title: Freezing Molecular Orientation under Stretch for High Mechanical Strength but Anisotropic Hydrogels.
abstract: The poor mechanical strength of hydrogels has largely limited their wide applications, and improving hydrogels' mechanical strength is a hot and important topic in the hydrogel research field. Although many successful strategies have been proposed to improve hydrogels' mechanical strength during the past decades, a hydrogel with a tensile stress surpassing dozens of mega Pascal is desirable, yet still a big challenge. To address this issue, the Fe(3+) -mediated physical crosslinking formed under stretch conditions was employed in a chemically crosslinked poly (acrylamide-co-acrylic acid) network to achieve a dual-crosslinked hydrogel. The expected molecular orientation occurs under stretch and allows the maximumu chelating interaction between pendant carboxylic anions and Fe(3+) and molecules conformation being frozen, leading to the mechanical strength improving dramatically. As a result, an unprecedentedly high mechanical strength, but anisotropic dual-crosslinked hydrogel was obtained. By optimizing the experimental parameters, the nominal tensile stress along pre-stretching direction can reach as high as ≈40 MPa with elastic modulus of ≈40 MPa at large strain (>200%). In addition, the molecular orientation also leads to big difference of mechanical performance between parallel and perpendicular direction.
authors.affiliation: State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Lin
authors.affiliation: State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.
authors.forename: Xiaolong
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Yu
authors.affiliation: State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhou
mesh_terms: D016880:Anisotropy; D005615:Freezing; D020100:Hydrogels / Q000737:chemistry*; D013718:Tensile Strength
chemical_list: D020100:Hydrogels
keywords: anisotropy; hydrogels; molecular orientation; prestretch; ultra-high strength