Authors:	Naga, Abhinav
Title:	Capillary Interactions in Wetting: Rotation of Particles at Interfaces and Removal of Particles by Drops
Online publication date:	15-Oct-2021
Year of first publication:	2021
Language:	english
Abstract:	In this thesis, I have experimentally and theoretically investigated the mechanism by which a liquid drop removes a single solid particle from a surface. To address this problem, I designed a method based on laser scanning confocal microscopy to image drop-particle collisions dynamically (speeds 10 to 10 000 µm/s) and to measure the horizontal force acting on the drop during these collisions. Water drops, glass particles and crosslinked polydimethylsiloxane surfaces were used in most of the experiments. Two main collision outcomes were observed: either the particle collided with the drop and remained attached to the liquid-air interface (successful removal), or the particle entered and exited the drop (unsuccessful removal). The viscous force measured when the particle moved through the drop was negligible compared to the capillary force acting on the particle when it was attached to the liquid-air interface. Consequently, the dominant force that determines particle removal is the capillary force. A liquid-air interface will successfully remove a particle when the capillary force exceeds the resistive force that the particle has to overcome to move (roll/slide) on the surface. To understand the difference between the forces acting on a rolling particle and a sliding particle, I theoretically modelled the capillary force for both cases. There are two main results. Firstly, a rolling particle enters a drop more easily than a non-rolling particle (up to 40% less force is required). Secondly, a particle experiences a resistive capillary torque when rolling at an interface. This torque significantly increases the rolling resistance of the particle. The theoretical model for the resistive capillary torque is directly applicable in addressing broader questions on the motion of particles at interfaces and the mobility of moist granular matter. Moreover, the experimental method presented in this thesis can be applied to study a variety of problems in the field of wetting (and beyond), where the combination of microscopic imaging and friction force measurements is often insightful.
DDC:	500 Naturwissenschaften 500 Natural sciences and mathematics 530 Physik 530 Physics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 08 Physik, Mathematik u. Informatik
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-6385
URN:	urn:nbn:de:hebis:77-openscience-aa536adc-9e52-4d5f-92ce-2ae84f8c0bc67
Version:	Original work
Publication type:	Dissertation
License:	CC BY
Information on rights of use:	https://creativecommons.org/licenses/by/4.0/
Extent:	vi, 141 Seiten, Illustrationen, Diagramme
Appears in collections:	JGU-Publikationen