Surface chemistry dynamics

In recent years, advances in experimental capabilities have fueled a great deal of activity in the study of the electrified solid-liquid interface. This has been the subject of a recent workshop and review article [145] discussing structural characterization, interfacial dynamics and electrode materials. The field of surface chemistry has also received significant attention due to many surface-sensitive means to interrogate the molecular processes occurring at the electrode surface. Reviews by Hubbard [146, 147] and others [148] detail the progress. In this and the following section, we present only a brief summary of selected aspects of this field. 

Harris J 1991 Mechanicai energy transfer in particie-surface coiiisions Dynamics of Gas-Surface Interactions ed C T Rettner and M N R Ashfoid (London Royai Society of Chemistry) p 1... 

Carter L E and Carter E A 1995 Fj reaction dynamics with defective Si(IOO) defect-insensitive surface chemistry Surf. Sci. 323 39-50... 

Radeke M R and Carter E A 1997 Ab initio dynamics of surface chemistry Ann. Rev. Phys. Chem. 48 243-70... 

The development of new and improved catalysts requires advances in our understanding of how to make catalysts with specified properties the relationships between surface stracture, composition, and catalytic performance the dynamics of chemical reactions occurring at a catalyst surface the deployment of catalytic surface within supporting microstracture and the dynamics of transport to and from that surface. Research opportmuties for chemical engineers are evident in four areas catalyst synthesis, characterization of surface stracture, surface chemistry, and design. 

The formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

It is found that the CNF-HT has not catalytic activity for ODP. After oxidation, all the three samples show hi ly catalytic performances, which are shown in Fig.3. CNF-HL has the longest induction period among the three samples, and it has relatively low activity and propene selectivity at the beginning of the test. During the induction periods, the carbon balance exceeds 105% and then fall into 100 5%, which implies the CNF structure is stable and the surface chemistry of CNF reaches a dynamic equilibrium eventually. These results indicate that the catalytic activity of ODP can be attributed to the existence of surface oxygen complexes which are produced by oxidation. The highest propene yield(lS.96%) is achieve on CNF-HL at a 52.97% propane conversion. 

Thus, the glass polyalkenoate cement has distinct biological advantages stemming from its dynamic surface chemistry, which is favourable to bone... 

While experiment and theory have made tremendous advances over the past few decades in elucidating the molecular processes and transformations that occur over ideal single-crystal surfaces, the application to aqueous phase catalytic systems has been quite limited owing to the challenges associated with following the stmcture and dynamics of the solution phase over metal substrates. Even in the case of a submersed ideal single-crystal surface, there are a number of important issues that have obscured our ability to elucidate the important surface intermediates and follow the elementary physicochemical surface processes. The ability to spectroscopically isolate and resolve reaction intermediates at the aqueous/metal interface has made it difficult to experimentally estabhsh the surface chemistry. In addition, theoretical advances and CPU limitations have restricted ab initio efforts to very small and idealized model systems. 

The Wilhelmy hanging plate method (13) has been used for many years to measure interfacial and surface tensions, but with the advent of computer data collection and computer control of dynamic test conditions, its utility has been greatly increased. The dynamic version of the Wilhelmy plate device, in which the liquid phases are in motion relative to a solid phase, has been used in several surface chemistry studies not directly related to the oil industry (14- 16). Fleureau and Dupeyrat (17) have used this technique to study the effects of an electric field on the formation of surfactants at oil/water/rock interfaces. The work presented here is concerned with reservoir wettability. 

Central to the understanding of surface-related phenomena has been the study of gas-surface reactions. A comprehensive understanding of these reactions has proven challenging because of the intrinsic many-body nature of surface dynamics. In terms of theoretical methods, this complexity often forces us either to treat complex realistic systems using approximate approaches, or to treat simple systems with realistic approaches. When one is interested in studying processes of technological importance, the latter route is often the most fruitful. One theoretical technique which embodies the many-body aspect of the dynamics of surface chemistry (albeit in a very approximate manner) is molecular dynamics computer simulation. 

Fruitful interplay between experiment and theory has led to an increasingly detailed understanding of equilibrium and dynamic solvation properties in bulk solution. However, applying these ideas to solvent-solute and surface-solute interactions at interfaces is not straightforward due to the inherent anisotropic, short-range forces found in these environments. Our research will examine how different solvents and substrates conspire to alter solution-phase surface chemistry from the bulk solution limit. In particular, we intend to determine systematically and quantitatively the origins of interfacial polarity at solid-liquid interfaces as well as identify how surface-induced polar ordering... 

Complementing the equilibrium measurements will be a series of time resolved studies. Dynamics experiments will measure solvent relaxation rates around chromophores adsorbed to different solid-liquid interfaces. Interfacial solvation dynamics will be compared to their bulk solution limits, and efforts to correlate the polar order found at liquid surfaces with interfacial mobility will be made. Experiments will test existing theories about surface solvation at hydrophobic and hydrophilic boundaries as well as recent models of dielectric friction at interfaces. Of particular interest is whether or not strong dipole-dipole forces at surfaces induce solid-like structure in an adjacent solvent. If so, then these interactions will have profound effects on interpretations of interfacial surface chemistry and relaxation. 

This chapter focuses on the dynamics of gas-surface chemistry as defined above. Both the theoretical and experimental methodology inherent in such an approach borrow much from an older sibling, i.e., the study of the dynamics of atom-molecule chemical reactions in the gas phase [1]. However, gas-surface reactions are more... 

Two techniques are principally responsible for the experimental development of dynamics in surface chemistry. These are the application of molecular beams and laser state-to-state techniques to gas-surface interactions. This roughly parallels their application to gas phase chemistry, although there are certainly some different technical requirements. More detailed discussion of some of these experimental techniques are in Refs. [104] and [105]. 

The 02 dissociation on Pt(lll) is another of the well-studied paradigms in the dynamics of surface chemistry, both because of the richness of its dynamics and because Pt is an important oxidation catalyst, e.g., in automotive exhausts. 

Certainly most surface chemistry occurs as adsorbates come together as a result of thermal diffusion on the surface. When both reagents are in thermal equilibrium with the surface before reacting, the surface chemistry is described as a Langmuir-Hinschelwood (LH) mechanism. Even most gas-surface reactions occur via this mechanism. However, when the product of the reaction also remains on the surface, no dynamic information is available. Therefore, the only LH reactions discussed in this chapter are when the product of the reaction is a gas phase species. One example already discussed extensively is associative desorption. Here, another well-studied example is considered. 

Single molecule chemistry induced by an STM is one of the new frontiers in surface chemistry, and it is beyond the scope of this chapter to treat this in any meaningful way. Only a brief discussion of one system is given to illustrate the relationship to many of the dynamic principles discussed here. The reader is referred to an excellent review article for recent status in this field [417]. 

It is clear that equilibrium measurements of surface thermodynamics cannot predict surface composition under the dynamic conditions of catalytic oxidation. Nevertheless, such measurements will provide a sounder base than bulk thermodynamics for understanding the surface chemistry and permit working backward, from direct measurements of surface chemistry during reaction, to predictions concerning the microenvironment at the surface under reaction conditions. 

Andrade JD, Gregonis DE, Smith LM (1985) Polymer surface dynamics. In Andrade JD (ed) Surface and interfacial aspects of biomedical polymers, vol 1 surface chemistry and physics. Plenum, New York... 

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