Nanostructures of polyelectrolyte gel-surfactant complexes in uniaxially stretched networks

Nanostructures of poly(acrylate) gel and dodecylpyridinium complexes equlibrated with the NaCl aqueous solution (from 5 to 100mM) and their time evolution after stretching uniaxially were investigated by means of time-resolved small-angle x-ray scattering. The scattering profile revealed the existence of the cubic nanostructure belonging to Pm3n space group in the gel before and long after the stretch. Each of the three intensive peaks was found to be resolved into two, which suggested the existence of two cubic structures with the slightly different lattice spacings. On the other hand, the splits of scattering peaks were not observed for the linear poly(acrylate) and dodecylpyridinium complexes. This indicates that the existence of the cross-linked chain is concerned in the formation of the double structure in the complex system. A series of time-resolved experiments demonstrated that the peaks corresponding to the longer lattice constant disappeared once just after stretching and regenerated to grow up, whereas the peaks corresponding to the shorter lattice constant were continuously observed. The growing rates of the peaks increased with the NaCl concentration. It was also found that a two-dimensional scattering pattern changed from the Debye-Scherrer ring type into the Laue spot type with stretching at the lower NaCl concentrations. This indicates that the single-crystal-like domains align in the stretched network due to the strong electrostatic interaction between the dodecylpyridinium cation and poly(acrylate) anion.