Competitive Adsorption at the Air–Water Interface: A Second Harmonic Generation Study

Infrared spectroscopy of 2-oxo-octanoic acid in multiple phases

“…Surface specific methods used to study the air-water interface include second-harmonic generation, [72][73][74] X-ray photoelectron spectroscopy, 75 sum-frequency generation (SFG), [76][77][78][79][80][81][82][83][84][85][86][87][88][89] and Infrared Reflectance Absorption Spectroscopy (IRRAS). 56,57,[90][91][92][93][94][95][96][97][98][99][100][101] Of these, IRRAS and SFG allow for vibrational characterization of molecules and also provide information about the surface morphology including orientation and packing of interfacial species.…”

On Electronic and Charge Interference in Second Harmonic Generation Responses from Gold Metal Nanoparticles at Supported Lipid Bilayers

“…Second harmonic generation (SHG) has been used for probing metal nanoparticles for over 25 years (see, for instance, references − ) and is a promising technique for studying these materials in aqueous media − and at solid–liquid interfaces. − Second-order spectroscopy has also been used to characterize ligand–nanoparticle interactions ,− and to follow nanoparticle interactions with biologically relevant systems ,− such as supported lipid bilayers, which serve as important model systems for studying the nano-bio interface. , For the specific case of applying SHG to metal nanoparticles in aqueous environments, one may need to consider that the SHG signal can contain contributions from electronic resonance by the nanoparticle (either at the fundamental or the second harmonic frequency), the electrostatic potential at the particle surface, or both, according to Here, I SHG and E SHG are the SHG signal intensity and electric field ( E -field), respectively; E ω is the incident E -field oscillating at the fundamental frequency ω; χ (2) and χ (3) are the second- and third-order nonlinear susceptibilities of the system; Φ 0 is the electrostatic potential at zero distance from the particle surface; and Δγ is the relative phase between the second- and third-order terms. , Adsorbates exhibiting an electronic transition that is on resonance with the incident or second harmonic wavelength produce second harmonic responses dominated by the resonant component of the χ (2) term − and, in the case of charged species with electronic resonances at the relevant photon energies, the χ (3) term. In the absence of electronic resonance and provided that an interfacial potential exists that can polarize species (e.g., water molecules) in the SHG active region (the region in which a second-order response can be generated), the SHG response is given by the nonresonant contributions from χ (2) and from the interfacial potential-dependent term (“χ (3) Φ 0 ” in eq…”

Probing Liquid Interfaces with Room-Temperature Ionic Liquids Using the Excited-State Dynamics of a Cationic Dye

“…This concentration coincides also with the concentration above which the stationary SSHG signal decreases. The fact that the stationary signal decreases, whereas the SSHG profile stays constant, could be explained by a competition for adsorption between the MG dyes and the IL ions. − If the IL ions have a higher interfacial affinity than MG, the adsorption of the dye is hampered above a certain concentration, that should coincide with c TR max , at which most of the adsorption sites are occupied by the IL ions. This should lead to a decrease of the stationary SSHG intensity as MG is somehow repelled from the interface.…”