17 research outputs found
Graphene Flake Self-Assembly Enhancement via Stretchable Platforms and External Mechanical Stimuli
While the green production and application of 2D functional nanomaterials, such as graphene flakes, in films for stretchable and wearable technologies is a promising platform for advanced technologies, there are still challenges involved in the processing of the deposited material to improve properties such as electrical conductivity. In applications such as wearable biomedical and flexible energy devices, the widely used flexible and stretchable substrate materials are incompatible with higherature processing traditionally employed to improve the electrical properties, which necessitates alternative manufacturing approaches and new steps for enhancing the film functionality. We hypothesize that a mechanical stimulus, in the form of substrate straining, may provide such a low-energy approach for modifying deposited film properties through increased flake packing and reorientation. To this end, graphene flakes were exfoliated using an unexplored combination of ethanol and cellulose acetate butyrate for morphological and percolative electrical characterization prior to application on polydimethylsiloxane (PDMS) substrates as a flexible and stretchable electrically conductive platform. The deposited percolative free-standing films on PDMS were characterized via in situ resistance strain monitoring and surface morphology measurements over numerous strain cycles, with parameters extracted describing the dynamic modulation of the film's electrical properties. A reduction in the film resistance and strain gauge factor was found to correlate with the surface roughness and densification of a sample's (sub)surface and the applied strain. High surface roughness samples exhibited enhanced reduction in resistance as well as increased sensitivity to strain compared to samples with low surface roughness, corresponding to surface smoothing, which is related to the dynamic settling of graphene flakes on the substrate surface. This procedure of incorporating strain as a mechanical stimulus may find application as a manufacturing tool/step for the routine fabrication of stretchable and wearable devices, as a low energy and compatible approach, for enhancing the properties of such devices for either high sensitivity or low sensitivity of electrical resistance to substrate strain
Twisting fatigue in multilayer films of Ag-alloy with indium tin oxide on polyethylene terephthalate for flexible electronics devices
Twisting monotonic and fatigue experiments were conducted on multi-layered films of Ag-alloy based indium tin oxide (ITO) deposited on polyethylene terephthalate (PET). In the twisting tests, crack development and electrical resistance were monitored in situ. Cracks initiated at an angle of 39° ± 1.7° and propagated towards the direction of the sample length. Two sets of experiments were performed; the first set of experiments was conducted to study the effect of twisting angle and temperature on the film's electromechanical performance. The other set of experiments was conducted to study the effect of temperature in the absence of cyclic twisting deformation. The change in electrical resistance increased with number of twisting cycles and twisting angle. In addition, the highest change in electrical resistance was observed for samples subjected to cyclic fatigue at 100 °C, which is attributed to crack growth and oxidation of the Ag-alloy layer. The cracks were observed to initiate not only from coating defects but also from edge defects. Development of cracks is accelerated due to the combined effects of the external repeated stress and temperature. Therefore, it is suggested that controlling temperature when using ITO/Ag-alloy/ITO thin film under mechanical stress is important for electrical device performance; temperatures in both fabrication and use should not exceed 50 °C
Environmentally Friendly Engineering and Three-Dimensional Printing of TiO<sub>2</sub> Hierarchical Mesoporous Cellular Architectures
Three-dimensional
(3D) printing of hierarchically ordered cellular
materials with tunable microstructures is a major challenge from both
synthesis and scalable manufacturing perspectives. A simple, environmentally
friendly, and scalable concept to realize morphologically and microstructurally
engineered cellular ceramics is herein demonstrated by combining direct
foam writing with colloidal processing. These cellular structures
are widely applicable across multiple technological fields including
energy harvesting, waste management/water purification, and biomedicine.
Our concept marries sacrificial templating with direct foaming to
synthesize multiscale porous TiO<sub>2</sub> foams that can be 3D
printed into planar, free-standing, and spanning hierarchical structures.
The latter being reported for the first time. We show how by varying
the foam-inks’ composition and frothing conditions, the rheological
properties and foam configurations (i.e., open- or closed-cell) are
tuned. Furthermore, our printing studies indicate a synergy between
intermediate extrusion pressures and low speeds for realizing spanning
features. Additionally, the dimensional changes associated with the
postprocessing of the different foam configurations are discussed.
We investigate the effects of the foams’ composition on their
microstructure and surface area properties. Additionally, the foams’
photocatalytic performance is correlated with their microstructure,
improving for open-cell architectures. The proposed synthesis and
scalable manufacturing method can be extended to fabricate similar
structures from alternative ceramic foam systems, where control of
the porosity and surface properties is crucial, demonstrating the
great potential of our synthesis approach
Early Assessment and Correlations of Nanoclay’s Toxicity to Their Physical and Chemical Properties
Nanoclays’ functionalization
with organic modifiers increases
their individual barrier properties, thermal stability, and mechanical
properties and allows for ease of implementation in food packaging
materials or medical devices. Previous reports have shown that, while
organic modifiers integration between the layered mineral silicates
leads to nanoclays with different degrees of hydrophobicity that become
easily miscible in polymers, they could also pose possible effects
at inhalation or ingestion routes of exposure. Through a systematic
analysis of three organically modified and one pristine nanoclay,
we aimed to relate for the first time the physical and chemical characteristics,
determined via microscopical and spectroscopical techniques, with
the potential of these nanoclays to induce deleterious effects in
in vitro cellular systems, i.e. in immortalized and primary human lung
epithelial cell lines. To derive information on how functionalization
could lead to toxicological profiles throughout nanoclays’
life cycle, both as-received and thermally degraded nanoclays were
evaluated. Our analysis showed that the organic modifiers chemical
composition influenced both the physical and chemical characteristics
of the nanoclays as well as their toxicity. Overall, when cells were exposed to nanoclays with
organic modifiers containing bioreactive groups, they displayed lower cellular
numbers as well more elongated cellular morphologies relative to the
pristine nanoclay and the nanoclay containing a modifier with long carbon
chains. Additionally, thermal degradation caused loss of the organic
modifiers as well as changes in size and shape of the nanoclays, which
led to changes in toxicity upon exposure to our model cellular systems. Our study provides insight into the synergistic
effects of chemical composition, size, and shape of the nanoclays
and their toxicological profiles in conditions that mimic exposure
in manufacturing and disposal environments, respectively, and can
help aid in safe-by-design manufacturing of nanoclays with user-controlled
functionalization and lower toxicity levels when food packaging applications
are considered
Short-Term Pulmonary Toxicity Assessment of Pre- and Post-incinerated Organomodified Nanoclay in Mice
Organomodified nanoclays
(ONCs) are increasingly used as filler
materials to improve nanocomposite strength, wettability, flammability,
and durability. However, pulmonary risks associated with exposure
along their chemical lifecycle are unknown. This study’s objective
was to compare pre- and post-incinerated forms of uncoated and organomodified
nanoclays for potential pulmonary inflammation, toxicity, and systemic
blood response. Mice were exposed <i>via</i> aspiration
to low (30 μg) and high (300 μg) doses of preincinerated
uncoated montmorillonite nanoclay (CloisNa), ONC (Clois30B), their
respective incinerated forms (I-CloisNa and I-Clois30B), and crystalline
silica (CS). Lung and blood tissues were collected at days 1, 7, and
28 to compare toxicity and inflammation indices. Well-dispersed CloisNa
caused a robust inflammatory response characterized by neutrophils,
macrophages, and particle-laden granulomas. Alternatively, Clois30B,
I-Clois30B, and CS high-dose exposures elicited a low grade, persistent
inflammatory response. High-dose Clois30B exposure exhibited moderate
increases in lung damage markers and a delayed macrophage recruitment
cytokine signature peaking at day 7 followed by a fibrotic tissue
signature at day 28, similar to CloisNa. I-CloisNa exhibited acute,
transient inflammation with quick recovery. Conversely, high-dose
I-Clois30B caused a weak initial inflammatory signal but showed comparable
pro-inflammatory signaling to CS at day 28. The data demonstrate that
ONC pulmonary toxicity and inflammatory potential relies on coating
presence and incineration status in that coated and incinerated nanoclay
exhibited less inflammation and granuloma formation than pristine
montmorillonite. High doses of both pre- and post-incinerated ONC,
with different surface morphologies, may harbor potential pulmonary
health hazards over long-term occupational exposures
Short-Term Pulmonary Toxicity Assessment of Pre- and Post-incinerated Organomodified Nanoclay in Mice
Organomodified nanoclays
(ONCs) are increasingly used as filler
materials to improve nanocomposite strength, wettability, flammability,
and durability. However, pulmonary risks associated with exposure
along their chemical lifecycle are unknown. This study’s objective
was to compare pre- and post-incinerated forms of uncoated and organomodified
nanoclays for potential pulmonary inflammation, toxicity, and systemic
blood response. Mice were exposed <i>via</i> aspiration
to low (30 μg) and high (300 μg) doses of preincinerated
uncoated montmorillonite nanoclay (CloisNa), ONC (Clois30B), their
respective incinerated forms (I-CloisNa and I-Clois30B), and crystalline
silica (CS). Lung and blood tissues were collected at days 1, 7, and
28 to compare toxicity and inflammation indices. Well-dispersed CloisNa
caused a robust inflammatory response characterized by neutrophils,
macrophages, and particle-laden granulomas. Alternatively, Clois30B,
I-Clois30B, and CS high-dose exposures elicited a low grade, persistent
inflammatory response. High-dose Clois30B exposure exhibited moderate
increases in lung damage markers and a delayed macrophage recruitment
cytokine signature peaking at day 7 followed by a fibrotic tissue
signature at day 28, similar to CloisNa. I-CloisNa exhibited acute,
transient inflammation with quick recovery. Conversely, high-dose
I-Clois30B caused a weak initial inflammatory signal but showed comparable
pro-inflammatory signaling to CS at day 28. The data demonstrate that
ONC pulmonary toxicity and inflammatory potential relies on coating
presence and incineration status in that coated and incinerated nanoclay
exhibited less inflammation and granuloma formation than pristine
montmorillonite. High doses of both pre- and post-incinerated ONC,
with different surface morphologies, may harbor potential pulmonary
health hazards over long-term occupational exposures