Assembling Vanadium(V) Oxide and Gelatin into Novel Bionanocomposites with Unexpected Rubber-like Properties

A new kind of bionanocomposites is prepared for the first time in soft conditions by a complex coacervation process and consists of an assembly of decavanadate polyanions and gelatin chains in triple helices and coils conformation. Before drying, well-defined homogeneous monoliths with a striking rubber-like behavior were obtained. These mechanical properties were thoroughly characterized by tensile measurements at large strain revealing a complex behavior (strain hardening, large hysteresis during cycling experiments, Mullins effect) associated with characteristics (E = 0.27 MPa, λbreak = 8.6, and σbreak = 1.4 MPa) that were never reported for gelatin based materials. These results were discussed in the frame of classical biopolymer-based materials and in the emerging field of rubbery polyelectrolyte hydrogels. Compared to gelatin based composites which depict a ductile behavior, the improved strain properties of decavanadate-gelatin composite may be attributed to an adequate gelatin triple helices/coils ratio which depends strongly on gelatin concentration, aging time, temperature, and also on the charge matching between decavanadate and gelatin. Upon aging, the nucleation and growth of V2O5 ribbon like particles occurs in situ in the gelatin matrix that exerts a significant control on vanadium condensation from a kinetics and structural point of view.