Bulk Contributions Modulate the Sum-Frequency Generation Spectra of Interfacial Water on Model Sea-Spray Aerosols

Abstract

Vibrational sum-frequency generation (vSFG) spectroscopy is used to determine the molecular structure of water at the interface of palmitic acid monolayers. Both measured and calculated spectra display speci c features due to third-order contributions to the vSFG response which are associated with nite interfacial electric potentials. We demonstrate that theoretical modeling enables to separate the third-order contributions, thus allowing for a systematic analysis of the strictly surface-sensitive, second-order component of the vSFG response. This study provides fundamental, molecular-level insights into the interfacial structure of water in a neutral surfactant system with relevance to single layer bio-membranes and environmentally relevant sea-spray aerosols. These results emphasize the key role that computer simulations can play in interpreting vSFG spectra and revealing microscopic details of water at complex interfaces, which can be difficult to extract from experiments due to the mixing of second-order, surface-sensitive and third-order, bulk-dependent contributions to the vSFG response.

Elucidating Trivalent Ion Adsorption at Floating Carboxylic Acid Monolayers: Charge Reversal or Water Reorganization?

“…The two bands roughly centered at 3250 and 3550 cm -1 wavenumbers are attributed to the relatively stronger and weaker hydrogen bonded water molecules, respectively. 33 At a relatively low [Nd]t of 400 nM, the OH region is significantly affected with a near uniform drop in the bimodal intensities. From the XFNTR results (Figure 2) this corresponds to ~ 1/3 coverage of Nd 3+ species.…”

“…18,20 SFG spectroscopy provides an indirect measure of ion adsorption, through the changes happening to the interfacial water structure or the surface functional groups. [26][27]33 Recently, Sthoer et al reported an observation of overcharging of Y 3+ and La 3+ ions at arachidic acid (AA) monolayers with SFG spectroscopy. 27 The intensity of -OH region signal (3200 -3700 cm -1 ) decreased as the bulk concentration is increased from 100 nM to 10 M, which is typical due to the decreasing surface charge and disturbed interfacial water organization.…”

Monovalent Ion - Graphene Oxide Interactions are Controlled by Carboxylic Acid Groups: Sum Frequency Generation Spectroscopy Studies

“…The SFG signal mainly consists of two broad bands centered at ~3200 cm -1 and ~3400 cm -1 , which are assigned to stronger hydrogen bonded and weaker hydrogen bonded water populations at the interface, respectively. 56 The https://doi.org/10.26434/chemrxiv-2023-dj4m0-v3 ORCID: https://orcid.org/0000-0003-3278-5570 Content not peer-reviewed by ChemRxiv. License: CC BY-NC-ND 4.0 quantitative definition of hydrogen bonding strength is an active topic of discussion.…”