title: Stretching-induced ion complexation in physical polyampholyte hydrogels.
abstract: Recently, we have developed a series of charge balanced polyampholyte (PA) physical hydrogels by random copolymerization in water, which show extraordinarily high toughness, self-healing ability and viscoelasticity. The excellent performance of PA hydrogels is ascribed to dynamic ionic bond formation through inter- and intra-chain interactions. The randomness results in ionic bonds of wide strength distribution, the strong bonds, which serve as permanent crosslinking, imparting the elasticity, while the weak bonds reversibly break and re-form, dissipating energy. In this work, we developed a simple physical method, called a pre-stretching method, to promote the performance of PA hydrogels. By imposing a pre-stretching on the sample in the as-prepared state, ion complexation during dialysis is prominently accelerated and the final performance is largely promoted. Further analysis suggests that the strong bond formation induced by pre-stretching is responsible for the change in final performance. Pre-stretching decreases the entropy of the system and increases the chain alignment, resulting in an increased possibility for strong bond formation.
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan. gong@mail.sci.hokudai.ac.jp.
authors.forename: Kunpeng
authors.initials: K
authors.lastname: Cui
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan. gong@mail.sci.hokudai.ac.jp and Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan.
authors.forename: Tao Lin
authors.initials: TL
authors.lastname: Sun
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan. gong@mail.sci.hokudai.ac.jp and Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kurokawa
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan. gong@mail.sci.hokudai.ac.jp and Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan.
authors.forename: Tasuku
authors.initials: T
authors.lastname: Nakajima
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan. gong@mail.sci.hokudai.ac.jp and Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nonoyama
authors.affiliation: Graduate School of Life Science, Hokkaido University, Sapporo, Japan.
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan. gong@mail.sci.hokudai.ac.jp and Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan.
authors.forename: Jian Ping
authors.initials: JP
authors.lastname: Gong