Interfacial interactions interface reliability

The versatility of the SPR technique has been shown by a vast amount of publications in the past decades the method has matured into a well-accepted analytical tool for the characterization of interfaces and thin films as well as for the sensitive detection of interfacial biomolecular interaction. With a significant input from engineering, SPR has reached a decent signal-to-noise level with a lower limit for a reliable signal detection corresponding to an effective layer of about 0.3 A [6], which is sufficient for most thin film studies. However, the intrinsic label-free characteristic of SPR detection technique still imposes limitation on further sensitivity improvement, especially if the analysis involves small molecules. 

Thermoporimetry [10,11] can reliably be used to obtain the pore-size distribution of porous particles suspended in water. The basis of the technique is that the surface area of the ice-liquid water interface increases when the ice penetrates narrow pores. As the diameter of a pore is smaller, the increase in interfacial area is larger. To freeze the water in narrower pores thus requires lower temperatures. The temperature at which the heat of solidification of water is set free thus indicates the width of the pores, and the amount of heat released indicates the pore volume. Measurement by DSC (differential scanning calorimetry) can provide the data for determination of the pore-size distribution of porous particles suspended in pure water. It has been observed that the first layer of water molecules present on the surface of oxides cannot be frozen apparently the interaction with the surface of the oxides is so high that the layer is already frozen without attaining the structure of ice. Thermoporimetry can, therefore, also provide data about the interaction of water with the surfaces of solids. Thermoporimetry with other liquids, e. g. benzene, can provide information about the interaction of surfaces with, e. g., apolar liquids. 

Since the substrate may influence the anisotropic optical properties of the overlying film [595], the method of Buffeteau et al. [247, 566-568, 593] is conceptually more reliable when the MO is studied on solid transparent substrates, whereas the initial anisotropic optical constants are extracted from normal- and oblique-incidence transmission or polarized reflection of the same film on the same substrate. In the case when different substrates participate into the measurements (e.g., when MO in monolayers at the AW interface is studied), the comparison of the simulated and experimental spectra can be used for distinguishing chemical effects generated by specific film-substrate interactions [568b]. In particular, the kmm values derived from spectra of monolayers at the AW interface obtained by IRRAS are usually larger than those obtained by eUipsometric measurements of thin films on solid supports [247]. This difference has been attributed to a gradient in the optical properties of the interfacial water [71]. 

The obtained electrostatic potential profiles and ion distributions can in principle be used to calculate surface or interfacial tensions. However, up to now only few PMFs for ion-water surface interactions are available from MD simulations and there are no reliable experimental data of interfacial tensions for SAM-solution interfaces. Therefore it is not yet possible to check if the correct Hofmeister series can be obtained with this new approach. 

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