Investigating Mechanisms Underlying Hydrophobic Interaction Between Extended Surfaces in Aqueous Environments
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Sreekiran Pillai Dissertation.pdf
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PhD Dissertation
Type
DissertationAuthors
Pillai, Sreekiran
Advisors
Mishra, Himanshu
Committee members
Nunes, Suzana Pereira
Alshareef, Husam N.

Drummond, Carlos
Date
2019-11Embargo End Date
2019-11-26Permanent link to this record
http://hdl.handle.net/10754/660262
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At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2019-11-26.Abstract
The hydrophobic interaction refers to a mutually attractive force experienced by hydrophobic surfaces or molecules across water. At the molecular scale, it drives the selfassembly of lipid vesicles and micelles and accelerates interfacial chemical reactions. At the macroscale, it confers upon numerous plants and insects the ability to repel water and is harnessed in practical applications, such as water-proofing and desalination. However, despite its ubiquity and significance, mechanistic insights into the hydrophobic interaction between macroscopic surfaces remain unclear. A significant body of experimental data on surface force measurements exists, which were obtained following this protocol: hydrophobic molecules (typically organosilanes) are physisorbed onto molecularly smooth mica films that are glued onto transparent rigid silica discs and driven towards each other while measuring forces and distances. We developed a protocol for functionalizing mica surfaces with perfluorodecyltrichlorosilane (FDTS) to achieve robust, ultra-smooth hydrophobic surfaces. Then we investigated the consequences of nuclear quantum effects (NQEs) in water on the hydrophobic interaction. Whereas NQEs are known to influence physical and chemical properties of water, their impact on the hydrophobic interaction has remained largely unexplored. We find that the attractive forces between FDTS-coated mica surfaces were ~ 10% higher in light water (H2O) than in heavy water (D2O) even though macroscopic measurables, such as the interfacial tensions and contact angles are indistinguishable. This is the first-ever experimental demonstration of nuclear quantum effects at play in modulating hydrophobic surface forces. Towards practical applications, we investigated the partitioning of small, amphiphilic molecules onto our molecularly smooth FDTS-coated mica films. These scenarios are relevant in wastewater treatment, bioresource processing, fermenter broths, and food & beverage industries. Water-soluble short chain alcohols (ethanol) readily partitioned onto FDTS surfaces and remained attached onto the surface. The presence of alcohols was confirmed by surface force measurements, contact angle goniometry of water drops, and gas chromatography. We investigated protocols for characterizing fouled surfaces and cleaning them. These protocols were tested on realistic desalination membranes and proved effective. Thus, our findings could be used to develop robust protocols for characterizing membrane fouling and cleaning protocols in various separation processes.Citation
Pillai, S. (2019). Investigating Mechanisms Underlying Hydrophobic Interaction Between Extended Surfaces in Aqueous Environments. KAUST Research Repository. https://doi.org/10.25781/KAUST-5099Yae974a485f413a2113503eed53cd6c53
10.25781/KAUST-5099Y