Hydrophobicity Across Length Scales

: The Role of Surface Criticality

Abstract

From proteins to plant leaves, hydrophobicity is ubiquitous. Despite this, the underlying physical mechanism relating hydrophobicity on the microscopic and macroscopic length scales remains undetermined. In part, this is due to the wealth of disciplines involved, from solvation to surface science, which provide unique views on hydrophobicity but whose relation to one another has rarely been considered.

Studies of hydrophobicity on both microscopic and macroscopic length scales have reported an enhancement of local density fluctuations. Within recent studies of a Lennard- Jones fluid on macroscopic length scales, similar density fluctuations have been attributed to the existence of a surface critical point called drying. Within this thesis, it is postulated that this drying critical point is also responsible for hydrophobic density fluctuations on both microscopic and macroscopic length scales, and provides the relation of hydrophobicity across length scales. As this drying critical point influences Lennard-Jones fluids, it is also postulated that hydrophobicity is no more than a specific case of solvophobicity.

To explore these postulates, a mesoscopic thermodynamic analysis is performed to anticipate how hydrophobic and solvophobic systems, subject to a drying critical point, on all length scales should be expected to behave. These predictions are then tested for a Lennard- Jones fluid numerically using classical density functional theory, and for a simple water model using Grand Canonical Monte Carlo. Combined, these results provide clear evidence that the mechanism underlying hydrophobicity and solvophobicity across microscopic and macroscopic length scales is a drying surface critical point.

Date of Award	2 Dec 2021
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Nigel B Wilding (Supervisor)