University Events

Description: Mechanical Engineering MS Thesis Defense by Mr. Ali Nosrati

New DATE:
December 13, 2023

New TIME:
1:00 p.m. - 3:00 p.m.

LOCATION:
Science & Engineering (SENG) Building, Room 110
and Zoom link:
https://umassd.zoom.us/j/94943769488?pwd=a0E0eHJLRUdTbnBrT1J5YklxaGZJQT09 (contact hling1@umassd.edu or scunha@umassd.edu for Passcode)

TOPIC:
An Experimental Study of the Longevity of Super-Hydrophobic Surfaces in Undersaturated Liquid Due to Gas Diffusion

ABSTRACT:
Superhydrophobic surfaces (SHS), created based on a combination of surface texture and hydrophobic chemistry, have a variety of applications from reducing drag to protecting underwater surfaces from icing, corrosion, and biofouling. These applications mainly rely on the presence of micro/nano-scale gas bubbles trapped within the surface texture when the SHS contacts with the liquid. However, the gas on the SHS can be slowly dissolved by the surrounding liquid if the liquid is undersaturated with gas. Once all the gas is dissolved, the SHS is a purely rough surface and loses most of the aforementioned benefits. This thesis aims to understand the longevity of SHS in undersaturated liquid due to the effect of gas diffusion. First, we developed an experimental method which improved the measurement accuracy of SHS longevity compared to prior works. The higher measurement accuracy in our experiments was achieved for three reasons: (i) to measure the status of gas on SHS, we applied a non-intrusive optical method that did not disturb the gas diffusion process; (ii) to address the uneven gas diffusion at different regions of the SHS, we measured the SHS longevity based on the gas status at the entire SHS sample; and (iii) we induced the gas diffusion by using liquid with a low dissolved gas concentration so that the stability of SHS was not affected by pressure. Second, we studied the influence of the undersaturation level of the liquid on the SHS longevity, which is an open question in the literature. We defined the undersaturation level of liquid s as the ratio of the gas concentration in the liquid to the gas concentration at the gas-liquid interface. We found that the SHS longevity tf and the undersaturation level s followed a power-law relation: tf~(1-s)-2, which is in good agreement with a previous numerical model. This scaling relation suggested that as gas slowly dissolves into the liquid, the gas concentration in liquid near the SHS increases, and the mass flux of gas from SHS to the liquid decreases. We also found that the diffusion length, representing the height of the liquid affected by gas dissolution, was inversely proportional to the undersaturation level. Lastly, we studied the influences of SHS texture height, chamber height, and surfactant on the SHS longevity. Overall, this study improved our understanding of SHS longevity in undersaturated liquids and could guide the applications of SHS for reducing icing, corrosion, and biofouling.

ADVISORS:
- Dr. Hangjian Ling, Assistant Professor, Department of Mechanical Engineering, UMass Dartmouth
- Dr. Mehdi Raessi, Professor, Department of Mechanical Engineering, UMass Dartmouth

COMMITTEE MEMBER:
- Dr. Alex Fowler, Professor, Department of Mechanical Engineering, UMass Dartmouth

Open to the public. All MNE students are encouraged to attend.

For more information, please contact Dr. Hangjian Ling (hling1@umassd.edu).

Open to the public. All MNE students are encouraged to attend.

For more information, please contact Dr. Hangjian Ling (hling1@umassd.edu) or Sue Cunha (scunha@umassd.edu) for more information, or the Passcode).