Physisorption Characterizing Surfaces and Pores

Adsorption on a solid surface is the process of a species present in a gas or liquid phase adhering to the surface of the solid [46,104,105], This adsorption occurs due to molecular interactions between the adsorbing species and the solid. If adsorption is characterized by relatively weak interactions, such as those typical of van der Waals forces, the process is called physisorption. Because such weak forces occur between all molecules, physisorption is typically reversible and will occur at any surface when the normalized concentration of the adsorbing species is sufficiently high. For a gas-phase species, the normalized concentration is equal to pipa where p is the partial pressure of the species and po is its saturation vapor pressure. The endpoint for physisorption occurs when the concentration of the adsorbing species reaches its saturation value. For a gaseous contacting phase, condensation occurs at this point, (i.e., when p = po). 

Physisorption on a surface can be used as a method of probing the molecular interactions occurring at a solid surface. Since the nature of the adsorbing species can be known, this provides a technique for probing the properties of the solid 

These considerations may also explain the nonmcmotonic frequency responses with vapor partial pressure observed for adsorption of non-polar molecules onto the quartz surface of a SAW sensor [114]. Since it is well known that surface coverage increases monotonically with partial pressure, these trends are inconsistent with a simple mass-loading interpretation. In this paper, the authors no-posed a coverage-dependent SAW-adsorbate interaction to explain the anomalous results for the weaker binding non-polar s )ecies (no anomalous trends were observed with polar adsorbates). 

2 Characterizing Film Surface Area and Pore Size Distribution 

There are applications of thin films where it is im iortant to obtain information regarding pro )erties relating to the microstructure of the coating. Some exam- 

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