Structural changes within film

A relation between the surface stress and the structural change within the Pb UPD layer on Au film electrode has been studied, applying a bending beam method [487]. A maximum in the surface stress versus potential dependence emerged at the onset of UPD, similarly as in electrocapillary curve. 

The structural changes within LBK films upon irradiation can cause morphological changes, too. Irradiation of LBK films of azobenzene amphiphile 43 results in an increase of the surface roughness, as shown by AFM measurements. The roughness is most likely caused by a recrystalliza-tion of the azobenzene amphiphiles in the irradiated area. 

Oznuluer and Demir [88] have employed electrochemical atomic layer epitaxy (ALE) to the investigations of kinetics of structural changes occurring within initial monolayers of thin Bi2S3 films on Au(l 11). 

Returning to Fig. 2.19(A), we can compare the observed potential dependence for the oxidation of NADH with the electrochemistry and changes in conductivity of the poly(aniline) film over the same potential range plotted in Fig. 2.19(B). Comparing Figs. 2.19(A) and (B), it is clear that there is no response to NADH when the film is at its maximum conductivity—between -0.075 and -0.05 V vs. SCE. This supports the idea that the oxidation of NADH is a chemical reaction mediated by particular structural units within the poly(aniline) film, rather than the film acting as a metallic electrode. In the discussion below, we will return to the potential dependence once the mechanism has been established. 

In the SFA experiments there is no way to determine whether shear occurs primarily within the film or is localized at the interface. The assumption, made by experimentalists, of a no-slip flow boundary condition is invalid when shear localizes at the interface. It has also not been possible to examine structural changes in shearing films directly. MD simulations offer a way to study these properties. Simulations allow one to study viscosity profiles of fluids across the slab [21], local effective viscosity inside the solid-fluid interface and in the middle part of the film [28], and actual viscosity of confined fluids [29]. Manias et al. [28] found that nearly all the shear thinning takes place inside the adsorbed layer, whereas the response of the whole film is the weighted average of the viscosity in the middle and inside the interface. Furthermore, MD simulations also allow one to examine the structures of thin films during a shear process, resulting in an atomic-scale explanation [12] of the stick-slip phenomena observed in SFA experiments of boundary lubrication [7]. 

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