Date of Award

2020

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

Lei Pan

Committee Member 1

Jeffrey Allen

Committee Member 2

Caryn Heldt

Committee Member 3

Michael Mullins

Abstract

Liquid films are widely involved in many processes, such as froth flotation, oil extraction, foam/bubble stabilization, etc. In the meantime, air films are commonly seen in diverse fields like dust control, ink print, coating industry, and so on. Stabilities of these liquid/air films are of great importance to improve the processes. As more and more researchers are paying increasing attention to liquid/air films, tremendous efforts have been made to explore the properties of the films. On the one hand, some theoretical models have also been well developed in recent decades. State-of-the-art technologies, such as AFM, SFA, and RICM, have also been employed to visualize the films in either a direct or indirect manner. However, due to the limitations of the techniques, it is still challenging to fully uncover the mechanisms of the film stabilities. A new and powerful methodology to characterize the film properties has been a top priority.

In this work, a novel technique, namely Synchronized Tri-wavelength Reflection Interferometry Microscope (STRIM), was developed in our lab. It allows the accurate measurement of a separation distance within a range of few nanometers to micrometers. Based on the previous RICM, STRIM employs two additional light sources and achieves the determination of the absolute distance. The accuracy of the film thickness measurements was found to be within 1 nm over a range of 0-200 nm and within 3 nm over the range of 200–1000 nm. By recording the thinning process of films, STRIM is able to reconstruct the spatiotemporal profiles, which contain massive information. First, the conditions under which the films are stable or unstable are the urges to figure out for industrial applications. Besides, the films' stabilities are closely related to the interfacial properties, and thus they can be alternative indicators of some essential properties, such as hydrophobicity. Additionally, the interactions and surface forces across the films between involved surfaces can be calculated by the dynamic film thinning kinetics, unraveling the underlying mechanisms for the processes of interest. Furthermore, other approaches, including AFM, contact angle measurement, and flotation, are also referred to in this work and confirm the drawn conclusions. The STRIM can investigate both the liquid and air films with the flexibility of controlling the involved objects like the surfaces with adjustable hydrophobicity and media with designed properties. This newly-developed equipment has the potential to be extensively used within the colloid and interfacial science and engineering areas.

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