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, λ break = 8.6, and σ break = 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 V 2 O 5 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.