Adsorption ellipsometrically

A proper choice of the dipping time presupposes a study of the adsorption kinetics. In situ measurements of the adsorption of PAH (from a 0.01 M solution with 0.5 M MnCl2 added) on a PSS-coated optical waveguide showed that the adsorption is practically completed after 3 minutes [107]. It was shown that the kinetics of adsorption are not transport limited. Similar results hold for subsequent polyelectrolyte adsorption. Ellipsometric measurements of the thickness of... 

Smith [113] studied the adsorption of n-pentane on mercury, determining both the surface tension change and the ellipsometric film thickness as a function of the equilibrium pentane pressure. F could then be calculated from the Gibbs equation in the form of Eq. ni-106, and from t. The agreement was excellent. Ellipsometry has also been used to determine the surface compositions of solutions [114,115], as well polymer adsorption at the solution-air interface [116]. 

Tengvall P, Lundstrom I, Liedberg B (1998) Protein adsorption studies on model organic surfaces an ellipsometric and infrared spectroscopic approach. Biomaterials 19 407-422... 

Ellipsometric Study of Adsorption of Polyelectrolyte onto a Metal Surface... 

For homopolyelectrolyte, we first studied the ellipsometric measurement of the adsorption of sodium poly(acrylate) onto a platinum plate as a function of added sodium bromide concentration (5). We measured the effect of electrolyte on the thickness of the adsorbed layer and the adsorbances of the polyelectrolyte. It was assumed that the Donnan equilibrium existed between the adsorbed layer and the bulk phase. The thickness was larger and the adsorbance of the polyelectrolyte was lower for the lower salt concentration. However, the data on the molecular weight dependence of both the adsorbance and the thickness of the adsorbed polyelectrolyte have been lacking compared with the studies of adsorption of nonionic polymers onto metal surfaces (6-9). 

Gebhard and Killmann69 reported an ellipsometric study of the adsorption of polystyrene onto various metal surfaces from theta solvents, M ranging from 76 x 103 to 340 x 103. A proportionality between t,ms and M1/2 was also observed, and the adsorb-ance was found to increase with rising M. 

Recently, Takahashi et al.70) measured ellipsometrically the thicknesses of the polystyrene layers adsorbed on a chrome plate from cyclohexane at 35 °C over a very wide range of M from 10 x 103 to 13.4 x 106. The resulting adsorption isotherms are shown in Fig. 11. Initially, the adsorption isotherms rise sharply with increasing bulk polymer concentration and reach a wide plateau region. The plots of t against bulk polymer... 

The first ellipsometric measurement of the thickness of the adsorbed layer and the adsorbance of a polyelectrolyte and a negative adsorbance of salt onto a solid surface was reported by Takahashi et al.U4) They measured the adsorption of sodium poly(acrylate) (M = 950 x 103) onto a platinum plate as a function of the concentration of added sodium bromide. In an aqueous polyelectrolyte solution with an added simple salt, the bulk phase is a three-component system which consists of a polyelectrolyte, a simple salt, and water. The adsorbed layer on the solid surface is a three-component phase as well. The adsorbance of polyelectrolytes thus cannot easily be determined from measurements of the refractive index nf of the adsorbed phase. Hence, it was assumed that the adsorbed layer is a homogeneous layer of thickness t and further that nf is represented by the Lorenz-Lorentz equation as follows ... 

Figure 9.13 Adsorption of nitrogen to a single basal plane of graphite at a temperature of 46.2 K as determined by ellipsometry. Plotted is the change in the ellipsometric angle A versus pressure. The subsequent adsorption of at least four layers at defined pressures can clearly be distinguished. Redrawn from Ref. [389].

Fig. 12. 53. Experimental coverage-potential relation for n-valeraldehyde on platinum as a function of electrode potential. Two things should be noted First, adsorption-potential plots are roughly parabolic. Second, there is medium-good agreement between two entirely different methods, one based on the interpretation of ellipsometric data and the other on FTIR measurements. (Reprinted from J. O M. Bockris and K. T. Jeng, J. Electroanal-chem. 330 553, copyright 1992, with permission from Elsevier Science.)...

In extreme cases, such as boiling HC1 in contact with stainless steel, inhibitors can still be found that work very well indeed. Ellipsometric measurements show that they can form polymer layers five and six molecular layers thick—a kind of in situ formation of a paint film, built up by successive adsorption, layer upon layer. 

Ellipsometric measurements with processed photoresists showed a long-time swelling over several days. Attempts to investigate the adsorption after addition of surfactant delivered only an continued swelling. It could not be distinguished between the effects of swelling and of the surfactant adsorption. 

It can be summarized that ellipsometric measurements proved the formation of a surfactant adsorption layer on the photoresist surface. At ceg- it is assumed to form a monolayer. To get more information about the adsorption layer and its influence on the surface properties of the photoresist, an electrokinetic characterization of unexposed and processed photoresist in solutions of the cationic surfactant was carried out. The zeta potential of the photoresist layers is given in Fig. 8 as a function of the surfactant concentration. The measurement was performed at pH = 6 in a background electrolyte (KC1) concentration of 10-5 M to ensure the minimum conductivity of the solution necessary for the measurement. 

At a substrate temperature of 340 K, the adsorption of CH3 is observed with ellipsometry. The change of the ellipsometric signal is depicted in Fig. 11.7. The points 1, 2, and 3 label consecutive stages in the evolution of the ellipsometry data points in the plane point 1 represents the C D layer at the beginning of the experiment. With the onset of the CH3 flux, the ellipsometric angles shift at first to larger values of and A (point 1 to 2), followed by a shift to larger values of but smaller values of A (point 2 to 3). 

An optical three-layer model has proved superior to a one-layer model for the interpretation of the ellipsometric data. The refractive indices of the film and surface layers are determined and it is found that the index for the surface is higher than that for the film core. A Lorenz-Lorentz type treatment of NBF reveals that there are approximately seven water molecules per molecule of surfactants in both NaDoS and NaDoBS films. The optical data obtained by the three-layer model for NBF from NaDoS indicate that the thickness of the aqueous core is zero while that of the adsorption monolayers of surfactant molecules with refractive index 1.365 is 1.8 nm, i.e. the thickness of NBF is 3.6 nm. 

Lassen and Malmsten have performed ellipsometrically determined in situ protein adsorption measurements on the above plasma polymer surfaces with human serum albumin (HSA). human immunoglobulin (IgG), and human fib-... 

This value can be converted into the more conventional units of m /g by calculating the film mass/area (m/) mf—h( —fp)Psh where h is film thickness, is the finctional praosity, and p k is the skeletal density of the oxide matrix. Based on ellipsometric analysis, this film is 165 nm thick and has a refractive index of 1.21. Using the Lorentz-Lx)renz relationship [130] and a skeletal refractive index of 1.45, a fractional porosity of 0.50 is estimated. However, from the total amount of adsorption in the plateau region at high p/po values, a fractional porosity of... 

Kim, et al., ( ) have utilized radioiodinated (I proteins to measure adsorption of individual proteins and protein mixtures on LTI carbon surfaces. Their results indicate a very rapid adsorption of albumin onto the LTI carbon surface, consistent with Kim s model of blood interactions via a platelet-adhesion mechanism (.8). Microcalorimetric and electrophoretic mobility studies of protein adsorption on LTI carbon surfaces have been done by Chiu, et al., ( 5). The extension of the adsorbed protein layers have been directly measured by Fenstermaker, et al., ( ) and Stromberg et al., 7) at NBS using ellipsometric methods. 

Fig. 3.7 Adsorption of fibrinogen on an EG2/EG6 gradient at pH 7.4. The incremental changes in ellipsometric thickness (filled circles) and the integrated area of the amide I peak obtained by FTIR-spectroscopy (open circles) are displayed...

Poncet C, Tiberg F, Audebert R. Ellipsometric study of the adsorption of hydrophobically modified polyacrylates at hydrophobic surfaces. Langmuir 1998 14 1697-1704. 

Table I Includes the results of ellipsometric adsorption studies of water on a similar (and similarly prepared) PE to that of Ref. 14. (18) In addition, the adsorption was determined for a surface partially oxidized by treatment with an acid dlchromate solution. As might be expected, the effect of the introduction of polar sites reduces 6, Increases and Increases both Cq nd B. The relaxation distance for Is Increased, while that for the distortion term Is decreased. Systematic studies of this type should lead to a much better understanding of the nature of adsorbed films near F°.

There are many applications of ellipsometry in the measurement of mono-layer and sub-monolayer films. The theory of the optical signal to be expected from an adsorbed layer less than one monolayer thick has been placed on a firm footing by Smith [15] in some elegant experiments on adsorption in a Langmuir trough. Simultaneous ellipsometric and surface potential measurements were made on various molecules spread in thin layers on mercury as the surface pressure was varied. One conclusion was the simple result that the effective thickness divided by the thickness of the island molecules in the adsorbed islands was equal to the fractional coverage of the surface area. 

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