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1.
Nanoscale ; 11(41): 19278-19284, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31312823

RESUMO

Inspired by the Bogolanfini dyeing technique, we report how flexible nanofibrillated cellulose (CNF) films can be functionalized and patterned by surface-bound nanoparticles of hydrolyzable tannins and multivalent metal ions with tunable colors. Molecular dynamics simulations show that gallic acid (GA) and ellagic acid (EA) rapidly adsorb and assemble on the CNF surface, and atomic force microscopy confirms that nanosized GA assemblies cover the surface of the CNF. CNF films were patterned with tannin-metal ion nanoparticles by an in-fibre reaction between the pre-impregnated tannin and the metal ions in the printing ink. Spectroscopic studies show that the FeIII/II ions interact with GA and form surface-bound, stable GA-FeIII/II nanoparticles. The functionalization and patterning of CNF films with metal ion-hydrolyzable tannin nanoparticles is a versatile route to functionalize films based on renewable materials and of interest for biomedical and environmental applications.

2.
Nanomaterials (Basel) ; 9(7)2019 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-31336855

RESUMO

Maghemite nanoparticles with high surface area were obtained from the dehydroxylation of lepidocrocite prismatic nanoparticles. The synthesis pathway from the precursor to the porous maghemite nanoparticles is inexpensive, simple and gives high surface area values for both lepidocrocite and maghemite. The obtained maghemite nanoparticles contained intraparticle and interparticle pores with a surface area ca. 30 × 103 m2/mol, with pore volumes in the order of 70 cm3/mol. Both the surface area and pore volume depended on the heating rate and annealing temperature, with the highest value near the transformation temperature (180-250 °C). Following the transformation, in situ X-ray diffraction (XRD) allowed us to observe the temporal decoupling of the decomposition of lepidocrocite and the growth of maghemite. The combination of high-angle annular dark-field imaging using scanning transmission electron microscopy (HAADF-STEM) and surface adsorption isotherms is a powerful approach for the characterization of nanomaterials with high surface area and porosity.

3.
Langmuir ; 35(10): 3600-3606, 2019 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-30730750

RESUMO

The ability to probe the assembly, gelation, and helicoidal consolidation of cellulose nanocrystal (CNC) dispersions at high concentrations can provide unique insight into the assembly and can assist optimized manufacturing of CNC-based photonic and structural materials. In this Feature Article, we review and discuss the concentration dependence of the structural features, characterized by the particle separation distance and the helical pitch, at CNC concentrations ( c) that range from the isotropic state, over the biphasic range, to the fully liquid crystalline state. The structure evolution of CNC dispersions probed by time-resolved small-angle X-ray scattering during evaporation-induced assembly highlighted the importance of gelation and consolidation at high concentrations. We briefly discuss how the homogeneity of helicoidal nanostructures in dry CNC films can be improved and present an outlook for future work.

4.
Langmuir ; 35(6): 2289-2302, 2019 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-30672300

RESUMO

In this paper, we use dynamic light scattering in polarized and depolarized modes to determine the translational and rotational diffusion coefficients of concentrated rodlike cellulose nanocrystals in aqueous suspension. Within the range of studied concentrations (1-5 wt %), the suspension starts a phase transition from an isotropic to an anisotropic state as shown by polarized light microscopy and viscosity measurements. Small-angle neutron scattering measurements also confirmed the start of cellulose nanocrystal alignment and a decreasing distance between the cellulose nanocrystals with increasing concentration. As expected, rotational and translational diffusion coefficients generally decreased with increasing concentration. However, the translational parallel diffusion coefficient was found to show a local maximum at the onset of the isotropic-to-nematic phase transition. This is attributed to the increased available space for rods to move along their longitudinal axis upon alignment. This increased parallel diffusion coefficient thus confirms the general idea that rodlike particles gain translational entropy upon alignment while paying the price for losing rotational degrees of freedom. Once the concentration increases further, diffusion becomes more hindered even in the aligned regions due to a reduction in the rod separation distance. This leads once again to a decrease in translational diffusion coefficients. Furthermore, the relaxation rate for fast mode translational diffusion (parallel to the long particle axis) exhibited two regimes of relaxation behavior at concentrations where significant alignment of the rods is measured. We attribute this unusual dispersive behavior to two length scales: one linked to the particle length (at large wavevector q) and the other to a twist fluctuation correlation length (at low wavevector q) along the cellulose nanocrystal rods that is of a larger length when compared to the actual length of rods and could be linked to the size of aligned domains.

5.
Nanoscale ; 10(48): 23157-23163, 2018 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-30515496

RESUMO

The formation of nematically-ordered cellulose nanofiber (CNF) suspensions with an order parameter fmax≈ 0.8 is studied by polarized optical microscopy, small-angle X-ray scattering (SAXS), and rheological measurements as a function of CNF concentration. The wide range of CNF concentrations, from 0.5 wt% to 4.9 wt%, is obtained using osmotic dehydration. The rheological measurements show a strong entangled network over all the concentration range whereas SAXS measurements indicate that at concentrations >1.05 wt% the CNF suspension crosses an isotropic-anisotropic transition that is accompanied by a dramatic increase of the optical birefringence. The resulting nanostructures are modelled as mass fractal structures that converge into co-existing nematically-ordered regions and network-like regions where the correlation distances decrease with concentration. The use of rapid, upscalable osmotic dehydration is an effective method to increase the concentration of CNF suspensions while partly circumventing the gel/glass formation. The facile formation of highly ordered fibers can result in materials with interesting macroscopic properties.

6.
Nanoscale ; 10(38): 18113-18118, 2018 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-30238947

RESUMO

Assembly of bio-based nano-sized particles into complex architectures and morphologies is an area of fundamental interest and technical importance. We have investigated the assembly of sulfonated cellulose nanocrystals (CNC) dispersed in a shrinking levitating aqueous drop using time-resolved small angle X-ray scattering (SAXS). Analysis of the scaling of the particle separation distance (d) with particle concentration (c) was used to follow the transition of CNC dispersions from an isotropic state at 1-2 vol% to a compressed nematic state at particle concentrations above 30 vol%. Comparison with SAXS measurements on CNC dispersions at near equilibrium conditions shows that evaporation-induced assembly of CNC in large levitating drops is comparable to bulk systems. Colloidal states with d vs. c scalings intermediate between isotropic dispersions and unidirectional compression of the nematic structure could be related to the biphasic region and gelation of CNC. Nanoscale structural information of CNC assembly up to very high particle concentrations can help to fabricate nanocellulose-based materials by evaporative methods.

7.
ACS Appl Mater Interfaces ; 9(43): 37712-37720, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-28972727

RESUMO

Carboxylated cellulose nanofibers (CNF) prepared using the TEMPO-route are good binders of electrode components in flexible lithium-ion batteries (LIB). However, the different parameters employed for the defibrillation of CNF such as charge density and degree of homogenization affect its properties when used as binder. This work presents a systematic study of CNF prepared with different surface charge densities and varying degrees of homogenization and their performance as binder for flexible LiFePO4 electrodes. The results show that the CNF with high charge density had shorter fiber lengths compared with those of CNF with low charge density, as observed with atomic force microscopy. Also, CNF processed with a large number of passes in the homogenizer showed a better fiber dispersibility, as observed from rheological measurements. The electrodes fabricated with highly charged CNF exhibited the best mechanical and electrochemical properties. The CNF at the highest charge density (1550 µmol g-1) and lowest degree of homogenization (3 + 3 passes in the homogenizer) achieved the overall best performance, including a high Young's modulus of approximately 311 MPa and a good rate capability with a stable specific capacity of 116 mAh g-1 even up to 1 C. This work allows a better understanding of the influence of the processing parameters of CNF on their performance as binder for flexible electrodes. The results also contribute to the understanding of the optimal processing parameters of CNF to fabricate other materials, e.g., membranes or separators.

8.
Sci Rep ; 7(1): 2802, 2017 06 05.
Artigo em Inglês | MEDLINE | ID: mdl-28584236

RESUMO

Understanding the assembly of nanoparticles into superlattices with well-defined morphology and structure is technologically important but challenging as it requires novel combinations of in-situ methods with suitable spatial and temporal resolution. In this study, we have followed evaporation-induced assembly during drop casting of superparamagnetic, oleate-capped γ-Fe2O3 nanospheres dispersed in toluene in real time with Grazing Incidence Small Angle X-ray Scattering (GISAXS) in combination with droplet height measurements and direct observation of the dispersion. The scattering data was evaluated with a novel method that yielded time-dependent information of the relative ratio of ordered (coherent) and disordered particles (incoherent scattering intensities), superlattice tilt angles, lattice constants, and lattice constant distributions. We find that the onset of superlattice growth in the drying drop is associated with the movement of a drying front across the surface of the droplet. We couple the rapid formation of large, highly ordered superlattices to the capillary-induced fluid flow. Further evaporation of interstitital solvent results in a slow contraction of the superlattice. The distribution of lattice parameters and tilt angles was significantly larger for superlattices prepared by fast evaporation compared to slow evaporation of the solvent.

9.
Nano Lett ; 16(11): 6838-6843, 2016 11 09.
Artigo em Inglês | MEDLINE | ID: mdl-27779885

RESUMO

Mesocrystals composed of crystallographically aligned nanocrystals are present in biominerals and assembled materials which show strongly directional properties of importance for mechanical protection and functional devices. Mesocrystals are commonly formed by complex biomineralization processes and can also be generated by assembly of anisotropic nanocrystals. Here, we follow the evaporation-induced assembly of maghemite nanocubes into mesocrystals in real time in levitating drops. Analysis of time-resolved small-angle X-ray scattering data and ex situ scanning electron microscopy together with interparticle potential calculations show that the substrate-free, particle-mediated crystallization process proceeds in two stages involving the formation and rapid transformation of a dense, structurally disordered phase into ordered mesocrystals. Controlling and tailoring the particle-mediated formation of mesocrystals could be utilized to assemble designed nanoparticles into new materials with unique functions.

10.
ACS Appl Mater Interfaces ; 8(34): 22477-83, 2016 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-27502034

RESUMO

The exchange bias properties of Co/CoO coaxial core/shell nanowires were investigated with cooling and applied fields perpendicular to the wire axis. This configuration leads to unexpected exchange-bias effects. First, the magnetization value at high fields is found to depend on the field-cooling conditions. This effect arises from the competition between the magnetic anisotropy and the Zeeman energies for cooling fields perpendicular to the wire axis. This allows imprinting predefined magnetization states to the antiferromagnetic (AFM) shell, as corroborated by micromagnetic simulations. Second, the system exhibits a high-field magnetic irreversibility, leading to open hysteresis loops attributed to the AFM easy axis reorientation during the reversal (effect similar to athermal training). A distinct way to manipulate the high-field magnetization in exchange-biased systems, beyond the archetypical effects, was thus experimentally and theoretically demonstrated.

11.
Nanoscale ; 8(34): 15571-80, 2016 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-27448065

RESUMO

A precise control over the meso- and microstructure of ordered and aligned nanoparticle assemblies, i.e., mesocrystals, is essential in the quest for exploiting the collective material properties for potential applications. In this work, we produced evaporation-induced self-assembled mesocrystals with different mesostructures and crystal habits based on iron oxide nanocubes by varying the nanocube size and shape and by applying magnetic fields. A full 3D characterization of the mesocrystals was performed using image analysis, high-resolution scanning electron microscopy and Grazing Incidence Small Angle X-ray Scattering (GISAXS). This enabled the structural determination of e.g. multi-domain mesocrystals with complex crystal habits and the quantification of interparticle distances with sub-nm precision. Mesocrystals of small nanocubes (l = 8.6-12.6 nm) are isostructural with a body centred tetragonal (bct) lattice whereas assemblies of the largest nanocubes in this study (l = 13.6 nm) additionally form a simple cubic (sc) lattice. The mesocrystal habit can be tuned from a square, hexagonal to star-like and pillar shapes depending on the particle size and shape and the strength of the applied magnetic field. Finally, we outline a qualitative phase diagram of the evaporation-induced self-assembled superparamagnetic iron oxide nanocube mesocrystals based on nanocube edge length and magnetic field strength.

12.
Nano Lett ; 16(8): 5068-73, 2016 08 10.
Artigo em Inglês | MEDLINE | ID: mdl-27383904

RESUMO

The physicochemical properties used in numerous advanced nanostructured devices are directly controlled by the oxidation states of their constituents. In this work we combine electron energy-loss spectroscopy, blind source separation, and computed tomography to reconstruct in three dimensions the distribution of Fe(2+) and Fe(3+) ions in a FeO/Fe3O4 core/shell cube-shaped nanoparticle with nanometric resolution. The results highlight the sharpness of the interface between both oxides and provide an average shell thickness, core volume, and average cube edge length measurements in agreement with the magnetic characterization of the sample.

13.
Langmuir ; 31(48): 13127-37, 2015 Dec 08.
Artigo em Inglês | MEDLINE | ID: mdl-26559158

RESUMO

Mineral surfaces exposed to moist air stabilize nanometer- to micrometer-thick water films. This study resolves the nature of thin water film formation at multifaceted hematite (α-Fe2O3) nanoparticle surfaces with crystallographic faces resolved by selected area electron diffraction. Dynamic vapor adsorption (DVA) in the 0-19 Torr range at 298 K showed that these particles stabilize water films consisting of up to 4-5 monolayers. Modeling of these data predicts water loadings in terms of an "adsorption regime" (up to 16 H2O/nm(2)) involving direct water binding to hematite surface sites, and of a "condensation regime" (up to 34 H2O/nm(2)) involving water binding to hematite-bound water nanoclusters. Vibration spectroscopy identified the predominant hematite surface hydroxo groups (-OH, µ-OH, µ3-OH) through which first layer water molecules formed hydrogen bonds, as well as surface iron sites directly coordinating water molecules (i.e., as geminal η-(OH2)2 sites). Chemometric analyses of the vibration spectra also revealed a strong correspondence in the response of hematite surface hydroxo groups to DVA-derived water loadings. These findings point to a near-saturation of the hydrogen-bonding environment of surface hydroxo groups at a partial water vapor pressure of ∼8 Torr (∼40% relative humidity). Classical molecular dynamics (MD) resolved the interfacial water structures and hydrogen bonding populations at five representative crystallographic faces expressed in these nanoparticles. Simulations of single oriented slabs underscored the individual roles of all (hydro)oxo groups in donating and accepting hydrogen bonds with first layer water in the "adsorption regime". These analyses pointed to the preponderance of hydrogen bond-donating -OH groups in the stabilization of thin water films. Contributions of µ-OH and µ3-OH groups are secondary, yet remain essential in the stabilization of thin water films. MD simulations also helped resolve crystallographic controls on water-water interactions occurring in the "condensation regime". Water-water hydrogen bond populations are greatest on the (001) face, and decrease in importance in the order (001) > (012) ≈ (110) > (014) ≫ (100). Simulations of a single (∼5 nm × âˆ¼ 6 nm × âˆ¼ 6 nm) nanometric hematite particle terminated by the (001), (110), (012), and (100) faces also highlighted the key roles that sites at particle edges play in interconnecting thin water films grown along contiguous crystallographic faces. Hydroxo-water hydrogen bond populations showed that edges were the preferential loci of binding. These simulations also suggested that equilibration times for water binding at edges were slower than on crystallographic faces. In this regard, edges, and by extension roughened surfaces, are expected to play commanding roles in the stabilization of thin water films. Thus, in focusing on the properties of nanometric-thick water layers at hematite surfaces, this study revealed the nature of interactions between water and multifaced particle surfaces. Our results pave the way for furthering our understanding of mineral-thin water film interfacial structure and reactivity on a broader range of materials.


Assuntos
Compostos Férricos/química , Água/química , Adsorção , Ligação de Hidrogênio , Propriedades de Superfície
14.
Langmuir ; 31(23): 6507-13, 2015 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-26020691

RESUMO

The packing of cellulose nanocrystals (CNC) in the anisotropic chiral nematic phase has been investigated over a wide concentration range by small-angle X-ray scattering (SAXS) and laser diffraction. The average separation distance between the CNCs and the average pitch of the chiral nematic phase have been determined over the entire isotropic-anisotropic biphasic region. The average separation distances range from 51 nm, at the onset of the anisotropic phase formation, to 25 nm above 6 vol % (fully liquid crystalline phase) whereas the average pitch varies from ≈15 µm down to ≈2 µm as ϕ increases from 2.5 up to 6.5 vol %. Using the cholesteric order, we determine that the twist angle between neighboring CNCs increases from about 1° up to 4° as ϕ increases from 2.5 up to 6.5 vol %. The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.


Assuntos
Celulose/química , Cristais Líquidos/química , Nanopartículas/química , Anisotropia , Lasers , Luz , Espalhamento a Baixo Ângulo , Água/química , Difração de Raios X
15.
Acc Chem Res ; 48(5): 1391-402, 2015 May 19.
Artigo em Inglês | MEDLINE | ID: mdl-25938915

RESUMO

Mesocrystals, which originally was a term to designate superstructures of nanocrystals with a common crystallographic orientation, have now evolved to a materials concept. The discovery that many biominerals are mesocrystals generated a large research interest, and it was suggested that mesocrystals result in better mechanical performance and optical properties compared to single crystalline structures. Mesocrystalline biominerals are mainly found in spines or shells, which have to be mechanically optimized for protection or as a load-bearing skeleton. Important examples include red coral and sea urchin spine as well as bones. Mesocrystals can also be formed from purely synthetic components. Biomimetic mineralization and assembly have been used to produce mesocrystals, sometimes with complex hierarchical structures. Important examples include the fluorapatite mesocrystals with gelatin as the structural matrix, and mesocrystalline calcite spicules with impressive strength and flexibility that could be synthesized using silicatein protein fibers as template for calcium carbonate deposition. Self-assembly of nanocrystals can also result in mesocrystals if the nanocrystals have a well-defined size and shape and the assembly conditions are tuned to allow the nanoparticles to align crystallographically. Mesocrystals formed by assembly of monodisperse metallic, semiconducting, and magnetic nanocrystals are a type of colloidal crystal with a well-defined structure on both the atomic and mesoscopic length scale.Mesocrystals typically are hybrid materials between crystalline nanoparticles and interspacing amorphous organic or inorganic layers. This structure allows to combine disparate materials like hard but brittle nanocrystals with a soft and ductile amorphous material, enabling a mechanically optimized structural design as realized in the sea urchin spicule. Furthermore, mesocrystals can combine the properties of individual nanocrystals like the optical quantum size effect, surface plasmon resonance, and size dependent magnetic properties with a mesostructure and morphology tailored for specific applications. Indeed, mesocrystals composed of crystallographically aligned polyhedral or rodlike nanocrystals with anisotropic properties can be materials with strongly directional properties and novel collective emergent properties. An additional advantage of mesocrystals is that they can combine the properties of nanoparticles with a structure on the micro- or macroscale allowing for much easier handling.


Assuntos
Minerais/química , Nanopartículas/química , Animais , Coloides/química , Recifes de Corais , Ouriços-do-Mar/química
16.
Nanoscale ; 7(7): 3002-15, 2015 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-25600147

RESUMO

The intimate relationship between stoichiometry and physicochemical properties in transition-metal oxides makes them appealing as tunable materials. These features become exacerbated when dealing with nanostructures. However, due to the complexity of nanoscale materials, establishing a distinct relationship between structure-morphology and functionalities is often complicated. In this regard, in the FexO/Fe3O4 system a largely unexplained broad dispersion of magnetic properties has been observed. Here we show, thanks to a comprehensive multi-technique approach, a clear correlation between the magneto-structural properties in large (45 nm) and small (9 nm) FexO/Fe3O4 core/shell nanoparticles that can explain the spread of magnetic behaviors. The results reveal that while the FexO core in the large nanoparticles is antiferromagnetic and has bulk-like stoichiometry and unit-cell parameters, the FexO core in the small particles is highly non-stoichiometric and strained, displaying no significant antiferromagnetism. These results highlight the importance of ample characterization to fully understand the properties of nanostructured metal oxides.

17.
Nat Nanotechnol ; 10(3): 277-83, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-25362476

RESUMO

High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m(-1) K(-1), which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.

18.
Nanoscale ; 6(22): 13803-8, 2014 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-25292411

RESUMO

We demonstrate how the acquisition and processing of 3D electron diffraction data can be extended to characterize structural features on the mesoscale, and show how lattice distortions in superlattices of self-assembled spherical Pd nanoparticles can be quantified by three-dimensional small-angle electron diffraction tomography (3D SA-EDT). Transmission electron microscopy real space imaging and 3D SA-EDT reveal a high density of stacking faults that was related to a competition between fcc and hcp arrangements during assembly. Information on the orientation of the stacking faults was used to make analogies between planar defects in the superlattices and Shockley partial dislocations in metallic systems.

19.
Langmuir ; 30(30): 9017-21, 2014 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-25055062

RESUMO

The impact of lepidocrocite (γ-FeOOH) nanoparticle aggregation on mineral surface charge development was resolved in aqueous solutions of NaCl and NaClO4. Synthetic rod-like particles exhibiting charged edge (100) and neutrally/low-charged (010) faces self-aggregated in salt-free solutions. Aggregation was notably imaged by high-resolution transmission electron microscopy, and inferred by decreases in N2(g)-B.E.T. specific surface area from 94 m(2)/g to 77 m(2)/g after 12 months, and to 66 m(2)/g after 33 months storage. Potential determining (H(+), OH(-)) ions loadings in the 4-11 pH range were unchanged only if the particles remained aggregated in NaCl but only if they were disaggregated in NaClO4. These differences, alongside molecular simulations and experimental ion loadings resolved in other studies from our group, point to important controls on background electrolyte ion identity on the aggregation and charge development in lepidocrocite. These results may apply further to other mineral surfaces of comparable surface (hydr)oxo populations.

20.
Chemphyschem ; 15(7): 1477-84, 2014 May 19.
Artigo em Inglês | MEDLINE | ID: mdl-24677344

RESUMO

The intrinsic ability of cellulose nanocrystals (CNCs) to self-organize into films and bulk materials with helical order in a cholesteric liquid crystal is scientifically intriguing and potentially important for the production of renewable multifunctional materials with attractive optical properties. A major obstacle, however, has been the lack of control of helix direction, which results in a defect-rich, mosaic-like domain structure. Herein, a method for guiding the helix during film formation is introduced, which yields dramatically improved uniformity, as confirmed by using polarizing optical and scanning electron microscopy. By raising the CNC concentration in the initial suspension to the fully liquid crystalline range, a vertical helix orientation is promoted, as directed by the macroscopic phase boundaries. Further control of the helix orientation is achieved by subjecting the suspension to a circular shear flow during drying.

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