Tag: optical properties

 Flexible composite with switchable magnetic and optical properties

 Flexible composite with switchable magnetic and optical properties

A team of researchers from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN), Jagiellonian University, and AGH University of Kraków has developed a switchable composite material that combines the remarkable properties of molecular magnets with the mechanical robustness and flexibility of polymer fibers. The paper was published in the journal Nanoscale.

A key component of the composite is the coordination chain {NH₄[Ni(cyclam)][Fe(CN)₆]·5H₂O}ₙ, which exhibits reversible intermetallic charge transfer between iron and nickel centers. Changes in temperature, humidity, or pressure can induce a transition between different states of the material, accompanied by a pronounced and reversible change in color as well as changes in its magnetic properties. This enables the material to function simultaneously as an active magnetic component and as a visual indicator of the transition taking place within the material.

An important challenge in the practical application of such materials is their physical form. The crystalline coordination compound is brittle and has limited stability when exposed to polar liquids, particularly water, which can lead to its degradation and loss of its desired properties. To address this issue, the researchers developed a composite in which the molecular magnetic chain was incorporated into polymer fibers produced by electrospinning. Two polymer matrices were used: poly(ε-caprolactone) (PCL) and a poly(2-vinylpyridine-co-styrene) copolymer (P2VP-PS). This approach preserved the switchable properties of the coordination compound while converting it into a flexible fibrous mat with improved mechanical properties. In particular, the use of hydrophobic PCL proved highly beneficial, providing protection against the adverse effects of water.

Characterization of the resulting materials required several complementary experimental techniques, with X-ray absorption spectroscopy (XAS) playing a particularly important role. This technique makes it possible to investigate the local atomic environment of selected elements and their electronic states. XAS measurements were performed at the SOLARIS National Synchrotron Radiation Centre in Kraków, on the ASTRA beamline, by recording spectra around the K-absorption edges of iron and nickel. These measurements provided important complementary information to the magnetic and spectroscopic studies, making it possible to correlate the observed changes in the material’s properties with changes in its electronic structure.

Read more on the SOLARIS website

Image: Temperature-dependent XAS spectra recorded at the Fe and Ni K-edges for the coordination polymer {NH4[Ni(cyclam)][Fe(CN)6]·5H2O}n in the low-temperature (LT, 260 K) and high-temperature (HT, 330 K) states. Changes in the shape and position of the absorption edges indicate a change in the electronic configuration of the Fe and Ni centers induced by temperature change. The middle panel shows the structure of the coordination polymer {NH4[Ni(cyclam)][Fe(CN)6]·5H2O}n, together with a schematic representation of electron transfer between the metal centers. The bottom panel presents the electronic configuration of the coordination polymer {NH₄[Ni(cyclam)][Fe(CN)₆]·5H₂O}ₙ in the LT and HT states. Photographs of the samples clearly show the change in color occurring between the low-temperature (LT) and high-temperature (HT) states.

Advanced materials research in microgravity earns NASA recognition

Advanced materials research in microgravity earns NASA recognition

Key Points

  • Collaborative research has advanced an understanding of how colloidal clusters form and behave in microgravity
  • The microgravity environment aboard the ISS minimised sedimentation and convection, providing a unique opportunity to observe the pure self-assembly of particles with unique optical properties
  • Structural analyses were later conducted using neutron scattering instruments at the Australian Centre for Neutron Scattering

A pioneering study led by Professor Junpei Yamanaka of Nagoya City University and an international team that included ANSTO has delivered transformative insights into the behaviour of colloidal particles under microgravity. 

Conducted aboard the International Space Station (ISS), this research has not only been prominently featured in NASA’s 2024 Annual Highlights of Results from the International Space Station Science but also promises to reshape future material technologies—including revolutionary optical devices and even the elusive cloaking devices reminiscent of science fiction.

Colloidal clusters—aggregates of nano- and micrometre-sized particles suspended in a fluid—play a pivotal role in various industrial and scientific applications. 

“On Earth, gravity-induced effects, such as sedimentation and convection, can obscure the intrinsic properties of these clusters, hindering our ability to study their natural assembly,” explained Principal Instrument Scientist Assoc Professor Jitendra Mata at ANSTO’s Australian Centre for Neutron Scattering. 

“However, the microgravity environment aboard the ISS minimises these disturbances, providing a unique opportunity to observe the pure self-assembly of particles.”

In a specialised experimental setup, the research team mixed oppositely charged colloidal particles in an aqueous solution, allowing them to cluster in of the absence of gravity, providing opportunity to understand fundamental science of association. 

Once these structures were formed, they were immobilised in a gel using ultraviolet (UV) light curing—a process that preserved the delicate architecture of the clusters for subsequent analysis back on Earth. 

Optical microscopy revealed that even minimal gravitational effects post-return can significantly influence the formation of colloidal structures, underscoring the value of space-based research.

This landmark research exemplifies robust international collaboration. The groundwork for the experiments began in Japan in 2018, with critical contributions from Nagoya City University, Japan Space Forum, Advance Engineering Services, and the Japan Aerospace Exploration Agency (JAXA). 

Structural analyses were later conducted in partnership with A/Prof Mata using the Small-angle neutron scattering instrument Quokka and Ultra-small neutron scattering instrument Kookaburra.

“This collaboration has been instrumental in advancing our understanding of how colloidal clusters form and behave in microgravity,” he said.

The significance of these experiments extends well beyond fundamental science. Colloidal clusters have been shown to scatter light in the visible to near-infrared spectrum, making them highly promising for applications in photonics, optical communications, and laser technologies. 

Their unique light-manipulating properties hint at future breakthroughs, including the potential development of advanced optical materials and even cloaking devices—innovations that capture the imagination much like the futuristic technologies portrayed in Star Trek.

Moreover, the ability to study these clusters in a space-based environment opens up new avenues for designing better materials. “

Read more on ANSTO website

X-ray Excited Optical Luminescence (XEOL)

X-ray Excited Optical Luminescence (XEOL)

XEOL is an X-ray photon in/optical photon out technique that is related to the conversion of the X-ray energy absorbed by the materials to optical photons, involving multi-step energy transfer cascade processes. XEOL is often used together with XANES to reveal the electronic structure and optical properties of the system of interest, such as rare earth down conversion phosphors, quantum confined semiconductors, heterogeneous materials etc., and is applied in display/lighting technologies (TV, smartphone and LED lamps), scintillators, rechargeable batteries and energy conversion devices (photovoltaic cells). XEOL is now available at the end station of BM-08 XAFS/XRF beamline with emission spectra measurement capability under irradiation with X-ray beam.

Read more in SESAME website

Image: General view of the XEOL experimental setup at BM-08 XAFS/XRF beamline.  Sample environment with optical fiber for collecting the luminescence signals