Insights into the Headgroup and Chain Length Dependence of Surface Characteristics of Organic-Coated Sea Spray Aerosols

Abstract

The structure of sea spray aerosols (SSAs) has been described as a saline core coated by organic surfactants. The presence of surface-active compounds at the air-water interface can have a large impact on physical, chemical and optical properties of SSAs. The surfactant molecules chosen for this study, palmitic acid (PA), stearic acid (SA), arachidic acid (AA), methyl palmitate (MP), methyl stearate (MS) and methyl arachidate (MA), were used to investigate the effect of alkyl chain-length, head-groups and sea salts on the surface properties of these monolayers. A Langmuir trough was used for measuring surface pressure−area (π−A) isotherms to reveal macroscopic phase behavior of the surface films at the air-water interface. Infrared reflection absorption spectroscopy (IRRAS) was employed to have a molecular-level understanding of the interfacial molecular organization. The π−A isotherms indicated that sea salts, present in the subphase, exert a strong condensing effect on fatty acid monolayers, while exerting expanding effect on fatty acid methyl ester monolayers, which was confirmed by results from IRRAS experiments. IRRAS further revealed that the alkyl chains were in an all-trans conformation, which can be evidenced by the relatively low νa(CH2) and νs(CH2) stretching frequencies. The conformational order changes in the alkyl chains of different film-forming species (C16 < C18 < C20) were directly revealed by analyzing the relative intensity of the νa(CH2) and νs(CH2) peaks in the C-H stretching region. Thus, all the three factors alter the phase behavior and molecular packing of the monolayers at the air-aqueous interface.

Spectroscopic Analysis of Cu(II)-Complexed Thin Films to Characterize Molecular-Level Interactions and Film Behavior

“…Figure shows the reflectance spectra for monolayers deposited from the solid phase region of the isotherm at pH values below and above the AA p K a . We believe that the Cu 2+ is transferred with the monolayer onto the support during the deposition process, based on literature precedent. ,, A reference spectrum for an AA film without metal ions is also shown, with the asymmetric and symmetric −CH 2 stretching bands present at 2918 and 2849 cm –1 , respectively (Figure ), consistent with literature values. ,, The spectra of Cu 2+ -complexed films deposited at low subphase pH values resemble that for the AA layer without Cu 2+ ions (Figure ). In the spectra of monolayers deposited at pH values approaching and surpassing the AA p K a (i.e., pH 5.3, 5.5, and 6.2 in Figure ), band positions were seen to be at slightly lower frequencies: 2915 and 2846 cm –1 for asymmetric and symmetric stretches, respectively (Figure ).…”

Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces

“…Two important types of surfactant molecules naturally found in the SSML are fatty acids and fatty alcohols. − These molecules were recently discovered to exist in a 9:1 ratio in oceanic emission samples . Octadecanoic acid (OA, stearic acid, C 18 OOH), a C 18 saturated fatty acid, is known to be enriched in sea spray aerosol, and octadecanol (OL, stearyl alcohol, C 18 OH) is its C 18 saturated fatty alcohol analogue. , OA is often used as a proxy for the organic film on sea spray aerosol surfaces, because it is the most prevalent oceanic fatty acid along with hexadecanoic acid (palmitic acid, C 16 OOH), both of which are derived from biogenic material including marine organisms. − An aim of this study is to emulate and observe the behavior of mixed monolayers containing OA and OL in ocean-relevant ratios to provide insight on how film composition impacts metal–carboxylic acid binding and thus metal cation enrichment at the air–aqueous interface.…”

Formation of CdSe/CdS/ZnS Quantum Dots Floating Monolayers on the NiCl2 Containing Subphase

“…The presence or absence of ions in a subphase can also influence properties of forming floating layers. It was shown that when metal ions are added to the subphase during the formation and compression of a surfactant monolayer, the carboxyl group of surfactant molecule interacts with metal ion in the subphase andforms a salt [4]. In this case, the -A isotherm shifts Жидкие кристаллы и их практическое использование.…”