Because of growing environmental concerns, the development of lead-free piezoelectric materials with enhanced properties has become of great interest. Here, we report a giant piezoelectric coefficient (d) of 550 pC/N and a high Curie temperature (T) of 237 °C in (1-x-y)KNaNbSbOxBiFeOyBiNaZrO (KNNS-xBF-yBNZ) ceramics by optimizing x, y, z, and w. Atomic-resolution polarization mapping by Z-contrast imaging reveals the intimate coexistence of rhombohedral (R) and tetragonal (T) phases inside nanodomains, that is, a structural origin for the R-T phase boundary in the present KNN system. Hence, the physical origin of high piezoelectric performance can be attributed to a nearly vanishing polarization anisotropy and thus low domain wall energy, facilitating easy polarization rotation between different states under an external field.
A 3D spongy collagen cryogel was prepared using DAS as the cross‐linker. FTIR and CD studies demonstrate that crosslinking is achieved through the reaction of the DAS aldehyde groups with the free amino groups in collagen without affecting the triple helix of collagen. SEM demonstrates that the cryogel has a heteroporous structure with interconnecting pores. DSC measurements reveal that the cryogels have improved thermal stability in comparison with pure collagen. Moreover, the ESR shows that the water uptake of the cryogel decreases with DAS content. Evaporation tests indicate that the cryogel can hold moisture for a long time. Since both collagen and DAS are nontoxic and the resultant cryogel is blood‐compatible, the cryogel is expected to be useful, e.g., as wound dressing.magnified image
We have investigated the effects of Cr3+ on the hierarchical structure of pigskin collagen fibers by use of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), wide-angle X-ray diffraction (WAXD), confocal laser micro-Raman spectroscopy (CLRS), and circular dichroism (CD). Our results demonstrate that the introduction of Cr3+ leads to the formation of a cluster of 20-40 nm between collagen fibrils, while the unique axial periodic structure (D periodicity) of the fibrils does not change. As the Cr3+ concentration increases, the order of intermolecular lateral packing, crystallite structure within helical chains, and N and C telopeptide regions decrease. The present study reveals that Cr3+ only cross-links with collagen but does not disrupt its triple helical structure.
Due to the presence of pores and low density, a high recoverable
energy density (W
rec) value is usually
obtained at the cost of energy storage efficiency (η) in lead-free
potassium sodium niobate [(K, Na)NbO3, KNN] based ceramics,
which also affects the hardness of ceramics, finally limiting the
further development of practical applications. A high W
rec (∼3.60 J/cm3 ) and a high η
(∼74.2%) are obtained in 0.975K0.5Na0.5NbO3-0.025LaBiO3 (0.975KNN-0.025LB) ceramics
simultaneously under a high dielectric breakdown strength (DBS) of
340 kV/cm, together with a fast discharge rate (t
0.9 ∼ 46 ns) and high power density (P
D ∼ 49.4 MW/cm3). Further analysis of
the intrinsic electronic structure is carried out via the first-principles
calculation based on the density functional theory (DFT). An ultrahigh
hardness (H) of 6.63 GPa can be accordingly obtained.
This work combines excellent energy storage properties and ultrahigh
hardness, which provides significant guidelines for applications in
pulsed-power systems.
Polyurethane (PU) with zwitterionic side chains has been prepared to resist nonspecific adsorption of proteins. First, dihydroxy-terminated poly(2-(dimethylamino)ethyl methacrylate) (PDEM(OH)(2)) is synthesized by free radical polymerization with 3-mercapto-1,2-propanediol as the chain transfer agent, which polyadds with diisocyanate to yield a PU with PDEM side chains. Such side chains are zwitterionized by 1,3-propane sultone. Proton nuclear magnetic resonance spectroscopy ((1)H NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) show that the zwitterionic side chains are incorporated into the PU. Thermal analysis demonstrates the thermal stability is greatly affected by the content of the side chains. By use of quartz crystal microbalance with dissipation (QCM-D), we have investigated the adsorption of fibrinogen, bovine serum albumin, and lysozyme on a surface constructed by such a PU. It shows the PU has a controllable protein resistance depending on the content of the zwitterionic side chains.
Poly(sodium 4-styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) are flexible polyelectrolytes, whereas sulfated chitosan (SC) and cationic guar gum (CGG) are semiflexible polyelectrolytes. By use of a quartz crystal microbalance with dissipation (QCM-D), a zeta potential analyzer (ZPA), and atomic force microscopy (AFM), we have investigated the growth of PSS/PDDA, PSS/CGG, SC/PDDA, and SC/CGG multilayers as a function of NaCl concentration (C(NaCl)). For the same layer number, the changes of frequency (-Δf) and dissipation (ΔD) regarding PSS/PDDA multilayer increase with C(NaCl), whereas -Δf and ΔD for SC/CGG multilayer increase at C(NaCl) < 0.1 M and decrease at C(NaCl) > 0.1 M as C(NaCl) increases. In the cases of PSS/CGG and SC/PDDA multilayer, for the same layer number, -Δf and ΔD increase with C(NaCl) in the range of C(NaCl) < 0.5 M, and they decrease with the increasing C(NaCl) in the case of SC/PDDA multilayer but slightly change for the PSS/CGG multilayer at C(NaCl) > 0.5 M. QCM-D studies indicate that the growth of multilayers as a function of salt concentration is determined by the delicate balance between the weakening of electrostatic repulsion between identically charged groups and the decrease of electrostatic attraction between neighboring layers. ZPA and AFM measurements demonstrate that the extent of surface charge overcompensation and the surface morphology of the multilayers are controlled by the chain conformation.
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