6 research outputs found

    BaTiO<sub>3</sub> Supercages: Unusual Oriented Nanoparticle Aggregation and Continuous Ordering Transition in Morphology

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    Here we report the organic-free mesocrystalline superstructured cages of BaTiO<sub>3</sub>, <i>i.e.</i>, the BaTiO<sub>3</sub> supercages, which are synthesized by a one-step templateless and additive-free route using molten hydrated salt as the reaction medium. An unusual three-dimensional oriented aggregation of primary BaTiO<sub>3</sub> nanoparticles in the medium of high ionic strength, which normally favors random aggregation, is identified to take place at the early stage of the synthesis. The spherical BaTiO<sub>3</sub> aggregates further experience a remarkable continuous ordering transition in morphology, consisting of nanoparticle faceting and nanosheet formation steps. This ordering transition in conjunction with Ostwald ripening-induced solid evacuation leads to the formation of unique supercage structure of BaTiO<sub>3</sub>. Benefiting from their structure, the BaTiO<sub>3</sub> supercages exhibit improved microwave absorption property

    Cononsolvency Revisited: Solvent Entrapment by <i>N</i>‑Isopropylacrylamide and <i>N</i>,<i>N</i>‑Diethylacrylamide Microgels in Different Water/Methanol Mixtures

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    Aqueous dispersions of homo- and copolymer microgels of <i>N</i>-isopropylacrylamide (NiPAm) and <i><i>N</i></i>,<i><i>N</i></i>-diethylacrylamide (DEAm) with different compositions are temperature-dependently studied by means of proton nuclear magnetic resonance spectroscopy (<sup>1</sup>H NMR) and differential scanning calorimetry (DSC). Furthermore, the effect of varying the solvent composition by adding methanol is investigated. Methanol addition leads to a broadening of the thermally induced volume phase transition in case of NiPAm-containing samples, as confirmed by DSC. At the same time, the width of transition approaches the one of neat PDEAm. Two different solvent species, namely bulk-like and restricted solvent, are observed as separate lines in <sup>1</sup>H NMR experiments when the gels deswell. The restricted nature of the second species is affirmed by pulsed field gradient (PFG) NMR self-diffusion experiments. The temperature <i>T</i><sub>split</sub> from which on the restricted species is found cannot be directly related to the volume phase transition temperature determined by DSC. The difference between <i>T</i><sub>split</sub> and the DSC peak temperature changes depending on the NiPAm-content of the microgel. An increase in the shift difference between the two solvent signals with temperature indicates a continuous change of the restricted solvent environment. At even higher temperature, the shift difference of restricted and bulk solvent approaches asymptotically a constant value. In general, the observed effects of methanol addition are consistent with an increasing complexation of the amide protons of the microgel (originating from the NiPAm units) with methanol. In contrast, poly­(DEAm) does not show any anomaly concerning transition width and <i>T</i><sub>split</sub> upon methanol addition. This is attributed to the lack of amide protons. The results indicate that the presence of cononsolvency can be explained by the presence of the amide proton

    Intralanthanide Separation on Layered Titanium(IV) Organophosphate Materials via a Selective Transmetalation Process

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    The lanthanides (Ln) are an essential part of many advanced technologies. Our societal transformation toward renewable energy drives their ever-growing demand. The similar chemical properties of the Ln pose fundamental difficulties in separating them from each other, yet high purity elements are crucial for specific applications. Here, we propose an intralanthanide separation method utilizing a group of titanium­(IV) butyl phosphate coordination polymers as solid-phase extractants. These materials are characterized, and they contain layered structures directed by the hydrophobic interaction of the alkyl chains. The selective Ln uptake results from the transmetalation reaction (framework metal cation exchange), where the titanium­(IV) serves as sacrificial coordination centers. The “tetrad effect” is observed from a dilute Ln<sup>3+</sup> mixture. However, smaller Ln<sup>3+</sup> ions are preferentially extracted in competitive binary separation models between adjacent Ln pairs. The intralanthanide ion-exchange selectivity arises synergistically from the coordination and steric strain preferences, both of which follow the reversed Ln contraction order. A one-step aqueous separation of neodymium (Nd) and dysprosium (Dy) is quantitatively achievable by simply controlling the solution pH in a batch mode, translating into a separation factor of greater than 2000 and 99.1% molar purity of Dy in the solid phase. Coordination polymers provide a versatile platform for further exploring selective Ln separation processes via the transmetalation process

    Thermoresponsiveness of PDMAEMA. Electrostatic and Stereochemical Effects

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    Isotactic triads are introduced into poly­(dimethylaminoethyl methacrylate) (PDMAEMA) when a Lewis acid yttrium­(III)­trifluoromethanesulfonate, Y­(OTf)<sub>3</sub>, is present during the ATRP polymerization. The changes in the tacticities of the polymers are modest. However, the tacticity affects the phase separation process but in a different way in two studied cases, at pH 8 and 9. The pH, and thus the charge of the polymer, affects the balance between electrostatic and stereochemical effects. Upon the chain collapse, the zeta potential of the polymer decreases discontinuously at pH 9, whereas at pH 8 the potential keeps almost constant. However, even in the latter case the influence of the isotactic segments on the thermal transition may be observed. Increasing isotacticity is suggested to decrease the flexibility of the polymer chain. It also causes the polymers to adsorb in a more organized manner to the air/water interface than the atactic ones do. The change in the thermoresponsive behavior due to the changing tacticity of the polymer has been studied at the interface by observing the surface tension and by surface rheology and in the solution by conventional rheology. Differences in the elastic and viscous moduli owing to the different tacticities of the polymers are compared to those attributed to different molar masses and to varying pH

    Interfacial and Fluorescence Studies on Stereoblock Poly(<i>N</i>‑isopropylacryl amide)s

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    Aqueous solution and water–air interfacial properties of associative thermally responsive A–B–A stereoblock poly­(<i>N</i>-isopropylacryl amide), PNIPAM, polymers were studied and compared to atactic PNIPAM. The A–B–A polymers consist of atactic PNIPAM as a hydrophilic block (either A or B) and a water-insoluble block of isotactic PNIPAM. The surface tensions of aqueous PNIPAM solutions were measured as a function of both temperature and concentration. The isotactic blocks did not have an effect on the surface activity of the solutions. Rheological measurements on the water–air interface showed that the aggregated PNIPAMs containing isotactic blocks increased the elasticity of the surface significantly as compared to the atactic reference upon heating. Two fluorescence probes, pyrene and (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4<i>H</i>-pyran (4HP), added to the aqueous polymer solutions were concluded to reside in surroundings with lower polarity and increased microviscosity in cases when the polymers contained isotactic blocks, as compared to ordinary atactic polymers

    Thermoresponsive Nanocellulose Hydrogels with Tunable Mechanical Properties

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    Cellulose microfibrils physically bound together by soft hemicellulose chains form the scaffolding that makes plant cell walls strong. Inspired by this architecture, we designed biomimetic thermoreversible hydrogel networks based on reinforcing cellulose nanocrystals (CNC) and thermoresponsive methylcellulose (MC). Upon dissolving MC powder in CNC aqueous dispersions, viscoelastic dispersions were formed at 20 °C, where the storage modulus (<i>G</i>′) is tunable from 1.0 to 75 Pa upon increasing the CNC concentration from 0 to 3.5 wt % with 1.0 wt % MC. By contrast, at 60 °C a distinct gel state is obtained with <i>G</i>′ ≫ <i>G</i>″, <i>G</i>′ ∼ ω<sup>0</sup>, with an order of magnitude larger <i>G</i>′ values from 110 to 900 Pa upon increasing the CNC concentration from 0 to 3.5 wt % with constant 1.0 wt % MC, due to the physical cross-links between MC and CNCs. Therefore, simply mixing two sustainable components leads to the first all-cellulose thermoreversible and tunable nanocellulose-based hydrogels