141 research outputs found
Compression-Responsive Photonic Crystals Based on Fluorine-Containing Polymers
Fluoropolymers represent a unique class of functional polymers due to their various interesting and important properties such as thermal stability, resistance toward chemicals, repellent behaviors, and their low refractive indices in comparison to other polymeric materials. Based on the latter optical property, fluoropolymers are particularly of interest for the preparation of photonic crystals for optical sensing application. Within the present study, photonic crystals were prepared based on core-interlayer-shell particles focusing on fluoropolymers. For particle assembly, the melt-shear organization technique was applied. The high order and refractive index contrast of the individual components of the colloidal crystal structure lead to remarkable reflection colors according to Braggâs law of diffraction. Due to the special architecture of the particles, consisting of a soft core, a comparably hard interlayer, and again a soft shell, the resulting opal films were capable of changing their shape and domain sizes upon applied pressure, which was accompanied with a (reversible) change of the observed reflection colors as well. By the incorporation of adjustable amounts of UV cross-linking agents into the opal film and subsequent treatment with different UV irradiation times, stable and pressure-sensitive opal films were obtained. It is shown that the present strategy led to (i) pressure-sensitive opal films featuring reversibly switchable reflection colors and (ii) that opal films can be prepared, for which the written patternâresulting from the compressed particlesâcould be fixed upon subsequent irradiation with UV light. The herein described novel fluoropolymer-containing photonic crystals, with their pressure-tunable reflection color, are promising candidates in the field of sensing devices and as potential candidates for anti-counterfeiting materials
Complex 3DâPrinted Mechanochromic Materials with Iridescent Structural Colors Based on CoreâShell Particles
A scalable protocol for design and subsequent 3D-printing of polymeric coreshell-particles is reported. The particle synthesis by emulsion polymerization
in starved-feed mode is used for tailoring particle architecture and composition. Control of size, mechanical properties, and chemical functionalities allow
to achieve the specific requirement profile for subsequent extrusion-based
additive manufacturing. The core-shell particles consist of hard polystyrene
cores and a comparably soft polyalkylacrylate-based shell. Size and monodispersity, as well as core-to-shell ratio, are determined by means of dynamic light
scattering and transmission electron microscopy. Thermal and rheological
properties are investigated by means of dynamic scanning calorimetry and
thermogravimetric analysis as well as oscillation and capillary rheometry.
During 3D-printing, the monodisperse particles self-assemble into an ordered
close packed lattice structure, leading to visible reflection colors according to
Braggâs law of diffraction. Distinct and angle-dependent reflection colors are
recorded via UV-vis spectroscopy. As the structural color depends, inter alia,
on the underlying particle sizes, resulting colors are easily tunable by adjusting
the applied synthesis parameters. Under mechanical deformation, the color
changes due to controlled lattice deformation, which enables mechanochromic
sensing with the printed objects. They are also promising candidates for decorative ornaments, smart optical coatings, or advanced security devices
Cross-Linking Strategies for Fluorine-Containing Polymer Coatings for Durable Resistant Water- and Oil-Repellency
Functional coatings for application on surfaces are of growing interest. Especially in the
textile industry, durable water and oil repellent finishes are of special demand for implementation
in the outdoor sector, but also as safety-protection clothes against oil or chemicals. Such oil and
chemical repellent textiles can be achieved by coating surfaces with fluoropolymers. As many
concerns exist regarding (per)fluorinated polymers due to their high persistence and accumulation
capacity in the environment, a durable and resistant coating is essential also during the washing
processes of textiles. Within the present study, different strategies are examined for a durable
resistant cross-linking of a novel fluoropolymer on the surface of fibers. The monomer 2-((1,1,2-
trifluoro-2-(perfluoropropoxy)ethyl)thio)ethyl acrylate, whose fluorinated side-chain is degradable
by treatment with ozone, was used for this purpose. The polymers were synthesized via free radical
polymerization in emulsion, and different amounts of cross-linking reagents were copolymerized.
The final polymer dispersions were applied to cellulose fibers and the cross-linking was induced
thermally or by irradiation with UV-light. In order to investigate the cross-linking efficiency, tensile
elongation studies were carried out. In addition, multiple washing processes of the fibers were
performed and the polymer loss during washing, as well as the effects on oil and water repellency
were investigated. The cross-linking strategy paves the way to a durable fluoropolymer-based
functional coating and the polymers are expected to provide a promising and sustainable alternative
to functional coatings
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Dye-Loaded Mechanochromic and pH-Responsive Elastomeric Opal Films
In this work, the preparation and fabrication of elastomeric opal films revealing reversible mechanochromic and pH-responsive features are reported. The coreâinterlayerâshell (CIS) particles are synthesized via stepwise emulsion polymerization leading to hard core (polystyrene), crosslinked interlayer (poly(methyl methacrylate-co-allyl methacrylate), and soft poly(ethyl acrylate-co-butyl acrylate-co-(2-hydroxyethyl) methacrylate) shell particles featuring a size of 294.9 ± 14.8 nm. This particle architecture enables the application of the melt-shear organization technique leading to elastomeric opal films with orange, respectively, green brilliant reflection colors dependent on the angle of view. Moreover, the hydroxyl moieties as part of the particle shell are advantageously used for subsequent thermally induced crosslinking reactions enabling the preparation of reversibly tunable mechanochromic structural colors based on Bragg's law of diffraction. Additionally, the CIS particles can be loaded upon extrusion or chemically by a postfunctionalization strategy with organic dyes implying pH-responsive features. This convenient protocol for preparing multi-responsive, reversibly stretch-tunable opal films is expected to enable a new material family for anti-counterfeiting applications based on external triggers
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Dye-Loaded Mechanochromic and pH-Responsive Elastomeric Opal Films
In this work, the preparation and fabrication of elastomeric opal films revealing reversible mechanochromic and pH-responsive features are reported. The core-interlayer-shell (CIS) particles are synthesized via stepwise emulsion polymerization leading to hard core (polystyrene), crosslinked interlayer (poly(methyl methacrylate-co-allyl methacrylate), and soft poly(ethyl acrylate-co-butyl acrylate-co-(2-hydroxyethyl) methacrylate) shell particles featuring a size of 294.9 ± 14.8 nm. This particle architecture enables the application of the melt-shear organization technique leading to elastomeric opal films with orange, respectively, green brilliant reflection colors dependent on the angle of view. Moreover, the hydroxyl moieties as part of the particle shell are advantageously used for subsequent thermally induced crosslinking reactions enabling the preparation of reversibly tunable mechanochromic structural colors based on Bragg's law of diffraction. Additionally, the CIS particles can be loaded upon extrusion or chemically by a postfunctionalization strategy with organic dyes implying pH-responsive features. This convenient protocol for preparing multi-responsive, reversibly stretch-tunable opal films is expected to enable a new material family for anti-counterfeiting applications based on external triggers
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Mechanically Stable, BinderâFree, and FreeâStanding Vanadium Trioxide/Carbon Hybrid Fiber Electrodes for LithiumâIon Batteries
Binder is a crucial component in present-day battery electrodes but commonly contains fluorine and requires coating processing using organic (often
toxic) solvents. Preparing binder-free electrodes is an attractive strategy to
make battery electrode production and its end-of-use waste greener and safer.
Herein, electrospinning is employed to prepare binder-free and self-standing
electrodes. Such electrodes often suffer from low flexibility, and the correlation between performance and flexibility is usually overlooked. Processing
parameters affect the mechanical properties of the electrodes, and for the
first time it is reported that mechanical flexibility directly influences the
electrochemical performance of the electrode. The importance is highlighted
when processing parameters advantageous to powder materials, such as
a higher heat treatment temperature, harm self-standing electrodes due to
deterioration of fiber flexibility. Other strategies, such as conductive carbon
addition, can be employed to improve the cell performance, but their effect
on the mechanical properties of the electrodes must be considered. Rapid
heat treatment achieves self-standing V2O3 with a capacity of 250 mAh gâ1
at
250 mA gâ1
and 390 mAh gâ1
at 10 mA gâ
Combining Soft Polysilazanes with Melt-Shear Organization of CoreâShell Particles: On the Road to Polymer-Templated Porous Ceramics
The preparation of ordered macroporous SiCN ceramics has attracted significant interest and is an attractive area for various applications, e.g., in the fields of catalysis, gas adsorption, or membranes. Non-oxidic ceramics, such as SiCN, own a great stability based on the covalent bonds between the containing elements, which leads to interesting properties concerning resistance and stability at high temperature. Their peculiar properties have become more and more important for a manifold of applications, like catalysis or separation processes, at high temperatures. Within this work, a feasible approach for the preparation of ordered porous materials by taking advantage of polymer-derived ceramics is presented. To gain access to free-standing films consisting of porous ceramic materials, the combination of monodisperse organic polymer-based colloids with diameters of 130 nm and 180 nm featuring a processable preceramic polymer is essential. For this purpose, the tailored design of hybrid organic/inorganic particles featuring anchoring sites for a preceramic polymer in the soft shell material is developed. Moreover, polymer-based core particles are used as sacrificial template for the generation of pores, while the preceramic shell polymer can be converted to the ceramic matrix after thermal treatment. Two different routes for the polymer particles, which can be obtained by emulsion polymerization, are followed for covalently linking the preceramic polysilazane Durazane1800 (Merck, Germany): (i) Free radical polymerization and (ii) atom transfer radical polymerization (ATRP) conditions. These hybrid hard core/soft shell particles can be processed via the so-called melt-shear organization for the one-step preparation of free-standing particle films. A major advantage of this technique is the absence of any solvent or dispersion medium, enabling the core particles to merge into ordered particle stacks based on the soft preceramic shell. Subsequent ceramization of the colloidal crystal films leads to core particle degradation and transformation into porous ceramics with ceramic yields of 18â54%
Combining Soft Polysilazanes with Melt-Shear Organization of CoreâShell Particles: On the Road to Polymer-Templated Porous Ceramics
The preparation of ordered macroporous SiCN ceramics has attracted significant interest and is an attractive area for various applications, e.g., in the fields of catalysis, gas adsorption, or membranes. Non-oxidic ceramics, such as SiCN, own a great stability based on the covalent bonds between the containing elements, which leads to interesting properties concerning resistance and stability at high temperature. Their peculiar properties have become more and more important for a manifold of applications, like catalysis or separation processes, at high temperatures. Within this work, a feasible approach for the preparation of ordered porous materials by taking advantage of polymer-derived ceramics is presented. To gain access to free-standing films consisting of porous ceramic materials, the combination of monodisperse organic polymer-based colloids with diameters of 130 nm and 180 nm featuring a processable preceramic polymer is essential. For this purpose, the tailored design of hybrid organic/inorganic particles featuring anchoring sites for a preceramic polymer in the soft shell material is developed. Moreover, polymer-based core particles are used as sacrificial template for the generation of pores, while the preceramic shell polymer can be converted to the ceramic matrix after thermal treatment. Two different routes for the polymer particles, which can be obtained by emulsion polymerization, are followed for covalently linking the preceramic polysilazane Durazane1800 (Merck, Germany): (i) Free radical polymerization and (ii) atom transfer radical polymerization (ATRP) conditions. These hybrid hard core/soft shell particles can be processed via the so-called melt-shear organization for the one-step preparation of free-standing particle films. A major advantage of this technique is the absence of any solvent or dispersion medium, enabling the core particles to merge into ordered particle stacks based on the soft preceramic shell. Subsequent ceramization of the colloidal crystal films leads to core particle degradation and transformation into porous ceramics with ceramic yields of 18â54%
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Single-Polymer Friction Force Microscopy of dsDNA Interacting with a Nanoporous Membrane
Surface-grafted polymers can reduce friction between solids in liquids by compensating the normal load with osmotic pressure, but they can also contribute to friction when fluctuating polymers entangle with the sliding counter face. We have measured forces acting on a single fluctuating double-stranded DNA polymer, which is attached to the tip of an atomic force microscope and interacts intermittently with nanometer-scale methylated pores of a self-assembled polystyrene-block-poly(4-vinylpyridine) membrane. Rare binding of the polymer into the pores is followed by a stretching of the polymer between the laterally moving tip and the surface and by a force-induced detachment. We present results for the velocity dependence of detachment forces and of attachment frequency and discuss them in terms of rare excursions of the polymer beyond its equilibrium configuration
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