Surfactant-Free Polyurethane Nanocapsules via Inverse Pickering Miniemulsion

We report on a surfactant-free synthesis of Pickering-stabilized submicrometer-sized capsules in inverse miniemulsion. Functionalized silica nanoparticles are able to stabilize water-in-cyclohexane miniemulsions to form stable polyurethane shells via interfacial polyaddition. The effect of the type of silica functionalization on the stabilizing properties is demonstrated by varying the hydrophobicity and, therefore, the contact angle between silica and the two liquid phases. Addition of small amounts of salt leads to a reduction of the capsule size and to a narrow size distribution. The impermeability of the formed capsule shell is proven by encapsulation of an organic fluorescent dye and release studies in aqueous environment. In addition, we show the possibility to encapsulate large amounts of inorganic salts without negative effects concerning the stability of the emulsion, which enables the application for phase-change materials

Molecularly Controlled Coagulation of Carboxyl-Functionalized Nanoparticles Prepared by Surfactant-Free Miniemulsion Polymerization

We present the synthesis of molecularly controlled “CO₂-switchable” polystyrene nanoparticles by surfactant-free miniemulsion polymerization using a carboxyl-functionalized surface-active monomer, which acts as comonomer and stabilizer at the same time. The obtained nanoparticles are about 100 nm in size and show a small size distribution, confirmed by dynamic light scattering (DLS) and electron microscopy. Under ambient conditions, the latex particles form a stable suspension that can be coagulated by bubbling CO₂. The redispersion of the coagulated particles can be easily achieved by ultrasonication. The reversibility of the coagulation is confirmed after several coagulation/redispersion cycles (CO₂ bubbling and ultrasonification) from DLS and zeta potential measurements

Ceria/Polymer Hybrid Nanoparticles as Efficient Catalysts for the Hydration of Nitriles to Amides

We report the synthesis of ceria/polymer hybrid nanoparticles and their use as effective supported catalysts for the hydration of nitriles to amide, exemplified with the conversion of 2-cyanopiridine to 2-picolinamide. The polymeric cores, made of either polystyrene (PS) or poly­(methyl methacrylate) (PMMA), are prepared by miniemulsion copolymerization in the presence of different functional comonomers that provide carboxylic or phosphate groups: acrylic acid, maleic acid, and ethylene glycol methacrylate phosphate. The functional groups of the comonomers generate a corona around the main polymer particle and serve as nucleating agents for the in situ crystallization of cerium­(IV) oxide. The obtained hybrid nanoparticles can be easily redispersed in water or ethanol. The conversion of amides to nitriles was quantitative for most of the catalytic samples, with yields close to 100%. According to our experimental observations by high-performance liquid chromatography (HPLC), no work up is needed to separate the product from unreacted substrate. The substrate remains absorbed on the catalyst surface, whereas the product can be easily separated. The catalysts are shown to be recyclable and can be reused for a large number of cycles without loss in efficiency

Luminescent and Magnetoresponsive Multifunctional Chalcogenide/Polymer Hybrid Nanoparticles

Cadmium sulfide/magnetite/polymer multifunctional hybrid nanoparticles are prepared by crystallizing CdS in a controlled manner on the surface of phosphonate-functionalized polystyrene particles with a magnetic core. The supporting polymer magnetoresponsive nanoparticles are produced by a modified miniemulsion polymerization process: a first miniemulsion containing the core monomer (styrene) and a phosphonate-functionalized surface-active monomer is mixed with a second miniemulsion containing magnetite nanoparticles capped with oleic acid and the same surface-active monomer. The chalcogenide formation occurs in situ at the surface of the polymer particles by adding a precipitating agent (sodium sulfide) at a controlled rate. The phosphonate groups on the surface of the polymer particles have the ability to bind the cadmium ions and act as nucleating centers from which the controlled crystallization of CdS takes place. The resulting hybrid particles show a “raspberry-like” structure, with CdS nanocrystals surrounding the polymeric core. The superparamagnetic behavior of the initial iron oxide nanoparticles, without a recognizable blocking temperature, is retained in the final hybrids particles. The obtained hybrids show luminescence in the visible light with a maximum at 620 nm (2.00 eV)

Cerium-Doped Copper(II) Oxide Hollow Nanostructures as Efficient and Tunable Sensors for Volatile Organic Compounds

Tuning sensing capabilities of simple to complex oxides for achieving enhanced sensitivity and selectivity toward the detection of toxic volatile organic compounds (VOCs) is extremely important and remains a challenge. In the present work, we report the synthesis of pristine and Ce-doped CuO hollow nanostructures, which have much higher VOC sensing and response characteristics than their solid analogues. Undoped CuO hollow nanostructures exhibit high response for sensing of acetone as compared to commercial CuO nanoparticles. As a result of doping with cerium, the material starts showing selectivity. CuO hollow structures doped with 5 at. % of Ce return highest response toward methanol sensing, whereas increasing the Ce doping concentration to 10%, the material shows high response for bothacetone and methanol. The observed tunability in selectivity is directly linked to the varying concentration of the oxygen defects on the surface of the nanostructures. The work also shows that the use of hollow nanostructures could be the way forward for obtaining high-performance sensors even by using conventional and simple metal or semiconductor oxides

Hybrid Poly(urethane–urea)/Silica Nanocapsules with pH-Sensitive Gateways

We have produced hybrid poly­(urethane–urea)/silica nanocapsules with controlled molecular-scale regimes of silica that break upon introduction into basic media. The miniemulsion technique used is simple and scalable but yields complex molecular-scale morphologies that create molecular gates for the release of hydrophilic components. The hybrid nanocapsules displayed no microphase separation, indicating the formation of microscopically mixed regions of silica and poly­(urethane–urea). Using atomic force microscopic techniques, we characterize the mechanical properties of individual capsules and identify the tailorability of the capsule modulus by changing the ratio of isocyanate to silica in the precursor mixture. The compositions of the hybrids were confirmed by infrared spectroscopy and thermogravimetric analysis. The change in size of a nanocapsule with pH and time was monitored by fluorescence correlation spectroscopy to evaluate their potential as nanocontainers and show a pH-responsive release

Crystallinity Tunes Permeability of Polymer Nanocapsules

Permeability is the key property of nanocapsules because it dictates the release rate of encapsulated payloads. Herein, we engineer the crystallinity of polymers confined in the shell of nanocapsules. Nanocapsules with crystalline shells are formed from polyurea and polyphosphoester. The thermal properties, such as crystallization temperature and degree of crystallinity, are different from the bulk. The degree of crystallinity is used to control the shell permeability and, therefore, the release of encapsulated payloads, such as fluorescent dyes, typically used as model components for biomedical applications

A New Design Strategy for the Synthesis of Unsubstituted Polythiophene with Defined High Molecular Weight

Unsubstituted polythiophene (PT) with defined and known high molecular mass (up to ca. 36 000 g mol^–1 (<i>M</i>_w)) and low structural defects (ca. 3.6 mol %) as highly attractive semiconducting material is presented. The new synthetic strategy for this polymer is based on the combination of Stille-type polycondensation reactions, ultrasound-assisted dispersion technique, and microwave-assisted ring-closure reactions. The use of Stille-type polycondensation produces a diketal prepolymer with good solubility and prescient and controllable degree of polymerization (DP) for the final insoluble PT. Ultrasonication preserves a high interfacial area, while microwave provides fast and effective heating for the last heterophase ring-closure reaction. The characterization of the final product by solid-state NMR, TEM, UV–vis absorption and fluorescence emission spectroscopy, XRD, TGA, and conductivity measurements exhibits significant features for electronic and photoelectronic applications, such as broadened absorption, relatively high crystallinity, high thermal stability, and typical semiconducting properties

Calcium-Induced Molecular Rearrangement of Peptide Folds Enables Biomineralization of Vaterite Calcium Carbonate

Proteins can control mineralization of CaCO₃ by selectively triggering the growth of calcite, aragonite or vaterite phases. The templating of CaCO₃ by proteins must occur predominantly at the protein/CaCO₃ interface, yet molecular-level insights into the interface during active mineralization have been lacking. Here, we investigate the role of peptide folding and structural flexibility on the mineralization of CaCO₃. We study two amphiphilic peptides based on glutamic acid and leucine with β-sheet and α-helical structures. Though both sequences lead to vaterite structures, the β-sheets yield free-standing vaterite nanosheet with superior stability and purity. Surface-spectroscopy and molecular dynamics simulations reveal that reciprocal structuring of calcium ions and peptides lead to the effective synthesis of vaterite by mimicry of the (001) crystal plane