Lawrence Livermore National Laboratory

Colloidal Nanoparticles with Dynamic Color

Lawrence Livermore researchers have developed a technique to change the color of assembled nanoparticles with an electrical stimulant. The team used an electrophoretic deposition process to build amorphous photonic material (APM) structures with nanoparticles having cores of iron oxide and shells of silica. Instantaneous color changes are possible and fully reversible with noticeable differences between transmitted and reflected colors. The research is featured on the cover of the April 3, 2017, edition of Advanced Optical Materials.

The team used nanoparticles to improve color contrast and expand color schemes by combining pigmentary color (from inherent properties) and structural color (from particle assemblies) and by varying nanoparticle concentrations, shell thicknesses, and external electric stimuli. The resulting colors are dynamically tunable because the structure of the nanoparticles and their interparticle distances are highly affected by the electric field. Jinkyu Han, lead author of the paper, says, “The assemblies of the nanoparticles can not only imitate interesting colors observed in living organisms, but can also be applied in electronic paper displays and colored-reflective photonic displays.”

A nanoparticle arrangement that is not perfectly ordered or crystalline forms the APM structures, resulting in colors that do not change with the viewing angle. “The angle independence of the observed colors from the assemblies is quite a unique and interesting property of our system and is ideal for display applications,” says Han. The team’s technique can be applied to electronic devices, such as digital signs, mobile phones, electronic billboards, and e-readers.

Contact: Jinkyu Han (925) 423-2517 (

Two Pathways to Polymeric Molecule Crystallization

In research appearing in the April 17, 2017, edition of Nature Materials, scientists from Lawrence Livermore and Pacific Northwest National Laboratory (PNNL) investigated crystallization pathways for polymeric molecules. A better understanding of these pathways can lead to improvements in pharmaceutical development and energy technologies that depend upon complex molecular crystals. In the study, the scientists compared the beginning crystallization of a peptoid, a simple biomimetic polymer, to that of a slightly altered version.

The one-step crystallization process is well understood—simple molecules assemble by attaching together one molecule after another. However, experiments suggest that complex molecules require a two-step crystallization process, wherein the molecules first form a disordered group and then rearrange into a crystal. “The findings address an ongoing debate about crystallization pathways,” says materials scientist Jim De Yoreo, a former Livermore employee who is now affiliated with PNNL and the University of Washington. “They imply one can control the various stages of materials assembly by carefully choosing the structure of the starting molecules.”

Using Livermore’s new ultrafast atomic force microscope to characterize the crystallization process, Laboratory scientists Aleksandr Noy and Yuliang Zhang found that the simpler peptoid followed the one-step process while the other proceeded in two steps. “We were not expecting that such a minor change would make the peptoids behave this way,” says De Yoreo. “The results are leading us to think about the system in a new way, which we believe will lead to more predictive control over the design and assembly of biomimetic materials.”

Contact: Aleksandr Noy (925) 423-3396 (

CASTing New Limits on the Search for Dark Matter

Livermore researchers, leading an international collaboration on the CERN Axion Solar Telescope (CAST, see image below), presented new results on the properties of axions in a paper published in the May 1, 2017, edition of Nature Physics. Axions are hypothetical particles that could constitute some or all of the universe’s mysterious and abundant dark matter. Lawrence Livermore has been an active collaborator in CAST since 2005, primarily funded through support from the Laboratory Directed Research and Development Program.

The CAST experiment searches for axions using a helioscope, which tracks the Sun as it moves across the sky. The CAST helioscope has operated since 2003 and follows the movement of the Sun for 90 minutes at dawn and dusk over several months each year. Any solar axions entering CAST’s 10-meter-long, 50-ton magnet would be converted by its strong magnetic field into x-ray photons. The x-ray telescope developed by Livermore researchers focuses the photons into a small spot, greatly enhancing the instrument’s sensitivity.

During the latest data-gathering campaign, from 2013 to 2015, CAST demonstrated a factor-of-three improvement in signal-to-noise ratio. This improvement was made possible, in large part, through more enhanced detection systems with lower background levels. Livermore’s Mike Pivovaroff, a member of the CAST collaboration and an author of the paper, says, “This work is ground-breaking science with implications for elucidating the nature of dark matter, solving a long-standing particle physics problem (hinting at physics beyond the Standard Model) and constraining cosmological models.” The results are also important to the development of the International Axion Observatory (IAXO), a proposed successor to CAST in which Livermore will have a major leadership role.

Contact: Julia Vogel (925) 424-4815 (