Free-evolution kinetics in a high-swelling polymeric hydrogel.

We employ nuclear magnetic resonance microimaging to study the kinetics of a high-swelling ionic polymer gel. This includes the time evolution of the sphere diameter and also the evolution of the swollen-unswollen boundary. The experimental results for spherical ionic polyacrylamide gels are compared with the predictions of a nonlinear poroelastic theory by numerically solving the equations for the evolution.

Morphology and dynamics of craterlike structures created by recoiling elongated particles.

We study the morphology and dynamics of craterlike structures formed when free-falling, randomly oriented, elongated particles bounce off a flat surface in a single particle scattering mode. The origin of a sharply defined rim with its associated structure, the factors determining the rim diameter, and the scaling of the diameter with impact velocity are examined. The probability distribution of rebounding particle ranges is calculated for a particular example and shown to provide a precursor description of structure formation.

Intercalated water in synthetic fluorhectorite clay.

(7)Li and (1)H nuclear magnetic resonance together with X-ray diffraction measurements in powdered samples and pseudocrystalline films of synthetic fluorhectorite as a function of relative ambient humidity permit to address several aspects of the structure and dynamics of intercalated water molecules. The role of proton exchange as a possibly dominant mechanism of charge transport in the one-water layer regime of hydration is reexamined. The experimental results in Li-fluorhectorite support the result of molecular simulations which predict, for Li-montmorillonite, the existence of an intermediate regime, between one-water layer and two-water layer states.

The isotropic-nematic interface in suspensions of Na-fluorohectorite synthetic clay.

Colloidal suspensions of Na-fluorohectorite synthetic clay platelets in saline water exhibit coexisting isotropic and nematic phases, due to gravitational separation of the polydisperse particles. We study the ordering of the platelets at the interfaces between various coexisting phases. Four different experimental techniques are employed: visual observation of birefringence, synchrotron wide angle and small-angle X-ray scattering, and magnetic resonance imaging.

Fluid imbibition in paper fibers: precursor front.

We employ nuclear magnetic resonance imaging to study water penetration in cylindrical blocks of unsized paper prepared under different molding pressures. From the measured kinetics of the imbibition profiles, we determine the dependence of the effective transport diffusivity upon degree of saturation of the pores by the penetrating fluid. In general, the transport process is found to be non-Fickian and we discuss different methods of data analysis adapted to this situation.