Publication date: 21 April 2017
Source:Polymer, Volume 115
Author(s): Ryosuke Mishima, Ayuka Nakao, Shinichi Sakurai, Kenji Urayama
An inherent structural nanoheterogeneity in statistical hydrogels leads to a peculiarity in macroscopic tensile properties. Some types of statistical hydrogels with considerable degrees of non-uniform distribution of cross-link, which are formed via free radical copolymerization of mono- and bi-functional monomers, are unusually extensible: The elongation at break before and after equilibrium swelling remains almost unchanged, although the gels undergo a significant increase in volume by swelling, i.e., a finite degree of pre-stretching of network strands. This peculiar extensibility emerges exclusively in uniaxial stretching whereas it is not observed in biaxial stretching including equi-biaxial and planar extension. The concentration ranges of the mono- and bi-functional monomers which result in the gels with the peculiar extensibility are revealed. The two-dimensional SAXS patterns of the uniaxially stretched swollen gels with marked extensibility show the presence of a spatially long-range structure of ca. 50 nm which results from the significantly non-affine deformation of the networks composed of densely and loosely cross-linked regions.
Graphical abstract
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