Public defence in Neuroscience and Biomedical Engineering, M.Sc. Alex Drago González

Title of the thesis: Dynamic interactions between ultrasound and water-repellent surfaces

Thesis defender: Alex Drago González
Opponent: Professor Michael Baudoin, Université de Lille, France
Custos: Professor Heikki Nieminen, Aalto University School of Science

This thesis investigates how ultrasound can be used to actively and reversibly control water-repellent surfaces. Two types of surfaces were studied: superhydrophobic surfaces (SHSs), which trap air pockets to repel water, and slippery liquid-infused porous surfaces (SLIPSs), which are coated with an oil layer that allows droplets to slide freely.

The purpose of the study was to develop contactless methods to control wetting, heat transfer, and fluid motion at small scales. Ultrasound, through its acoustic radiation force, was used to locally and precisely manipulate the state of these surfaces and the fluids interacting with them.

The research shows that focused ultrasound can switch SHSs between the Cassie-Baxter and the Wenzel  wetting states within microseconds, allowing dynamic regulation of heat and acoustic energy underwater. In SLIPSs, ultrasound enabled precise droplet manipulation, allowing translation, merging, splitting, and atomization of droplets without any physical contact.

These findings reveal ultrasound as a versatile tool for real-time surface and fluid control. The results are relevant to fields such as microfluidics, biomedical engineering, and microrobotics, where non-invasive, efficient, and programmable control of liquids is essential.

Keywords: Ultrasound; Wetting

Contact information: alex.dragogonzalez@aalto.fi 

Thesis available for public display 7 days prior to the defence at Aaltodoc.