Superparamagnetic Properties of Carbon-Encapsulated Ni Nanoparticle Assemblies

Abstract

Carbon-encapsulated Ni nanoparticles [Ni(C)] were synthesized using a modified arc-discharge reactor under methane atmosphere. The average particle size was revealed to be typically 10.5 nm with a spherical shape. The intimate and contiguous carbon fringe around these Ni nanoparticles is good evidence for complete encapsulation by carbon shell layers. Superparamagnetic property studies indicate that the blocking temperature (TB) is around 115 K at 1000 Oe applied field. Below TB, the temperature dependence of the coercivity is given by Hc = Hci[1 -(T/TB)1/2], with Hci approximately 500 Oe. Above TB, the magnetization M(H, T) can be described by the classical Langevin function L using the relationship M/Ms(T = 0) = coth(microH/kT)-kT/microH. The particle size can be inferred from the Langevin fit (particle moment mu) and the blocking temperature theory (TB), with values slightly larger than the high-resolution transmission electron microscopy observations. It is suggested that these assemblies of carbon-encapsulated Ni nanoparticles have typical single-domain, field-dependent superparamagnetic relaxation properties.

Controlling cell adhesion using layer-by-layer approaches for biomedical applications

“…In a simple picture, it forms polyelectrolyte multilayer film coatings by alternately depositing complementary molecules on a surface by dip coating through either electrostatic or other interactions [11][12][13]. Other methods to assemble LbL films include spin [14][15][16], spray [17,18], electromagnetic [19][20][21][22] and fluidic [23] assembly. One significant advantage of the LbL assembly is its versatility to tune surface properties [24][25][26][27][28][29][30] with a wide choice of building blocks and assembly parameters such as dipping solution pH and ionic strength [24,29,31].…”

Controlled Electrodissolution of Polyelectrolyte Multilayers: A Platform Technology Towards the Surface‐Initiated Delivery of Drugs

“…There are few studies that have investigated the influence of an electric field during the build-up process of polyelectrolyte multilayers. LbL assembly of a strong polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), alternated with CdTe nanocrystals [37][38][39] or enzymes [40,41] under an electric field has been investigated by Gao and co-workers. In their work, the polarity of the substrate (the working electrode) was reversed at each new adsorption to obtain favorable deposition conditions, i.e., opposite polarity between material and surface.…”

Electrophoretic deposition to promote layer-by-layer assembly for in situ gene delivery application

“…Compared with conventional LbL assemblies in which polyelectrolytes are suspended in solutions for passive adsorption, electric fields can be used to guide the movement of charged materials toward electrodes, leading to significant reductions in required deposition times. Accordingly, Feldmann et al applied electric fields to LbL assembly of anionic CdTe nanocrystals and cationic poly(diallyldimethylammonium chloride) (PDDA) on conductive material surfaces [9][10][11]. In their study, electric potentials were altered to create electrostatically favorable surface according to the deposition steps to accelerate adsorption, i.e.…”

“…Hence, various conductive materials, such as pyrolytic graphite, gold and indium-tin-oxide (ITO) glass, have been used as electrodes for electrophoretic deposition. However, these electrodes are not frequently used as implant materials, and their clinical applications are limited [9][10][11][12]14]. In a previous study, we fabricated conductive polypyrrole (PPy) films that are biocompatible and transparent, allowing easy observation of surface cells [15].…”

“…Although deposition efficiency can be highly enhanced by the electric field treatments, electrochemical reactions on electrode surfaces may interfere with adsorption [7,9]. In addition, polyelectrolytes within multilayers tend to move in opposite directions during electric field treatments, leading to increase interpenetration [4].…”