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Charging of Carboxylic Acid Monolayers with Monovalent Ions at Low Ionic Strengths: Molecular Insight Revealed by Vibrational Sum Frequency Spectroscopy

Tyrode, Eric C.; Corkery, R.

Description

The charging of arachidic acid Langmuir monolayers as a function of subphase pH and monovalent ion concentration below 100 mM was investigated using vibrational sum frequency spectroscopy. Molecular information was obtained by targeting the vibrational modes of the carboxylic acid headgroups, alkyl chains, and water molecules in the immediate surface and diffuse double layers. The surface charge in the monolayer was experimentally determined by monitoring the hydrated carboxylate...[Show more]

dc.contributor.authorTyrode, Eric C.
dc.contributor.authorCorkery, R.
dc.date.accessioned2020-10-21T05:20:43Z
dc.identifier.issn1932-7447
dc.identifier.urihttp://hdl.handle.net/1885/212807
dc.description.abstractThe charging of arachidic acid Langmuir monolayers as a function of subphase pH and monovalent ion concentration below 100 mM was investigated using vibrational sum frequency spectroscopy. Molecular information was obtained by targeting the vibrational modes of the carboxylic acid headgroups, alkyl chains, and water molecules in the immediate surface and diffuse double layers. The surface charge in the monolayer was experimentally determined by monitoring the hydrated carboxylate stretching modes. The charging behavior was found to be in excellent agreement with that predicted by Gouy−Chapman theory using a thermodynamic pKa of 5.1 ± 0.2. This resulted in an apparent pKa of ∼10.8 when the only ions present in solution were those associated with adjusting the pH. Water molecules with a preferred orientation in the immediate surface region were found to primarily interact with the uncharged carboxylic acid moiety, decreasing in number as the monolayer further deprotonated. Contributions from water molecules in the diffuse double layer, partly aligned by the exponentially decaying surface electric field, closely followed the predictions of a recently proposed theoretical framework that accounts for interference and screening effects. Finally, the charging of the monolayer was experimentally found to be independent of the identity of either the monovalent cation (i.e., Li+ , Na+ , Rb+ ) or anion (i.e., F−, Cl−, I−) at low salt concentrations.
dc.description.sponsorshipFunding by the Swedish Research Council (VR) and the Swedish Foundation for Strategic Research (SSF) through the program “Future Research Leaders-5” is gratefully acknowledged.
dc.format.mimetypeapplication/pdf
dc.language.isoen_AU
dc.publisherAmerican Chemical Society
dc.rights© 2018 American Chemical Society
dc.sourceJournal of Physical Chemistry C
dc.titleCharging of Carboxylic Acid Monolayers with Monovalent Ions at Low Ionic Strengths: Molecular Insight Revealed by Vibrational Sum Frequency Spectroscopy
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume122
dc.date.issued2018
local.identifier.absfor030601 - Catalysis and Mechanisms of Reactions
local.identifier.ariespublicationu3102795xPUB153
local.publisher.urlhttp://pubs.acs.org/journal/jpccck/about.html
local.type.statusPublished Version
local.contributor.affiliationTyrode, Eric C., KTH Royal Institute of Technology
local.contributor.affiliationCorkery, R., College of Science, ANU
local.description.embargo2037-12-31
local.bibliographicCitation.issue50
local.bibliographicCitation.startpage28775
local.bibliographicCitation.lastpage28786
local.identifier.doi10.1021/acs.jpcc.8b09505
local.identifier.absseo970103 - Expanding Knowledge in the Chemical Sciences
dc.date.updated2020-07-06T08:20:41Z
local.identifier.scopusID2-s2.0-85058663712
CollectionsANU Research Publications

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