The spreading of a thin film of suspension on a spinning disk and the accompanying contact line instability is studied through flow visualization experiments. The critical radius for the onset of instability shows an increase with increase in the particle fraction (ϕp) before decreasing slightly at the highest value of ϕp studied, while the instability wavelength (λ) exhibits a non-monotonic dependence. The value of λ is close to that for a partially wetting liquid at lower ϕp, it decreases with increasing ϕp to a minimum before increasing again at largest ϕp. The non-monotonic trends observed for λ are discussed in light of the linear stability analysis of thin film equations derived for suspensions by Cook et al. [“Linear stability of particle-laden thin films,” Eur. Phys. J.: Spec. Top. 166, 77 (2009)] and Balmforth et al. [“Surface tension driven fingering of a viscoplastic film,” J. Non Newtonian Fluid Mech. 142, 143 (2007)].

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