Thomas Lunkenbein

UV‐Cured, Flexible, and Transparent Nanocomposite Coating with Remarkable Oxygen Barrier

A polymer-layered silicate nanocomposite coating is prepared by combining a novel synthetic lithium-hectorite and an UV-curable, cationic polyurethane. Oxygen transmission measurements clearly indicate the supremacy of the lithium-hectorite as compared to a standard montmorillonite. In addition, a very high degree of optical transparency of the nanocomposite coating is achieved, rendering this material highly interesting for flexible packaging and encapsulation applications.

Barrier Properties of Synthetic Clay with a Kilo‐Aspect Ratio

Intrinsic anisometry, the appearance in plate-like pseudocrystals (tactoids) with high aspect ratios, and their rich intercalation chemistry (cation-exchange, swelling) are some of the essential features of clays, which render them interesting as functional particles for a variety of applications. [ 1–3 ] Long before Nielsen’s [ 4 ] essay about the tortuous path theory appeared in the late 1960s, composite materials were prepared of inorganic platelets in a continuous macromolecular phase. [ 5 ] Aside from mechanically toughening of polymeric matrices via the incorporation of stiff platelets, [ 6–9 ] diffusion-barrier, [ 10–12 ] and fl ame retardant applications [ 13 ] are the main focus of current research. Since both, experiments and simulations have emphasized the key importance of high aspect ratios ( α ) of fi llers, in particular for gas permeability, [ 14 , 15 ] material scientists continue hunting for higher α exploring a variety of lamellar materials including graphene. [ 16 ]

Shear stiff, surface modified, mica-like nanoplatelets: a novel filler for polymer nanocomposites

Synthesis of polymer nanocomposites with novel shear stiff, mica-like nanoplatelets from a synthetic layered silicate is presented. This novel synthetic clay filler shows high aspect ratios while organophilization may be selectively restricted to external surfaces minimizing the organic content of the filler. The obtained nanocomposite shows superior mechanical, thermal and fire properties as compared to commonly used natural clays. Furthermore, the influence of the blending method on the nanocomposite properties was investigated.

Shaping Colloidal Rutile into Thermally Stable and Porous Mesoscopic Titania Balls

High crystallinity and controlled porosity are advantageous for many applications such as energy conversion and power generation. Despite many efforts in the last decades, the direct synthesis of organic-inorganic composite materials with crystalline transition metal oxides is still a major challenge. In general, molecules serve as inorganic precursors and heat treatment is required to convert as-synthesized amorphous composites to stable crystalline materials. Herein, an alternative approach to the direct synthesis of crystalline polymer-metal oxide composites by using a spherical polyelectrolyte brush as the template system is presented. Pre-synthesized electrostatically stabilized rutile nanocrystals that carry a positive surface charge are used as inorganic precursors. In this approach, the strong Coulomb interactions between anionic polyelectrolyte brush chains and cationic crystalline rutile colloids, whose surfaces are not capped and therefore reactive, are the key factors for the organic-inorganic crystalline composite formation. Stepwise calcination first under argon and followed with a second calcination in air lead to the complete removal of the polymer template without collapse and porous rutile balls are obtained. The results suggest that any colloids that carry a surface charge might serve as inorganic precursors when charged templates are used. It is expected that this hierarchical route for structuring oxides at the mesoscale is generally applicable.

A facile polymer templating route toward high-aspect-ratio crystalline titania nanostructures.

High-aspect-ratio rutile and anatase hybrid nanowires are produced via a template-directed process using a novel cylindrical polyelectrolyte brush template. Loading the highly negatively charged 1D templates with pre-synthesized TiO(2) nanocrystals, results in the fabrication of soluble crystalline TiO(2) hybrid nanowires.

Hierarchically porous tungsten oxide nanotubes with crystalline walls made of the metastable orthorhombic polymorph

A simple route towards highly crystalline and hierarchically porous tungsten oxide nanotubes is presented. Interestingly, due to the limited wall thickness, the metastable orthorhombic high-temperature polymorph could be stabilized for the first time at room temperature without doping. In brief, ammonium metatungstate (AMT) is grafted over core-crosslinked poly(butadiene)-block-poly(2-vinylpyridine) (PB-b-P2VP) nanorods at pH 3. Coulomb interactions between protonated PB-b-P2VP nanorods (pKa 4.5) and metatungstate anions promote hybrid formation. Subsequent calcination of the PB-b-P2VP–AMT hybrid material at 490 °C results in a non-woven structure of hierarchically porous and crystalline, orthorhombic tungsten oxide nanotubes as confirmed by electron microscopy, X-ray diffraction, and nitrogen physisorption.

Particle nanosomes with tailored silhouettes

The interest in hollow structures with defined porosities has promoted the fabrication of colloidosomes, i.e.capsules from spherical colloids. The hierarchically organized architectures were built from microparticles or multiple layers of nanoparticles to make sure that the capsule walls were sufficiently robust. Herein, we present for the first time a strategy towards submicron-sized capsules with walls that consist of a single layer of nanoscopic inorganic constituents. Nanoparticles and oppositely charged polymer colloids were joined at the surface of evaporating emulsion droplets. The heteroaggregates exhibited well-defined core–shell morphologies, with clusters of the polymer colloids as the core and a dense monolayer of nanoparticles as the shell. Various complex yet well-defined global shapes can be obtained in respect to the number of polymer particles. Subsequent removal of the polymer core led to capsules, which exhibited regular compartmentalized shapes. A high density of nanopores was obtained on objects with dimensions of less than half a micron. Regardless of the fact that the capsules consisted of a single layer of nanoparticles with tiny contacts keeping them together, they did not collapse or break apart. Monte Carlo computer simulations demonstrated that the nanoscopic constituents can be trapped into structurally arrested states.

Towards mesoporous Keggin-type polyoxometalates – systematic study on organic template removal

Here, we present systematic studies on the removal of the polymer template from inverse hexagonally ordered poly(butadiene-block-2-dimethylaminoethyl methacrylate)–phosphomolybdic acid (H3PMo12O40) nanocomposites. Highly ordered mesophases are obtained via an evaporation-induced self-assembly process. Different techniques are used to remove the organic template: direct calcination in air, a two-step heat treatment ((1) argon atmosphere and (2) oxidative atmosphere), and a combination of heat and plasma treatment. Our studies show that direct calcination in air and two-step heat treatment lead to a collapse of mesostructure before complete carbon removal is accomplished. In contrast, plasma etching of heat treated ultra-microtomed samples results in hexagonally ordered porous nanofilms.