Characterization of size and dispersion stability of colloidal photonic crystal solutions made easy

Characterisation of Magnetically Tunable Colloidal Photonic Crystals Using the Zetasizer Nano

Abstract

Highly charged Fe₃O₄ nanocrystals have found applications in telecommunication devices, drug delivery and contrast agents. The Zetasizer Nano can characterize the size and stability of these photonic crystal dispersions easily and quickly.

Introduction

Recently, a magnetically tuneable photonic crystal system has been developed by assembling highly charged Fe₃O₄ colloidal nanocrystal clusters (CNCs) [1,2]. They have attracted much attention because of their optoelectronic applications such as photonic components in tele-communication devices, lasers, sensors, drug delivery system (DDS) and MRI contrast agents [1,2].

Stabilized by the balance of attractive (magnetic) and repulsive(electrostatic) forces, the colloids form ordered structures along the direction of the external magnetic field with a regular interparticle spacing on the order of hundreds of nanometers. As a result, the solutions strongly diffract visible light [1,2]. CNCs can tune the diffraction wavelength throughout the entire visible spectrum by changing the strength of the external field [1,2]. The tuning range of the diffraction wavelength is related to the average size of the colloidal nanocrystal clusters. In general, crystals of large clusters (160-180 nm) preferentially diffract red light in a relatively weak magnetic field. Small clusters (60-100 nm) form ordered structures only when the magnetic field is strong and the crystals preferentially diffract blue light [1,2].

The size and dispersion stability of the photonic crystal system can be characterized by measuring the mean particle size and zeta potential respectively, because the optical response is sensitive to both the size of the colloids and the ionic strength of the solution.