Biological and particulate contaminants in interfaces

Abstract

The transport of biological, chemical, or particulate contaminants shapes disease transmission, chemical spills, climate, ecology, and bio-hazard risks. Yet, little is understood on the mechanisms controlling droplet formation and selection of droplet sizes and contamination levels from a contaminated water bulk. Bubbles play a critical role in shaping this transfer of chemicals, particulates, and biological organisms from water to air. They surface, and eventually burst, emitting myriads of droplets into the air. Despite recent progress in our understanding of bubble formation and bursting at the air-water interface, the factors selecting the loads that they carry and emit into the air remain unknown in part due to limitation in direct measurements. In this thesis, we discuss a method of direct visualization and quantification of particulates contained in contaminated bubble films at interfaces. The calibration of this method is key to progress in our understanding of particulate transport from water to air. In particular, although our method allows to reveal contaminants within films via the appearance of spots, the exact link between the size of such spots and the size of the original particles or organisms, their shape, wetting, and the size of the film remain unexplored. In this thesis, we performed a series of systematic measurements and calibrations using bacteria, particles, and rods of various sizes and wetting properties to calibrate the spot sizes observed on contaminated bubbles and films. We rationalized the dependencies observed using a combination of optical ray-tracing and modelling of film distortion in the presence of contaminant. Our results have important implications for in situ study of particles and bacterial communities within large scale complex interfaces.