Figure 2. Structure factor S ( q ) as a function of the dimensionless wavevector q D ( diameter D = 100 nm ) for samples: c sub p /c sub p* = 0.0 ( hard spheres, crosses ), 0.08 ( equilibrium fluid, squares ), and 0.10 ( Gel, triangles ), for the same phi and R sub g /R as Figure 1. Each subsequent data set is offset by 1 for clarity. Dotted lines show relevant baselines signifying S ( q ) = 0 for each data set. Solid lines are the zero-adjustable parameter PRISM-mPY theory predictions. The structure factor which depicts the packing of particles with respect to each other in solution is calculated from the data of Figure 1 by dividing the intensities of the respective suspensions by that of the form factor and then multiplying by the ratio of the volume fractions ( phi sub FormFactor / phi sub Sample = 0.02/0.4 ) [ 3, 4 ]. The location of the first peak ( q* ) in the structure factor shifts to higher q¡¯s as more polymer is added to the system indicating that the particles are getting closer to each other on an average. When the suspension gels, the particles are frozen in space and q* is constant with added polymer as one traverses deeper into the gel [ 3, 4 ]. The increased S ( 0 ) for the gel sample is indicative of increased compressibility in the system due to clustering of particles ( cluster size is approximately 5 dash C8 particle diameters ). The structure of the gels based on the calculated S ( q ) is hypothesized to consist of clusters of particles with randomly distributes voids which gives rise to the steep upturns in S ( q ) at low q [ 3, 4 ].
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