| 1. |
- Crassous, Jerome, et al.
(author)
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Advanced multiresponsive comploids: from design to possible applications.
- 2014
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 6:15, s. 8726-8735
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Journal article (peer-reviewed)abstract
- We extend the commonly used synthesis strategies for responsive microgels to the design of novel multiresponsive and multifunctional nanoparticles that combine inorganic magnetic, metallic/catalytic and thermoresponsive organic moieties. Magnetic responsiveness is implemented through the integration of silica-coated maghemite nanoparticles into fluorescently labeled crosslinked poly(N-isopropylmethacrylamide) microgels. These particles are then employed as templates for the in situ reduction of catalytically active gold nanoparticles. In order to tune the reactivity of the catalyst through a thermally controlled barrier, an additional layer of crosslinked poly(N-isopropylacrylamide) is added in the final step. We subsequently demonstrate that these particles can be employed as smart catalysts. We show that the thermoresponsive nature of the outer particle shell not only provides control over the catalytic activity, but when combined with a magnetic core allows for very efficient removal of the catalytic system through temperature-controlled reversible coagulation and subsequent magnetophoresis in an applied magnetic field gradient. We finally discuss the use of this design principle for the synthesis of complex hybrid particles for various applications that would all profit from their multiresponsive and multifunctional nature.
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| 2. |
- Crassous, Jerome, et al.
(author)
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Preparation and characterization of ellipsoidal-shaped thermosensitive microgel colloids with tailored aspect ratios
- 2012
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:13, s. 3538-3548
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Journal article (peer-reviewed)abstract
- Prolate model colloids with defined properties can be obtained by the stretching of spherical polymeric particles, which is well-known for polystyrene and poly(methyl methacrylate) latices. The present study aims to extend this approach to functional core-shell particles in order to achieve a new class of anisotropic colloidal materials where both the aspect ratio and the effective volume fraction can be controlled by temperature. We describe the synthesis and characterization of these functional anisotropic core-shell particles consisting of a polystyrene (PS) core onto which a crosslinked thermoresponsive microgel shell of poly(N-isopropylmethacrylamide) (PNIPMAm) was grafted. Embedded into a film of polyvinylalcohol (PVA), the spherical composite microgels are heated above the glass transition temperature (T-g) of the polystyrene core and then stretched with different deformations g. During the stretching, the particles adopt an elongated shape, that they retain after cooling to room temperature as confirmed by small-angle X-ray scattering performed on the films. Anisotropic composite microgels with aspect ratios ranging from 2.2 to 6.5 are recovered after dissolution of the PVA and purification, and are fully characterized by diverse methods such as transmission electron microscopy, confocal microscopy and light scattering. The temperature sensitivity of these anisotropic composite microgels is maintained as confirmed by dynamic light scattering and cryogenic electron microscopy performed below and above the volume phase transition of the shell.
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| 3. |
- Liu, Li-Hong, et al.
(author)
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Photoinitiated Coupling of Unmodified Monosaccharides to Iron Oxide Nanoparticles for Sensing Proteins and Bacteria
- 2009
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In: Bioconjugate chemistry. - : American Chemical Society (ACS). - 1043-1802 .- 1520-4812. ; 20:7, s. 1349-1355
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Journal article (peer-reviewed)abstract
- We report a versatile approach for the immobilization of unmodified monosaccharides onto iron oxide nanoparticles. Covalent coupling of the carbohydrate onto iron oxide nanoparticle surfaces was accomplished by the CH insertion reaction of photochemically activated phosphate-functionalized perfluorophenylazides (PFPAs), and the resulting glyconanoparticles were characterized by IR, TGA, and TEM. The surface-bound D-mannose showed the recognition ability toward Concanavalin A and Escherichia coli strain ORN178 that possesses mannose-specific receptor sites. Owing to the simplicity and versatility of the technique, together with the magnetic property of iron oxide nanoparticles, the methodology developed in this study serves as a general approach for the preparation of magnetic glyconanoparticles to be used in clinical diagnosis, sensing, and decontamination.
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| 4. |
- Malik, Vikash, et al.
(author)
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A closer look at the synthesis and formation mechanism of hematite nanocubes
- 2014
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In: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 445, s. 21-29
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Journal article (peer-reviewed)abstract
- We have synthesized hematite cube-shaped nanoparticles using different synthesis paths to examine the effect of the intermediate product akaganeite (beta-FeOOH) on the size and shape of the final hematite particles. Akaganeite spindles and hematite nanocubes are prepared using forced hydrolysis of iron chloride (FeCI3) salt. We use a combination of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM),selected area electron diffraction (SAED) and dynamic light scattering (DLS). Akaganeite particles are found to be spindles, with an average length that depends linearly on the FeCI3 concentration, while their aspect ratio is hardly affected by the same parameter. Adjusting the akaganeite concentration from 0.01 M to 0.10 M equivalent of FeCI3 in the subsequent transformation to hematite leads to single crystal nanocubes with sizes ranging from 37 to 175 nm. The combination of akaganeite concentration and size is found to be the key parameter to control the size and crystallinity of the resulting hematite particles. Possible formation mechanisms of single and polycrystalline hematite nanocubes are discussed. (c) 2014 Elsevier B.V. All rights reserved.
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| 5. |
- Malik, Vikash, et al.
(author)
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Hybrid magnetic iron oxide nanoparticles with tunable field-directed self-assembly
- 2017
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In: Nanoscale. - 2040-3364. ; 9:38, s. 14405-14413
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Journal article (peer-reviewed)abstract
- We describe the synthesis of hybrid magnetic ellipsoidal nanoparticles that consist of a mixture of two different iron oxide phases, hematite (α-Fe2O3) and maghemite (γ-Fe2O3), and characterize their magnetic field-driven self-assembly. We demonstrate that the relative amount of the two phases can be adjusted in a continuous way by varying the reaction time during the synthesis, leading to strongly varying magnetic properties of the particles. Not only does the saturation magnetization increase dramatically as the composition of the spindles changes from hematite to maghemite, but also the direction of the induced magnetic moment changes from being parallel to the short axis of the spindle to being perpendicular to it. The magnetic dipolar interaction between the particles can be further tuned by adding a screening silica shell. Small-angle X-ray scattering (SAXS) experiments reveal that at high magnetic field, magnetic dipole–dipole interaction forces the silica coated particles to self-assemble into a distorted hexagonal crystal structure at high maghemite content. However, in the case of uncoated maghemite particles, the crystal structure is not very prominent. We interpret this as a consequence of the strong dipolar interaction between uncoated spindles that then become arrested during field-induced self-assembly into a structure riddled with defects.
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| 6. |
- Martchenko, Ilya, et al.
(author)
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Anisotropic magnetic particles in a magnetic field
- 2016
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 12:42, s. 8755-8767
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Journal article (peer-reviewed)abstract
- We characterize the structural properties of magnetic ellipsoidal hematite colloids with an aspect ratio ρ ≈ 2.3 using a combination of small-angle X-ray scattering and computer simulations. The evolution of the phase diagram with packing fraction φ and the strength of an applied magnetic field B is described, and the coupling between orientational order of magnetic ellipsoids and the bulk magnetic behavior of their suspension addressed. We establish quantitative structural criteria for the different phase and arrest transitions and map distinct isotropic, polarized non-nematic, and nematic phases over an extended range in the φ-B coordinates. We show that upon a rotational arrest of the ellipsoids around φ = 0.59, the bulk magnetic behavior of their suspension switches from superparamagnetic to ordered weakly ferromagnetic. If densely packed and arrested, these magnetic particles thus provide persisting remanent magnetization of the suspension. By exploring structural and magnetic properties together, we extend the often used colloid-atom analogy to the case of magnetic spins.
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| 7. |
- Martchenko, Ilya, et al.
(author)
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Hydrodynamic Properties of Magnetic Nanoparticles with Tunable Shape Anisotropy: Prediction and Experimental Verification
- 2011
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In: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:49, s. 14838-14845
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Journal article (peer-reviewed)abstract
- We describe the characterization of the hydrodynamic properties of anisotropic magnetic nanoparticles using a combination of transmission electron microscopy (TEM) and dynamic as well as depolarized dynamic light scattering (DLS/DDLS). The particles used are nearly monodisperse hematite spindles with an average length of 280 nm and a minor axis of 57 nm, coated with a layer of silica of variable thickness that allows us to tune the particle aspect ratio between 5 and 2. Their geometrical dimensions can thus be determined easily and quantitatively from TEM. Moreover, their size is ideal to employ DLS and DDLS to measure the translational and rotational diffusion coefficients D-T and D-R, while the presence of a magnetic core opens a plethora of opportunities for future studies and applications. We demonstrate that we can successfully predict the hydrodynamic properties of the different particles based on a TEM characterization of their size distribution and using established theoretical models for the hydrodynamic properties of anisotropic particles. When compared with the theoretical predictions, our light scattering measurements are in quantitative agreement. This agreement between theory and experiment is achieved without having to invoke any adjustable free parameter, as the TEM results are used to calculate the corresponding diffusion coefficients on an absolute scale We demonstrate that this is achieved due to a new and simple method for the statistical weighting of the TEM information, and the use of the correct hydrodynamic models for the observed particle shape. In addition, we also demonstrate an enhanced sensitivity of the rotational diffusion for the surface properties of ellipsoidal nanoparticles, and point out that this may serve as an ideal tool toward characterizing functionalized surfaces.
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| 8. |
- Mihut, Adriana, et al.
(author)
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Enhanced properties of polyurea elastomeric nanocomposites with anisotropic functionalised nanofillers
- 2013
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In: Polymer. - : Elsevier BV. - 0032-3861. ; 54:16, s. 4194-4203
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Journal article (peer-reviewed)abstract
- We report on the network characterization of a series of hybrid nanocomposites consisting of integrated anisotropic nanoparticles (NPs) within a polyurea elastomeric matrix with low weight fractions ranging from 0.3 to 1.2 wt%. The grafting method employed to incorporate the silica-coated spindle-type hematite nanoparticles (SCH NPs), promotes the stability of the NPs in dispersion, and further enables their integration within the elastomeric polymer matrix, where the NPs are acting as multifunctional chemical crosslinkers and reinforcing fillers. The mechanical properties of these nanocomposite materials have systematically been investigated for both small and large deformations as a function of the particles concentration in the matrix. The results indicate that significant reinforcement of the hybrid nanocomposite is achieved even at very low NP loading with respect to the pristine elastomeric matrix. (C) 2013 Elsevier Ltd. All rights reserved.
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| 9. |
- Mihut, Adriana, et al.
(author)
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Towards smart self-assembly of colloidal silica particles through diblock copolymer crystallization
- 2013
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In: Polymer. - : Elsevier BV. - 0032-3861. ; 54:15, s. 3874-3881
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Journal article (peer-reviewed)abstract
- An innovative associative strategy, crystallization-driven self-assembly, is discussed for hybrid inorganicorganic materials. We report the use of a semicrystalline poly(butadiene)-b-poly(ethylene oxide)(PB-b-PEO) diblock copolymer (BCP) that self-assembles with silica nanoparticles (NPs) in a selective solvent. In ethanol, at 60 degrees C, that is above the melting temperature T-m of the PEO block, the BCP forms amorphous spherical micelles consisting of a liquid PEO-corona and a core of PB-chains. The controlled formation of hybrid structures is achieved using temperature quenches below T-m of the BCP where the PEO block crystallizes in the micellar corona, leading to the formation of lamellar structures. The crystallization further dictates the spatial distribution and drives the self-assembly of the colloidal particles into the BCP lamellar domains. Such association is tunable and reversible, following the crystallization temperature T. The employed method offers new perspectives for the directed self-assembly of colloidal particles through an underlying controlled crystallization process of semicrystalline BCP in solution. (C) 2013 Elsevier Ltd. All rights reserved.
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| 10. |
- Pravaz, Olivier, et al.
(author)
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The influences of the transfer method and particle surface chemistry on the dispersion of nanoparticles in nanocomposites
- 2012
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 4:21, s. 6856-6862
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Journal article (peer-reviewed)abstract
- The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS).
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