Research tools for understanding soft wetting

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The applicant intends to investigate the dynamic wetting behaviour of liquids on soft surfaces. The way a soft material responds to an oncoming droplet is non-trivial and significantly different from rigid surfaces. Soft materials exhibit promising potential in designing liquid-repellent self-cleaning and anti-fouling surfaces and offer several advantages over the conventional micro/nanostructured or liquid infused surfaces, including reliability in a wide range of operational spectrum and long-term durability. However, scientific endeavour on understanding the dynamic response of a soft surface towards a droplet is relatively scarce. In this research, the applicant intends to seek answers to two fundamental questions in dynamic soft wetting. First, how does a droplet spread upon its initial contact with soft surfaces and second, what happens when a liquid droplet impinges on a soft deformable surface? Both of these phenomena are intrinsically transient, with a typical duration of only a few seconds. Recently the applicant has installed a Dual Wavelength Reflection Interference Contrast Microscopy (DW-RICM) system in the lab, designed specifically for probing the complex interaction of liquid droplets with soft surfaces, often occurring at nanoscale. Preliminary experiments on static wetting have indicated the promising potential of this technique in gaining valuable insights on wetting behaviour. An in-house image processing algorithm has also been developed by the applicant's research group to interpret the experimental data. However, with its in-built CCD cameras in place, DW-RICM is intrinsically restricted to image at a low frame rate (maximum 60 fps for the required field of view), severely limiting its applicability in capturing the transient wetting dynamics. The applicant intends to overcome this bottleneck by replacing the existing detection system of DW-RICM with two high-speed cameras. This will revamp the imaging rate to 160,000 fps, enabling the users to probe the wetting dynamics with desired spatiotemporal accuracy. These two cameras will work in tandem to image transient wetting behaviour (spreading and impact) of liquid drops on soft surfaces from the bottom. Each one captures the dynamic interference signature generated by surface illumination with one of the two laser sources present in the dual-wavelength system. Another high-speed camera (already available in the applicant's lab) will be integrated with the system to capture the side view for obtaining a holistic description of the dynamic interaction. The generated insights from this study will expand the boundaries of fundamental understanding of soft wetting and create opportunities for practical application, especially in the pharmaceutical and food packaging industries, ultimately propelling the Canadian economy forward. Additionally, this state-of-the-art system will be made available to the interface science community across Canada once commissioned.