145 research outputs found
Control of silver-polymer aggregation mechanism by primary particle spatial correlations in dynamic fractal-like geometry
Silver nanocrystals have been prepared by reacting silver nitrate with
ascorbic acid in aqueous solution containing a low concentration of a
commercial polynaphtalene sulphonate polymer (Daxad 19). Various crystalline
morphologies have been obtained simply by tuning the reaction temperature. We
have investigated the nanoparticle formation mechanism at three different
temperatures by in situ and time resolved Small Angle X ray Scattering
measurements. By modeling the scattering intensity with interacting spherical
particles in a fractal-like polymer-Ag matrix, we found signatures of
nucleation, growth and assembly of primary particles of about 15-20 nm. We
observed how the time evolution of both spatial correlations between primary
particles and the dynamic fractal geometry of the polymer-Ag matrix could
influence and determine both the aggregation mechanism and the morphology of
forming nanostructures in solution
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Magnetostriction of field-structured magnetoelastomers.
Field-structured magnetic particle composites are an important new class of materials that have great potential as both sensors and actuators. These materials are synthesized by suspending magnetic particles in a polymeric resin and subjecting these to magnetic fields while the resin polymerizes. If a simple uniaxial magnetic field is used, the particles will form chains, yielding composites whose magnetic susceptibility is enhanced along a single direction. A biaxial magnetic field, comprised of two orthogonal ac fields, forms particle sheets, yielding composites whose magnetic susceptibility is enhanced along two principal directions. A balanced triaxial magnetic field can be used to enhance the susceptibility in all directions, and biased heterodyned triaxial magnetic fields are especially effective for producing composites with a greatly enhanced susceptibility along a single axis. Magnetostriction is quadratic in the susceptibility, so increasing the composite susceptibility is important to developing actuators that function well at modest fields. To investigate magnetostriction in these field-structured composites we have constructed a sensitive, constant-stress apparatus capable of 1 ppm strain resolution. The sample geometry is designed to minimize demagnetizing field effects. With this apparatus we have demonstrated field-structured composites with nearly 10,000 ppm strain
Dendrimer-Functionalized Iron Oxide Nanoparticles for Specific Targeting and Imaging of Cancer Cells
We demonstrated a unique approach that combines a layer-by-layer (LbL) self-assembly method with dendrimer chemistry to functionalize Fe 3 O 4 nanoparticles (NPs) for specific targeting and imaging of cancer cells. In this approach, positively charged Fe 3 O 4 NPs (8.4 nm in diameter) synthesized by controlled co-precipitation of Fe II and Fe III ions were modified with a bilayer composed of polystyrene sulfonate sodium salt and folic acid (FA)- and fluorescein isothiocyanate (FI)-functionalized poly(amidoamine) dendrimers of generation 5 (G5.NH 2 -FI-FA) through electrostatic LbL assembly, followed by an acetylation reaction to neutralize the remaining surface amine groups of G5 dendrimers. Combined flow cytometry, confocal microscopy, transmission electron microscopy, and magnetic resonance imaging studies show that Fe 3 O 4 /PSS/G5.NHAc-FI-FA NPs can specifically target cancer cells overexpressing FA receptors. The present approach to functionalizing Fe 3 O 4 NPs opens a new avenue to fabricating various NPs for numerous biological sensing and therapeutic applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57409/1/3043_ftp.pd
Recognition-Mediated Assembly of Quantum Dot Polymer Conjugates with Controlled Morphology
We have demonstrated a polymer mediated “bricks and mortar” method for the self-assembly of quantum dots (QDs). This strategy allows QDs to self-assemble into structured aggregates using complementary three-point hydrogen bonding. The resulting nanocomposites have distinct morphologies and inter-particle distances based on the ratio between QDs and polymer. Time resolved photoluminescence measurements showed that the optical properties of the QDs were retained after self-assembly
In quest of a systematic framework for unifying and defining nanoscience
This article proposes a systematic framework for unifying and defining nanoscience based on historic first principles and step logic that led to a “central paradigm” (i.e., unifying framework) for traditional elemental/small-molecule chemistry. As such, a Nanomaterials classification roadmap is proposed, which divides all nanomatter into Category I: discrete, well-defined and Category II: statistical, undefined nanoparticles. We consider only Category I, well-defined nanoparticles which are >90% monodisperse as a function of Critical Nanoscale Design Parameters (CNDPs) defined according to: (a) size, (b) shape, (c) surface chemistry, (d) flexibility, and (e) elemental composition. Classified as either hard (H) (i.e., inorganic-based) or soft (S) (i.e., organic-based) categories, these nanoparticles were found to manifest pervasive atom mimicry features that included: (1) a dominance of zero-dimensional (0D) core–shell nanoarchitectures, (2) the ability to self-assemble or chemically bond as discrete, quantized nanounits, and (3) exhibited well-defined nanoscale valencies and stoichiometries reminiscent of atom-based elements. These discrete nanoparticle categories are referred to as hard or soft particle nanoelements. Many examples describing chemical bonding/assembly of these nanoelements have been reported in the literature. We refer to these hard:hard (H-n:H-n), soft:soft (S-n:S-n), or hard:soft (H-n:S-n) nanoelement combinations as nanocompounds. Due to their quantized features, many nanoelement and nanocompound categories are reported to exhibit well-defined nanoperiodic property patterns. These periodic property patterns are dependent on their quantized nanofeatures (CNDPs) and dramatically influence intrinsic physicochemical properties (i.e., melting points, reactivity/self-assembly, sterics, and nanoencapsulation), as well as important functional/performance properties (i.e., magnetic, photonic, electronic, and toxicologic properties). We propose this perspective as a modest first step toward more clearly defining synthetic nanochemistry as well as providing a systematic framework for unifying nanoscience. With further progress, one should anticipate the evolution of future nanoperiodic table(s) suitable for predicting important risk/benefit boundaries in the field of nanoscience
Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies
Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed
Controlling the number of dendrimers in dendrimicelle nanoconjugates from 1 to more than 100
Nursing Management Diagnoses : Validation in Gerontological Nursing Management
The purpose of this investigation is three-fold: (a) to validate nursing management diagnoses previously identified by nurse managers, (b) to examine how frequently the validated nursing management diagnoses are perceived to occur in nursing management practice and the level of disruption caused by organizational problems in meeting nursing’s goals, and (c) to establish a correlation between frequency of occurrence and level of disruption in a gerontological nursing management setting. This investigation is a partial replication of Morrison’s (1995) study validating nursing management diagnoses
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Directed self -assembly of nanoparticles
Nanotechnology promises to revolutionize the way we think about, but more importantly create new materials. The key to making this promise a reality is a commitment to fundamental research in critical areas including synthesis, fabrication, and characterization of nanoscale components. Nanoparticles have attracted wide attention as such components due to their unique size dependent properties including, superparamagnetism, chemilumiescents, and catalysis. To fully harness the potential capabilities of nanoparticles we need to develop new methods to assemble them into useful patterns or structures. Directed self-assembly using noncovalent interactions can be used to achieve this goal. This dissertation outlines experiments demonstrating several methods of polymer-mediated assembly of gold and iron oxide nanoparticles. Directed self-assembly using various polymer architectures provided a direct means to: (1) control the overall size of nanoparticle aggregates, (2) control interparticle spacing between particles, (3) control the collective behavior in nanoparticle ensembles
Onze keuze tusschen twee tegenovergestelde richtingen en een blik in onzen verdedigingstoestand
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