The Internal Network Dynamics of Poly(NIPAM) Based Copolymer Micro- and Macrogels: A Comparative Neutron Spin-Echo Study

Hertle Y, Zeiser M, Fouquet P, Maccarini M, Hellweg T. The Internal Network Dynamics of Poly(NIPAM) Based Copolymer Micro- and Macrogels: A Comparative Neutron Spin-Echo Study. Zeitschrift für Physikalische Chemie. 2014;228(10-12):1053-1075.Microgels are generally synthesised above the lower critical solution temperature (LCST) of the used polymer (poly(N-isopropyl-acrylamide)(PNIPAM) in the present case) and there is evidence that, due to the "bad" solvent conditions and due to the differences in reactivity between the monomers and the crosslinker, an inhomogeneous crosslinker distribution in the network is created. In contrast, macrogels are statistically crosslinked, because they are polymerised below the LCST (good solvent conditions). With the neutron spin-echo (NSE) technique, the diffusion of the polymer network on a local length scale can be studied. Due to essentially different crosslinker distributions in the micro-and macrogels, a difference in the collective diffusion of the network could be expected. However, the measured intermediate scattering functions of the studied micro-and macrogel are similar and can both be described by a single exponential decay without a q-dependent baseline. Hence, both systems behave pseudo-ergodically on the length scale available in the NSE experiment. A determination of the diffusion coefficient of the breathing mode D-G of the gel network and the dynamic correlation length xi leads to comparable values for the homologous micro-and macrogels. The studied microgels contain butenoic acid as comonomer and also the pH dependence of the network dynamics is investigated