Award Date

12-1-2022

Degree Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Mechanical Engineering

First Committee Member

Jeremy Cho

Second Committee Member

Hui Zhao

Third Committee Member

Kwang Kim

Fourth Committee Member

Erica Marti

Abstract

Surfactants are biphilic monomers that adsorb to interfaces and have the ability to reduce interfacial tension. From this reduction in interfacial tension, surfactants are able to function as emulsifiers, detergents, and wetting agents among a variety of other things. Despite their ubiquity surfactants and surfactant behaviors, in particular those in highly dynamic environments, are not yet well characterized. In these environments, surfactants undergo significant distortions to droplet, bubble, and foam geometries which induce changes to the surface tension. This establishes a need to understand how surfactants respond to distortions of geometry through diffusion and dilational effects. To address this need, we characterize the dilational interfacial rheology of a pulsating pendant bubble in water-surfactant mixtures using the nonionic surfactants TWEEN 20 and TWEEN 40. This study considers two separate but concurrent processes: dilation of the bubble interface and diffusion of surfactants to the bubble interface. Through a timescale comparison of both of these separate processes, a new way to contextualize surfactant adsorption behavior and bubble mechanics was developed based on a single dimensionless Peclet number. This dimensionless parameter accurately describes changes to the surface tension for different surfactants and concentrations through a combination of both diffusion and dilation effects. We hope that a detailed analysis consisting of a single dimensionless number capable of capturing the effects caused by the combination of both diffusion and dilation will better inform a selection of surfactants for specific industries and applications.

Keywords

Interfacial rheology; Langmuir isotherm; Pendant drop tensiometry; Surface tension; Surfactant diffusion; Surfactants

Disciplines

Mechanical Engineering

File Format

pdf

File Size

3200 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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