Fatty acid monolayers as atmospheric reaction fields investigated by heterodyne-detected sum frequency generation spectroscopy

2023 Fiscal Year Final Research Report

• Project/Area Number: 22K14644
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 32010:Fundamental physical chemistry-related
• Research Institution: University of Tsukuba
• Principal Investigator: Nojima Yuki 筑波大学, 数理物質系, 助教 (90756404)
• Project Period (FY): 2022-04-01 – 2024-03-31
• Keywords: 脂肪酸単分子膜 / 和周波発生分光 / ヘテロダイン検出 / エアロゾル表面

Outline of Final Research Achievements

Aerosols can have a large influence on the climate and the human health, and air/liquid and solid/liquid interfaces play an important role on their formation processes. We investigated the molecular orientation of chains of fatty acids at air/water interfaces, which can be a good model of aerosol surfaces, by heterodyne-detected sum frequency generation spectroscopy. The estimated molecular orientation for the fatty acid/water solution showed an odd-even effect: higher molecular orientational order for even-numbered fatty acids. Proton dissociation of fatty acids can affect the distribution of fatty acids between the interface and the bulk. Thus, molecular orientation of fatty acids for the acidic and the basic solutions were also estimated. In contrast to the water solution, the estimated orientation showed no clear odd-even effect. The presence of both hydrated and dehydrated fatty acids may be related to the observed odd-even effect.

Free Research Field

分光物理化学

Academic Significance and Societal Importance of the Research Achievements

海洋エアロゾルを覆う有機酸の膜として，パルミチン酸(炭素数16)やステアリン酸(炭 素数18)などのノナン酸よりも炭化水素鎖が長い脂肪酸に関する研究は数多く報告されてい るが，ノナン酸のように溶液界面で Gibbs膜を形成する脂肪酸の微視的構造に関する報告はまだ少なく，基礎的なデータも十分 に揃っていない.ノナン酸をはじめとする炭素数9から12の脂肪酸は香料などにも利用され るため，これらの脂肪酸の水溶液界面における微視的構造について調べることで，大気化学 に限らず，工業分野にとっても有益な情報を提供できる.