Application of Transient Evanescent Grating Techniques to the Study of Liquid/Liquid Interfaces

Abstract

Transient grating experiments performed with evanescent fields resulting from total internal reflection at an interface between a polar absorbing solution and an apolar transparent solvent are described. The time evolution of the diffracted intensity was monitored from picosecond to millisecond time scales. The diffracted signal originates essentially from two density phase gratings: one in the absorbing phase induced by thermal expansion and one in the transparent solvent due to electrostriction. A few nanoseconds after excitation, the latter grating is replaced by a thermal grating due to thermal diffusion from the absorbing phase. The speed of sound and the acoustic attenuation measured near the interface are found to be essentially the same as in the bulk solutions. However, after addition of a surfactant in the polar phase, the speed of sound near the interface differs substantially from that in the bulk with the same surfactant concentration. This effect is interpreted in terms of adsorption at the liquid/liquid interface. Other phenomena, which are not observed in bulk experiments, such as acoustic echoes and a fast oscillation of the signal intensity, are also described.

Photoinduced Electron Transfer Reactions: From the Elucidation of Old Problems in Bulk Solutions Towards the Exploration of Interfaces

“…Among the various approaches developed to limit or circumvent this problem, [38,39] the most powerful are probably those probing the second order nonlinear optical susceptibility, which is only nonzero in anisotropic media, such as the interface between two isotropic liquid phases. This is the case of the surface-second harmonic (SSHG) and surface-sum frequency generation (SSFG) techniques, which have become the most widely used optical methods for investigating all kinds of interfaces.…”

Physical Chemistry at the University of Geneva

“…14). [36] The second is transient surface second-harmonic generation where the material response that is probed is zero in the bulk and non-zero at the interface. [37] Both methods are complementary and are used to study the dynamics of photoinduced processes at liquid interfaces, two examples being illustrated in Fig.…”

Probing Liquid–Liquid Interfaces with Spatially Resolved NMR Spectroscopy

“…Probing liquid–liquid interfaces with scanning probe techniques still remains a challenge, though first results from atomic force microscopy (AFM)10 and scanning electron microscopy (SEM)11 have been obtained. Transient phase grating experiments with evanescent fields resulting from total internal reflection at an interface between a polar absorbing and a nonpolar transparent phase were used to measure the dimension of liquid–liquid interfaces 12. Vibrational sum frequency spectroscopy (VSF)13 selectively probes the molecular structure at hydrocarbon–water interfaces and shows that the hydrogen bonding between adjacent water molecules at the interface is weak and results in a substantial orientation of the water molecules in the interfacial region 14.…”