Abstract
The relaxation dynamics of the contact angle between a viscous liquid and a smooth substrate is studied at the nanoscale. Through atomic force microscopy measurements of polystyrene nanostripes we simultaneously monitor both the temporal evolution of the liquid-air interface and the position of the contact line. The initial configuration exhibits high curvature gradients and a non-equilibrium contact angle that drive liquid flow. Both these conditions are relaxed to achieve the final state, leading to three successive regimes in time: (i) stationary contact line levelling; (ii) receding contact line dewetting; (iii) collapse of the two fronts. For the first regime, we reveal the existence of a self-similar evolution of the liquid interface, which is in excellent agreement with numerical calculations from a lubrication model. For different liquid viscosities and film thicknesses we provide evidence for a transition to dewetting featuring a universal critical contact angle and dimensionless time.
Highlights
Thin liquid films are ubiquitous in many natural systems and technological applications, spanning from e.g. the corneal fluid in the human eye and the aqueous glue in spiders silk to mechanical lubrication, protective coatings, microelectronics fabrication and lithography.[1,2,3,4,5] understanding the stability and dynamics of thin films is a crucial task
One separate experiment has been performed on thick oxide layer Si wafers, and it has not shown any significant difference with respect to the experiments on a native Si oxide layer: the values of the contact angles for this experiment perfectly collapse on the master curve in Fig. 5 and the contact angle at the transition is preserved
In this article we have studied the relaxation dynamics of the contact angle between a viscous liquid and a smooth solid substrate
Summary
Thin liquid films are ubiquitous in many natural systems and technological applications, spanning from e.g. the corneal fluid in the human eye and the aqueous glue in spiders silk to mechanical lubrication, protective coatings, microelectronics fabrication and lithography.[1,2,3,4,5] understanding the stability and dynamics of thin films is a crucial task. When a thin liquid layer is deposited on a low-energy surface the substrate might be spontaneously exposed to the vapor phase in order to reduce the energy of the system. This phenomenon is achieved either by the nucleation of holes in the film, or by the amplification of capillary waves at the liquid surface,[6,7,8,9] a situation referred to as spinodal dewetting. This apparent paradox can be solved by including microscopic effects like, for instance, slip at the solid–liquid boundary,[17] the presence of a precursor film ahead the line[18] or a height dependence of the interfacial tension.[19]
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