Interfaces dilute charged monolayers

Surface Equation of State for Very Dilute Charged Monolayers at Aqueous Interfaces... 

We describe in a companion paper (33) the salient features of our procedures for measuring low surface pressures, and we provide n-A isotherms for octadecyl trimethylammonium bromide (Ci8 TAB) and sodium octadecyl sulfate (Ci8 sulfate) monolayers spread at A/W and O/W interfaces. Here we extend some of these data to higher A using, in some instances, some of our earlier reported measurements. We have also taken from literature the few reported isotherms for dilute charged monolayers and discuss them in the light of our results and the predictions of Equations 7 and 8. 

The polystyrene latex particles carry a charge in aqueous solution resulting from the surface sulfate groups, and as mentioned the particle dispersions are stable. Particle monolayers can be formed at air/solution surfaces as well as at oil/solution interfaces. There is obviously an electrical double layer formed around the parts of the particle surface in contact with the aqueous phase. Lateral repulsions in the monolayer due to double-layer interactions can be screened by addition of inert electrolyte to the aqueous phase. Images of relatively dilute monolayers on 10 mM aqueous NaCl are depicted in Fig. 18. Monolayers at the air/0.01 M NaCl solution surface are much less ordered than those at the octane/solution interface, although there is very little particle aggregation. Monolayers at the octane/solution interface retain... 

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