9 research outputs found
Size-Controlled Polyelectrolyte Complexes: Direct Measurement of the Balance of Forces Involved in the Triggered Collapse of Layer-by-Layer Assembled Nanocapsules
Polyelectrolyte multilayers
composed of polyÂ(allylamine hydrochloride)
and polyÂ(styrene sulfonate) were assembled on 13 nm gold nanoparticles
and characterized by Transmission Electron Microscopy and Atomic Force
Microscopy. The direct measurement of the interactions at the molecular
level using a Surface Force Apparatus revealed that the colloidal
stability of such coated particles in aqueous media is brought about
concomitantly by electrostatic and steric repulsive interactions.
The cyanide induced dissolution of the gold cores yields either hollow
nanocapsules or collapsed nanospheres, two species which are very
difficult to distinguish. In contrast to the established micron sized
hollow capsules, the dissolution of the nanosized gold cores may induce
a substantial swelling of the polyelectrolyte complex into the central
void as induced by the temporary local increase of the ionic strength.
At least three layer pairs are required to maintain the structural
integrity of the polyelectrolyte shells to yield hollow nanospheres.
At about three layer pairs, thin nanocapsules are mechanically compressible
and may collapse on themselves following mechanical stimulation to
form even smaller spherical polyelectrolyte complex particles that
retain the small polydispersity of the gold cores. Thus, the templating
of polyelectrolyte shells around, e.g., gold nanoparticles followed
by the dissolution of the respective cores constitutes a new method
for the synthesis of extremely small polyelectrolyte complex particles
with very low polydispersity
Nanoprotective Layer-by-Layer Coatings with Epoxy Components for Enhancing Abrasion Resistance: Toward Robust Multimaterial Nanoscale Films
Layer-by-Layer (LbL) assembled films offer many interesting applications (<i>e.g.</i>, in the field of nanoplasmonics), but are often mechanically feeble. The preparation of nanoprotective films of an oligomeric novolac epoxy resin with poly(ethyleneimine) using covalent LbL-assembly is described. The film growth is linear, and the thickness increment per layer pair is easily controlled by varying the polymer concentration and/or the adsorption times. The abrasion resistance of such cross-linked films was tested using a conventional rubbing machine and found to be greatly enhanced in comparison to that of classic LbL-films that are mostly assembled through electrostatic interactions. These robust LbL-films are then used to mechanically protect LbL-films that would completely be removed by a few rubbing cycles in the absence of a protective coating. A 45 nm thick LbL-film composed of gold nanoparticles and poly(allylamine hydrochloride) was chosen as an especially weak example for a functional multilayer system. The critical thickness for the protective LbL-coatings on top of the weak multilayer was determined to be about 6 layer pairs corresponding to about only 10 nm. At this thickness, the whole film withstands at least 25 abrasion cycles with a reduction of the total thickness of only about 2%
Bio-Inspired Multiproperty Materials: Strong, Self-Healing, and Transparent Artificial Wood Nanostructures
Nanocomposite films possessing multiple interesting properties (mechanical strength, optical transparency, self-healing, and partial biodegradability) are discussed. We used Layer-by-Layer assembly to prepare micron thick wood-inspired films from anionic nanofibrillated cellulose and cationic poly(vinyl amine). The film growth was carried out at different pH values to obtain films of different chemical composition, whereby, and as expected, higher pH values led to a higher polycation content and also to 6 times higher film growth increments (from 9 to 55 nm per layer pair). In the pH range from 8 to 11, micron thick and optically transparent LbL films are obtained by automated dipping when dried regularly in a stream of air. Films with a size of 10 cm<sup>2</sup> or more can be peeled from flat surfaces; they show tensile strengths up to about 250 MPa and Youngâs moduli up to about 18 GPa as controlled by the polycation/polyanion ratio of the film. Experiments at different humidities revealed the plasticizing effect of water in the films and allowed reversible switching of their mechanical properties. Whereas dry films are strong and brittle (Youngâs modulus: 16 GPa, strain at break: 1.7%), wet films are soft and ductile (Youngâs modulus: 0.1 GPa, strain at break: 49%). Wet film surfaces even amalgamate upon contact to yield mechanically stable junctions. We attribute the switchability of the mechanical properties and the propensity for self-repair to changes in the polycation mobility that are brought about by the plastifying effect of water
Generating in-Plane Orientational Order in Multilayer Films Prepared by Spray-Assisted Layer-by-Layer Assembly
We present a simple
yet efficient method for orienting cellulose
nanofibrils in layer-by-layer assembled films through spray-assisted
alignment. While spraying at 90° against a receiving surface
produces films with homogeneous in-plane orientation, spraying at
smaller angles causes a macroscopic directional surface flow of liquid
on the receiving surface and leads to films with substantial in-plane
anisotropy when nanoscale objects with anisotropic shapes are used
as components. First results with cellulose nanofibrils demonstrate
that such fibrils are easily aligned by grazing incidence spraying
to yield optically birefringent films over large surface areas. We
show that the cellulosic nanofibrils are oriented parallel to the
spraying direction and that the orientational order depends for example
on the distance of the receiving surface from the spray nozzle. The
alignment of the nanofibrils and the in-plane anisotropy of the films
were independently confirmed by atomic force microscopy, optical microscopy
between crossed polarizers, and the ellipsometric determination of
the apparent refractive index of the film as a function of the in-plane
rotation of the sample with respect to the plane of incidence of the
ellipsometer
Layer-by-Layer Photocatalytic Assembly for Solar Light-Activated Self-Decontaminating Textiles
Novel
photocatalytic nanomaterials that can be used to functionalize
textiles, conferring to them efficient solar-light-activated properties
for the decontamination of toxic and lethal agents, are described.
Textiles functionalized with one-dimensional (1D) SnS<sub>2</sub>-based
nanomaterials were used for photocatalytic applications for the first
time. We showed that 1D SnS<sub>2</sub>/TiO<sub>2</sub> nanocomposites
can be easily and strongly affixed onto textiles using the layer-by-layer
deposition method. Ultrathin SnS<sub>2</sub> nanosheets were associated
with anatase TiO<sub>2</sub> nanofibers to form nano-heterojunctions
with a tight interface, considerably increasing the photo-oxidative
activity of anatase TiO<sub>2</sub> due to the beneficial interfacial
transfer of photogenerated charges and increased oxidizing power.
Moreover, it is easy to process the material on a larger scale and
to regenerate these functionalized textiles. Our findings may aid
the development of functionalized clothing with solar light-activated
photocatalytic properties that provide a high level of protection
against chemical warfare agents
Supramolecular Organic Nanowires as Plasmonic Interconnects
Metallic
nanostructures are able to interact with an incident electromagnetic
field at subwavelength scales by plasmon resonance which involves
the collective oscillation of conduction electrons localized at their
surfaces. Among several possible applications of this phenomenon,
the theoretical prediction is that optical circuits connecting multiple
plasmonic elements will surpass classical electronic circuits at nanoscale
because of their much faster light-based information processing. However,
the placement and coupling of metallic elements smaller than optical
wavelengths currently remain a formidable challenge by top-down manipulations.
Here, we show that organic supramolecular triarylamine nanowires of
â1 nm in diameter are able to act as plasmonic waveguides.
Their self-assembly into plasmonic interconnects between arrays of
gold nanoparticles leads to the bottom-up construction of basic optical
nanocircuits. When the resonance modes of these metallic nanoparticles
are coupled through the organic nanowires, the optical conductivity
of the plasmonic layer dramatically increases from 259 to 4271 Ω<sup>â1</sup>·cm<sup>â1</sup>. We explain this effect
by the coupling of a hot electron/hole pair in the nanoparticle antenna
with the half-filled polaronic band of the organic nanowire. We also
demonstrate that the whole hybrid system can be described by using
the abstraction of the lumped circuit theory, with a far field optical
response which depends on the number of interconnects. Overall, our
supramolecular bottom-up approach opens the possibility to implement
processable, soft, and low cost organic plasmonic interconnects into
a large number of applications going from sensing to metamaterials
and information technologies
Spray-Deposited Anisotropic Assemblies of Plasmonic Nanowires for Direction-Sensitive Strain Measurement
The development of nanoscale composites with hierarchical
architecture
and complex anisotropies enables the fabrication of new classes of
devices. Stretchable strain sensors have been developed in the past
for applications in various fields such as wearable electronics and
soft robotics, yet the sensing capacities of most of these sensors
are independent of the direction of deformation. In the present work,
we report on the preparation of a direction-sensitive strain sensor
using the anisotropic optical properties of a monolayer of oriented
plasmonic 1D nano-objects. Grazing incidence spraying (GIS) is used
for depositing a monolayer of in-plane aligned silver nanowires with
a controlled density on a deformable and transparent substrate. Using
the selective excitation of transverse and longitudinal localized
plasmon resonance modes of silver nanowires by polarized UVâvisibleâNIR
spectroscopy, we show that the macroscopic anisotropic properties
of the monolayer upon stretching are highly dependent on the stretching
direction and light polarization. Measuring the polarized optical
properties of the anisotropic thin films upon stretching thus allow
for retrieving both the local strain and the direction of the deformation
using a simple model
Supramolecular Organic Nanowires as Plasmonic Interconnects
Metallic
nanostructures are able to interact with an incident electromagnetic
field at subwavelength scales by plasmon resonance which involves
the collective oscillation of conduction electrons localized at their
surfaces. Among several possible applications of this phenomenon,
the theoretical prediction is that optical circuits connecting multiple
plasmonic elements will surpass classical electronic circuits at nanoscale
because of their much faster light-based information processing. However,
the placement and coupling of metallic elements smaller than optical
wavelengths currently remain a formidable challenge by top-down manipulations.
Here, we show that organic supramolecular triarylamine nanowires of
â1 nm in diameter are able to act as plasmonic waveguides.
Their self-assembly into plasmonic interconnects between arrays of
gold nanoparticles leads to the bottom-up construction of basic optical
nanocircuits. When the resonance modes of these metallic nanoparticles
are coupled through the organic nanowires, the optical conductivity
of the plasmonic layer dramatically increases from 259 to 4271 Ω<sup>â1</sup>·cm<sup>â1</sup>. We explain this effect
by the coupling of a hot electron/hole pair in the nanoparticle antenna
with the half-filled polaronic band of the organic nanowire. We also
demonstrate that the whole hybrid system can be described by using
the abstraction of the lumped circuit theory, with a far field optical
response which depends on the number of interconnects. Overall, our
supramolecular bottom-up approach opens the possibility to implement
processable, soft, and low cost organic plasmonic interconnects into
a large number of applications going from sensing to metamaterials
and information technologies
Altering the Static Dipole on Surfaces through Chemistry: Molecular Films of Zwitterionic Quinonoids
The adsorption of molecular films made of small molecules
with a large intrinsic electrical dipole has been explored. The data
indicate that such dipolar molecules may be used for altering the
interface dipole screening at the metal electrode interface in organic
electronics. More specifically, we have investigated the surface electronic
spectroscopic properties of zwitterionic molecules containing 12Ï
electrons of the <i>p</i>-benzoquinonemonoimine type, C<sub>6</sub>H<sub>2</sub>(<u>···</u>NHR)<sub>2</sub>(<u>···</u>O)<sub>2</sub> (R = H (<b>1</b>), <i>n</i>-C<sub>4</sub>H<sub>9</sub> (<b>2</b>), C<sub>3</sub>H<sub>6</sub>âSâCH<sub>3</sub> (<b>3</b>), C<sub>3</sub>H<sub>6</sub>âOâCH<sub>3</sub> (<b>4</b>), CH<sub>2</sub>âC<sub>6</sub>H<sub>5</sub> (<b>5</b>)), adsorbed on Au. These molecules are stable
zwitterions by virtue of the meta positions occupied by the nitrogen
and oxygen substituents on the central ring, respectively. The structures
of <b>2</b>â<b>4</b> have been determined by single
crystal X-ray diffraction and indicate that in these molecules, two
chemically connected but electronically not conjugated 6Ï electron
subunits are present, which explains their strong dipolar character.
We systematically observed that homogeneous molecular films with thickness
as small as 1 nm were formed on Au, which fully cover the surface,
even for a variety of R substituents. Preferential adsorption toward
the patterned gold areas on SiO<sub>2</sub> substrates was found with <b>4</b>. Optimum self-assembling of <b>2</b> and <b>5</b> results in ordered close packed films, which exhibit n-type character,
based on the position of the Fermi level close to the conduction band
minimum, suggesting high conductivity properties. This new type of
self-assembled molecular films offers interesting possibilities for
engineering metalâorganic interfaces, of critical importance
for organic electronics