Drop deformation dynamics in extensional flows : influence of chemical-, mechanical- and photo-degradation.

Polymer drop impact on a solid substrate is commonplace in many industrial applications, such as inkjet printing, agricultural pesticides, and spray coating, where dyes and surfactants are used to enhance various functionalities. Pesticide spray droplets can sometimes deviate from their intended targets due to splashing, drifting, and bouncing, posing significant challenges for efficient delivery. Various studies investigated how the rheological properties of the polymer influence the drop impact outcome (i.e., suppression of splashing and rebound). However, polymers can deteriorate over time, which contributes to a decrease in effectiveness of pesticides and reduces their shelf life. Therefore, understanding polymer degradation is crucial for achieving better performance. While there is extensive research on the polymer drop impact, the influence of dye and light on the polymer drop impact dynamics remains relatively unexplored. This work bridges the existing knowledge gap in understanding how polymer degradation can alter the drop impact dynamics. First, we focused on investigating the effects of dye salts (e.g., anionic and cationic) on the rheology of different types of aqueous polymer (e.g., anionic, cationic, and neutral polymer). Our findings revealed that when polymer-dye pairs with opposite charges, they displayed a pronounced decrease in the extensional viscosity and relaxation time. We also investigated how the photodegradation of the polymer-dye changes the drop impact dynamics. We found that the light-irradiated polymer-dye drops splashed upon impact on a parafilm surface, which was not observed for non-irradiated polymer-dye drops. The final part of this work seeks to understand the high molecular weight polymer drop rebound and deposition phenomena, particularly in the dilute regime. Here, we varied polymer molecular weight, concentrations, and zeta potential. We found that when the charge between the polymer and the surface is unfavorable, the drop will rebound due to electrostatic repulsion. Conversely, when the charges are favorable, the polymer drop will stick to the surface even in the dilute regimes. The results indicate that molecular weight alone is a poor predictor of drop rebounding, and the polymers may exhibit a range of sticking to bouncing regimes depending on the polymer charge and interaction with the surface.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Doctoral

Grantor

Baylor University.

Year dc:date.issued

2025

Author dc:creator

• Upoma, Marufa Akter, 1996-

Advisor dc:contributor.advisor

• Pack, Min Y.

• Polymer.
• Drop impact dynamics.
• Splashing.
• Drop rebound.
• Rheology.
• Polymer degradation.

Statement dc:rights

• Baylor University works are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. Contact libraryquestions@baylor.edu for inquiries about permission.

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2104/14077

OAI identifier oai:identifier

oai:baylor-ir.tdl.org:2104/14077