Colloidal synthesis offers a route to nanoparticles (NPs) with controlled composition and structural features. This Perspective describes the use of polyvinylpyrrolidone (PVP) to obtain such nanostructures. PVP can serve as a surface stabilizer, growth modifier, nanoparticle dispersant, and reducing agent. As shown with examples, its role depends on the synthetic conditions. This dependence arises from the amphiphilic nature of PVP along with the molecular weight of the selected PVP. These characteristics can affect nanoparticle growth and morphology by providing solubility in diverse solvents, selective surface stabilization, and even access to kinetically controlled growth conditions. This Perspective includes discussions of the properties of PVP-capped NPs for surface enhanced Raman spectroscopy (SERS), assembly, catalysis, and more. The contribution of PVP to these properties as well as its removal is considered. Ultimately, the NPs accessed through the use of PVP in colloidal syntheses are opening new applications, and the concluding guidelines provided herein should enable new nanostructures to be accessed facilely.

/pdf/polyvinylpyrrolidone-pvp-in-nanoparticle-synthesis-4i444sejw5.pdf

Polyvinylpyrrolidone (PVP) in nanoparticle synthesis

Thin-film technology is widely implemented in numerous applications1. Although flat substrates are commonly used, we report on the advantages of using curved surfaces as a substrate. The curvature induces a lateral film-thickness variation that allows alteration of the properties of the deposited material2,3. Based on this concept, a variety of implementations in materials science can be expected. As an example, a topographic pattern formed of spherical nanoparticles4,5 is combined with magnetic multilayer film deposition. Here we show that this combination leads to a new class of magnetic material with a unique combination of remarkable properties: The so-formed nanostructures are monodisperse, magnetically isolated, single-domain, and reveal a uniform magnetic anisotropy with an unexpected switching behaviour induced by their spherical shape. Furthermore, changing the deposition angle with respect to the particle ensemble allows tailoring of the orientation of the magnetic anisotropy, which results in tilted nanostructure material.

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-000595.pdf

Magnetic multilayers on nanospheres

Fabrication of hybrid MOF-on-MOF heteroarchitectures can create novel and multifunctional platforms to achieve desired properties. However, only MOFs with similar crystallographic parameters can be hybridized by the classical epitaxial growth method (EGM), which largely suppressed its applications. A general strategy, called internal extended growth method (IEGM), is demonstrated for the feasible assembly of MOFs with distinct crystallographic parameters in an MOF matrix. Various MOFs with diverse functions could be introduced in a modular MOF matrix to form 3D core-satellite pluralistic hybrid system. The number of different MOF crystals interspersed could be varied on demand. More importantly, the different MOF crystals distributed in individual domains could be used to further incorporate functional units or enhance target functions.

Controllable Modular Growth of Hierarchical MOF-on-MOF Architectures

Study of structural and magnetic properties of cobalt ferrite (CoFe 2 O 4 ) nanostructures

This article discusses on stability and agglomeration of particles, an important occurring phenomenon that greatly affects the properties of magnetic fluid. Magnetoviscous behaviour and thermomagnetic convection is a special characteristic of this fluid, which have promising prospects in advanced applications like in electronic cooling devices and pipe systems, heat exchangers, magnetic clutch, dynamic sealing and servo rheological devices. The purpose of this article is to review recent investigations in this field that focuses on the magnetoviscous effects and thermomagnetic convection of magnetic fluids. This review also emphasises both numerical and experimental approaches for deeper understanding of those properties.

Magnetoviscous effect and thermomagnetic convection of magnetic fluid: A review

CoFe2O4 ferrites were synthesized by sol–gel method, having metal nitrates as precursors and PVA as surfactant, followed by a heat treatment at 960 °C for 2 h. The ultrafine ferrite powders obtained have been characterized by X-ray diffraction, thermal gravimetry, differential scanning calorimetry and room temperature magnetic measurement studies. The morphology of the powder was identified by high resolution-scanning electron microscopy. X-ray diffraction results indicate that the resultant CoFe2O4 crystallites consist of spinel phase. Significant differences in magnetic properties of CoFe2O4 samples synthesized with various concentrations of PVA were observed. The magnetisation measurements show that when the PVA concentration increased, coercivity initially decreased and then increased where as retentivity and magnetisation decreased. The optimum concentration of PVA for the synthesis of CoFe2O4 ferrites is obtained from this investigation. Obviously this material can be used as an efficient candidate for practical recording purpose.

Synthesis of CoFe2O4 powder via PVA assisted sol–gel process

CoFe2O4 particles were synthesized using metallic nitrates and polyvinylpyrolidone (PVP) using sol–gel method followed by calcination for 2 h at 960 °C. PVP performed as a surfactant and the effect of various concentrations of PVP on the resultant CoFe2O4 powder was studied. The resultant samples were characterized by XRD, TG/DSC, HR-SEM and VSM. X-ray diffraction results indicated the crystalline phase of CoFe2O4 particles and impurity phase of hematite was observed for higher PVP concentrations. SEM images demonstrated the influence of PVP concentration on the size of the particles. By VSM measurements, the variations in magnetic properties with respect to PVP concentration are studied. All the magnetic characteristics H
 c
 , M
 s
 and M
 r
 increased for 6 wt% and 15 wt% of PVP concentration. The CoFe2O4 particles synthesized with the optimum concentration of PVP may be very attractive for potential applications because of their outstanding magnetic properties (M
 s
 =81.1 Am2/kg, H
 c
 =831 Gauss).

/pdf/study-of-cofe2o4-particles-synthesized-with-various-q7rju8fuw0.pdf

Study of CoFe2O4 Particles Synthesized with Various Concentrations of PVP Polymer

Cobalt ferrite (CoFe2O4) particles were synthesized by sol–gel method using metal nitrates, citric acid (CA) and polyvinyl alcohol (PVA). X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), thermogravimetry/differential scanning calorimetry analysis and vibrating sample magnetometer were used to study the structural, thermal and magnetic properties of the CoFe2O4 powder. XRD results indicate that the resultant particles have crystalline, pure single phase spinel structure. From HR-SEM images, a systematic decrease in particle size is observed with an increase in PVA concentration, along with addition of CA. CA at various concentrations of PVA significantly enhance the magnetic properties of the materials.

/pdf/synthesis-characterization-and-effects-of-citric-acid-and-18rndxvtn0.pdf

R. Suresh Babu

Papers

Synthesis of CoFe2O4 powder via PVA assisted sol–gel process

Study of CoFe2O4 Particles Synthesized with Various Concentrations of PVP Polymer

Synthesis, Characterization and Effects of Citric Acid and PVA on Magnetic Properties of CoFe2O4