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Instabilities And Breakup In Thin Liquid Films

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Instabilities And Breakup In Thin Liquid Films

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Author : Vineeth Chandran Suja
language : en
Publisher:
Release Date : 2020

Instabilities And Breakup In Thin Liquid Films written by Vineeth Chandran Suja and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.

Liquid films having dimensions that are relatively small in the direction normal to their surface are commonly referred to as thin liquid films. Due to their prevalence in nature and due to their unique geometrical characteristics, a comprehensive understanding of thin film dynamics including instabilities and break-up within thin liquid films is of fundamental and practical interest. Practically this understanding is crucial to tuning the stability thin films in a number of important applications such as for stabilizing foams in foods and beverages, destabilizing foams in lubricants, avoiding surface irregularities in liquid coatings and treating ophthalmic disorders originating from the unnatural breakup of the tear film. Fundamentally, the microscopic thickness of these liquid films along with their large surface to volume ratio presents a convenient framework to investigate characteristics of two dimensional flows, and probe the effects of surface phenomenon such as evaporation and surfactant dynamics on fluid flows. Motivated by the importance of thin liquid films, in this thesis, we experimentally investigate the instabilities and break-up within thin liquid films. In the first part of the thesis (Chapters 2 - 4), we develop and optimize experimental tools and protocols for systematically studying thin liquid films. Notably, we show that single bubble/drop experiments are a convenient and complementary technique to study the dynamics of thin liquid films. Subsequently, we detail a new technique for automatically and robustly measuring the spatiotemporal thickness of thin liquid films - hyperspectral interferometry coupled with machine learning. Finally, we will also establish the operating regimes within which the size of bubbles formed on capillaries for single bubble experiments can be precisely controlled to avoid an air compressibility driven shape instabilities. In the subsequent parts of the thesis we utilize the developed tools to study four different problems - Bubble stability in worm like micellar (WLM) polymer solutions (Chapter 5), Lubricant foaming (Chapters 6 - 8), Drying of thin polymer films (Chapter 9) and Dewetting of the tear film (Chapter 10). In Chapter 5, we explore a problem relevant for the cosmetic industry, and characterize the drainage characteristics of thin films between bubbles and flat wormlike micellar solution - air interfaces. The supramolecular structure and elasticity of the wormlike micelles alters the dynamics of film drainage in WLM as compared to those in thin films containing pure surfactants. The unique features of film drainage include film elasticity driven 'dimple recoil' and a single step transition to a Newton black film beyond a critical film thickness. In Chapters 6 - 8, we explore a problem relevant for the lubricant industry, and study the stability of thin liquid films in lubricants with and without antifoams. Utilizing single bubble experiments, we reveal that the stability of thin films between bubbles in lubricant base oils are enhanced by Marangoni flows driven by the differential evaporation of the various components in the oil. Fundamentally, we also show that the spatiotemporal characteristics of these Marangoni flows are regulated by the concentration and volatility of the volatile species in the oil. Interestingly when the concentration of the volatile species approaches 50%, evaporation driven Marangoni flows become chaotic, with disordered spatial structure, chaotic fluctuations, spatially invariant mean film thickness statistics, high sensitivity to initial conditions, rapidly decaying spatial correlation and a power spectrum for thickness fluctuation that obeys a power law scaling that closely resembles the Kolmogorov's -5/3rd scaling. In the presence of filtered lubricants with antifoams, we reveal that the stability of thin films are positively correlated to the number of filtration cycles, and inversely correlated to the nominal filter pore size and the initial antifoam concentration. In Chapter 9 we explore a problem relevant for film coating, and study the drying of aqueous polymer solutions. Depending on the polymer concentration and the polymer diffusivities, we show that a classical Rayleigh-Taylor instability can develop within the drying solution. We also present the scaling laws describing the onset time of the instability as a function of the physical properties and initial polymer concentrations of the solutions. In Chapter 10 we report a platform to characterize the thickness of the tear film in vivo. By qualitatively comparing the dewetting characteristics observed in vivo with in vitro experiments, we will show that the mechanisms of dewetting is influenced by the presence of interfacial rheology. Further we also reveal that the spatial locations that are prone to dewetting are determined by the presence of interfacial rheology and the spatiotemporal drainage characteristics of the tear film. In Chapter 11 we summarize the findings in this thesis and discuss a number of interesting venues for future research.

Instabilities In Falling Liquid Films

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Author : Souradip Chattopadhyay
language : en
Publisher: Mohammed Abdul Sattar
Release Date : 2023-11-21

Instabilities In Falling Liquid Films written by Souradip Chattopadhyay and has been published by Mohammed Abdul Sattar this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023-11-21 with categories.

The ﬂows of thin ﬁlm form the core of a large number of scientiﬁc, technological, and engineering applications. The occurrence of such ﬂows can be observed in nature, for example on the windshield of vehicles in rainy weather. Thin ﬁlm ﬂows are also found in various engineering, geophysical, and biophysical ap- plications. Speciﬁc examples are nanoﬂuidics, microﬂuidics, coating ﬂows, intensive processing, tear-ﬁlm rupture, lava ﬂows, and dynamics of continental ice sheets. Important industrial applications of thin ﬁlms include nuclear fusion research - for cooling the chamber walls surrounding the plasma, complex coating ﬂows - where a thin ﬁlm adheres to a moving substrate, distillation units, condensers, and heat exchangers, microﬂuidics, geophysical settings, such as gravity currents, mud, granular and debris ﬂows, snow avalanches, ice sheet models, lava ﬂows, biological and biophysical scenarios, such as ﬂexible tubes, tear-ﬁlm ﬂows and many more. The dynamics of such ﬁlms are quite complex and display rich behavior and this attracted many mathematicians, physicists, and engineers to the ﬁeld. In the past three decades, the work in the area has progressed a lot with considerable stress on revealing the stability and dynamics of the ﬁlm where the ﬂow is driven by various forces such as gravity, capillarity, thermocapillarity, centrifugation, and inter- molecular. The ﬂow may happen over structured or smooth and impermeable or slippery surfaces. The investigation approaches include modeling and analytical work, numerical simulations, and performing experiments to explain the instabilities that the ﬁlm can exhibit. Direct analysis of the equations of the model of the interfacial ﬂows is a very complicated mathematical exercise due to the existence of a free, evolving interface that bounds the liquid ﬁlm. The mathematical complexity emerges from a number of things: (a) The Navier-Stokes (or Stokes or Euler) equations need to be solved in changing domains; (b) In certain applications one has to solve for the temperature or electrostatic or electromagnetic ﬁelds apart from the ﬂuid equations; (c) Several nonlinear boundary conditions should be speciﬁed at the unknown interface(s) and (d) The solutions may not exist for all times. In fact in thin ﬁlm problems, one may encounter ﬁnite-time singularities accompanied by topological transitions. The breakup of liquid jets is an example of that. However, in the subsequent chapters, we shall see that it is possible to use the diﬀerent length scales appearing in thin ﬁlm ﬂows to our advantage. Thin ﬁlms are characterized by much smaller length scales in the vertical direction as compared to those in the stream-wise direction. This gives rise to a small aspect ratio which makes the problem amenable for small amplitude perturbation expansions.

Thin Liquid Films

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Author : Ralf Blossey
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-05-22

Thin Liquid Films written by Ralf Blossey and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-05-22 with Science categories.

This book is a treatise on the thermodynamic and dynamic properties of thin liquid films at solid surfaces and, in particular, their rupture instabilities. For the quantitative study of these phenomena, polymer thin films (sometimes referred to as “ultrathin”) have proven to be an invaluable experimental model system. What is it that makes thin film instabilities special and interesting? First, thin polymeric films have an important range of applications. An understanding of their instabilities is therefore of practical relevance for the design of such films. The first chapter of the book intends to give a snapshot of current applications, and an outlook on promising future ones. Second, thin liquid films are an interdisciplinary research topic, which leads to a fairly heterogeneous community working on the topic. It justifies attempting to write a text which gives a coherent presentation of the field which researchers across their specialized communities might be interested in. Finally, thin liquid films are an interesting laboratory for a theorist to confront a well-established theory, hydrodynamics, with its limits. Thin films are therefore a field in which a highly fruitful exchange and collaboration exists between experimentalists and theorists. The book stretches from the more concrete to more abstract levels of study: we roughly progress from applications via theory and experiment to rigorous mathematical theory. For an experimental scientist, the book should serve as a reference and guide to what is the current consensus of the theoretical underpinnings of the field of thin film dynamics. Controversial problems on which such a consensus has not yet been reached are clearly indicated in the text, as well as discussed in a final chapter. From a theoretical point of view, the field of dewetting has mainly been treated in a mathematically ‘light’ yet elegant fashion, often making use of scaling arguments. For the untrained researcher, this approach is not always easy to follow. The present book attempts to bridge between the ‘light’ and the ‘rigorous’, always with the ambition to enhance insight and understanding - and to not let go the elegance of the theory.

Thin Liquid Films

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Author : Ivan Ivanov
language : en
Publisher: CRC Press
Release Date : 1988-08-31

Thin Liquid Films written by Ivan Ivanov and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1988-08-31 with Science categories.

Thin Liquid Films furnishes a fundamental overview of thermodynamics of thin liquid films. Generously illustrated with equations, tables and drawling and containing more than 2,200 citations to pertinent literature.