The ubiquitous role of water in biochemical, electrochemical, and geochemical systems has driven scientific interest in studying the fundamental hydrogen-bonding interactions that water molecules exhibit in the presence of different materials.Specifically, we focus on the interactions characterizing water at the interface between two bulk media, as these are essential to numerous chemical processes, including protein folding, corrosion, dissolution, and mineralization. To this end, this thesis seeks to provide insight on the structure of interfacial water molecules at the surface of both biological and inorganic materials using a surface-selective technique called vibrational sum frequency generation (SFG) spectroscopy. To study the nature of water at biological interfaces, the polycation, poly(allylamine hydrochloride) (PAH), is introduced to an idealized model of cell membranes known as supported lipid bilayers (SLBs). Perturbations to the interfacial water structure are assessed as a function of polycation concentration and lipid headgroup charge. The experimental results from this study are discussed in detail and placed within a much larger analysis that includes work that has been previously done in our group studying the electrostatics, thermodynamics, and molecular structure at the polycation:lipid membrane interface. To obtain insight into the structure of water at inorganic interfaces, the hydrogen-bonding network of interfacial water molecules is probed at the Ni:NiOx:water interface using SFG spectroscopy. Interpretation of the SFG signals at this interface is made notoriously difficult due to the overwhelming presence of spectral artifacts arising from Fresnel factors. This thesis includes a detailed discussion of the efforts made to overcome this challenge, including the optimal nickel film thickness, and it also discusses how hydrogen-bonding changes with pH and ionic strength. Lastly, this thesis discusses preliminary and future experiments directed towards studying the nanolayer nickel film surface at a high relative humidity to elucidate surface hydroxyl groups. Despite their apparent differences, both studies outlined in this thesis resulted in one main takeaway: hydrogen-bonding of water molecules at the interface is complex, however, fundamental studies such as those carried out here are necessary to begin understanding the mechanisms associated with the function of new or existing materials.

Creator

• Dalchand, Naomi

DOI

• https://doi.org/10.21985/n2-nyre-c373

Subject

• Chemistry

Language

• en

Alternate Identifier

• etdadmin_upload_842499
• http://dissertations.umi.com/northwestern:15708

Date created

• 2021-01-01

Resource type

• Dissertation

Rights statement

• In Copyright