The uncharged temperature responsive polymer MHEC-g-PNIPAAM (modified hydroxyethylcellulose graft poly(N-isopropylacrylamide)), and its anionic analogue were characterized by the aid of dynamic light scattering (DLS), rheology, turbidity and rheo-small angle light scattering (rheo-SALS). The temperature sensitive PNIPAAM groups cause intramolecular associations in the system at elevated temperatures. At low concentrations (0.02 wt% - 0.5 wt%), DLS and turbidity was used to measure the complex interactions as the temperature was increased. The DLS data show that at low temperatures, the relaxation process is bimodal for all concentrations of the charged polymer, while above the lower critical solution temperature (LCST) only one mode has been observed. For the neutral polymer, a bimodal relaxation process has been detected up to 0.3 wt % below LCST. At higher polymer concentrations and above LCST only one mode is evident. The general feature for all polymer concentrations is the marked contraction of the polymer clusters at moderate temperatures, most visible at the LCST. After the LCST, the cluster sizes gradually increase for charged polymer while the neutral polymer gradually reduces the cluster sizes. The turbidity increases as the radius of the aggregates decrease.
Viscosity enhancements were observed for semidilute samples (0.5 wt%-5 wt%) around LCST. The light scattering pattern from rheo-SALS reveals that the system reorganize at elevated temperatures both in the presence and absence of shear forces. It is also shown that when a shear force is applied to the system, the neutral polymer has a random organization throughout the whole considered temperature region, while the charged polymer is anisotropic around LCST in the presence of shear forces.