115 research outputs found

    Editorial

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    Capsules: Their Past and Opportunities for Their Future

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    Capsules are often used as mobile delivery vehicles, for example, in pharmacy, food, and cosmetics, or as stationary containers that are embedded in a matrix to functionalize materials. Progress achieved in polymer chemistry opened up new possibilities to tune the properties of capsules with a much higher precision, thereby allowing the fabrication of advanced materials. This viewpoint summarizes recent developments in the design of functional capsules and highlights some of the challenges involved in the use of capsules to functionalize existing and to build new materials

    Self-Assembly of Iron Oxide-Poly(ethylene glycol) Core–Shell Nanoparticles at Liquid–Liquid Interfaces

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    Nanoparticles (NPs) play an increasingly important role in the fabrication of functional advanced materials. Two major steps need to be carried out in order to achieve control of the material properties. First of all, the properties of the single NPs have to be under control, especially in relation to colloidal stability; aggregation and corrosion negate all the benefits associated to the nanoscopic dimensions. Secondly, the assembly process has to be controlled to achieve a material with the desired properties. We propose here to use stabilized ceramic NPs consisting of a magnetite core, coated by a poly(ethylene glycol) (PEG) shell and study their assembly at polar/non-polar liquid interfaces, en route to fabricating functional NP membranes. These NPs show extraordinary stability in aqueous solutions achieved by anchoring linear PEG chains through an end-terminating nitroDOPA group to their surface. Furthermore, the core and shell sizes of these NPs can be independently varied with ease. We first describe the details of the NP synthesis and stabilization in bulk solutions, discussing the PEG molecular weight needed to achieve bulk stability. Subsequently, we demonstrate self-assembly of these particles at liquid–liquid interfaces (SALI) into monolayers of stable properties. SALI has been chosen as path for the assembly given its suitability for fabricating two-dimensional materials. We report here results from pendant drop tensiometry which illustrate the kinetics of NP adsorption at the liquid–liquid interface and highlight the role played by the molecular weight of the PEG shell in the interfacial assembly. In particular we show that the requisites to ensure particle stability at a liquid interface are more stringent compared to the bulk case

    Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol-gel process

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    Combination of the surfactant-free nonaqueous sol-gel approach with the microwave technique makes it possible to synthesize Fe3O4, CoFe2O4, MnFe2O4, and NiFe2O4 nanoparticles of about 5-6nm and with high crystallinity and good morphological uniformity. The synthesis involves the reaction of metal acetates or acetylacetonates as precursors with benzyl alcohol at 170°C under microwave irradiation of 12min. Immersion of glass substrates in the reaction solution results in the deposition of homogeneous metal ferrite films whose thickness can be adjusted through the precursor concentration. If preformed nickel nanoparticles are used as a type of curved substrate, the ferrite nanoparticles coat the seeds and form core-shell structures. These results extend the microwave-assisted nonaqueous sol-gel approach beyond the simple synthesis of nanoparticles to the preparation of thin films on flat or curved substrate

    Stabilization and functionalization of iron oxide nanoparticles for biomedical applications

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    Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface presentation of functionalities. This review is focused on different aspects of the stability of superparamagnetic iron oxide NPs, from its practical definition to its implementation by molecular design of the dispersant shell around the iron oxide core and further on to its influence on the magnetic properties of the superparamagnetic iron oxide NPs. Special attention is given to the selection of molecular anchors for the dispersant shell, because of their importance to ensure colloidal and functional stability of sterically stabilized superparamagnetic iron oxide NPs. We further detail how dispersants have been optimized to gain close control over iron oxide NP stability, size and functionalities by independently considering the influences of anchors and the attached sterically repulsive polymer brushes. A critical evaluation of different strategies to stabilize and functionalize core-shell superparamagnetic iron oxide NPs as well as a brief introduction to characterization methods to compare those strategies is given. © 2011 The Royal Society of Chemistry

    Crystallization of undercooled liquid fenofibrate

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    Formulation of hydrophobic drugs as amorphous materials is highly advantageous as this increases their solubility in water and therefore their bioavailability. However, many drugs have a high propensity to crystallize during production and storage, limiting the usefulness of amorphous drugs. We study the crystallization of undercooled liquid fenofibrate, a model hydrophobic drug. Nucleation is the rate-limiting step; once seeded with a fenofibrate crystal, the crystal rapidly grows by consuming the undercooled liquid fenofibrate. Crystal growth is limited by the incorporation of molecules into its surface. As nucleation and growth both entail incorporation of molecules into the surface, this process likely also limits the formation of nuclei and thus the crystallization of undercooled liquid fenofibrate, contributing to the good stability of undercooled liquid fenofibrate against crystallization

    Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol-gel process

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    Combination of the surfactant-free nonaqueous sol-gel approach with the microwave technique makes it possible to synthesize Fe3O4, CoFe2O4, MnFe2O4, and NiFe 2O4 nanoparticles of about 5-6 nm and with high crystallinity and good morphological uniformity. The synthesis involves the reaction of metal acetates or acetylacetonates as precursors with benzyl alcohol at 170 °C under microwave irradiation of 12 min. Immersion of glass substrates in the reaction solution results in the deposition of homogeneous metal ferrite films whose thickness can be adjusted through the precursor concentration. If preformed nickel nanoparticles are used as a type of curved substrate, the ferrite nanoparticles coat the seeds and form core-shell structures. These results extend the microwave-assisted nonaqueous sol-gel approach beyond the simple synthesis of nanoparticles to the preparation of thin films on flat or curved substrates. © 2010 Springer Science+Business Media, LLC

    Yielding of weakly attractive nanoparticle networks

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    We propose a scaling law that explicitly correlates the macroscopic yield stress of weakly attractive nanoparticle networks with features of the microscopic aggregates that form the percolating gel. The proposed law correctly predicts experimental data obtained from a model colloidal system covering a wide range of particle sizes, volume fractions and interparticle attractive forces. The agreement between theory and experiments supports the idea that yielding is ultimately caused by the rupture of a few interparticle bonds within the aggregates of the mechanically loaded network. © 2011 The Royal Society of Chemistry

    Characterization of supported lipid bilayers incorporating the phosphoinositides phosphatidylinositol 4,5-biphosphate and phosphoinositol-3,4,5-triphosphate by complementary techniques

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    Phosphoinositides are involved in a large number of processes in cells and it is very demanding to study individual protein-lipid interactions in vivo due to their rapid turnover and involvement in simultaneous events. Supported lipid bilayers (SLBs) containing controlled amounts of phosphoinositides provide a defined model system where important specific recognition events involving phosphoinositides can be systematically investigated using surface sensitive analytical techniques. The authors have demonstrated the formation and characterized the assembly kinetics of SLBs incorporating phosphatidylinositol 4,5-biphosphate (PIP2; 1, 5, and 10 wt %) and phosphoinositol-3,4,5-triphosphate (1 wt %) using the quartz crystal microbalance with dissipation monitoring and fluorescence recovery after photobleaching. An increased fraction of phosphoinositides led to a higher barrier to liposome fusion, but full fluidity for the phosphatidylcholine lipids in the formed SLB. Significantly, the majority of phosphoinositides were shown to be immobile. X-ray photoelectron spectroscopy was used for the first time to verify that the PIP2 fraction of lipids in the SLB scales linearly with the amount mixed in from stock solutions. © 2010 American Vacuum Society
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