Nav: Home

X-ray study reveals way to control molecular vibrations that transmit heat

June 08, 2017

UPTON, NY--Scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have developed a new way to track dynamic molecular features in soft materials, including the high-frequency molecular vibrations that transmit waves of heat, sound, and other forms of energy. Controlling these vibrational waves in soft materials such as polymers or liquid crystal compounds could lead to a range of energy-inspired innovations--from thermal and acoustic insulators, to ways to convert waste heat into electricity, or light into mechanical motion.

In a paper just published in Nano Letters, the scientists describe using the newly constructed inelastic x-ray scattering (IXS) beamline at the National Synchrotron Light Source II (NSLS-II), which has unprecedented energy resolution, to monitor the propagation of vibrations through a liquid crystal compound in three different phases. Their findings show that the nanoscale structural changes that occur with increasing temperature--as the liquid crystals become less ordered--dramatically disrupt the flow of vibrational waves. Thus choosing or changing the "phase," or arrangement of molecules, could control the vibrations and the flow of energy.

"By tuning the structure, we can change the dynamic properties of this material," said Brookhaven physicist Dima Bolmatov, the paper's lead author.

The technique could also be used to study dynamic processes in other soft systems such as biological membranes or any kind of complex fluid.

"For example, we could look at how the lipid molecules in a cell membrane cooperate with each other to create tiny porous regions where even smaller molecules, like oxygen or carbon dioxide, can pass through--to see how gas exchange operates in gills and lungs," Bolmatov said.

The ability to track such fast dynamic properties would not be possible without the unique capabilities of NSLS-II--a DOE Office of Science User Facility at Brookhaven Lab. NSLS-II produces extremely bright x-rays for studies in a wide range of scientific fields.

At the IXS beamline, scientists bombard samples with these x-rays and measure the energy they give up or gain with a precision to within two thousandths of an electron volt, as well as the angle at which they scatter off the sample--even at very small angles.

"The energy exchange tells us how much energy it took to make some molecules vibrate in a wave-like motion. The scattering angle probes the vibrations propagating over different length scales inside the sample--from nearly a single molecule to tens of nanometers. The new IXS beamline at NSLS-II can resolve those length scales with unprecedented precision," said Yong Cai, the lead scientist of the IXS beamline.

"These two parameters--the scattering angle and the energy--have never before been so well measured in soft materials. So the technical properties of this beamline enable us to precisely locate the vibrations and track their propagation in different directions over different length scales--even in materials that lack a well-ordered solid structure," he added.

In the liquid crystal study, the Brookhaven Lab scientists and their collaborators at Kent State University and the University at Albany made measurements at three different temperatures as the material went from an ordered, crystalline phase through transitions to a less-ordered "smectic" state, and finally an "isotropic" liquid. They easily detected the propagation of vibrational waves through the most ordered phase, and showed that the emergence of disorder "killed" the propagation of low energy "acoustic shear" vibrations. Acoustic shear vibrations are associated with a compression of the molecules in a direction perpendicular to the direction of propagation.

"Knowing where the dynamic boundary is--between the material behaving like an ordered solid and a disordered soft material--gives us a way to control the transmission of energy at the nanoscale," Bolmatov said.

In the "smectic" phase, the scientists also observed a vibration that was associated instead with molecular tilt. This type of vibration can interact with light and absorb it because the terahertz frequency of the vibrations matches the frequency of infrared light or heat waves. So changing the material properties can control the way these forms of energy move through the material. Those changes can be achieved by changing the temperature of the material, as was done in this experiment, but also by applying external electric or magnetic fields, Bolmatov said.

This paves the way for new so-called phononic or optomechanical applications, where sound or light is coupled with the mechanical vibrations. Such coupling makes it possible to control a material by applying external light and sound or vice versa.

"We're all familiar with applications using the optical properties of liquid crystals in display screens," Bolmatov said. "We've found new properties that can be controlled or manipulated for new kinds of applications."

The team will continue studies of soft materials at IXS, including planned experiments with block copolymers, nanoparticle assemblies, lipid membranes, and other liquid crystals over the summer.

"The IXS beamline is also now opened to external users--including scientists interested in these and other soft materials and biological processes," said Cai.
The research team included Dima Bolmatov, Mikhail Zhernenkov, Alexey Suvorov, Ronald Pindak, Yong Cai, and Alessandro Cunsolo of NSLS-II, and Lewis Sharpnack, Deña M. Agra-Kooijman of Kent State University, and Satyendra Kumar of the University at Albany .

This research was supported by the DOE Office of Science.

DOE/Brookhaven National Laboratory

Related Molecules Articles:

The inner lives of molecules
Researchers from Canada, the UK and Germany have developed a new experimental technique to take 3-D images of molecules in action.
Novel technique helps ID elusive molecules
Stuart Lindsay, a researcher at Arizona State University's Biodesign Institute, has devised a clever means of identifying carbohydrate molecules quickly and accurately.
How solvent molecules cooperate in reactions
Molecules from the solvent environment that at first glance seem to be uninvolved can be essential for chemical reactions.
A new way to display the 3-D structure of molecules
Berkeley Lab and UC Berkeley Researchers have developed nanoscale display cases that enables new atomic-scale views of hard-to-study chemical and biological samples.
Bending hot molecules
Hot molecules are found in extreme environments such as the edges of fusion reactors.
At attention, molecules!
University of Iowa chemists have learned about a molecular assembly that may help create quicker, more responsive touch screens, among other applications.
Folding molecules into screw-shaped structures
An international research team describes the methods of winding up molecules into screw-shaped structures.
Artificial molecules
A new method allows scientists at ETH Zurich and IBM to fabricate artificial molecules out of different types of microspheres.
Molecules that may keep you young and alive
A new study may have uncovered the fountain of youth: plant extracts containing the six best groups of anti-aging molecules ever seen.
Fun with Lego (molecules)
A great childhood pleasure is playing with LegosĀ® and marveling at the variety of structures you can create from a small number of basic elements.

Related Molecules Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...