Colloidal Self Assembly

Monodispersed colloids self-assemble into 2-D and 3-D crystalline arrays, which allows one to obtain interesting and useful functionalities not only from the constituent materials but also from the long-range, mesoscopic order that characterizes periodic structures. A crystalline colloidal array has numerous applications in areas such as photonic crystals, sensing materials, etch masks for large area micro and nanostructure fabrication, coatings and so on. Colloidal spheres can be self-assembled into ordered 2D arrays on solid supports or in thin films by different techniques. However, spin coating is the preferential technique because of its high-throughput, low-cost of fabrication and ease of control for fabrication of large-area ordered monolayer arrays. We have experimentally optimised the parameters required to obtain perfect HCP and non-HCP arrays of different type of colloids on flat and patterned substrates by spin coating. Since this is a very rigorous approach and requires extensive experimentation, a colloidal transfer printing technique has been developed in our lab. The most important and novel feature of the developed colloidal transfer technique lies in the fact that particles can be transferred onto any type of substrate, including rough and non-planar surfaces. All the existing transfer printing techniques are either material specific or require a transfer medium. Based on this transfer technique, monolayer HCP arrays were transferred on zinc oxide (ZnO) surfaces. Subsequently, this colloidal template assisted ZnO Nanorods (NRs) were grown by hydrothermal method on any surface. The ZnO NRs displayed superhydrophobicity and self-cleaning property. Apart from transferring colloidal particles, Janus particles were transferred into a liquid medium by UV induced degradation of a sacrificial PMMA layer. We have been successful in dislodging surface-bound Janus particles without any damage and hence have successfully studied their assembly on different type of substrates. An inherent advantage of the transfer technique is that it works for all type of particles, and particles can be transferred from any type of PMMA matrix. This feature has been taken into advantage for transferring different arrangements of particles confined in a PMMA matrix.