Swelling butylammonium vermiculite crystals

FIGURE 10.5 Schematic illustration of the swelling of n-butylammonium vermiculite in a 0.1 M n-butylammonium chloride solution (a) represents the n-butylammonium vermiculite crystal id =2 nm) prior to swelling, (b) the gel id =12 nm) formed by a homogeneous sixfold expansion in the range 0°C < T < 14°C, and (c) the tactoid formed when the gel collapses at T < 0°C or T > 14°C. In (c), the dashed line represents the fact that the tactoid structure occupies roughly the same volume as the gel structure. 

Figure 6. Butylammonium-vermiculite crystals before and after swelling in water (lateral dimensions of crystals approximately 2i x mm).

FIGURE 1.3 Butylammonium vermiculite (Kenya) crystals before and after swelling in water (lateral dimensions of the crystals approximately 2.5 x 2.5 mm). (Reproduced with kind permission of the Clay Minerals Society, from Garrett, W.G. and Walker, G.F., Clays Clay Min., 9, 557, 1962.)... 

The samples for the diffraction experiments were prepared as follows. A crystal of the n-butylammonium vermiculite was cut to a thickness of about 0.5 mm and an area of about 5x5 mm and soaked in the appropriate solution of protonated n-butylammonium chloride in D20. DzO was used because it gave a lower incoherent-scattering background than H20. The gel was allowed to come to its equilibrium swelling distance for 48 hours in a cold room at a temperature of 7°C. A slice of this swollen gel about 1 mm thick was then transferred to a quartz cell of internal dimensions 30 x 5 x 2 mm. The remainder of the quartz cell was filled with some of the original solution. The cell was sealed with Parafilm to prevent loss of solution by evaporation, clamped into an aluminum block, as shown in Figure 1.5, and... 

For these experiments, some of which were also conducted on the ILL D17 small-angle diffractometer, crystals of n-butylammonium vermiculite exhibiting the fewest obvious structural defects were selected and trimmed to a rectangular cross section with a razor blade. This enabled the surface area, and therefore the applied pressure, to be measured accurately. The samples were then immersed in a dilute solution of n-butylammonium chloride of the desired concentration and allowed to swell freely. After equilibration for at least two days at 7°C, the swollen (or colloidal) gel phase samples were placed into the uniaxial pressure cell shown in Figure 3.1. 

Solutions of the required volume fraction of PVME were prepared by dissolving a known mass of the polymer (p = 1.03 g/cm3) in a known volume of a 0.1 M n-butylammonium chloride solution, itself prepared by dissolving a known mass of n-butylammonium chloride in D20. The clay crystals were prepared as described previously [5], After weighing, a single vermiculite crystal was placed in a quartz sample cell of dimensions 1 x 1 x 4.5 cm, and an appropriate amount of the polymer solution (typically 2.5 cm3) was added to prepare an r = 0.01 sample. The sample cells were identical to those used in the experiments on the LOQ instrument (ISIS, Didcot, U.K.) described in Chapter 5. As usual, the cells were sealed with parafilm and allowed to stand at 7°C for two weeks prior to the neutron scattering experiments to ensure that equilibrium swelling had been achieved [5],... 

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