Transition in solution dynamics of polyacrylic acid: An interplay between nonergodicity and triple mode relaxation

Abstract Dynamic light scattering (DLS) measurements have been performed on the polyacrylic acid (PAA) to investigate the polyelectrolyte effect on its solution dynamics. Viscosity measurements confirm the solution to be in the nondilute regime. The polyelectrolyte impacts are contrasted by using two solution pHs, five electrolyte concentrations, and in each with four different polymer concentrations. An interesting ergodic nonergodic ergodic transitions are being observed with variation in solution pH and electrolyte concentrations, which is directly coupled to a similar transition between bi‐modal and triple mode relaxation. The partial heterodyne method is used to analyze the DLS data exhibiting nonergodicity; otherwise, the standard Siegert relation is being employed. For the new third mode of relaxation, in addition to the conventional fast and slow mode, a novel term of nonergodic mode being coined because of a direct association between its presence with the sample becoming nonergodic. The fast relaxation time being analyzed through Rouse model and both the nonergodic and slow relaxation time show a monotonous increase with rise in polymer concentration. The stretched exponent , a measure of inhomogeneity, decreases with increase in solution pH and polymer concentration while increases with the addition of salt to the solution.