Bioinspired High-Strength Montmorillonite-Alginate Hybrid Film: The Effect of Different Divalent Metal Cation Crosslinking.

The natural nacre has a regular ordered layered structure of calcium carbonate tablets and ion crosslinking proteins stacked alternately, showing outstanding mechanical properties. Inspired by nacre, we fabricated different divalent metal cation-crosslinked montmorillonite-alginate hybrid films (MMT-ALG-X 2+ ; X 2+ = Cu 2+ , Cd 2+ , Ba 2+ , Ca 2+ , Ni 2+ , Co 2+ or Mn 2+ ). The effect of ionic crosslinking strength and hydrogen bond interaction on the mechanical properties of the nacre-mimetics was studied. With the cations affinities with ALG being increased (Mn 2+ < Co 2+ = Ni 2+ < Ca 2+ < Ba 2+ < Cd 2+ < Cu 2+ ), the tensile strength of nacre-mimetics showed two opposite influence trends: Weak ionic crosslinking (Mn 2+ , Co 2+ , Ni 2+ and Ca 2+ ) can synergize with hydrogen bonds to greatly increase the tensile properties of the sample; Strong ionic crosslinking (Ba 2+ , Cd 2+ , Cu 2+ ) and hydrogen bonding form a competitive relationship, resulting in a rapid decrease in mechanical properties. Mn 2+ crosslinking generates optimal strength of 288.0 ± 15.2 MPa with an ultimate strain of 5.35 ± 0.6%, obviously superior to natural nacre (135 MPa and 2%). These excellent mechanical properties arise from the optimum synergy of ion crosslinking and interfacial hydrogen bonds between crosslinked ALG and MMT nanosheets. In addition, these metal ion-crosslinked composite films show different colors, high visible transparency, and excellent UV shielding properties.