Stratification of confined fluids

To illustrate the relation between microscopic structure and experimentally accessible information, we focus on the computation of pseudo-experimental solvation-force curves F(h) /R [see Eqs. (5.57), (5.59), (5.63), and (E.46)j as they would be determined in SEA experiments. However, here these curves are computed from computer simulation data for and Pb where Pb is 

Plots of / ( ) and F h)/R versus s and h, respectively, are shown in Fig. 5.3. The oscillatory decay of both quantities is a direct consequence of the osciUatory dependence of on s, which has also been investigated by integral equations of varying degree of sophistication (157-161). As can be seen in Fig. 5.3, zeros of / (s ) correspond to successive extrema of F(h) /R 

Alternatively, one may employ colloidal probe atomic force microscopy (APM) to measure force distance curves such as the ones plotted in Fig. 5.1 [162]. The important difference between SFA and colloidal probe AFM experiments is that in the latter the entire force distance curve Is accessible rather than only that portion satisfying Eq. (5.66) [163, 164]. In Ref. 164 a comparison is presented between theoretical and experimental data for confined poly-electrol3Tte systems. 

In any case, structural changes accompanying the variation of F h) /R are rather obscure regardless of the experimental technique. These changes can be inferred more directly from Figs- 5.4-5.6 vrhere plots of the local 

Because of Eq. (5.60), experimentally accessible portions of the pseudo-experimental data can be related to the local stress at the point (0,0,. s = h) of minimum distance between the surfaces of the macroscopic sphere and the planar substrate (see Fig. 5.2). By correlating the local stress (h) with the confined fluid s local structure at (0,0,/i) via p z), one can establish a direct correspondence between pseudo-experimental data [i.e., F(h)/R] and the local microscopic structure of the confined fluid. 

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