| The properties of polymer networks on soil aggregates were studied both indirectly and directly. First, the properties of pure, hydrated polymer networks, or gels, to represent the adsorbed polymer network counterparts were tested since it is extremely difficult to test these networks in situ. Using membrane theory, it was determined that a 1 μm thick polymer layer, having the mechanical properties of the polyacrylamide compositions tested, on an a 1 mm diameter aggregate can support a range of maximum internal pressures from 0.046 to 2.5 kPa. Second, the atomic force microscope with a modified cantilever was used to directly probe actual adsorbed polymer networks. A new technique was developed that allowed the instrument to perform accurate force/approach curves between samples that are not atomically flat. This is an important new development as atomically flat samples are usually a prerequisite for atomic force microscopy. A range of maximum internal pressures (0.01–0.91 Pa) that the networks can apply to aggregates is reported. The observed difference between maximum internal pressures observed in the gel measurements and those obtained with the atomic force microscope indicates that the super-molecular structure of the adsorbed polymer network does not resemble that of bulk polyacrylamide or gellan gels. Rather, the nature of the ionic cross-links and the entanglements of the adsorbed networks are quite different than bulk gels and require more study into the nature of the network formation. |
