Adsorption stepwise function

FIG. 2 -potential as a function of layer number for PDADMAC/PSS multilayers on sulfate-stabilized polystyrene (PS) latices. The multilayers were assembled onto the negatively charged PS latices ( -potential of ca. -65 mV, layer number = 0) by the consecutive deposition of PDADMAC (odd layers) and PSS (even layers). Positive values are observed for PDADMAC deposition, and negative values for PSS adsorption. The alternating values are characteristic of stepwise growth of multilayer films on colloids. 

Underpotential deposition usually follows Frumkin-type adsorption isotherms due to strong lateral interactions and the interaction parameter, g, varies stepwise with coverage which is a function of the electrode potential. This is due to important structural and electric changes operative in the upd layers as coverage increases. 

The metal oxides prepared by conventional baking or by the CVD method are, in general, chemically stable, crystalline materials, and show excellent mechanical, electrical, optical, and physical properties. Flexible porous gel films obtained by the surface sol-gel process are totally different. In this chapter, we described a new preparative method for ultrathin metal oxide films by stepwise adsorption of various metal alkoxides. We named this method the surface sol-gel process. Structural characterization of the gel films thus obtained, the electrical property, and formation of nano-composites with organic compounds, were also explained. The soft porous gel contains many active hydroxyl groups at the surface and interior of the film. This facilitates adsorption of organic compounds, and consequent preparation of ultrathin metal oxide/polymer nano-composite films and organization of functional small molecules. In the nano-composites, proper selection of polymer components leads to the design of new materials with unique electrical, optical, and chemi-... 

The two-stage growth process of the pellicle is of importance to the structure and function of the pellicle. The first step has been explained by an initial adsorption of discrete proteins to the enamel surface, whereas the second step is the adsorption of salivary protein aggregates in the form of micelle-like structures that move more slowly towards the interfaces, and hence give a stepwise increase in the pellicle thickness [47]. The latter structures are believed to account for the globular surface morphology of acquired salivary pellicle. 

It is clear that on a uniform surface one would expect stepwise condensation. That this is not the case leads one to discard the assumption of uniformity, and assume that there is a distribution function of adsorption energies over the surface. If the surface is characterized by a distribution function. Vae, and the sites of equal energy are collected in patches, each patch will fill at a pressure p/po = erAE/RT. The total coverage will be... 

An example of this approach is represented by the growth of 3-D coordination polymers with SCO properties via stepwise adsorption reactions for multilayer films based entirely on intra- and interlayer coordination bonds Fe(pyrazine) [Pt(CN) ] [218, 219], Indeed, after functionalization of the surface with the appropriate anchoring layer the coordination polymer is built in a stepwise fashion, alternating the metal ion (Fe "), the platinum salt ([Pt(CN) ] ), and pyrazine. The polymer shows many interesting properties, with the SCO transition accompanied by a variation in the dielectric constant of the material accompanied by a room temperature hysteresis of the dielectric constants. This dielectric hysteretic property may be useful in building molecular memory devices that can store information by high- and low-capacitance states. What must be remarked here is that these appealing properties cannot be exploited in bulk materials, but only in thin films. 

One of the most often cited criticisms of this method is the assmnption of discontinuous filling of the micropores and the complete filling of a pore at a specific pressure characteristic of its size [9,45,47,50]. This assumption is commonly referred to as the condensation approximation in Hterature. However, other theoretical models for the prediction of adsorption such as Monte Carlo simulations or NL-DFT theory show that this picture is valid only for very small micropores (Z, < 2.0 run) For larger-sized pores, the filling process is shown to be stepwise and proceeds by the formation of an initial monolayer on the pore walls and the subsequent condensation of the sorbate in the inner part of the pore [47]. This aspect of the model often results in the calculated PSD to be more polydisperse than the true distribution and is quite difficult to correct. One of the remedies suggested by Kaminsky et al. [45] could be to consider the calculated PSD to be a convolution of the true PSD. If a smearing function characteristic of the method can be determined, the true distribution can be mathematically deconvoluted from the HK-predicted PSD. 

Adsorption of biologically important materials, such as fibrinogen from plasma proteins and barbiturates, " and organic molecules including corrosion inhibitors have been studied, often as functions of potential of the substrate, by ellipsometry in situ. Jovancicevic, Yang, and Bockris used time-resolved ellipsometry to measure the thickness, refractive index, and extinction coefficient of the adsorption layer of l-octyne-3-ol on iron as functions of time. They showed that the layer thickness increased stepwise, due to change of the adsorption configuration from flat... 

The effect of alcohol adsorption in flexible frameworks such as RPM-3 and RPM-4 has also been investigated. The results of these studies show a stepwise adsorption of alcohols as a function of pressure. Recently, several groups have tested MMOFs for separation of various alcohols from water for biofuel purification. For... 

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