15 research outputs found

    Probing Flexural Properties of Cellulose Nanocrystal–Graphene Nanomembranes with Force Spectroscopy and Bulging Test

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    The flexural properties of ultrathin freely standing composite nanomembranes from reduced graphene oxide (rGO) and cellulose nanocrystals (CNC) have been probed by combining force spectroscopy for local nanomechanical properties and bulging test for global mechanical properties. We observed that the flexural properties of these rGO–CNC nanomembranes are controlled by rGO content and deformational regimes. The nanomembranes showed the enhanced mechanical properties due to the strong interfacial interactions between interwoven rGO and CNC components. The presence of weak interfacial interactions resulted in time-dependent behavior with the relaxation time gradually decreased with increasing the deformational rate owing to the reducing viscous damping at faster probing regimes close to 10 Hz. We observed that the microscopic elastic bending modulus of 141 GPa from local force spectroscopy is close to the elastic tensile modulus evaluated from macroscopic bulging test, indicating the consistency of both approaches for analyzing the ultrathin nanomembranes at different spatial scales of deformation. We showed that the flexible rGO–CNC nanomembranes are very resilient in terms of their capacity to recover back into original shape

    Ligand-Exchange Dynamics on Gold Nanocrystals: Direct Monitoring of Nanoscale Polyvinylpyrrolidone–Thiol Domain Surface Morphology

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    We report direct high-resolution monitoring of an evolving mixed nanodomain surface morphology during thiol adsorption on polyvinylpyrrolidone (PVP)-stabilized single crystal gold nanocrystals. The thiol adsorption and replacement dynamics are much more complex than a simple complete substitution of the initial polymer ligand. We observed that during ligand exchange with linear thiol, the nanocrystal surface evolved from an initial 1 nm uniform PVP coating into a remarkably stable network of globular PVP domains 20–100 nm in size and ∼4 nm in height surrounded by thiol self-assembled monolayers. The final stability of such a mixed thiol–PVP surface morphology can possibly be attributed to the interfacial energy reduction from partially solvophilic surfaces and the entropic gain from mixed ligand surface layers. The ligand-exchange dynamics and the unusual equilibrium morphology revealed here provide important insights into both displacement dynamics of surface-bound molecules and the nanoscale peculiarities of surface functionalization of colloidal metal substrates

    Interfacial Shear Strength and Adhesive Behavior of Silk Ionomer Surfaces

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    The interfacial shear strength between different layers in multilayered structures of layer-by-layer (LbL) microcapsules is a crucial mechanical property to ensure their robustness. In this work, we investigated the interfacial shear strength of modified silk fibroin ionomers utilized in LbL shells, an ionic–cationic pair with complementary ionic pairing, (SF)-poly-l-glutamic acid (Glu) and SF-poly-l-lysine (Lys), and a complementary pair with partially screened Coulombic interactions due to the presence of poly­(ethylene glycol) (PEG) segments and SF-Glu/SF-Lys­[PEG] pair. Shearing and adhesive behavior between these silk ionomer surfaces in the swollen state were probed at different spatial scales and pressure ranges by using functionalized atomic force microscopy (AFM) tips as well as functionalized colloidal probes. The results show that both approaches were consistent in analyzing the interfacial shear strength of LbL silk ionomers at different spatial scales from a nanoscale to a fraction of a micron. Surprisingly, the interfacial shear strength between SF-Glu and SF-Lys­[PEG] pair with partially screened ionic pairing was greater than the interfacial shear strength of the SF-Glu and SF-Lys pair with a high density of complementary ionic groups. The difference in interfacial shear strength and adhesive strength is suggested to be predominantly facilitated by the interlayer hydrogen bonding of complementary amino acids and overlap of highly swollen PEG segments

    Template-Guided Assembly of Silk Fibroin on Cellulose Nanofibers for Robust Nanostructures with Ultrafast Water Transport

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    The construction of multilength scaled hierarchical nanostructures from diverse natural components is critical in the progress toward all-natural nanocomposites with structural robustness and versatile added functionalities. Here, we report a spontaneous formation of peculiar “shish kebab” nanostructures with the periodic arrangement of silk fibroin domains along straight segments of cellulose nanofibers. We suggest that the formation of these shish kebab nanostructures is facilitated by the preferential organization of heterogeneous (β-sheets and amorphous silk) domains along the cellulose nanofiber driven by modulated axial distribution of crystalline planes, hydrogen bonding, and hydrophobic interactions as suggested by all-atom molecular dynamic simulations. Such shish kebab nanostructures enable the ultrathin membrane to possess open, transparent, mechanically robust interlocked networks with high mechanical performance with up to 30 GPa in stiffness and 260 MPa in strength. These nanoporous robust membranes allow for the extremely high water flux, up to 3.5 × 10<sup>4</sup> L h<sup>–1</sup> m<sup>–2</sup> bar<sup>–1</sup> combined with high rejection rate for various organic molecules, capability of capturing heavy metal ions and their further reduction into metal nanoparticles for added SERS detection capability and catalytic functionalities

    Template-Guided Assembly of Silk Fibroin on Cellulose Nanofibers for Robust Nanostructures with Ultrafast Water Transport

    No full text
    The construction of multilength scaled hierarchical nanostructures from diverse natural components is critical in the progress toward all-natural nanocomposites with structural robustness and versatile added functionalities. Here, we report a spontaneous formation of peculiar “shish kebab” nanostructures with the periodic arrangement of silk fibroin domains along straight segments of cellulose nanofibers. We suggest that the formation of these shish kebab nanostructures is facilitated by the preferential organization of heterogeneous (β-sheets and amorphous silk) domains along the cellulose nanofiber driven by modulated axial distribution of crystalline planes, hydrogen bonding, and hydrophobic interactions as suggested by all-atom molecular dynamic simulations. Such shish kebab nanostructures enable the ultrathin membrane to possess open, transparent, mechanically robust interlocked networks with high mechanical performance with up to 30 GPa in stiffness and 260 MPa in strength. These nanoporous robust membranes allow for the extremely high water flux, up to 3.5 × 10<sup>4</sup> L h<sup>–1</sup> m<sup>–2</sup> bar<sup>–1</sup> combined with high rejection rate for various organic molecules, capability of capturing heavy metal ions and their further reduction into metal nanoparticles for added SERS detection capability and catalytic functionalities

    Positional cloning of the <i>D-h</i> gene.

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    <p>(a) Genetic mapping of the <i>D-h</i> locus with STS markers. (b) Fine mapping of the <i>D-h</i> locus with additional STS markers. (c) Candidate gene in the 48 kb genomic DNA region identified by fine mapping. (d) Co-segregation analysis in F<sub>2</sub> plants of the HD1×Hwacheongbyeo cross using STS marker S10460. A 583 bp PCR product was observed in the tall homozygotes, whereas a shorter 520 bp PCR product was observed in the dwarf homozygotes. In dwarf heterozygotes, both fragments were observed. Lane 1, Hwacheong; Lane 2, HD1; Lane 3, HD1×HwacheongF<sub>1</sub>; Lanes 4–19, dwarf phenotype, Lanes 20 to 34, tall phenotype. (e) Genotype of the STS marker S10460 among the HD1 and 33 rice cultivars having normal clum length. Lane 1, HD1; Lanes 2–34, rice cultivars.</p

    Comparison of the cDNA and predicted amino acid sequence alignments of <i>d-h</i>(WT)and<i>D-h</i>(MT).

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    <p>(a) Comparison of the cDNA sequences <i>d-h</i>(WT)and<i>D-h</i>(MT). Asterisks indicate single nucleotide substitution, <i>d-h</i> start codon, <i>D-h</i> start codon, and stop codon. (b) Sequence ekectrophoregrams of the RT-PCR products of <i>d-h</i>(WT)and<i>D-h</i>(MT). (c) Alignment of the predicted <i>d-h</i>protein with hypothetical proteins from <i>Zea mays</i> (NP_001147534), <i>Sorghum bicolor</i> (XP_002454989), and <i>Hordeumvulgare</i> gene (BAJ91554, AK360345).</p

    Characterization of the HD1.

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    <p>(a) Seedling phenotype of the HD1 and WT. Bar = 5 cm. (b) The HD1 and WT at 3 weeks after the heading stage. Bar = 20 cm. (c) Mature panicle and seeds of the HD1 and WT. Bottom bar = 5 cm (panicle), top bar = 5 mm (seeds). (d) Internode lengths of the HD1 and WT. The average values were calculated from measurements of at least 10 plants. (e) Parenchyma cells in the first internode in the HD1 and WT. Bars = 50 µm. (f) Quantitative measurements of the cell length and cell width of the HD1 and WT (n = 20). Data are mean±SD. Asterisks indicate a significant difference at P≤0.01 compared with the WT by Student's t test. (g) Induction of α-amylase activity by gibberellic acid (GA<sub>3</sub>) in the HD1 and WT. (h) Elongation of the second leaf sheath in the HD1 and the WT in response to GA<sub>3</sub>. Data are mean±SD (n = 10). Asterisks indicate a significant difference at P≤0.01 compared with the WT by Student's t test.</p

    Expression patterns of the <i>D-h</i> gene.

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    <p>(a) QuantitativeRT-PCR analysis of the <i>D-h</i> gene in organs. (b) Semi-quantitative RT-PCR analysis of the <i>D-h</i> gene in organs. (c)–(i) GUS activity detected in the <i>D-h</i> promoter::GUS transgenic plants.</p
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