PVP superabsorbent nanogels

Monomer free hydrogel nanoparticles (nanogels) were prepared by crosslinking preformed poly(N-vinyl-2-pyrrolidone) (PVP) entrapped in the aqueous pool of hexadecyltrimethylammonium bromide reverse micelles using the Fenton reaction. The PVP nanoparticles were spherical with a dry diameter of 27 nm. The diameter of the swollen particles was ten times higher, i.e., a swelling ratio, Q, above 900, characterizing this preparation as superabsorbent. PVP nanogel swelling was dependent on bound Fe3+ and varied with pH and ionic strength. Nanogel deswelling by salt followed the anions lyotropic series, i.e., SCN- < HSO3- < NO3- < I- < Cl- < CH3COO- < CF3SO3-. The value of Q reached 6,000 in iron-free PVP nanoparticles at low pH, making this nanogel one of the most efficient swelling systems so far described.