found a band gap, Steph? Sure!


    2. Charlotte would be pleased, Lego. SOME PUCK!

    3. Some pig in a puck? Or, some pig in a Pokemon?


    4. And Poketues, Pokewed, Pokethurs, Pokefri, Pokesat, Pokesun?

      Favorite children's book ever. How can you not love Charlotte?

  2. Replies
    1. That does not look like a red spot to me, Steph. It looks like a liver spot!

      Which suggests at least two things:
      1. That Jupiter is really old!
      2. If there is liver on Jupiter, there must also be life on Jupiter!


    2. Maybe political candidates would be better off hiring spiders to spin their stories. . .

    3. "The stuff looks red because it absorbs blue light strongly."
      Reminds me of the classic "why is the sky blue" question.
      In related news, reports of K-Mart's demise may have been exaggerated.
      Practically everything makes me think of a song. Bette's great, of course, but what about that BAND?! No gaps in that 'wall of sound'!


    4. You Bette, Paul. Fabulous.

      I'd forgotten about Dragline. Worth another look!

    5. Perhaps the Donald will spring Phil Spector from prison (or spector Bruce Springsteen from New Jersey) and hire him to build The Wall that Mexico will pay for. If Phil cannot be sprung (or Bruce cannot be spectored), there is always Pink Floyd.


    6. Thank God there is always Pink Floyd, Lego. . .

  3. Fish digging a hole. Fascinating. What are those floating vertical things in the beginning?

    1. I'm guessing they're some kind of pipefish.

    2. They are new to me. Interesting critters.

    3. Ah, Aeoliscus strigatus! Razorfish. Thanks for the video, jan.

    4. I had been trying to vet 'sea pens'. I bow to your superior acumen.

    5. Sea pens, sea whips, sea pansies, sea (sic--ha!) soft corals.

      They are attached to the sea bottom, I believe. Sea (sic-in case you missed it the first time) BENTHIC.

  4. Nice shot of Zoë's group. If they need any more bamboo, they're welcome to harvest my back yard. When is her tour/hitch/deployment up?

    1. September 30, 2017. She is thinking of a Master's in Public Health in London when she's completed her service.

      I am impressed you have bamboo. It grows really fast, right?

    2. You can practically hear it growing. It's unstoppable. It's all I can do to keep it from taking over the whole yard. We call it "bamboozling".

      Another year to go in Ethiopia, eh? Why London for the MPH? Great city, but very expensive. Or is she expecting Brexit to change that?

      Funny you should mention London now. My brother-in-law, who just spent a year there, is with us on his way back to CA, and we're watching The Lady in the Van at the moment.

    3. No bamboo here, too dry. Friends in AL have 3 1/2 acres of the stuff.

      Zoë has been bitten by the living outside the USA bug (thankfully, not a mosquito). Not sure exactly why London. She does like the idea of a one-year program. I am hoping the PC will make it reasonably easy for her to vote this fall!

      Have fun with your brother-in-law. Will check out the movie, too.

    4. "Master's in Public Health in London."

      The guv'ment picks up the tab for all that, right?

    5. Paul, I don't know the answer but, if so, that may well figure into her decision.

      And being outside the USA. She feels lucky to be missing all the political nonsense here this year.

  5. Replies
    1. The caffeine web is the scariest-looking one, IMHO.

      How was the movie (above)?

    2. OK. Quirky, quiet, English.

  6. New post on "Failure to Launch: Andes, Lava Coulée, and Chao Baby!" is now up.