38 research outputs found
The Influence of Long-Range Surface Forces on the Contact Angle of Nanometric Droplets and Bubbles
For a droplet or a bubble of dimensions
below 100 nm, long-range
surface forces such as long-range van der Waals forces can compete
with capillarity, which leads to a size dependence of the contact
angle. This is discussed in this work, where we also show that the
effect cannot simply be described by a normalized line tension. We
calculate interfacial profiles for typical values of van der Waals
forces and discuss the role of long-range surface forces on the contact
angle of nanobubbles and nanodrops
Surpassingly Competitive Electromagnetic Field Enhancement at the Silica/Silver Interface for Selective Intracellular Surface Enhanced Raman Scattering Detection
A thin plasmonic nanofilm is formed by preformed silver nanoparticles (30 nm) in the matrix of poly(vinyl alcohol) adsorbed on silica microparticles (1.5 μm) (SiO<sub>2</sub>@Ag-PVA). By applying finite element method (FEM) analysis the surface enhanced Raman spectroscopy (SERS) enhancement factors (EFs) can reach 10<sup>5</sup> with higher values from 10<sup>9</sup> to 10<sup>11</sup> in the silver layer of 5 nm thickness. Nanoparticles in the SiO<sub>2</sub>@Ag-PVA nanofilm need at least 15 nm radius to exhibit SERS EFs greater than 10<sup>7</sup>. High values of this enhancement at the silver/silica interface of spherical geometry can be reached faster by using a 532 nm compared to 785 nm excitation wavelength. By this approach different SERS spectral features can be distinguished between live fibroblasts with spread (“healthy” state) or round (“unhealthy” state) shapes. Characteristic features of secondary protein structures, detection of different acidic conditions and cholesterol with at least a 3-fold higher sensitivity are examined. Moreover, a greater amount of glucose (glucogen) and also tyrosine can be monitored in real time. This is important in identification of higher risk of diabetes as well as in several genetic metabolic disorders (<i>e.g.</i>, phenylketonuria, tyrosinaemia type II and tyrosinosis)
Influence of Embedded Nanocontainers on the Efficiency of Active Anticorrosive Coatings for Aluminum Alloys Part I: Influence of Nanocontainer Concentration
This work presents an effective anticorrosive coating
for the industrially
important aluminum alloy, AA2024-T3. The protective coating was designed
by dispersing mesoporous silica nanocontainers, loaded with the nontoxic
corrosion inhibitor, 2-mercaptobenzothiazole, in a hybrid sol–gel
(SiO<sub><i>x</i></sub>/ZrO<sub><i>x</i></sub>) layer. The concentration of the embedded nanocontainers was varied
(0.04–1.7 wt %) to ascertain the optimum conditions for anticorrosion
performance. Attaining high efficiency was found to be a compromise
between delivering sufficient corrosion inhibitor and preserving the
coating barrier properties. The impact of nanocontainer concentration
on the thickness and adhesion of freshly cured coatings was also investigated.
The barrier properties of the intact coatings were assessed by electrochemical
impedance spectroscopy. The active corrosion inhibition was evaluated
during a simulated corrosion process by the scanning vibrating electrode
technique. This study has led to a better understanding of the factors
influencing the anticorrosion performance and properties of active
anticorrosive coatings with embedded nanocontainers
Line Emission of Sodium and Hydroxyl Radicals in Single-Bubble Sonoluminescence
International audienceSpectroscopic studies of single-bubble sonoluminescence (SBSL) in water and aqueous sodium chloride solutions with a defined concentration of argon were performed as a function of the driving acoustic pressure. The broad-band continuum ranging from 200 to 700 nm is characterized by fits using Planck’s law of blackbody radiation. The obtained blackbody temperatures are in the range of 104 K and are revealed to be independent of the presence of a salt and the acoustic pressure, whereas the SL intensity increases by a factor of more than 10 within the studied acoustic pressure range. The different trends followed by SL intensity and blackbody temperatures question the blackbody model. In solutions with 70 mbar of argon, line emissions of OH• radicals and Na* are observed. The shape of the OH• radical emission spectrum is very similar to that in MBSL spectra, indicating the strong similarity of intrabubble conditions. An increase of the acoustic pressure causes the continuum to overlap the lines until they become indistinguishable. The emission line of Na* in NaCl is observed only at high NaCl concentrations. When sodium dodecylsulfate is used a pronounced Na* line is already observed in a 1 mM solution thanks to enrichment of sodium ions at the interface. The results presented in this work reveal the strong similarity of SBSL and MBSL under certain experimental conditions
Influence of Embedded Nanocontainers on the Efficiency of Active Anticorrosive Coatings for Aluminum Alloys Part II: Influence of Nanocontainer Position
The present work contributes to the coating design of
active anticorrosive coatings for the aluminum alloy, AA2024-T3. Part
II is a continuation of Part I: Influence of Nanocontainer Concentration
and describes further surprising aspects of the design of nanocontainer
based active anticorrosive coatings, which influence their performance.
The studied coating system consists of a passive sol–gel (SiO<sub><i>x</i></sub>/ZrO<sub><i>x</i></sub>) matrix
and inhibitor (2-mercaptobenzothiazole) loaded mesoporous silica nanocontainers
(MBT@NCs), which are dispersed only in half of the coating volume.
Varying position and concentration of MBT@NCs the synergetic effect
of inhibitor amount and path length on the metal surface were analyzed,
considering the balance between optimum barrier properties, active
protection and adhesion. The impact of MBT@NC position on passive
and active corrosion resistance was investigated by electrochemical
impedance spectroscopy and scanning vibrating electrode technique.
Increasing the distance between MBT@NCs and metal surface led to better
barrier properties but worse active corrosion inhibition. These findings
improve the understanding of the factors influencing the overall performance
of active anticorrosive coatings and enable the development of a coating
system with optimum anticorrosion efficiency
Plasmonic Nanochemistry Based on Nanohole Array
We
show that the growth of Ag nanoparticles (NPs) follows the areas
of maximum plasmonic field in nanohole arrays (NAs). We thus obtain
Ag NP rings not connected to the metallic rim of the nanoholes. The
photocatalytic effect resulting from the enhanced <i>E</i>-field of NAs boosts the reaction and is responsible for the site
selectivity. The strategy, using plasmonics to control a chemical
reaction, can be expanded to organic reactions, for example, synthesis
of polypyrrole. After the NA film is removed, ordered ring-shaped
Ag NPs are easily obtained, inspiring a facile micropatterning method.
Overall, the results reported in this work will contribute to the
control of chemical reactions at the nanoscale and are promising to
inspire a facile way to pursue patterned chemical reactions
One-Pot Synthesis of Polypeptide–Gold Nanoconjugates for <i>in Vitro</i> Gene Transfection
We present a general strategy to create polypeptide–gold nanoconjugates by a one-pot synthesis approach, where polypeptides act not only as capping agents but also as reductants for the formation of gold nanoparticles without the need of an additional reducing agent. The present approach is environmentally benign, facile, and flexible for the design of functional polypeptide–gold nanoconjugates. As a demonstration of as-synthesized nanoconjugates for biomedical applications, the resulting positively charged polypeptide-conjugated gold nanoparticles are applied for gene delivery. A gradual and prolonged intracellular uptake and transfection is achieved, and transfection activity is maintained for almost two weeks with no obvious cytotoxicity. The biologically based method presented in this work will provide a new alternative in creating a variety of multifunctional polypeptide–metallic nanoconjugates in a simple and straightforward manner, which will be more advantageous for their applications in biomedicine
Effect of Linear Elongation on Carbon Nanotube and Polyelectrolyte Structures in PDMS-Supported Nanocomposite LbL Films
Polyelectrolyte (PE) multilayer (PEM) thin films prepared
by layer-by-layer
self-assembly on flexible substrates are exposed to elongation in
many fields of technology. Upon elongation, these types of films are
showing interesting, but not understood, phenomena, such as controlled
wetting, stimuli-responsive nanovalves, and lithography-free surface
structuring. To investigate the mechanisms causing these interesting
phenomena, we employed spectroscopic investigations of supported PEM
films that were prepared from polystyrene sulfonate (PSS)-wrapped
single-walled carbon nanotubes (SWNTs) or pyrene-labeled PSS (PSS-PY)
and polydiallyldiammonium chloride. Our results show that the SWNTs
agglomerated upon deposition into the PEM and showed a strong change
in orientation upon uniaxial elongation of the PEM. Upon release of
elongation, the resulting wrinkling pattern was changing its wavelength
upon time, in the case of the SWNT-containing PEM. Fluorescence measurements
of the PSS-PY in the PEM showed that the PEs changed their orientation
due to constant mechanical force from elongation up to a time scale
of 2 days after beginning the elongation. The results prove that elongated
and released PEM films, until now considered static structures, possess
strong kinetics, which has to be taken into account for their application
Laser-Induced Cell Detachment, Patterning, and Regrowth on Gold Nanoparticle Functionalized Surfaces
We report on the selective cell detachment from nanoengineered gold nanoparticle (AuNP) surfaces triggered by laser irradiation, which occurs in a nonthermal manner. The gold nanoparticle-based surfaces reveal good adhesion of NIH3T3 fibroblast cells. Patterning is achieved by lithographic microcontact printing, selective gold nanoparticle deposition, and by laser beam profiling. It is shown that the effectiveness of fibroblast cell detachment depends on the cell age, laser power, and AuNP patterning profile. Heat distribution and temperature rise around gold nanoparticle functionalized surfaces is modeled, revealing low heating of nanoparticles by laser illumination. The nonthermal photochemical mechanism of cell detachment due to production of reactive oxygen species under illumination of gold nanoparticles by green laser light is studied. We also demonstrate that cells migrate from unirradiated areas leading to their reattachment and surface recovery which is important for controlled spatial organization of cells in wound healing and tissue engineering. Research presented in this work is targeted at designing biointerfaces for cell cultures
Resonant Optical Transmission through Topologically Continuous Films
A continuous thick (≥100 nm) Ag film is generally optically nontransparent, but here we show that <i>via</i> a dedicated structuring it can be made transparent. The enhanced optical transmission is realized by preparing metal films with a periodic array of hollow nanocones <i>via</i> an inexpensive and versatile colloidal lithography technique. These topologically continuous films possess the structural feature of sharp top tips and bottom nanoholes, leading to an effective resonance mode of coupling between the surface plasmons around the holes and cone tips. This introduces a resonant optical transmission that is much affected by the thickness and height of the hollow nanocones. Moreover, the topologically continuous films are highly sensitive to the surrounding environment, indicating great potential for plasmonic sensors. The experimental results are in good agreement with numerical simulations. On the basis of the hollow element and enhanced optical performance, hollow nanocone array films can be used as photosensitive microreactors, isolated cell culture bases, <i>etc.</i> This provides a combination of high optical sensitivity and chemistry in microcavities