Dilute Solution Properties of Sodium Polyacrylate

As early as 1951, Flory and Osterheld [18] could show that partially ionized polyacrylic acid in aqueous solution of an inert salt shrinks in size if the concentration of the inert salt is increased. This shrinking process can be pushed towards the unperturbed dimensions of the NaPA chains. Known from neutral polymers as 0-state, it is reached for fully ionized NaPA [50] at T=15 °C and 1.5 M KBr. In several papers, the dependence of the intrinsic viscosity was investigated as a function of the molar mass [51]. Data were 

In a first step, appropriate solvent conditions were established. This was achieved by investigating a single sample at Mw=3.3xl06 g/mol as a function of the NaCl content. The latter acts as an inert salt and screens the electrostatic interactions. Results are summarized in Fig. 6. 

The second virial coefficient decreases from a value of A2=6.5 10 3 molmL/g2 at 0.1 M NaCl to a value of A2 0 at 1.5 M NaCl. At the same 

Based on these indications, 0.1 M NaCl and 1.5 M NaCl were selected for measurement of the molar mass dependences of the light scattering parameters under two limiting solvent conditions respectively. The following scaling laws were found  

Clearly, the exponents offered further support for the assumed solvent conditions at 0.1 M NaCl and 1.5 M NaCl. Together with the results from the inert salt dependent experiments shown in Fig. 6, we were able to establish changes of size and shape of the NaPA chains which were induced by regular electrostatic screening effects. Now an important prerequisite has been met in order to successfully isolate and assess specific effects of multi-valent cations on these polyelctrolyte features in the presence of an additional inert salt. This will be discussed in Sect. 3.2. 

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