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  • 1 The University of Tokyo Research Center for Advanced Science and Technology 4-6-1 Komaba, Meguro-ku 153 Tokyo (Japan)
  • 2 The University of Tokyo Graduate School of Engineering 7-3-1 Hongo, Bunkyo-ku 113 Tokyo (Japan)
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Discontinuous and continuous volume phase transitions of organic polymer hydrogels, such as polyacrylamide (PAAm) and poly(N-isopropylamide) (PNIPA) gels, uponpH and temperature were studied by the positron annihilation lifetime measurement, which allows the estimation of size, intensity and size distribution of the free volume. Microscopic changes of physical and chemical interactions between gel network and solvent molecules and among conjugated solvent molecules at volume phase transitions of polyacrylamide gels were discussed.