Mica, surface free energy data

The SFA consists of a hermetically closed stainless steel chamber that can be filled with any transparent liquid or gas of choice. Mica is a preferred substrate in the SFA, though other surfaces, such as single-crystal sapphire plates have also been used [10]. In the SFA, the force acting between the surfaces, mounted in a crossed cylinder configuration, as a function of surface separation is measured. The data obtained are normally plotted as force, FC(D), normalised by the undeformed geometric mean radius of the surfaces, R This quantity is related to the free energy of interaction per unit area, G, between two flat surfaces at the same separation [11] ... 

FIGURE 5.29 Comparison of theory with experimental data measnred with solntion of 5 mM NaCl at pH = 6.3 between mica snrfaces the total interaction free energy,/=+ /j, + is plotted against the film thickness h (see Equations 5.162 and 5.233). The solid line is the best fit calculated with adsorption energy = -5.4 kT per Na+ ion, and area per surface ionizable group 0.714 nm. ... 

The data displayed in Figures 14-18 show that preadsorbed PCMA layers are strongly swelled by association with SDS once the SDS concentration has reached 0.1 cmc. This indicates that part of the polyelectrolyte chain is desorbed from the surface. However, most of the polyelectrolytes remain attached to the mica surface for a period of at least several days. When the swelled layers are pushed together, oscillating force curves are observed. The reason is that the internal structure of the adsorbed layer changes in order to minimize the free energy of the system. We note that similar but weaker oscillations with larger periodicity have been observed due to pack-... 

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