Molecules are often assembled by themselves with a large aspect ratio, leading to the formation of network structure based on their entanglements. Such systems, so-called "supramolecular network systems" possess hierarchical structure with various length scales ranging from nanometer to micrometer. Thus, to give a better understanding of dynamics for the supramolecular network systems, it is necessary to examine the structure and physical properties at various length scales, and clarify the correlation. By using optical tweezers and particle tracking techniques, we here show the local rheological properties in a worm-like micelle solution and a supramolecular hydrogel, which are formed by the networks based on the self-assembly of the amphiphilic molecules in water. In these techniques, viscoelastic information can be accessed on the basis of the movement of probe particles dispersed in a sample to be measured. For the worm-like micelle solution, we found that the viscoelastic functions (G′ and G″ ) varied depending on the location measured and the location-dependent variation of G′ and G″ was observed only at the measurement timescale being shorter than the relaxation time. This can be understood by taking into account that there exists a concentration fluctuation in the solution. Such fluctuation can be regard as a spatial heterogeneity when one takes a snapshot of the solution at a time shorter than the relaxation time. Also, the heterogeneity in the rheological properties was observed in a sol obtained by physically disrupting the supramolecular hydrogel. The extent of the heterogeneity decreased as a solto-gel transition proceeded. Such homogenization was associated with the change in the network structure rather than that in the molecular assembled state, which remains comparable in the sol and gel.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering