Effect of denaturant and polymer concentration on the structural and dynamical properties of aqueous solutions of poly(N-acetamido acrylamide)

Poly(N-acetamido acrylamide), PAAA, associates in aqueous solution. Dynamic and static light scattering and viscometry are employed to study this association in aqueous solution. The initial relaxation rate Omega(0) shows a q(3) dependence for PAAA in water (q is the magnitude of the scattering vector) even at concentrations as low as 0.03%. When this polymer is dissolved in 2 M aqueous sodium thiocyanate, only a diffusive (q(2)-dependent) relaxation mode is observed. The results of the reduced viscosity of very dilute PAAA-water solutions suggest the formation of clusters. Addition of sodium thiocyanate breaks up the clusters. From static light scattering of PAAA-water solutions, it is found that the fractal dimension increases with increasing polymer concentration. This indicates that the clusters become more compact at higher concentrations. This conjecture is supported by the viscosity results, where the reduced viscosity shows a large increase with concentration and passes through a well-pronounced maximum at c approximate to 0.05%.