Mica, forces between charged surfaces

Figure 2.14 Measured electrostatic double-layer and van der Waals forces between two surfaces of curved mica of radius 1 cm in (a) water and (b) dilute KNO3 and Ca(N03)2 solutions. The lines are the predictions of the DLVO theory with a Hamaker constant of 2.2 x 10 J in the limits of constant surface charge and constant surface potential here xfrQ = -(j/s, the particle surface potential. (The lines for constant surface charge are slightly higher than those for constant surface potential at small D.) The inset in (b) is the measured force in 0.1 M KNO3, which shows a force minimum at a distance of around 7 nm. Since this minimum in force occurs away from the deep minimum at the surface, it is called a secondary minimum. (From Israelachvili and Adams 1978 and Israelachvili 1992, reprinted with permission from Academic Press.)...

Kjellander, R., Marcelja, S., Pashley, R. M. and Quirk, J. P., A theoretical and experimental study of forces between charged mica surfaces in aqueous CaC12 solutions, J. Chem. Phys., 92, 4399-4407 (1990). 

Fig. 8. (A) Measured forces between two charged mica surfaces in 10" M KCl, where beyond 30 A (and out to 500 A) the repulsion is well described by conventional electrostatic double-layer force theory. Below 30 A there is an additional hydration repulsion, with oscillations superimposed below 15 A. (B) Forces between two uncharged lecithin bilayers in the fluid state in water. At long range there is an attractive van der Waals force, and at short range (i.e., below 25 A) there is a monotonically repulsive steric hydration force. (C) Forces between two hydrophobized mica surfaces in water where the hydrophobic interaction is much stronger than could be expected from van der Waals forces alone. From Israelachvili and Marra (1986).

FIG. 19 Force normalized by radius as a function of surface separation between mica surfaces precoated with AM-MAPTAC-30. The forces were measured across an aqueous 10-4 M KBr solution containing no SDS ( ) and 0.005 cmc SDS ( ). The solid lines are calculated DLVO forces using a surface potential of 45 mV and constant charge (upper line) and constant potential (lower line) boundary conditions. The arrows indicate inward jumps. (Adopted from Ref. 80.)... 

To compare the surface-force isotherms with theory, we have to consider several different surface-force contributions. Van der Waals forces between mica surfaces can be neglected here because the closest mica separations are beyond the range of detectable force. Due to the charged nature of both mica and poly-lysine, we need to consider the presence of double-layer forces. We invoke the well-known double-layer... 

Forces between BSM layers preadsorbed on negatively charged mica surfaces have also been reported by Dedi-naite et al. [33]. They also found long-range steric interactions to be predominant, but they did not explore the effect of ionic strength. However, they showed that the anionic surfactant sodium dodecyl sulfate, SDS, has the ability to remove mucin from the surface and that adsorption of chitosan, a cationic polysaccharide, on top of mucin can protect the mucin layer from being removed by the surfactant. 

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