(597e) Nano-Structured Functional Poly(Vinyl Pyrrolidone) Hydrogels Synthesized by Ionizing Irradiation

Nano-gel structures of poly(vinyl pyrrolidone) (PVP) by ionizing irradiation were synthesized and compared at various dose rates and radiation temperatures. The destruction of hydrogen bonds between PVP molecules and water at high temperature leads to the collapse of the molecular conformation. Pulsed electron beam irradiation at high repetition rate generates several carbon-centered free radicals along the same polymeric chain simultaneously and enhances the intra-crosslinking radical reactions. Smaller nano-gel particles with hydrodynamic radius (R_h) value of 12 nm were attained at higher pulse repetition rate (300 pulses per second). From the pulse radiolysis experiments, the second order reaction rate constants (2k) of PVP radical recombination are determined ca. 1.0 ? 3.0 x 10⁹ L mol^-1 s^-1 (PVP-H, ε_{390 nm} = 510 ± 30 L mol^-1 cm^-1). The activation energy (E_a) of this reaction is calculated from the Arrhenius plot of PVP radical decay rate constants at the series of temperatures and represents the different rate-determining mechanism in low and high temperature regions. The R_h of radiolytically produced hydrogel nano-particles was measured from the dynamic light scattering (DLS) experiments. The molecular weight and distribution were analyzed with asymmetric flow field flow fractionation (AFFF) chromatography method. Atomic force microscopy (AFM) was used to investigate the morphology of the synthesized nano-hydrogels. In addition, the nano-gel structure was synthesized using relatively low dose-rate radiation and nano-porous membrane, whereby the PVP molecules were sterically confined. An overview of the methods will be presented, along with a discussion on the effects of temperature and pulse repetition rate on the crosslinking yields and physical dimension (R_h) of the products.