Electrostatic co-assembly of iron oxide nanoparticles and polymers : towards the generation of highly persistent superparamagnetic nanorods

TL;DR

This paper presents a method to create highly persistent superparamagnetic nanorods by electrostatically assembling iron oxide nanoparticles with polymers, enabling potential applications in nanodevices and sensors.

Contribution

It introduces a novel protocol for fabricating elongated, superparamagnetic nanorods through electrostatic assembly of iron oxide nanoparticles and block copolymers, with tunable shapes and properties.

Findings

Successfully fabricated micrometer-scale nanorods with controlled dimensions.

Nanorods exhibit superparamagnetic behavior and reorient under magnetic fields.

The assembly process is controlled by ionic strength adjustments.

Abstract

A paradigm proposed recently by Boal et al. (A.K. Boal et al., Nature 404, 746-748, 2000) deals with the possibility to use inorganic nanoparticles as building blocks for the design and fabrication of colloidal and supracolloidal assemblies. It is anticipated that these constructs could be made of different shapes, patterns and functionalities and could constitute the components of future nanodevices including sensors, actuators or nanocircuits. Here we report a protocol that allowed us to fabricate such nanoparticle aggregates. The building blocks of the constructs were anionically coated iron oxide nanocrytals (superparamagnetic, size 7 nm) and cationic-neutral block copolymers. We have shown that the electrostatic interactions between charged species can be controlled by tuning the ionic strength of the dispersion. Under appropriate conditions, the control of electrostatics resulted in the elaboration of spherical or elongated aggregates at the micrometer length scale. The elongated aggregates were found to be rod-like, with diameters of a few hundred nanometers and lengths between 1 and 50 micrometers. In addition to their remarkable stiffness, the nanostructured rods were found to reorient along with an externally applied magnetic field, in agreement with the laws of superparamagnetism.