Deswelling of Poly(N-isopropylacrylamide) Derived Hydrogels and Their Nanocomposites with Iron Oxide Nanoparticles As Revealed by X-ray Photon Correlation Spectroscopy

Here we present results on the deswelling behavior of semi-interpenetrating polymer hydrogels of sodium alginate and poly( N -isopropylacrylamide) (PNIPAAm) containing iron oxide nanoparticles by means of X-ray photon correlation spectroscopy (XPCS). The experiments were carried out as a function of temperature starting from temperatures below the low critical solution temperature (LCST) of the materials to temperatures above their LCST. The hydrogels present a hyper-diffusive dynamics of similar nature as that found for the freeze-dried aerogels which has been attributed to their characteristic porous structure. The dynamics of the swollen samples is faster than that of the freeze-dried ones suggesting that water has an effect in accelerating the dynamics of the hydrogels. XPCS has been used to characterize the deswelling process as a function of temperature. Deswelling times for the different samples correlate well with the corresponding relaxation times of the relaxation processes measured by XPCS.