Surface chemistry analysis

Successfully developing a surface engineering strategy based on surfactant behavior at interfaces requires surface characterization techniques that can validate and quantify surface chemistry changes. This review describes the role of two surface chemistry analysis techniques that have proven highly successful in surfactant analysis x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). In Section II, the methods by which these techniques analyze surface chemistry are described. In Section III, recent examples of their application in surfactant-based surface engineering are described. 

Surfactant adsorption is an excellent method of tailoring microparticle surface chemistry because the surfactant can be designed to stabilize the forming particle surface during an emulsion-based fabrication procedure. Surface chemistry analysis is established as a vital component of the microparticle design process because it allows the amount of surfactant adsorbing to a surface to be quantified. 

It is of interest to note that the focus of research on the self-association of hydrotrope molecules was due, in part, to the early discussions about the fundamental nature of the solubility-enhancing capacity of hydrotrope molecules in aqueous solutions. These early attempts at clarification argued for the phenomena of colloidal solubilization versus molecular dispersion [6-8], This dispute was resolved by the results from traditional surface chemistry analysis of interfacial tension, etc., which favored a colloidal association of molecules at high concentrations [48,49], and from vapor pressure measurements [42],... 

Spatially (Laterally) Resolved Surface Chemistry Analysis... 

Chemical appHcations of Mn ssbauer spectroscopy are broad (291—293) determination of electron configurations and assignment of oxidation states in stmctural chemistry polymer properties studies of surface chemistry, corrosion, and catalysis and metal-atom bonding in biochemical systems. There are also important appHcations to materials science and metallurgy (294,295) (see Surface and interface analysis). 

The most useful application of ISS is in the detection and identification of sur-fece contamination, which is one of the major causes of product failures and problems in product development. The surface composition of a solid material is almost always different than its bulk. Therefore, surface chemistry is usually the study of unknown surfaces of solid materials. To better understand the concept of surface analysis, which is used very loosely among many scientists, we must first establish a definition for that term. This is particularly Important when considering ISS... 

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

Two capabilities of ISS are important in applications to the analysis of ceramics. One of these is its surface sensitivity. Many catalyst systems use ceramics where the surface chemistry of the outer 50 A or less is extremely important to performance. Comparing the ratio of H and O to AI or Si is equally important for many systems involving bonding operations, such as ceramic detectors, thin films, and hydroxyapatite for medical purposes. 

In a molded polymer blend, the surface morphology results from variations in composition between the surface and the bulk. Static SIMS was used to semiquan-titatively provide information on the surface chemistry on a polycarbonate (PC)/polybutylene terephthalate (PBT) blend. Samples of pure PC, pure PBT, and PC/PBT blends of known composition were prepared and analyzed using static SIMS. Fn ment peaks characteristic of the PC and PBT materials were identified. By measuring the SIMS intensities of these characteristic peaks from the PC/PBT blends, a typical working curve between secondary ion intensity and polymer blend composition was determined. A static SIMS analysis of the extruded surface of a blended polymer was performed. The peak intensities could then be compared with the known samples in the working curve to provide information about the relative amounts of PC and PBT on the actual surface. 

Models of chemical reactions of trace pollutants in groundwater must be based on experimental analysis of the kinetics of possible pollutant interactions with earth materials, much the same as smog chamber studies considered atmospheric photochemistry. Fundamental research could determine the surface chemistry of soil components and processes such as adsorption and desorption, pore diffusion, and biodegradation of contaminants. Hydrodynamic pollutant transport models should be upgraded to take into account chemical reactions at surfaces. 

XPS is among the most frequently used techniques in catalysis. It yields information on the elemental composition, the oxidation state of the elements and, in favorable cases, on the dispersion of one phase over another [ J.W. Niemantsverdriet, Spectroscopy in Catalysis, An Introduction (2000), Wiley-VCH, Weinheim G. Ertl and J. Kiippers, Low Energy Electrons and Surface Chemistry (1985), VCH, Weinheim L.C. Feldman and J.W. Mayer, Fundamentals of Surface and Thin Film Analysis (1986), North-Holland, Amsterdam]. 

We shall concern ourselves here with the use of an X-ray probe as a surface analysis technique in X-ray photoelectron spectroscopy (XPS) also known as Electron Spectroscopy for Chemical Analysis (ESCA). High energy photons constitute the XPS probe, which are less damaging than an electron probe, therefore XPS is the favoured technique for the analysis of the surface chemistry of radiation sensitive materials. The X-ray probe has the disadvantage that, unlike an electron beam, it cannot be focussed to permit high spatial resolution imaging of the surface. 

After a masterful introduction of the field and its new directions by Michael Sefton of the University of Toronto, Kristi Anseth of the University of Colorado offers a critical analysis of cell-materials interaction problems with emphasis on the nature of cell adhesions, adhesion ligands, and surface chemistry. 

Matthew Hyman and Will Medlin (University of Colorado) review the surface chemistry of electrode reactions, with the intent of introducing this subject to the non-electrochemists. They show the basics of both thermodynamic and kinetic analysis of these reactions, with examples that demonstrate these key principles. 

Chemical bronchitis, 25 479 Chemical bulk analysis, of silicon surface chemistry, 22 373... 

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