Structural characterization of ionic gelator studied by dynamic light scattering and small-angle neutron scattering.

Structural characterization of a hydrogel consisting of an oligomeric electrolyte, poly[pyridinium-1,4-diyliminocarbonyl-1,4-phenylenemethylene chloride] (1-Cl) as an ionic gelator was carried out by static and dynamic light scattering (SLS/DLS) and small-angle neutron scattering (SANS) techniques. All the measurements were performed by changing the concentration and temperature. We have successfully obtained the weight average molecular weight and the degree of polymerization of poly(1-Cl) by SLS. The sol-gel transition was clearly observed as large fluctuations in the scattering intensity of the time-intensity correlation function. Time correlation function of the scattering light intensity entailed a power law behavior at the sol-gel transition. 1-Cl hydrogel showed strong hysteresis and its hysteresis loop was observed both by DLS and theological methods. We have estimated the critical concentration of gelation and the gelation temperature by DLS. The enthalpy change for gelation was estimated to be ca. -10 kJ/mol. SANS experiments revealed that the unit structure of the gel network is responsible for the gelation of 1-Cl hydrogel.