3 research outputs found
Structural Dynamics of Strongly Segregated Block Copolymer Electrolytes
Polymer
electrolytes are promising materials for high energy density
rechargeable batteries. However, they have low ion transport rates
and gradually lose electrode adhesion during cycling. These effects
are dependent on polymer structure and dynamics. This motivates an
investigation of diblock copolymer electrolyte dynamics. Structural
and stress relaxations have been measured with X-ray photon correlation
spectroscopy (XPCS) and rheology, respectively, as a function of salt
concentration and temperature. The polymer electrolyte studied in
this work is a mixture of polyÂ(styrene-<i>b</i>-ethylene
oxide), SEO, and lithium bistrifluoromethaneÂsulfonimide (LiTFSI).
Results from XPCS experiments showed hyperdiffusive motion for various
lithium salt concentrations and at varying temperatures, which is
indicative of soft glassy materials. This behavior is attributed to
cooperative dynamics. The decay time was a weak, nonmonotonic function
of salt concentration and decreased with increasing temperature, in
an Arrhenius fashion. In contrast, the shear modulus decreased with
increasing salt concentration and increasing temperature. The entanglement
relaxation from rheological measurements followed Vogel–Fulcher–Tammann
behavior. The structural decay time was slower than the entanglement
relaxation time at temperatures above the glass transition temperature,
but they were approximately equal at <i>T</i><sub>g</sub> regardless of salt concentration. This may indicate a fundamental
connection between cooperative structural motion and polymer chain
motion in this material
Dynamics of Cadmium Sulfide Nanoparticles within Polystyrene Melts
We
present a detailed study of the dynamics of cadmium sulfide
nanoparticles suspended in polystyrene homopolymer matrices using
X-ray photon correlation spectroscopy for temperatures between 120
and 180 °C. For low molecular weight polystyrene homopolymers,
the observed dynamics show a crossover from diffusive to hyper-diffusive
behavior with decreasing temperatures. For higher molecular weight
polystyrene, the nanoparticle dynamics appear hyper-diffusive at all
temperatures studied. The relaxation time and characteristic velocity
determined from the measured hyper-diffusive dynamics reveal that
the activation energy and underlying forces determined are on the
order of 2.14 × 10<sup>–19</sup> J and 87 pN, respectively
Structural Diversity of Arthropod Biophotonic Nanostructures Spans Amphiphilic Phase-Space
Many organisms, especially arthropods, produce vivid interference
colors using diverse mesoscopic (100–350 nm) integumentary
biophotonic nanostructures that are increasingly being investigated
for technological applications. Despite a century of interest, precise
structural knowledge of many biophotonic nanostructures and the mechanisms
controlling their development remain tentative, when such knowledge
can open novel biomimetic routes to facilely self-assemble tunable,
multifunctional materials. Here, we use synchrotron small-angle X-ray
scattering and electron microscopy to characterize the photonic nanostructure
of 140 integumentary scales and setae from ∼127 species of
terrestrial arthropods in 85 genera from 5 orders. We report a rich
nanostructural diversity, including triply periodic bicontinuous networks,
close-packed spheres, inverse columnar, perforated lamellar, and disordered
spongelike morphologies, commonly observed as stable phases of amphiphilic
surfactants, block copolymer, and lyotropic lipid–water systems.
Diverse arthropod lineages appear to have independently evolved to
utilize the self-assembly of infolding lipid-bilayer membranes to
develop biophotonic nanostructures that span the phase-space of amphiphilic
morphologies, but at optical length scales