20 research outputs found
A New Route to Fluorescent SWNT/Silica Nanocomposites: Balancing Fluorescence Intensity and Environmental Sensitivity
We investigate the relationship between photoluminescence (PL) intensity and
environmental sensitivity of surfactant-wrapped single walled carbon nanotubes
(SWNTs). SWNTs were studied under a variety of conditions in suspension as well
as encapsulated in silica nanocomposites, which were prepared by an efficient
chemical vapor into liquids (CViL) sol-gel process. The dramatically improved
silica encapsulation process described here has several advantages, including
fast preparation and high SWNT loading concentration, over other encapsulation
methods used to prepare fluorescent SWNT/silica nanocomposites. Further,
addition of glycerol to SWNT suspensions prior to performing the CViL sol-gel
process allows for the preparation of freestanding fluorescent silica xerogels,
which to the best of our knowledge is the first report of such nanocomposites.
Our spectroscopic data on SWNTs suspended in aqueous surfactants or
encapsulated in silica show that achieving maximum PL intensity results in
decreased sensitivity of SWNT emission response to changes imparted by the
local environment. In addition, silica encapsulation can be used to "lock-in" a
surfactant micelle structure surrounding SWNTs to minimize interactions between
SWNTs and ions/small molecules. Ultimately, our work demonstrates that one
should consider a balance between maximum PL intensity and the ability to sense
environmental changes when designing new SWNT systems for future sensing
applications
Ultrafast Radiographic Imaging and Tracking: An overview of instruments, methods, data, and applications
Ultrafast radiographic imaging and tracking (U-RadIT) use state-of-the-art
ionizing particle and light sources to experimentally study sub-nanosecond
dynamic processes in physics, chemistry, biology, geology, materials science
and other fields. These processes, fundamental to nuclear fusion energy,
advanced manufacturing, green transportation and others, often involve one mole
or more atoms, and thus are challenging to compute by using the first
principles of quantum physics or other forward models. One of the central
problems in U-RadIT is to optimize information yield through, e.g.
high-luminosity X-ray and particle sources, efficient imaging and tracking
detectors, novel methods to collect data, and large-bandwidth online and
offline data processing, regulated by the underlying physics, statistics, and
computing power. We review and highlight recent progress in: a.) Detectors; b.)
U-RadIT modalities; c.) Data and algorithms; and d.) Applications.
Hardware-centric approaches to U-RadIT optimization are constrained by detector
material properties, low signal-to-noise ratio, high cost and long development
cycles of critical hardware components such as ASICs. Interpretation of
experimental data, including comparisons with forward models, is frequently
hindered by sparse measurements, model and measurement uncertainties, and
noise. Alternatively, U-RadIT makes increasing use of data science and machine
learning algorithms, including experimental implementations of compressed
sensing. Machine learning and artificial intelligence approaches, refined by
physics and materials information, may also contribute significantly to data
interpretation, uncertainty quantification and U-RadIT optimization.Comment: 51 pages, 31 figures; Overview of ultrafast radiographic imaging and
tracking as a part of ULITIMA 2023 conference, Mar. 13-16,2023, Menlo Park,
CA, US
Metal Halide Analogues of Chalcogenides: A Building Block Approach to the Rational Synthesis of Solid-State Materials
Stable and Fluid Multilayer Phospholipid–Silica Thin Films: Mimicking Active Multi-lamellar Biological Assemblies
Phospholipid-based nanomaterials are of interest in several applications including drug delivery, sensing, energy harvesting, and as model systems in basic research. However, a general challenge in creating functional hybrid biomaterials from phospholipid assemblies is their fragility, instability in air, insolubility in water, and the difficulty of integrating them into useful composites that retain or enhance the properties of interest, therefore limiting there use in integrated devices. We document the synthesis and characterization of highly ordered and stable phospholipid–silica thin films that resemble multilamellar architectures present in nature such as the myelin sheath. We have used a near room temperature chemical vapor deposition method to synthesize these robust functional materials. Highly ordered lipid films are exposed to vapors of silica precursor resulting in the formation of nanostructured hybrid assemblies. This process is simple, scalable, and offers advantages such as exclusion of ethanol and no (or minimal) need for exposure to mineral acids, which are generally required in conventional sol–gel synthesis strategies. The structure of the phospholipid–silica assemblies can be tuned to either lamellar or hexagonal organization depending on the synthesis conditions. The phospholipid–silica films exhibit long-term structural stability in air as well as when placed in aqueous solutions and maintain their fluidity under aqueous or humid conditions. This platform provides a model for robust implementation of phospholipid multilayers and a means toward future applications of functional phospholipid supramolecular assemblies in device integration
Fluid and Resistive Tethered Lipid Membranes on Nanoporous Substrates
Cell
membranes perform important biological roles including compartmentalization,
signaling, and transport of nutrients. Supported lipid membranes mimic
the behavior of cell membranes and are an important model tool for
studying membrane properties in a controlled laboratory environment.
Lipid membranes may be supported on solid substrates; however, protein
and lipid interactions with the substrate typically result in their
denaturation. In this report, we demonstrate the formation of intact
lipid membranes tethered on nanoporous metal thin films obtained via
a dealloying process. Uniform lipid membranes were formed when the
surface defect density of the nanoporous metal film was significantly
reduced through a two-step dealloying process reported here. We show
that the tethered lipid membranes on nanoporous metal substrates maintain
both fluidity and electrical resistivity, which are key attributes
to naturally occurring lipid membranes. The lipid assemblies supported
on nanoporous metals provide a new platform for investigating lipid
membrane properties, and potentially membrane proteins, for numerous
applications including next generation biosensor platforms, targeted
drug-delivery, and energy harvesting devices
Critical role of intercalated water for electrocatalytically active nitrogen-doped graphitic systems
Graphitic materials are essential in energy conversion and storage because of their excellent chemical and electrical properties. The strategy for obtaining functional graphitic materials involves graphite oxidation and subsequent dissolution in aqueous media, forming graphene-oxide nanosheets (GNs). Restacked GNs contain substantial intercalated water that can react with heteroatom dopants or the graphene lattice during reduction. We demonstrate that removal of intercalated water using simple solvent treatments causes significant structural reorganization, substantially affecting the oxygen reduction reaction (ORR) activity and stability of nitrogen-doped graphitic systems. Amid contrasting reports describing the ORR activity of GN-based catalysts in alkaline electrolytes, we demonstrate superior activity in an acidic electrolyte with an onset potential of ~0.9 V, a half-wave potential (E(½)) of 0.71 V, and a selectivity for four-electron reduction of >95%. Further, durability testing showed E(½) retention >95% in N(2)- and O(2)-saturated solutions after 2000 cycles, demonstrating the highest ORR activity and stability reported to date for GN-based electrocatalysts in acidic media