Stress, uniaxial, macroions

Until we discovered the constancy of the surface potential from the uniaxial stress results, like most other people, I had been more interested in constant surface charge models. If you do not know how the valency of a macroion varies with the external conditions, it is reasonable to assume it to be constant unless given evidence to the contrary. Given the evidence that y/0 70 mV is roughly constant for the n-butylammonium vermiculite system, what other consequences follow from this In particular, what happens if we apply the coulombic attraction theory with the constant surface potential boundary condition ... 

Before moving on to how the structure of the dressed macroion (see Figure 8.5) depends on uniaxial stress and sol concentration as well as salt concentration, and... 

We now wish to examine how the structure of the dressed macroion, as determined by our diffuse neutron scattering experiments, varies with applied uniaxial stress. The best data was obtained at c = 0.03 M, with r < 0.01, when the uniaxial pressure p was varied between 0 and 0.2 atm a single experiment conducted over two days on D16 gave clear ripples at different applied stresses, as described below. As in the experiments at c = 0.1 and 0.01 M described above, T and P were held constant at 10°C and 1 atm, respectively. The details of the experiment and the small-angle patterns observed are given in reference [4], Here we concentrate on how applied uniaxial pressure affects the higher g-rangc of the structure factors. 

The main feature of Figure 8.8 is that the curves (b), (c) and (d), measured at p = 0, 0.04 and 0.07 atm, respectively, are very similar to each other. Comparison with Figure 8.3 also reveals that they are very similar to the corresponding curve obtained with c = 0.1-M H-salt, and the same structural analysis applies in each case. Before considering the details, it is clear that the dressed macroion structure is basically unaffected by uniaxial stress over the pressure regime studied. 

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