Effect of functional group on the monolayer structures of biodegradable quaternary ammonium surfactants

Aqueous-phase aerosols on the air-water interface: Response of fatty acid Langmuir monolayers to atmospheric inorganic ions

Atmospheric aerosol particles composed of a mixture of organic and inorganic compounds are common and constitute an important fraction of air pollutants. In this study, the activities of common atmospheric inorganic ions (Ag⁺, Zn²⁺, Fe³⁺, Fe²⁺, Ca²⁺ and Al³⁺) and fatty acid molecules (stearic acid and arachidic acid) at air-aqueous interface were investigated by Langmuir methods and infrared reflection-absorption spectroscopy (IRRAS). In the presence of different inorganic ions, surface pressure-area isotherms of the Langmuir films showed compressed or expanded characteristics. IRRAS spectra confirmed that the existence of inorganic ions in the fatty acid monolayer changes the surface properties of aqueous-phase aerosols. Formation of different coordination types of carboxylates at the air-water interface alters the dissolution and partitioning behavior, which has significant influence of Raoult effect on nucleating cloud droplets. Our work displays the relationship between structure and surface properties for aqueous-phase aerosols and implies an efficient method for further understanding of their formation mechanism and potential atmospheric implications.

Theoretical and experimental examination of SFG polarization analysis at acetonitrile–water solution surfaces

Polarization analysis of SFG spectroscopy is thoroughly examined in collaboration of SFG measurements and MD simulations.

Effects of sodium chloride on adsorption at different interfaces and aggregation behaviors of disulfonate gemini surfactants

Schematic illustration of NaCl effects on the adsorption of C_n-DADS molecules at different interfaces (Cl⁻ is not shown).

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM)

The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

Origin of the Instability of Octadecylamine Langmuir Monolayer at Low pH

It has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284-285, 166-174). However, by lowering the pH further, ODA molecules reoccupy the surface, and a full monolayer is recovered at pH 2.5. Using surface sum-frequency spectroscopy and pressure-area isotherms, it is found that the recovered monolayer at very low pH has a larger area per molecule with many gauche defects in the ODA molecules as compared to that at high pH values. This structural change suggests that the reappearance of the monolayer is due to the adsorbed Cl(-) counterions to the protonated amine groups, leading to partial charge neutralization. This proposition is confirmed by intentionally adding monovalent salts (i.e., NaCl, NaBr, or NaI) to the subphase to recover the monolayer at pH 3.5, in which the detailed structure of the monolayer is confirmed by sum frequency spectra and the adsorbed anions by X-ray reflectivity.

Structural Reorganization and Fibrinogen Adsorption Behaviors on the Polyrotaxane Surfaces Investigated by Sum Frequency Generation Spectroscopy

Polyrotaxanes, such as supramolecular assemblies with methylated α-cyclodextrins (α-CDs) as host molecules noncovalently threaded on the linear polymer backbone, are promising materials for biomedical applications because they allow adsorbed proteins possessing a high surface flexibility as well as control of the cellular morphology and adhesion. To provide a general design principle for biomedical materials, we examined the surface reorganization behaviors and adsorption conformations of fibrinogen on the polyrotaxane surfaces with comparison to several random copolymers by sum frequency generation (SFG) vibrational spectroscopy. We showed that the polyrotaxane (OMe-PRX-PMB) with methylated α-CDs as the host molecule exhibited unique surface structures in an aqueous environment. The hydrophobic interaction between the methoxy groups of the methylated α-CD molecules and methyl groups of the n-butyl methacrylate (BMA) side chains may dominate the surface restructuring behavior of the OMe-PRX-PMB. The orientation analysis revealed that the orientation of the fibrinogen adsorbed on the OMe-PRX-PMB surface is close to a single distribution, which is different from the adsorption behaviors of fibrinogen on other polyrotaxane or random copolymer surfaces.

Molecular orientation of organic thin films on dielectric solid substrates: a phase-sensitive vibrational SFG study

Phase-sensitive SFG spectroscopy is employed to determine the absolute molecular orientation on the solid/air and solid/liquid interfaces.