posted on 2013-11-26, 00:00authored byRafael Libanori, Frieder
B. Reusch, Randall M. Erb, André R. Studart
Tuning the optical properties of
suspensions by controlling the
orientation and spatial distribution of suspended particles with magnetic
fields is an interesting approach to creating magnetically controlled
displays, microrheology sensors, and materials with tunable light
emission. However, the relatively high concentration of magnetic material
required to manipulate these particles very often reduces the optical
transmittance of the system. In this study, we describe a simple method
of generating particles with magnetically tunable optical properties
via sol–gel deposition and functionalization of a continuous
layer of silica on ultrahigh magnetically responsive (UHMR) alumina
microplatelets. UHMR microplatelets with tunable magnetic response
in the range of 15–36 G are obtained by the electrostatic adsorption
of 2 to 13% of superparamagnetic iron oxide nanoparticles (SPIONs)
on the alumina surface. The magnetized platelets are coated with a
20–50 nm layer of SiO2 through the controlled hydrolysis
and condensation reactions of tetraethylorthosilicate (TEOS) in an
NH3/ethanol mixture. Finally, the silica surface is covalently
modified with an organic fluorescent dye by conventional silane chemistry.
Because of the anisotropic shape of the particles, control of their
orientation and distribution using magnetic fields and field gradients
enables easy tuning of the optical properties of the suspension. This
strategy allows us to gain both spatial and temporal control over
the fluorescence emission from the particle surface, making the multifunctional
platelets interesting building blocks for the manipulation of light
in colloid-based smart optical devices and sensors.