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Analysis of Shaving Foam Physicochemical Properties

Schematic of project aims.

Liquid foams, colloidal dispersions of gas in continuous liquid matrices, have numerous applications ranging from personal care products to drug delivery to oil spill clean up. Our recent studies demonstrate that shaving cream-based foams composed of stearic acid (SA), triethanolamine (TEOA), and water are stable at long times (up to 40 hours) and expand to up to a 7:1 ratio of foam volume to foam solution volume. Further, these foam solutions have low surface tension and high bulk viscosity, key properties that lead to stable foam formation. In addition, we demonstrate a novel correlation between linear viscoelasticity of bulk foam solutions (quantified by the phase shift, delta, related to the ratio of viscous modulus to elastic modulus), and the stability of the foam solution in nitrous oxide gas (quantified by its half-life, the time taken to reach 50% of the initial foam expansion volume).

Despite the ubiquity of shaving cream, we do not yet understand why aqueous SA+TEOA systems foam so well, nor what chemistry underlies the high viscosity, low surface tension, and complex fluidic behavior that allow such stable foams to form. The literature describes the system of SA and TEOA without water as forming an acid (SA), a soap (triethanolamine stearate), and/or an acid-soap composed of two molecules of SA complexing with one molecule of soap, depending on the ratio of triethanolamine to stearic acid (the neutralization degree). 

This project aims to first solidify the correlation between SA+TEOA aqueous solution rheology and foam performance (i.e. ability to foam and foam stability). Subsequently, we seek to determine how the presence of different chemical species (acid, acid-soap, and soap) impact the bulk rheology of SA+TEOA aqueous solutions and whether the balance of these species changes in the presence of water by altering neutralization degree and concentration of SA+TEOA in aqueous solution. Finally, we aim to correlate the presence of acid, acid-soap, and soap in solution to foam performance.

Project by

RachelColer_Portrait2

Rachel Coler

Ph.D. Candidate

Keywords

Thesis Title

Characterization of Stearic Acid-Triethanolamine Stearate Foam Chemistry and Correlation to Rheology and Foam Performance

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