Dynamic Contact Angle of Spreading Thin Film on a Rotating Disk

Abstract

The effect of dynamic contact angle on fingering instability during spin coating is investigated by flow visualization experiment. A modified rotational Bond number, which demonstrates the dynamic contact angle of fluid front that affects the dimensionless critical radius, is proposed in this work. For high rotational Bond number, the variation in dimensionless critical radius is not linearly proportional to the rotational Reynolds number because of the variation in critical contact angle if the relaxation time is fixed at zero. By modifying the rotational Bond number with the change in critical contact angle, the dimensionless critical radius becomes a function of the modified rotational Bond number.