Supervisors: Dr. P. Baesjou, Dr. Arnout Imhof
Promotor: Prof.dr. Alfons van Blaaderen
Funding: STW
Employed: 1 February 2016 – 31 January 2020

Switchable Optics with responsive colloids

Historically, materials science has been involved with preparing materials with a vast range of tailorable characteristics such as: colour, opacity, refractive index, and ability to be used in photocatalysis [1]. Nowadays there is a growing interest in responsive material systems that allow for dynamical adjustment of the aforementioned properties. A number of mechanisms are employed in order to achieve responsive materials. These mechanisms include modifying particle morphology, orientation (e.g. liquid crystals) and phase transformations. Furthermore, we can modify spatial distributions by means of electrophoresis – the movement of charged colloidal particles in an electric field, or dielectrophoresis – the movement of particles in an electric field gradient [2].
However, there is a need to develop high refractive index nanoparticles which can form stable dispersions and be easily manipulated via external factors.
In this project, we will synthesise high refractive index nanocrystals with different shapes (i.e. nanorods, nanospheres), sizes, and structures (simple, core-shell) and produce stable colloidal dispersions. Afterwards, manipulation of the position and\or orientation of the abovementioned particles by external factors will be used to vary optical properties such as the local refractive index. This will enable the manipulation of light i.e. beam shape and direction.
Considering this aim, the desired particles should be both non-coloured and non-scattering. Titanium dioxide and zirconium dioxide are two promising candidates for achieving our goal.

Figure 1: a) TEM image of 25 nm TiO2 nanorods. b and c) Colloidal silica rods showing liquid crystal like behaviour by alignment in an electric field and influencing the diffraction of a laser beam (The scale bar is 2 cm.) [2].

[1] M. Cargnello et al., Chemical Reviews 114, 9319-9345 (2014).
[2] B. Liu et al., Nature Communications 5, 3092-3100 (2014).