What do common devices such as smartphones, CD’s and solar panels all have in common? They are all examples of innovative technology that is still limited to flat, rigid geometries. This is primarily due to the limitations of the manufacturing processes used to create components within these devices, key among them the thin polymer films produced through spin coating.

Spin coating is a technique used due to its ability to effectively create uniform films on the scale of micro or nanometres. However, it relies on a planar substrate to produce uniform layers, thus restricting the design of components manufactured using this process to simple, flat objects. As the requirement for curved device geometries expands, complex alternative fabrication methods are being implemented in industry.

For spin coating to remain relevant, a viable process for controlling the fluid flow over curved surfaces must be developed. This research investigates the hypothesis that coating distributions can be controlled through optimized rotation of a curved substrate. Where a multi-axis rotational manipulator and novel characterization system have been developed to investigate the fabrication of curved devices using the improved spin coating technique.

The phenomena of surface instabilities in a thin power-law fluid during spin coating are investigated. The set of Navier-Stokes equations with non-Newtonian behavior in the region of low Reynolds number serves as a mathematical description of the physical systems. Long-wave perturbation analysis is proposed to derive an evolution equation of the Ostwald de-Waele type fluid to govern the propagation of surface waves. Weakly nonlinear dynamics of film flow is studied by the multiple scales method. The amplitude of instability is determined by a Ginzburg-Landau equation. The study reveals that the degree of power-law index plays a vital role in stabilizing the film flow. The shear-thinning fluid is more unstable than the shear-thickening fluid in the stability analysis. Further, the nonlinear wave speed in the supercritical stability region decreases with increasing values of power-law index.

Silica-titania sub-close-packed single layers were deposited by spin coating titanium alkoxide sols containing inert 0.5 micrometer silica particles to study the process of reactive sintering more closely than has been done before. The sub-close-packed single layers were designed to achieve a coating density such that pairs or chains of silica particles were placed on the flat substrate and held together by the reactive titania thin films overlaid on the surface and in the neck regions of these essentially 2-D particle networks. Because of the low density of silica particles, all of the two-particle junctions and neck regions were aligned for geometrically direct viewing; as a result scanning electron microscopy was useful for observing the morphology of these neck regions. Image analysis was used to quantify the neck diameter for varying titania/silica precursor concentration ratios. Geometrical calculations that relate the change in neck volume to the neck radius are presented. Implications for design of reactive sintering systems are discussed.

The effect of Coriolis force on the rivulet (fingering) instability, the onset of rivulet phenomena during spin coating, is investigated by flow visualization experiments incorporating with dimensional analysis. This study demonstrates that the Coriolis force will affect significantly the critical radius of rivulet instability and the deflection angle of instability rivulet. For the cases of low Bond number, the effect of Coriolis force is a stabilizing factor, and the dimensionless critical radius increases slightly with increasing rotational Reynolds number Reω. In the case of high Bond number, the effect of Coriolis force becomes a destabilizing factor while Reω < 1, and a characteristic length is found by balancing the viscous force with the surface tension. For Reω > 1, the radial Corilois force, which is always pointing inward, plays a stabilizing role with magnitude Reω2.

In this paper we demonstrate high sensitive and fast response humidity sensors using layer-by-layer (LbL) nano-assembled films of Polypyrrole (PPY). Spin coated PPY films were used for sensitivity and response time comparisons. The change in electrical sheet resistance of the sensing films was monitored as the device was exposed to humidity. For 5% change in relative humidity sensitivity measured from layer-by-layer based devices was 10% and 8% for the spin coated devices. The response time for LbL based and spin coated device was measured as 25 seconds and 57 seconds respectively. The LbL nano-assembled films of PPY showed the better response in terms of sensitivity, response time, linearity and degradation. An intended application for these LbL nano-assembled devices is in disposable handheld instruments to monitor the presence of humidity in humidity sensitive environments.