|M.Sc Student||Krasovitski Elena|
|Subject||The Effect of Salts on a Polymer in Aqueous Solution|
|Department||Department of Chemical Engineering||Supervisor||Professor Yachin Cohen|
Poly(N-Isopropylacrylamide) (PNIPA) in aqueous solution possesses a unique property of thermosensitive phase separation. Due to this feature of PNIPA, this polymer became attractive for such applications as immobilization of enzymes, recyclable and size-selective absorbents. Since PNIPA has group components similar to polypeptides, it is used as a temperature and pH responsive system in drug delivery and actuators. The main objective of this work was characterization of the combined effect of salt type and concentration on the microstructure of PNIPA in dilute and semi-dilute solutions. The microstructure of the polymer systems in semi-solutions in the presence of different solutes (Na2SO4 and NaSCN) was studied using Small Angle X-ray Scattering (SAXS) technique. Dynamic and Static Laser Light Scattering techniques (LLS) were utilized for characterization of dilute solutions of PNIPA. The hydrodynamic radius and radius of gyration in the aqueous solutions of PNIPA in the presence of salts (Na2SO4 and NaSCN) were estimated. Microgel swelling of PNIPA in aqueous solution in the presence of Na2SO4 and NaSCN was observed using light microscope. It was found that Na2SO4 reduces the radius of gyration of PNIPA whereas NaSCN increases it, in accord with their effect on the cloud point of PNIPA solutions and their position in the lyotropic (Hoffmeister) series. SAXS measurements from semi-dilute solutions containing Na2SO4 did not conform to the usual Lorentzian form, and indicated the existence of nano-scale aggregates even below the phase transition temperature.