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

Abstract

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 -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 of the gel network and the dynamic correlation length 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.

Bulk Phase and Surface Dynamics of PEG Microgel Particles

“…The validity of this assumption was already demonstrated in NSE experiments on PNIPAM microgels. 23,24 As discussed above, the chosen high volume fraction of microgel particles allows to neglect the contribution of translational diffusion. Hence, the measured normalized intermediate scattering functions should completely decay to zero and S(Q,τ NSE )/S(Q,0) can be fitted by…”

“…23 A comparison of chemically identical PNIPAM micro-and macrogels revealed that the cooperative diffusion and the accociated dynamic correlation length are very similar. 24 Recent studies explored the influence of the cononsolvency on the dynamics. 25,26 Beside the cooperative diffusion, also Zimm-type dynamics at higher values of the momentum transfer Q were reported.…”

Looking inside Poly(N-isopropylacrylamide) Microgels: Nanomechanics and Dynamics at Solid–Liquid Interfaces

“…Hence, measurements of the polymer dynamics inside microgels can reveal additional information. As reported in the literature, neutron spin echo spectroscopy (NSE) is a suitable scattering technique to explore the dynamics in microgel dispersions and inside adsorbed microgel particles. − We employed neutron spin echo spectroscopy under grazing incidence (GINSES) to probe the internal dynamics of adsorbed PNIPAM-based microgels with comparatively high amounts of cross-linker (10 mol %). Microgel particles were prepared with a conventional batch method (“batch microgels”) and a continuous monomer feeding method (“feeding microgels”).…”

Static and dynamic behaviour of responsive graphene oxide–poly(N-isopropyl acrylamide) composite gels

“…It has proved to be an excellent tool for investigating dynamics in polymer gels. [40][41][42][43][44][45] It has been a fertile source of important new insights into polymer melt-silica nanocomposite systems, 46,47 but to our knowledge, no investigation of PNIPA hydrogel composite systems using NSE has yet been reported in the literature.…”