Aggregation behaviour of polygalacturonic acid in aqueous solution

Static and dynamic light scattering techniques have been used to study the aggregation behaviour of polygalacturonic acid (PG) in aqueous solution at different pH values. The dependence of apparent molecular weight, radius of gyration and hydrodynamic radius with time or concentration have been determined. Other structural parameters as contour length, Kuhn segment numbers, mass per unit length, persistence length, and average number of chains per cross section have been deduced from Casassa–Holtzer plots. The weight average molecular weight increases linearly with time suggesting that the aggregation kinetics follows a simple Smoluchowski equation in which all the kernels are identical, the aggregation rate being approximately two chains per day at pH 3.83. As a consequence of this growth the polydispersity of the aggregates increases with time. The growth of the hydrodynamic radius with time suggests that no water molecules remain trapped in the aggregate, explaining why the PG does not gel.