Stackable, covalently fused gels: Repair and composite formation

Combining modeling and experiment, we created multilayered gels where each layer was "stacked" on top of the other and covalently interconnected to form mechanically robust materials, which could integrate the properties of the individual layers. In this process, a solution of new initiator, monomer, and cross-linkers was introduced on top of the first gel, and these new components then underwent living (co)polymerization to form the subsequent layer. We simulated this process using dissipative particle dynamics (DPD) to isolate factors that affect the formation and binding of chemically identical gel as well as incompatible layers. Analysis indicates that the covalent bond formation between the different layers is primarily due to reactive chain-ends, rather than residual cross-linkers. In the complementary experiments, we synthesized multilayered gels using either free radical (FRP) or atom transfer radical polymerizations (ATRP) methods. Polymerization results demonstrated that chemically identical materials preserved their structural integrity independent of the polymerization method. For gels encompassing incompatible layers, the contribution of reactive chain-ends plays a particularly important role in the integrity of the material, as indicated by the more mechanically robust systems prepared by ATRP. These studies point to a new approach for combining chemically distinct components into one coherent, multifunctional material as well as an effective method for repairing severed gels.