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1.
ACS Appl Mater Interfaces ; 12(12): 13598-13612, 2020 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-32077678

RESUMO

Mesoporous silica nanoparticles (MSNs) have seen a fast development as drug delivery carriers thanks to their tunable porosity and high loading capacity. The employ of MSNs in biomedical applications requires a good understanding of their degradation behavior both to control drug release and to assess possible toxicity issues on human health. In this work, we study mesoporous silica degradation in biologically relevant conditions through in situ ellipsometry on model mesoporous nanoparticle or continuous thin films, in buffer solution and in media containing proteins. In order to shed light on the structure/dissolution relationship, we performed dissolution experiments far from soluble silicate species saturation. Via a complete decorrelation of dissolution and diffusion contributions, we proved unambiguously that surface area of silica vectors is the main parameter influencing dissolution kinetics, while thermal treatment and open mesoporous network architecture have a minor impact. As a logical consequence of our dissolution model, we proved that the dissolution lag-time can be promoted by selective blocking of the mesopores that limits the access to the mesoporous internal surface. This study was broadened by studying the impact of the organosilanes in the silica structure, of the presence of residual structuring agents, and of the chemical composition of the dissolution medium. The presence of albumin at blood concentration was found affecting drastically the dissolution kinetics of the mesoporous structure, acting as a diffusion barrier. Globally, we could identify the main factors affecting mesoporous silica materials degradation and proved that we can tune their structure and composition for adjusting dissolution kinetics in order to achieve efficient drug delivery.

2.
Langmuir ; 35(24): 7970-7977, 2019 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-31117733

RESUMO

To rationalize how the gelation ability of a low molecular weight gelator is influenced by its molecular structure, we performed extensive solubility tests of a group of thiazole-based gelators and made use of Hansen solubility parameter formalism. We observe that the increase of a linear alkyl chain in these gelators promotes an increase of the radius of the gelation sphere as well as a gradual shift of its center to lower values of the polar (δP) and hydrogen bonding (δH) components. The molecular packing within the fibers and the crystal habit were determined by a combination of X-ray diffraction and molecular modeling. We attribute the gradual and linear shift of the gelation sphere to the fact that all of the studied gelators share the same molecular packing, so that an increasing length of the alkyl chain reduces the proportion of polar groups at the surface, resulting in a gradual increase in the contact between apolar parts of the fiber and the solvent.

3.
Chem Asian J ; 14(6): 781-788, 2019 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-30561904

RESUMO

A series of aggregation-induced emission (AIE) fluorescent gelators (TPE-Cn -Chol) were synthesized by attaching tetraphenylethylene (TPE) to cholesterol through an alkyl chain. The properties of the gel, nano-/microaggregate, and condensed phases were studied carefully. TPE-Cn -Chol molecules form AIE fluorescent gels in acetone and in DMF. Their fluorescence can be reversibly switched between the "on" and "off" states by a gel-sol phase transition upon thermal treatment. The AIE properties of aggregated nano-/microstructures in acetone/water mixtures with different water fractions were studied by using fluorescence spectrometry and scanning electron microscopy (SEM). In different acetone/water mixtures, the TPE-Cn -Chol molecules formed different nano-/microaggregates, such as rodlike crystallites and spherical nanoparticles that showed different fluorescence colors. Finally, the condensed phase behavior of TPE-Cn -Chol was studied by using polarizing microscopy (POM), differential scanning calorimetry (DSC), fluorescence spectrometry, fluorescence optical microscopy, and wide-angle X ray scattering (WAXS). The clover-shaped TPE unit introduced into the rodlike cholesterol mesogen inhibits not only the formation of a liquid-crystal phase but also recrystallization upon cooling from the isotropic liquid phase. Very interestingly, TPE-Cn -Chol molecules in the condensed state change their fluorescence color under external stimuli, such as melting, grinding, and solvent fuming. The phase transition is the origin of these thermo-, mechano-, and vapochromic properties. These findings offer a simple and interesting platform for the creation of multistimuli-responsive fluorescent sensors.

4.
Soft Matter ; 14(23): 4805-4809, 2018 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-29808203

RESUMO

An organogel is obtained when a low molar mass compound forms a network of anisotropic fibres in a liquid that is therefore transformed into a macroscopic solid. Various approaches have been proposed to correlate organogel formation and Hansen solubility parameters. These approaches are well adapted to specific experimental datasets but lack universality. A general method to determine the gelation domain from the solubility data of low molecular weight gelators is here reported.

5.
Small ; 14(24): e1801038, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29770993

RESUMO

Lithium cobalt oxide nanobatteries offer exciting prospects in the field of nonvolatile memories and neuromorphic circuits. However, the precise underlying resistive switching (RS) mechanism remains a matter of debate in two-terminal cells. Herein, intriguing results, obtained by secondary ion mass spectroscopy (SIMS) 3D imaging, clearly demonstrate that the RS mechanism corresponds to lithium migration toward the outside of the Lix CoO2 layer. These observations are very well correlated with the observed insulator-to-metal transition of the oxide. Besides, smaller device area experimentally yields much faster switching kinetics, which is qualitatively well accounted for by a simple numerical simulation. Write/erase endurance is also highly improved with downscaling - much further than the present cycling life of usual lithium-ion batteries. Hence very attractive possibilities can be envisaged for this class of materials in nanoelectronics.

6.
ACS Nano ; 10(2): 2277-86, 2016 Feb 23.
Artigo em Inglês | MEDLINE | ID: mdl-26812588

RESUMO

Assembly of nanoparticles into supracrystals provides a class of materials with interesting optical and magnetic properties. However, supracrystals are mostly obtained from hydrophobic particles and therefore cannot be manipulated in aqueous systems, limiting their range of applications. Here, we show that hydrophobic-shaped supracrystals self-assembled from 8.2 nm cobalt nanoparticles can be dispersed in water by coating the supracrystals with lipid vesicles. A careful characterization of these composite objects provides insights into their structure at different length scales. This composite, suspended in water, retains the crystalline structure and paramagnetic properties of the starting material, which can be moved with an applied magnetic field.


Assuntos
Interações Hidrofóbicas e Hidrofílicas , Lipossomos/química , Nanopartículas Metálicas/química , Cobalto/química , Ácido Oleico/química , Fosfolipídeos/química
7.
Small ; 12(2): 220-8, 2016 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-26578032

RESUMO

In the present article, the successful coassembly of spherical 6.2 nm maghemite (γ-Fe2O3) nanocrystals and giant polyoxometalates (POMs) such as 2.9 nm {Mo132} is demonstrated. To do so, colloidal solutions of oleic acid-capped γ-Fe2O3 and long-chain alkylammonium-encapsulated {Mo132 } dispersed in chloroform are mixed together and supported self-organized binary superlattices are obtained upon the solvent evaporation on immersed substrates. Both electronic microscopy and small angles X-ray scattering data reveal an AB-type structure and an enhanced structuration of the magnetic nanocrystals (MNCs) assembly with POMs in octahedral interstices. Therefore, {Mo132} acts as an efficient binder constituent for improving the nanocrystals ordering in 3D films. Interestingly, in the case of didodecyldimethylammonium (C12)-encapsulated POMs, the long-range ordered binary assemblies are obtained while preserving the nanocrystals magnetic properties due to weak POMs-MNCs interactions. On the other hand, POMs of larger effective diameter can be employed as spacer blocks for MNCs as shown by using {Mo132} capped with dioctadecyldimethylammonium (C18) displaying longer chains. In that case, it is shown that POMs can also be used for fine-tuning the dipolar interactions in γ-Fe2O3 nanocrystal assemblies.

8.
Nano Lett ; 14(11): 6632-8, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25337812

RESUMO

Crystals of nanocrystals, also called supracrystals and nanocrystal superlattices, are expected to exhibit specific properties that differ from both the corresponding bulk material and nanosized elementary units. In particular, their surfaces have a great potential as nanoscale interaction plateforms. However, control of the symmetry, compacity, and roughness of their surfaces remains an open question. Here, we describe the spontaneous formation of upper vicinal surfaces for supracrystals of Au nanocrystals grown on a sublayer of ordered Co nanocrystals. Stepped or kinked surfaces vicinal to the {100}, {110}, and {111} planes are observed to be extended on the micrometer range. The formation of such high-index planes is explained by a heteroepitaxial relationship between both Co and Au nanocrystal superlattice.

9.
ACS Appl Mater Interfaces ; 6(19): 17102-10, 2014 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-25145291

RESUMO

In this work, unique functional devices exhibiting controlled gradients of properties are fabricated by dip-coating process in acceleration mode. Through this new approach, thin films with "on-demand" thickness graded profiles at the submillimeter scale are prepared in an easy and versatile way, compatible for large-scale production. The technique is adapted to several relevant materials, including sol-gel dense and mesoporous metal oxides, block copolymers, metal-organic framework colloids, and commercial photoresists. In the first part of the Article, an investigation on the effect of the dip coating speed variation on the thickness profiles is reported together with the critical roles played by the evaporation rate and by the viscosity on the fluid draining-induced film formation. In the second part, dip-coating in acceleration mode is used to induce controlled variation of functionalities by playing on structural, chemical, or dimensional variations in nano- and microsystems. In order to demonstrate the full potentiality and versatility of the technique, original graded functional devices are made including optical interferometry mirrors with bidirectional gradients, one-dimensional photonic crystals with a stop-band gradient, graded microfluidic channels, and wetting gradient to induce droplet motion.

10.
Langmuir ; 29(44): 13576-81, 2013 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-24083385

RESUMO

Au nanocrystals coated with thiol derivatives differing by the length of their alkyl chains are used to build 3D superlattices called supracrystals. In this study, we used two sets of Au nanocrystals differing by their sizes and size distributions. The average sizes are 5 nm (Au5) and 7 nm (Au7). From one experiment to the other, the size distribution slightly changes. For Au5 nanocrystals, it evolves from 6 to 8%, and for Au7 nanocrystals, it varies from 5 to 6%. The Au nanocrystals (Au5 and Au7) are first dispersed in toluene and produce fcc supracrystals by solvent evaporation. Here, by small-angle grazing X-ray diffraction, we observe a control in the average interparticle distance within the supracrystals. When the supracrystals are grown at zero toluene vapor pressure, the interparticle distances increase linearly with the alkyl chain length of the nanocrystals' coating agent regardless of their diameters. Furthermore, the dry supracrystals can swell and the interparticle distance within the superstructure be increased by subjecting the material to toluene vapor pressure after initial growth. This swelling process is reversible, and retraction occurs when the toluene vapor pressure drops. This indicates a strong ability of the dried supracrystals to trap toluene molecules. On increasing the toluene vapor pressure during the solvent evaporation process, the slope of the linear dependency of the interparticle distances to the alkyl chain length is markedly decreased and the interparticle distance reaches a quasi-plateau. This is explained by the influence of depletion forces created by the presence of thiol-containing molecules physisorbed on the coating molecules on the internal structure of these supracrystals. Recently, we demonstrated that, by using the same nanocrystals (Au5 and Au7), a hierarchy in the supracrystal growth process takes place from heterogeneous nucleation with the formation of a layer-by-layer film to homogeneous nucleation in solution with the formation of shaped supracrystals. Here it is shown that the interparticle distance is independent of the supracrystal growth mechanisms.

11.
Nano Lett ; 13(4): 1751-6, 2013 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-23517435

RESUMO

We present in situ monitoring of water filling of single-walled carbon nanotubes at room temperature, using X-ray scattering. A systematic method is developed to determine the water radial density profile. Water filling is homogeneous below about 5% in mass, whereas it structures into three layers above. These results should motivate further theoretical and simulations studies and allow getting a better understanding of the very peculiar properties of water confined in hydrophobic environment.


Assuntos
Nanotubos de Carbono/química , Água/química , Simulação por Computador , Interações Hidrofóbicas e Hidrofílicas , Espectrometria por Raios X
12.
J Phys Chem B ; 117(16): 4510-6, 2013 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-23083458

RESUMO

Under solvent saturation, a precipitation of full-grown supracrystals on the one hand and the formation of well-defined supracrystalline films at the air-liquid interface on the other hand were previously observed for the first time (J. Am. Chem. Soc.2012, 134, 3714-3719). Here, these two simultaneous growth processes are studied by additional experiments and by Brownian dynamics simulations. The thickness of the supracrystalline films and the concentration of free nanocrystals within the solution are measured as a function of the nanocrystal size. The simulations show that the first process of supracrystal growth is due to a homogeneous nucleation favored by solvent-mediated ligand interactions, while the second one is explained in terms of a diffusion process caused by a decrease in the surface energy when the particles penetrate the air-liquid interface. It is also verified that the presence of thiol molecules at the air-solution interface does not hinder the formation of supracrystalline films.

13.
Nano Lett ; 12(10): 5292-8, 2012 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-22989345

RESUMO

Spontaneous separation of single from polycrystalline 5 nm gold nanocrystals (NCs) is observed in colloidal solution. This segregation takes place upon self-assembling of single crystalline NCs at the air-solvent interface and in precipitated superlattices. Polycrystalline NCs are observed to remain in the suspension. Transmission electron microscopy analysis of the size distribution of NCs issued from the different populations indicates that the NC size does not change from each other, excluding therefore any size segregation in this process. Using both low-frequency Raman scattering and X-ray diffraction provides reliable characterization of nanocrystallinity for each population of NCs, thus confirming the crystallinity segregation. The single crystalline NCs are found by electron diffraction to self-assemble into close-packed superlattices with long-range translational and orientational ordering, while polycrystalline NCs behave like spheres with no preferential orientation. The face-to-face orientational ordering, which is only observed for single crystalline NCs, supports the relevance of the specific crystallinity-related morphologies of these NCs in their better ability to self-assemble. Exploiting this spontaneous segregation would open up a simple alternative to other demanding routes for controlling crystallinity of nanocrystals and optimizing their properties for potential applications.

14.
Langmuir ; 28(30): 11215-24, 2012 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-22747000

RESUMO

We study the self-assembly of a new family of amphiphilic liquid crystal (LC) copolymers synthesized by the anionic ring-opening polymerization of a new cholesterol-based LC monomer, 4-(cholesteryl)butyl ethyl cyclopropane-1,1-dicarboxylate. Using the t-BuP(4) phosphazene base and thiophenol or a poly(ethylene glycol) (PEG) functionalized with thiol group to generate in situ the initiator during the polymerization, LC homopolymer and amphiphilic copolymers with narrow molecular weight distributions were obtained. The self-assemblies of the LC monomer, homopolymer, and block copolymers in bulk and in solution were studied by small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and transmission electron microscopy (TEM). All polymers exhibit in bulk an interdigitated smectic A (SmA(d)) phase with a lamellar period of 4.6 nm. The amphiphilic copolymers self-organize in solution into vesicles with wavy membrane and nanoribbons with twisted and folded structures, depending on concentration and size of LC hydrophobic block. These new morphologies will help the comprehension of the fascinating organization of thermotropic mesophase in lyotropic structures.


Assuntos
Ciclopropanos/química , Ácidos Dicarboxílicos/química , Polímeros/química , Polímeros/síntese química , Varredura Diferencial de Calorimetria , Microscopia Eletrônica de Transmissão , Polietilenoglicóis/química
15.
J Am Chem Soc ; 134(8): 3714-9, 2012 Feb 29.
Artigo em Inglês | MEDLINE | ID: mdl-22329348

RESUMO

Natural systems give the route to design periodic arrangements with mesoscopic architecture using individual nanocrystals as building blocks forming colloidal crystals or supracrystals. The collective properties of such supracrystals are one of the main driving forces in materials research for the 21st century with potential applications in electronics or biomedical environments. Here we describe two simultaneous supracrystal growth processes from gold nanocrystal suspension, taking place in solution and at the air-liquid interface. Furthermore, the growth processes involve the crystallinity selection of nanocrystals and induce marked changes in the supracrystal mechanical properties.


Assuntos
Coloides/química , Ouro/química , Nanopartículas Metálicas/química , Tamanho da Partícula , Propriedades de Superfície
16.
Dalton Trans ; 41(5): 1582-90, 2012 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-22159371

RESUMO

Controlling the elaboration of Coordination Networks (CoNet) on surfaces at the nanoscale remains a challenge. One suitable technique is the Sequential Growth in Solution (SGS), which has the advantage to be simple, cheap and fast. We addressed two issues in this article: i) the controlled synthesis of ultra thin films of CoNet (thickness lower than 10 nm), and ii) the investigation of the influence of the precursors' concentration on the growth process. Si(100) was used because it is possible to prepare atomically flat Si-H surfaces, which is necessary for the growth of ultrathin films. We used, as a model system, the sequential reactions of K(4)[Fe(II)(CN)(6)] and [Ni(II)(H(2)O)(6)]Cl(2) that occur by the substitution of the water molecules in the coordination sphere of Ni(II) by the nitrogen atoms of ferrocyanide. We demonstrated that the nature of the deposited film depends mainly on the relative concentration of the anchoring sites versus the precursors' solution. Attenuated Total Reflection Fourier Transformed Infra Red (ATR-FTIR), X-ray reflectivity, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) were used to characterize the steps of the growth process.

17.
Materials (Basel) ; 5(3): 385-403, 2012 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-28817053

RESUMO

The research of new molecular materials able to replace classical solid materials in electronics has attracted growing attention over the past decade. Among these compounds photoswitchable Prussian blue analogues (PBA) are particularly interesting for the elaboration of new optical memories. However these coordination polymers are generally synthesised as insoluble powders that cannot be integrated into a real device. Hence their successful integration into real applications depends on an additional processing step. Nanostructured oxides elaborated by sol-gel chemistry combined with surfactant micelle templating can be used as nanoreactors to confine PBA precipitation and organize the functional nano-objects in the three dimensions of space. In this work we present the elaboration of different CoFe PBA/silica nanocomposites. Our synthetic procedure fully controls the synthesis of PBA in the porosity of the silica matrix from the insertion of the precursors up to the formation of the photomagnetic compound. We present results on systems from the simplest to the most elaborate: from disordered xerogels to ordered nanostructured films passing through mesoporous monoliths.

18.
J Trace Elem Med Biol ; 25(3): 160-5, 2011 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21763116

RESUMO

Kidney stone disease, or nephrolithiasis, is a common ailment. Among the different risk factors usually associated with nephrolithiasis are dehydration, metabolic defects (especially with regard to calcium and oxalate). The presence of a mineral deposit at the surface of the renal papilla (termed Randall's plaque) has all been recently underlined. Of note, Randall's plaque is made of the calcium phosphate, carbapatite, and serves as a nucleus for kidney stone formation. The process by which apatite nanocrystals nucleate and form Randall's plaque remains unclear. This paper deals with the possible relationship between trace elements and the formation of this mineral. The investigation has been performed on a set of Randall's plaques, extracted from human kidney stones, through µ-X-ray diffraction and µ-X-ray fluorescence analyses in order to determine the chemical composition of the plaque as well as the nature and the amount of trace elements. Our data provide evidence that Zn levels are dramatically increased in carbapatite of RP by comparison to carbapatite in kidney stones, suggesting that calcified deposits within the medullar interstitium are a pathological process involving a tissue reaction. Further studies, perhaps including the investigation of biomarkers for inflammation, are necessary for clarifying the role of Zn in Randall's plaque formation.


Assuntos
Cálculos Renais/diagnóstico por imagem , Cálculos Renais/metabolismo , Espectrometria por Raios X , Zinco/metabolismo , Calibragem , Humanos , Chumbo/metabolismo , Chumbo/urina , Radiografia , Estrôncio/metabolismo , Estrôncio/urina , Difração de Raios X , Zinco/urina
19.
Faraday Discuss ; 143: 235-50; discussion 265-75, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-20334105

RESUMO

A series of amphiphilic LC block copolymers, in which the hydrophobic block is a smectic polymer poly(4-methoxyphenyl 4-(6-acryloyloxy-hexyloxy)-benzoate) (PA6esterl) and the hydrophilic block is polyethyleneglycol (PEG), were synthesized and characterized. The self-assembly of one of them in both the pure state and the dilute aqueous solution was investigated in detail. Nano-structures in the pure state were studied by SAXS and WAXS on samples aligned by a magnetic field. A hexagonal cylindrical micro-segregation phase was observed with a lattice distance of 11.2 nm. The PEG blocks are in the cylinder, while the smectic polymer blocks form a matrix with layer spacing 2.4 nm and layer normal parallel to the long axis of the cylinders. Faceted unilamellar polymer vesicles, polymersomes, were formed in water, as revealed by cryo-TEM. In the lyotropic bilayer membrane of these polymersomes, the thermotropic smectic order in the hydrophobic block is clearly visible with layer normal parallel to the membrane surface.

20.
Chemphyschem ; 8(16): 2379-85, 2007 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-17926316

RESUMO

We have investigated dilute aqueous solutions of an anionic polymer (carboxymethylcellulose) mixed with cationic surfactants of different chain lengths (dodecyl to octadecyl trimethylammonium bromides: DTAB, TTAB, CTAB and OTAB). The structures of the concentrated phases formed above the precipitation threshold were studied by X-ray diffraction. Different body-centred cubic structures with space groups Pm3n were observed in the presence of surfactant with a short aliphatic chain (DTAB), despite the fact that the polymer persistence length is comparable to the repeat distance of the structure (5 nm). For larger surfactant chain lengths (TTAB and CTAB), the structure of the precipitates can be either cubic (Pm3n) or 2D hexagonal depending on the initial surfactant and polymer concentrations. For still larger chain length (OTAB), the structure becomes lamellar. This structural evolution from micellar cubic towards 2D hexagonal and lamellar is attributed to the decrease of the local curvature of the surfactant aggregates, as observed for flexible synthetic polymers and short DNA fragments under similar conditions. Furthermore, the structure of the bulk complexes formed just below the precipitation threshold anticipates the structure seen in the precipitated phases.


Assuntos
Carboximetilcelulose Sódica/química , Compostos de Amônio Quaternário/química , Tensoativos/química , Cátions , Cetrimônio , Compostos de Cetrimônio/química , Compostos de Trimetil Amônio/química , Difração de Raios X
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