Surface Induced Modification

Energetic particles interacting can also modify the structure and/or stimulate chemical processes on a surface. Absorbed particles excite electronic and/or vibrational (phonon) states in the near-surface region. Some surface scientists investigate the fiindamental details of particle-surface interactions, while others are concerned about monitormg the changes to the surface induced by such interactions. Because of the importance of these interactions, the physics involved in both surface analysis and surface modification are discussed in this section. 

This area of research is still at its beginning and many aspects are not resolved. This includes in particular the structure and conformation of polymers at an interface as well as the modification of polymer dynamics by the interface. We have given several examples of the potential of surface and interface analytical techniques. They provide information on surface roughness, surface composition, lateral structure, depth profiles, surface-induced order and interfacial mixing of polymers on a molecular and sometimes subnanometer scale. They thus offer a large variety of possible surface and interface studies which will help in the understanding of polymer structure and dynamics as it is modified by the influence... 

Quantitative Analysis. In its basic form, AES provides compositional information on a relatively large area ( 1 mm2 ) of surface, using a broad-focussed electron beam probe. Sufficient signal may be obtained in this way with a low incident electron flux, thus avoiding potential electron-induced modifications of the surface. 

Iametti, S. and Bonomi, F. 1993. Monitoring the surface hydrophobicity of milk proteins A realtime study on heat-induced modifications. Int. Diary Fed. Spec. Issue 9303 111-116. 

LOCAL MODIFICATION OF SURFACES INDUCED BY ADSORBED MOLECULES... 

Part V Local Modification of Surfaces Induced by Adsorbed Molecules... 

The growth of filamentous carbon along with the gas phase product analysis has been used to determine the influence of sulfur on the iron catalyzed decomposition of carbon containing gas mixtures at 600°C. Pretreatment of the metal in H2S was found to initially suppress the reactions leading to carbon deposition from the decomposition of CO/H2 mixtures. After a short time the activity was restored to approximately the same level as that exhibited by an unadulterated iron powder, suggesting that most of the sulfur atoms were being removed from the surface. The small residual fraction of adatoms did, however, induce modifications in the structural characteristics of the filamentous carbon deposit and also altered the reactivity pattern of the iron towards decomposition of a CO/C2H4/H2 mixture. 

Polymer films change their properties during ion implantation [25-29]. Carbonization mentioned above is one of the ion beam induced modification techniques for polymer surfaces. 

Brendle, M. and Colin, G., Friction-Induced Modifications at the Surface of Compacted Solid Lubricants, Proc. 8th Leeds/Lyon Symp. The Running-In Process in Tribology, Lyon, 1981. 

Peroxynitrite is a cytotoxic species generated by the reaction between superoxide and nitric oxide. Catechin polyphenols could also decrease the peroxynitrite-induced nitration of tyrosine and protect apolipoprotein B-lOO of LDL from peroxynihite-induced modification of critical amino acids, which contribute to its surface charge. ... 

The materials analyzed were blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) in various ratios. The two components are miscible in all proportions at ambient temperature. The photooxidation mechanisms of the homo-polymers PS and PVME have been studied previously [4,7,8]. PVME has been shown to be much more sensitive to oxidation than PS and the rate of photooxidation of PVME was found to be approximately 10 times higher than that of PS. The photoproducts formed were identified by spectroscopy combined with chemical and physical treatments. The rate of oxidation of each component in the blend has been compared with the oxidation rate of the homopolymers studied separately. Because photooxidative aging induces modifications of the surface aspect of the material, the spectroscopic analysis of the photochemical behavior of the blend has been completed by an analysis of the surface of the samples by atomic force microscopy (AFM). A tentative correlation between the evolution of the roughness measured by AFM and the chemical changes occurring in the PVME-PS samples throughout irradiation is presented. 

Several models have been proposed to explain these oscillatory rates. Sales et al. 47) associated the oscillation with a slow and reversible modification of the catalyst surface slow oxidation and reduction of the metal surface induces transitions between the two branches. 

MAGNETIC-FIELD-INDUCED MODIFICATION OF POROUS SILICON SURFACE AND PHOTOLUMINESCENCE... 

The final group of chapters by Bertolini and Jugnet, Rogriguez, Hrbek and Baddeley address issues more directly related to the chemical properties of these surfaces, the first three of these chapters being concerned directly with the relationship of the nature of the surface alloys (and alloy surfaces) and their reactivity, while Baddeley turns the problem round in addressing the issue of adsorbate-induced modification of surface segregation not only does the alloy surface modify the reactivity, but also the reaction modifies the surface alloy. 

Although the electrochemical nature of the nano structuring process is convincingly demonstrated, the role of the externally applied electric field should be once more considered. Field-induced modifications of a surface on an atomic scale have been reported from various vacuum experiments [46-49]. The fields required for such manipulations are much larger than those applied here and usually necessitate very small distances between tip and surface, close to mechanical contact... 

K. Aoki, T. Seki, M. Sakuragi, and K. Ichimura, Reversible alignment change of liquid crystals induced by photochromic molecular films, Part 15. Convenient methods to prepare command surfaces by surface-selective modifications of poly(vinyl alcohol) thin films with azobenzene units, Makromol. Chem. 193, 2163-2174 (1992). 

The variation of the chemical composition of the substrate (not realized in a continuous tunable fashion) leads to drastic modifications of surface fields exerted by the polymer/substrate (i.e.,II) interface [94,97, 111, 114,119]. The substrate may, for instance, change contact angles with the blend phase from zero to a finite value. As a result the final morphology changes from a layered structure of Fig. 5b into a column structure of Fig. 5c [94,114]. On the other hand our very recent experiment [16] has shown that the surface fields are temperature dependent. Therefore, although it has been shown that surface-induced spinodal decomposition yields coexisting bilayer structure (Fig. 5b) at a singular temperature [114,115], that in principle may not be necessary true for other temperatures. This motivated our comparative studies [107] on coexistence compositions determined with two techniques described above interfacial relaxation and spinodal decomposition. 

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