Change in Free Volume Parameters of Polyacrylamide Gels Studied by Positron Annihilation Lifetime Measurement

Investigation of Interfacial Interaction and Microstructure for Epoxy/CNTs Nanocomposites by PALS

“…5 clearly reveals that in glassy state (160 K), spectra are described by a single o-Ps lifetime, τ 3 ; but in rubbery state (303 K and 323 K), two well-separated o-Ps lifetimes were observed. This phenomenon was observed in other polymer composites [5,9]…”

Free-volume change in volume phase transition of polyacrylamide gel as studied by positron annihilation: Salt dependence

“…It is expected that a density fluctuation of the gel network results in both of the swollen and the collapsed phases nanoscopically, then affects the free-volume distribution. Similar results are found for the PAAm gel during the VPT in response to changes of solvent composition 44 and pH. 53 On the other hand, a pronounced broadening of the size distribution at a NaCl concentration of 1M suggests that the nanoscopic environment of the PAAm gel may be highly inhomogenized due to a strongly aggregated gel network with an increase of a shielding effect by sodium ions.…”

“…Dependence of the free-volume size of the swollen gel on NaCl concentration is not observed, and an extrapolated value to the NaCl concentration of zero coincides with the radius size of the swollen PAAm gel at the corresponding acetone content (60 vol % ϭ 27 mol %). 44 The slightly reduced free-volume size for the PAAm gel may indicate same evidence that the freevolume radius of the PAAm gel containing 4 mol % of carboxylate anion is smaller than that of the mixed solvent at just lower acetone concentration than the VPT point. 44 It somewhat seems to reflect a compositional change inside the gel due to the preferential sorption of water.…”

“…44 It somewhat seems to reflect a compositional change inside the gel due to the preferential sorption of water. However, the free-volume size of the gel significantly decreases, and the free-volume distribution becomes broader with an increase of acetone concentration up to the VPT point, 44 implying not only the compositional change of the swelling solvent in the gel, but also a change of something due to another factor. The difference of the free-volume size between the swollen gel and the mixed solvent lead us to infer that the change in the nanoscopic environment of the PAAm gel may occur near the macroscopic VPT point.…”