| dc.description.abstract | Polyvinyl alcohol (PVA) is a biocompatible and inexpensive nonionic polymer used in several industrial and pharmaceutical applications.1,2 One important property of the aqueous solutions of this polymer is the formation of hydrogels.3 These are usually obtained by lowering temperature.3 Although there is extensive fundamental research on PVA hydrogel materials, the formation and characterization of mesoscopic PVA hydrogels, i.e. PVA nanoparticles, in solution have hardly been explored. Here, we have successfully induced the formation of PVA nanoparticles by using aqueous salts. The choice of salts in our work was motivated by the extensive use of these additives to induce protein precipitation from aqueous solutions.4 Moreover, salts have been ranked according to their effectiveness in precipitating proteins. This ranking is known as the Hofmeister series.4 In this series, sulfates and chlorides are known to be strong and mild precipitating agents respectively. On the other hand, thiocyanates are known to protect proteins from precipitation. In our experiments with PVA, we found that Na2SO4 induces extensive macroscopic aggregation of this polymer in water. On the other hand, no aggregation was observed in the presence of NaSCN. Interestingly, in the case of NaCl, a slow PVA aggregation process occurred, leading to the formation of opaque samples. The NaCl-induced aggregation of PVA was investigated using Dynamic Light Scattering (DLS). Our results revealed that PVA-water solutions contain a small amount of aggregates with radius of 30 nm. In the presence of NaCl, these aggregates grow and reach a radius of about 100 nm. To explain our experimental findings a quantitative kinetic model was developed. | |
