Enhanced droplet spreading due to thermal fluctuations

fluid mechanics;thin liquid films;stochastic;statistical mechanics;molecular dynamics

Willis, Adam M.

关键词: fluid mechanics;    thin liquid films;    stochastic;    statistical mechanics;    molecular dynamics;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/24141/Willis_Adam.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The dynamics of thin film liquid interfaces (< 100 nm) play dominant roles in many macroscale phenomena, such as droplet break up, evaporation of a meniscus, boiling and heat transfer, and thin film dynamics.These processes are can be used in the manufacturing of microelectronics and biomedical devices.Unlike for thicker films, the thermal motion of the constitutive molecules can affect dynamics and may need to be included when modeling nanometer mechanical systems.Yet, explicitly modeling all of the molecules of a thin liquid film interface is often intractable.Thus there is a need for simplified continuum models that still contain the relevant physics of thin films.Theoretical methods do exist for including thermal energy into continuum equations; however experimental verification of these methods is still unavailable, primarily due to the complications of measuring dynamical quantities at the nanometer length scales.This dissertation focuses upon the study of molecular films via molecular dynamics simulations in order to assess the relevant physics needed for continuum modeling of thermally perturbed fluid flows.The first project of my dissertation compared the continuum predictions of capillary wave relaxation in thin fluid film interfaces to the behavior of molecular simulations.We found that for all but the smallest length scales in the free-fluid interface, continuum predictions matched that of the molecular simulations for the both the amplitude and the decay rates of the thermal capillary waves.However, at smaller length scales, there also existed a transition in behavior where the wave amplitudes of the continuum model and the molecular simulations matched, but the decay rates of waves in the molecular simulations adopted a new, molecular-size-dependent decay behavior.Expanding upon the success of the continuum modeling for all but the smallest length scales of thermally perturbed thin liquid films, in this work we study the spreading of a large molecular drop on a solid plate and test whether thermal forces can dominate spreading dynamics as predicted by Davidovitch et al..By comparing the spreading of a simulated molecular drop, we not only find an enhanced spreading rate, but also find that the spreading dynamics found well matched the predictions of a thermally augmented continuum model.