8 research outputs found
Multifunctional and Dual-Responsive Polymersomes as Robust Nanocontainers: Design, Formation by Sequential Post-Conjugations, and pH-Controlled Drug Release
Robust, multiresponsive, and multifunctional
nanovesicles are in
high demand not only as carrier systems but also for applications
in microsystem devices and nanotechnology. Hence, multifunctional,
pH-responsive, and photo-cross-linked polymersomes decorated with
adamantane and azide groups are prepared by mixed self-assembly of
suitably end-modified block copolymers and are used for the subsequent
postconjugation of the polymersome surface by using covalent and noncovalent
approaches. For the covalent approach, nitroveratryloxycarbonyl-protected
amine (NVOC) molecules as light-responsive moieties are introduced
into the polymersomes through an azide–alkyne click reaction.
After photocleavage of NVOC units, functional dye molecules react
with the now freely accessible amine groups. The noncovalent approach
is performed subsequently to introduce further moieties, making use
of the strong adamantane-β-cyclodextrin host–guest interactions.
It is quantitatively proven that all reactive groups have sufficient
accessibility as well selective and orthogonal reactivity throughout
these stepwise processes to allow the successful establishment of
aimed pH- and light-responsive multifunctional polymersomes. Moreover,
this sequential methodology is also applied to obtain doxorubicin-loaded
multifunctional polymersomes for an efficient pH-controlled drug release.
Overall, tunable membrane permeability combined with the potential
for introducing multiple targeting groups by light-exposure or host–guest
interactions make these smart polymersomes promising nanocontainers
for many applications
Tailored Synthesis of Intelligent Polymer Nanocapsules: An Investigation of Controlled Permeability and pH-Dependent Degradability
In this study, we present a new route to synthesize an intelligent polymer nanocapsule with an ultrathin membrane based on surface-initiated reversible addition–fragmentation chain-transfer polymerization. The key concept of our report is to use pH-responsive polydiethylaminoethylmethacrylate as a main membrane-generating component and a degradable disulfide bond to cross-link the membrane. The permeability of membrane, tuned by adjusting pH and using different lengths of the cross-linkers, was proven by showing a dramatic swelling behavior of the nanocapsules with the longest cross-linker from 560 nm at pH 8.0 to 780 nm at pH 4.0. Also, due to the disulfide cross-linker, degradation of the capsules using GSH as reducing agent was achieved which is further significantly promoted at pH 4.0. Using a rather long-chain dithiol cross-linker, the synthesized nanocapsules demonstrated a good permeability allowing that an enzyme myoglobin can be postencapsulated, where the pH controlled enzyme activity by switching membrane permeability was also shown
Flexible Electronic Circuits - Vertical Transistors and Passive Devices
<p>Poster shown on the European Conference on Molecular Electronics ECME 2017 in Dresden.<br></p><p>Organic large area electronics have the potential to enable fully
flexible applications. This requires efficient transistors on flexible
substrates as well as capacitors, inductors, and resistors to complete
an electrical circuit.</p><p>We operate Organic Permeable Base
Transistors (OPBT) on polymer substrates to combine impressive
transistor characteristics, facile manufacturing techniques and
mechanical flexibility. Large current densities and on/off-ratios are
achieved with simple shadow mask structuring well known from OLED
technology. Currently our flexible devices reach on/off-ratios
exceeding 10<sup>6</sup> and current densities above 1 A/cm².<br></p>Thin-film
capacitors and inductors are produced to fit the needs of a transmitter
circuit that we aim to use for indoor wireless localization
applications
Nanoporous Cathodes for High-Energy Li–S Batteries from Gyroid Block Copolymer Templates
This study reports on a facile approach to the fabrication of nanoporous carbon cathodes for lithium sulfur batteries using gyroid carbon replicas based on use of polystyrene-poly-4-vinylpyridine (PS-P4VP) block copolymers as sacrificial templates. The free-standing gyroid carbon network with a highly ordered and interconnected porous structure has been fabricated by impregnating the carbon precursor solution into the gyroid block copolymer nanotemplates and subsequently carbonizing them. A wide range of analytical tools have been employed to characterize fabricated porous carbon material. Prepared nanostructures are envisioned to have a great potential in myriad areas such as energy storage/conversion devices owing to their fascinating morphology exhibiting high surface area and uniform porosity with interconnected three-dimensional networks. The resulting carbon nanoporous structures infused with elemental sulfur have been found to work as a promising electrode for lithium sulfur batteries demonstrating a high cycling stability over more than 200 cycles
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Enhanced Electrochemical Energy Storage by Nanoscopic Decoration of Endohedral and Exohedral Carbon with Vanadium Oxide via Atomic Layer Deposition
Atomic layer deposition
(ALD) is a facile process to decorate carbon
surfaces with redox-active nanolayers. This is a particularly attractive
route to obtain hybrid electrode materials for high performance electrochemical
energy storage applications. Using activated carbon and carbon onions
as representatives of substrate materials with large internal or external
surface area, respectively, we have studied the enhanced energy storage
capacity of vanadium oxide coatings. While the internal porosity of
activated carbon readily becomes blocked by obstructing nanopores,
carbon onions enable the continued deposition of vanadia within their
large interparticle voids. Electrochemical benchmarking in lithium
perchlorate in acetonitrile (1 M LiClO<sub>4</sub>) showed a maximum
capacity of 122 mAh/g when using vanadia coated activated carbon and
129 mAh/g for vanadia coated carbon onions. There is an optimum amount
of vanadia between 50 and 65 wt % for both substrates that results
in an ideal balance between redox-activity and electrical conductivity
of the hybrid electrode. Assembling asymmetric (charge balanced) full-cells,
a maximum specific energy of 38 Wh/kg and 29 Wh/kg was found for carbon
onions and activated carbon, respectively. The stability of both systems
is promising, with a capacity retention of ∼85–91% after
7000 cycles for full-cell measurements
Multimetallic Aerogels by Template-Free Self-Assembly of Au, Ag, Pt, and Pd Nanoparticles
Nanostructured,
porous metals are of great interest for material scientists since
they combine high surface area, gas permeability, electrical conductivity,
plasmonic behavior, and size-enhanced catalytic reactivity. Here we
present the formation of multimetallic porous three-dimensional networks
by a template-free self-assembly process. Nanochains are formed by
the controlled coalescence of Au, Ag, Pt, and Pd nanoparticles in
aqueous media, and their interconnection and interpenetration leads
to the formation of a self-supporting network. The resulting noble-metal-gels
are transformed into solid aerogels by the supercritical drying technique.
Compared to previously reported results, the technique is facilitated
by exclusion of additional destabilizers. Moreover, temperature control
is demonstrated as a powerful tool, allowing acceleration of the gelation
process as well as improvement of its reproducibility and applicability.
Electron microscopy shows the nanostructuring of the network and its
high porosity. XRD and EDX STEM are used to investigate the alloying
behavior of the bimetallic aerogels and prove the control of the alloying
state by temperature induced phase modifications. Furthermore, the
resulting multimetallic aerogels show an extremely low relative density
(<0.2%) and a very high surface area (>50 m<sup>2</sup>/g) compared
to porous noble metals obtained by other approaches. Electrically
conductive thin films as well as hybrid materials with organic polymers
are depicted to underline the processability of the materials, which
is a key factor regarding handling of the fragile structures and integration
into device architectures. Owing to their exceptional and tunable
properties, multimetallic aerogels are very promising materials for
applications in heterogeneous catalysis and electrocatalysis, hydrogen
storage, and sensor systems but also in surface enhanced Raman spectroscopy
(SERS) and the preparation of transparent conductive substrates
Entrapped Styrene Butadiene Polymer Chains by Sol–Gel-Derived Silica Nanoparticles with Hierarchical Raspberry Structures
A sol–gel
transformation of liquid silica precursor to solid
silica particles was carried out in a one-pot synthesis way, where
a solution of styrene butadiene elastomer was present. The composites,
thus produced, offered remarkable improvements of mechanical and dynamic
mechanical performances compared to precipitated silica. The morphological
analysis reveals that the alkoxy-based silica particles resemble a
raspberry structure when the synthesis of the silica was carried out
in the presence of polymer molecules and represent a much more open
silica-network structure. However, in the absence of the polymer,
the morphology of the silica particles is found to be different. It
is envisaged that the special morphology of the in situ synthesized
silica particles contributes to the superior reinforcement effects,
which are associated with a strong silica–rubber interaction
by rubber chains trapped inside the raspberry-like silica aggregates.
Therefore, the interfaces are characterized in detail by low-field
solid-state <sup>1</sup>H NMR spectroscopy, <sup>29</sup>Si solid-state
NMR spectroscopy, and energy-dispersive X-ray spectroscopy. Low-field <sup>1</sup>H NMR-based double-quantum experiments provide a quantitative
information about the cross-link density of the silica-filled rubber
composites and about the influence of silane coupling agent on the
chemical cross-link density of the network and correlates well with
equilibrium swelling measurements. The special microstructure of the
alkoxy-based silica was found to be associated with the interaction
between alkoxy-based silica and rubber chains as a consequence of
particle growth in the presence of rubber chains
Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility
We review the Stille coupling synthesis
of PÂ(DPP2OD-T) (PolyÂ[[2,5-diÂ(2-octyldodecyl)ÂpyrroloÂ[3,4-<i>c</i>]Âpyrrole-1,4Â(2<i>H</i>,5<i>H</i>)-dione-3,6-diyl]-<i>alt</i>-[2,2′:5′,2″-terthiophene-5,5″-diyl]])
and show that high-quality, high molecular weight polymer chains are
already obtained after as little as 15 min of reaction time. The results
of UV–vis spectroscopy, grazing incidence wide-angle X-ray
scattering (GIWAXS), and atomic force microscopy show that longer
reaction times are unnecessary and do not produce any improvement
in film quality. We achieve the best charge transport properties with
polymer batches obtained from short reaction times and demonstrate
that the catalyst washing step is responsible for the introduction
of charge-trapping sites for both holes and electrons. These trap
sites decrease the charge injection efficiency, strongly reducing
the measured currents. The careful tuning of the synthesis allows
us to reduce the reaction time by more than 100 times, achieving a
more environmentally friendly, less costly process that leads to high
and balanced hole and electron transport, the latter being the best
reported for an isotropic, spin-coated DPP polymer