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Fundamental Surface Properties of Simple Fatty Acid Model Systems of Sea Spray Aerosols and the Sea Surface Microlayer.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Fundamental Surface Properties of Simple Fatty Acid Model Systems of Sea Spray Aerosols and the Sea Surface Microlayer./
Author:	Rudd, Bethany A.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
Description:	152 p.
Notes:	Source: Dissertations Abstracts International, Volume: 80-12, Section: B.
Contained By:	Dissertations Abstracts International80-12B.
Subject:	Chemistry. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13906076
ISBN:	9781392177976

Fundamental Surface Properties of Simple Fatty Acid Model Systems of Sea Spray Aerosols and the Sea Surface Microlayer.
Rudd, Bethany A.

Fundamental Surface Properties of Simple Fatty Acid Model Systems of Sea Spray Aerosols and the Sea Surface Microlayer. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 152 p.

Source: Dissertations Abstracts International, Volume: 80-12, Section: B.

Thesis (Ph.D.)--The Ohio State University, 2018.

This item must not be sold to any third party vendors.

Upon wind action on the ocean surface, sea spray aerosols (SSA) are generated and released to the atmosphere. SSA are enriched in the organics and ions present in the sea surface microlayer (SSML) due to the selective transfer of these species to the aerosol phase, and can impact the climate through multiple mechanisms. Aerosols and clouds contribute the largest uncertainty in the prediction of climate change, so an understanding of SSA chemistry is of importance. The organic coatings identified on SSA contain a diverse array of surface-active molecules such as fatty acids. These coatings impact the reactivity, reflectivity, lifetime, and nucleating abilities of the aerosol particles. As these organic films impact the climate-relevant properties of SSA, an understanding of the fundamental physical chemistry phenomena of lipids and ions at these interfaces warrants investigation. In this dissertation, surface sensitive techniques were utilized to probe the structure and properties of fatty acid model systems under various pH and ion conditions.In the first part of this study, the surface-pKa values of medium-chain (C8-C10) fatty acids were quantified through the use of surface tension titration. Our simple surface tension titration technique quantified the surface-pKa of medium-chain octanoic (C8), nonanoic (C9), and decanoic (C10) fatty acids as 4.9, 5.8, and 6.4, respectively. The surface-pKa determined with surface tension differs from the bulk value obtained during a standard acid-base titration, and differences between surface- and bulk-pKa are observed starting at chain lengths of nine carbon atoms. In the titration curves of the C8 and C9 acids, surface tension minima are observed near the surface-pKa as a result of the formation of highly surface active acid-soap complexes. The direction of the titration was shown to affect the measured surface-pKa of the C9 system due to differences in Na+ concentration in the solution at pH values near the pKa.Palmitic acid (PA, C16) is one of the most abundant fatty acids observed in SSA and the SSML. In the second part of this study, the effect of protonation state on the surface structure of PA monolayers is evaluated under two pH regimes (in the presence of a 100 mM NaCl background electrolyte) corresponding to monolayers that are fully and 50% protonated. The protonation state, surface structure and stability of the monolayers was measured using infrared reflection-absorption spectroscopy (IRRAS) and surface tension equilibrium spreading pressure (ESP) measurements. Both PA and PA/PA- monolayers pack in a 2D hexagonal lattice structure, and the deprotonation in the PA/PA- system causes an elevation in the ESP. Vibrational sum frequency generation (VSFG) spectroscopy and surface potential measurements were used to determine the interfacial water structure and organization at the interface. Both monolayers changed the interfacial water structure, relative to the bare air-water surface, with the PA/PA- system inducing a greater ordering due to the presence of charged surfactant species.Of the major cations in seawater, Ca2+ has been identified as the most enriched in the aerosol phase. In the final part of this work, the binding of Ca2+ to the carboxylic acid headgroup of PA, and the impact such binding has on the stability of PA monolayers, was investigated in both equilibrium and non-equilibrium systems. IRRAS measurements of spread monolayers on aqueous CaCl2 subphases (10 μM ≤ [Ca2+] ≤ 300 mM) reveal ion-induced deprotonation of the PA carboxylic acid headgroup with varying degrees of hydration. Surface tensiometry was used to determine the thermodynamic ESP of PA on the aqueous CaCl2 subphases. Up to concentrations of 1 mM Ca2+, each system reached equilibrium, and Ca2+:PA surface complexation gave rise to lower energy states revealed by elevated surface pressures relative to water. However, PA films are not thermodynamically stable at marine aerosol-relevant Ca2+ concentrations ([Ca2+] ≥ 10 mM). Non-equilibrium relaxation (NER) experiments were conducted and monitored by Brewster angle microscopy (BAM) to determine the effect of the Ca2+ ions on PA stability. At high surface pressures, the relaxation mechanisms of PA varied among the systems and were dependent on Ca2+ concentration in the subphase. Differences in ESP and NER trends reveal the intricacies in evaluating monolayer stability from thermodynamic and non-equilibrium measurements. (Abstract shortened by ProQuest).

ISBN: 9781392177976Subjects--Topical Terms:

516420
Chemistry.

Fundamental Surface Properties of Simple Fatty Acid Model Systems of Sea Spray Aerosols and the Sea Surface Microlayer.
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520 $a Upon wind action on the ocean surface, sea spray aerosols (SSA) are generated and released to the atmosphere. SSA are enriched in the organics and ions present in the sea surface microlayer (SSML) due to the selective transfer of these species to the aerosol phase, and can impact the climate through multiple mechanisms. Aerosols and clouds contribute the largest uncertainty in the prediction of climate change, so an understanding of SSA chemistry is of importance. The organic coatings identified on SSA contain a diverse array of surface-active molecules such as fatty acids. These coatings impact the reactivity, reflectivity, lifetime, and nucleating abilities of the aerosol particles. As these organic films impact the climate-relevant properties of SSA, an understanding of the fundamental physical chemistry phenomena of lipids and ions at these interfaces warrants investigation. In this dissertation, surface sensitive techniques were utilized to probe the structure and properties of fatty acid model systems under various pH and ion conditions.In the first part of this study, the surface-pKa values of medium-chain (C8-C10) fatty acids were quantified through the use of surface tension titration. Our simple surface tension titration technique quantified the surface-pKa of medium-chain octanoic (C8), nonanoic (C9), and decanoic (C10) fatty acids as 4.9, 5.8, and 6.4, respectively. The surface-pKa determined with surface tension differs from the bulk value obtained during a standard acid-base titration, and differences between surface- and bulk-pKa are observed starting at chain lengths of nine carbon atoms. In the titration curves of the C8 and C9 acids, surface tension minima are observed near the surface-pKa as a result of the formation of highly surface active acid-soap complexes. The direction of the titration was shown to affect the measured surface-pKa of the C9 system due to differences in Na+ concentration in the solution at pH values near the pKa.Palmitic acid (PA, C16) is one of the most abundant fatty acids observed in SSA and the SSML. In the second part of this study, the effect of protonation state on the surface structure of PA monolayers is evaluated under two pH regimes (in the presence of a 100 mM NaCl background electrolyte) corresponding to monolayers that are fully and 50% protonated. The protonation state, surface structure and stability of the monolayers was measured using infrared reflection-absorption spectroscopy (IRRAS) and surface tension equilibrium spreading pressure (ESP) measurements. Both PA and PA/PA- monolayers pack in a 2D hexagonal lattice structure, and the deprotonation in the PA/PA- system causes an elevation in the ESP. Vibrational sum frequency generation (VSFG) spectroscopy and surface potential measurements were used to determine the interfacial water structure and organization at the interface. Both monolayers changed the interfacial water structure, relative to the bare air-water surface, with the PA/PA- system inducing a greater ordering due to the presence of charged surfactant species.Of the major cations in seawater, Ca2+ has been identified as the most enriched in the aerosol phase. In the final part of this work, the binding of Ca2+ to the carboxylic acid headgroup of PA, and the impact such binding has on the stability of PA monolayers, was investigated in both equilibrium and non-equilibrium systems. IRRAS measurements of spread monolayers on aqueous CaCl2 subphases (10 μM ≤ [Ca2+] ≤ 300 mM) reveal ion-induced deprotonation of the PA carboxylic acid headgroup with varying degrees of hydration. Surface tensiometry was used to determine the thermodynamic ESP of PA on the aqueous CaCl2 subphases. Up to concentrations of 1 mM Ca2+, each system reached equilibrium, and Ca2+:PA surface complexation gave rise to lower energy states revealed by elevated surface pressures relative to water. However, PA films are not thermodynamically stable at marine aerosol-relevant Ca2+ concentrations ([Ca2+] ≥ 10 mM). Non-equilibrium relaxation (NER) experiments were conducted and monitored by Brewster angle microscopy (BAM) to determine the effect of the Ca2+ ions on PA stability. At high surface pressures, the relaxation mechanisms of PA varied among the systems and were dependent on Ca2+ concentration in the subphase. Differences in ESP and NER trends reveal the intricacies in evaluating monolayer stability from thermodynamic and non-equilibrium measurements. (Abstract shortened by ProQuest).
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