Thermal capillary wave growth and surface roughening of nanoscale liquid films

Abstract

Abstract

Modification of the fluctuation dynamics of ultra-thin wetting films

“…The resulting van der Waals forces can be either attractive or repulsive. In the case of attractive interactions, the fluctuations are amplified by intermolecular forces and the film is predicted to be unstable [13][14][15][16]. This is confirmed by experimental observations on dewetting polymer films of nanometric thickness [7].…”

Fluctuation-driven dynamics in nanoscale thin-film flows: Physical insights from numerical investigations

“…It was shown that thermal noise changes the spectrum of thermal capillary waves from an exponential decay to a power law for large wavenumbers, which was then confirmed by the experimental observations on the dewetting of polymer films [18]. The same behaviour of spectrum was also confirmed in MD simulations, first done by Willis & Freund [19] in 2010 and recently, followed by Zhang et al [20], who showed that interfacial roughening falls into a universality class [11]. However, theories based on small deviations from equilibrium cannot, inevitably, describe inherently nonlinear events such as film breakup.…”

“…The fluctuations of the interface in thermal equilibrium [11,17] can be described by the classical theory for thermal capillary waves [7,18] with the static spectra of each surface mode (wavenumber) derived from the equipartition theorem. To capture the development of thermal capillary waves towards the equilibrium state, more advanced theories that include the time evolution of wave spectra were derived by applying linear stability analysis to the SLE [20,22]; we will use the model from Ref.…”

“…An important physical factor at the nanoscale is thermal noise, which has been shown experimentally to influence interfacial dynamics through the observation of thermal capillary waves on interfaces of (ultra-low surface-tension) colloid-polymer mixtures [7]. Recently, by the use of molecular dynamics (MD) simulations, it has been discovered that fluctuation-driven nanowaves dominate a range of nanoscale interfacial-flow phenomena, such as nanothread breakup [8], nanojet instablity [9], nanodroplet coalescence [10] and development of rough interfaces on nanoscale thin films [11]. Notably, the observations of nanothread breakup in MD were further confirmed by an analytical model [12] and experiments with colloid-polymer mixtures [13,14].…”

Relaxation of Thermal Capillary Waves for Nanoscale Liquid Films on Anisotropic-slip Substrates

“…Scaling relations are found for the process of surface roughening and the time scale for a smooth surface to reach thermal equilibrium is extracted. 19 When in thermal equilibrium, it is well known that the temporal correlations of surface modes show an exponential decay, with a decay rate given by the dispersion relation of the system. Based on this, X-ray Photon Correlation Spectroscopy (XPCS) or similar techniques, can be used to infer the features of liquid-solid systems such as surface tension, viscoelasticity, and substrate surface structures.…”