17 research outputs found
Observation of a Snap-Through Instability in Graphene
We examine the competition between adhesive and bending energies for
few-layered graphene samples placed on rigid, microscale-corrugated substrates.
Using atomic force microscopy, we show that the graphene undergoes a sharp
"snap-through" transition as a function of layer thickness, where the material
transitions between conforming to the substrate and lying flat on top of the
substrate. By utilizing the critical snap-through thickness in an elasticity
model for the FLG's bending, we extract a value for graphene-surface adhesion
energy that is larger than expected for van der Waals forces.Comment: 8 pages, 3 figure
Colloidal Properties and Stability of Graphene Oxide Nanomaterials in the Aquatic Environment
While
graphene oxide (GO) has been found to be the most toxic graphene-based
nanomaterial, its environmental fate is still unexplored. In this
study, the aggregation kinetics and stability of GO were investigated
using time-resolved dynamic light scattering over a wide range of
aquatic chemistries (pH, salt types (NaCl, MgCl<sub>2</sub>, CaCl<sub>2</sub>), ionic strength) relevant to natural and engineered systems.
Although pH did not have a notable influence on GO stability from
pH 4 to 10, salt type and ionic strength had significant effects on
GO stability due to electrical double layer compression, similar to
other colloidal particles. The critical coagulation concentration
(CCC) values of GO were determined to be 44 mM NaCl, 0.9 mM CaCl<sub>2</sub>, and 1.3 mM MgCl<sub>2</sub>. Aggregation and stability of
GO in the aquatic environment followed colloidal theory (DLVO and
Schulze-Hardy rule), even though GO’s shape is not spherical.
CCC values of GO were lower than reported fullerene CCC values and
higher than reported carbon nanotube CCC values. CaCl<sub>2</sub> destabilized
GO more aggressively than MgCl<sub>2</sub> and NaCl due to the binding
capacity of Ca<sup>2+</sup> ions with hydroxyl and carbonyl functional
groups of GO. Natural organic matter significantly improved the stability
of GO in water primarily due to steric repulsion. Long-term stability
studies demonstrated that GO was highly stable in both natural and
synthetic surface waters, although it settled quickly in synthetic
groundwater. While GO remained stable in synthetic influent wastewater,
effluent wastewater collected from a treatment plant rapidly destabilized
GO, indicating GO will settle out during the wastewater treatment
process and likely accumulate in biosolids and sludge. Overall, our
findings indicate that GO nanomaterials will be stable in the natural
aquatic environment and that significant aqueous transport of GO is
possible
Deposition and Release of Graphene Oxide Nanomaterials Using a Quartz Crystal Microbalance
Interactions of graphene oxide (GO)
with silica surfaces were investigated
using a quartz crystal microbalance with dissipation monitoring (QCM-D).
Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration
and in NaCl, CaCl<sub>2</sub>, and MgCl<sub>2</sub> as a function
of ionic strength (IS). Under favorable conditions (PLL-coated positive
surface), GO deposition rates increased with GO concentration, as
expected from colloidal theory. Increased NaCl concentration resulted
in a greater deposition attachment efficiency of GO on the silica
surface, indicating that deposition of GO follows Derjaguin–Landau–Verwey–Overbeek
(DLVO) theory; GO deposition rates decreased at high IS, however,
due to large aggregate formation. GO critical deposition concentration
(CDC) on the silica surface is determined to be 40 mM NaCl which is
higher than the reported CDC values of fullerenes and lower than carbon
nanotubes. A similar trend is observed for MgCl<sub>2</sub> which
has a CDC value of 1.2 mM MgCl<sub>2</sub>. Only a minimal amount
of GO (frequency shift <2 Hz) was deposited on the silica surface
in CaCl<sub>2</sub> due to the bridging ability of Ca<sup>2+</sup> ions with GO functional groups. Significant GO release from silica
surface was observed after adding deionized water, indicating that
GO deposition is reversible. The release rates of GO were at least
10-fold higher than the deposition rates under similar conditions
indicating potential high release and mobility of GO in the environment.
Under favorable conditions, a significant amount of GO was released
which indicates potential multilayer GO deposition. However, a negligible
amount of deposited GO was released in CaCl<sub>2</sub> under favorable
conditions due to the binding of GO layers with Ca<sup>2+</sup> ions.
Release of GO was significantly dependent on salt type with an overall
trend of NaCl > MgCl<sub>2</sub> > CaCl<sub>2</sub>
Response to Comment on “Colloidal Properties and Stability of Graphene Oxide Nanomaterials in the Aquatic Environment”
Three-Dimensional Printing of Cytocompatible, Thermally Conductive Hexagonal Boron Nitride Nanocomposites
Hexagonal
boron nitride (hBN) is a thermally conductive yet electrically
insulating two-dimensional layered nanomaterial that has attracted
significant attention as a dielectric for high-performance electronics
in addition to playing a central role in thermal management applications.
Here, we report a high-content hBN-polymer nanocomposite ink, which
can be 3D printed to form mechanically robust, self-supporting constructs.
In particular, hBN is dispersed in polyÂ(lactic-<i>co</i>-glycolic acid) and 3D printed at room temperature through an extrusion
process to form complex architectures. These constructs can be 3D
printed with a composition of up to 60% vol hBN (solids content) while
maintaining high mechanical flexibility and stretchability. The presence
of hBN within the matrix results in enhanced thermal conductivity
(up to 2.1 W K<sup>–1</sup> m<sup>–1</sup>) directly
after 3D printing with minimal postprocessing steps, suggesting utility
in thermal management applications. Furthermore, the constructs show
high levels of cytocompatibility, making them suitable for use in
the field of printed bioelectronics
Recommended from our members
Identification and Optimization of Carbon Radicals on Hydrated Graphene Oxide for Ubiquitous Antibacterial Coatings.
While the antibacterial properties of graphene oxide (GO) have been demonstrated across a spectrum of bacteria, the critical role of functional groups is unclear. To address this important issue, we utilized reduction and hydration methods to establish a GO library with different oxidation, hydroxyl, and carbon radical (•C) levels that can be used to study the impact on antibacterial activity. Using antibiotic-resistant bacteria as a test platform, we found that the •C density is most proximately associated with bacterial killing. Accordingly, hydrated GO (hGO), with the highest •C density, had the strongest antibacterial effects through membrane binding and induction of lipid peroxidation. To explore its potential applications, we demonstrated that coating of catheter and glass surfaces with hGO is capable of killing drug-resistant bacteria. In summary, •C is the principle surface moiety that can be utilized for clinical applications of GO-based antibacterial coatings
Recommended from our members
Differences in the Toxicological Potential of 2D versus Aggregated Molybdenum Disulfide in the Lung.
2D molybdenum disulfide (MoS2 ) has distinct optical and electronic properties compared to aggregated MoS2 , enabling wide use of these materials for electronic and biomedical applications. However, the hazard potential of MoS2 has not been studied extensively. Here, a comprehensive analysis of the pulmonary hazard potential of three aqueous suspended forms of MoS2 -aggregated MoS2 (Agg-MoS2 ), MoS2 exfoliated by lithiation (Lit-MoS2 ), and MoS2 dispersed by Pluronic F87 (PF87-MoS2 )-is presented. No cytotoxicity is detected in THP-1 and BEAS-2B cell lines. However, Agg-MoS2 induces strong proinflammatory and profibrogenic responses in vitro. In contrast, Lit- and PF87-MoS2 have little or no effect. In an acute toxicity study in mice, Agg-MoS2 induces acute lung inflammation, while Lit-MoS2 and PF87-MoS2 have little or no effect. In a subchronic study, there is no evidence of pulmonary fibrosis in response to all forms of MoS2 . These data suggest that exfoliation attenuates the toxicity of Agg-MoS2 , which is an important consideration toward the safety evaluation and use of nanoscale MoS2 materials for industrial and biological applications
Identification and Optimization of Carbon Radicals on Hydrated Graphene Oxide for Ubiquitous Antibacterial Coatings
While the antibacterial properties
of graphene oxide (GO) have
been demonstrated across a spectrum of bacteria, the critical role
of functional groups is unclear. To address this important issue,
we utilized reduction and hydration methods to establish a GO library
with different oxidation, hydroxyl, and carbon radical (•C)
levels that can be used to study the impact on antibacterial activity.
Using antibiotic-resistant bacteria as a test platform, we found that
the •C density is most proximately associated with bacterial
killing. Accordingly, hydrated GO (hGO), with the highest •C
density, had the strongest antibacterial effects through membrane
binding and induction of lipid peroxidation. To explore its potential
applications, we demonstrated that coating of catheter and glass surfaces
with hGO is capable of killing drug-resistant bacteria. In summary,
•C is the principle surface moiety that can be utilized for
clinical applications of GO-based antibacterial coatings