For decades, inorganic fillers have been introduced into polymer resins to form composites with mechanical properties that combine desired physical and mechanical properties of the constituent phases. However, due to the common mismatch in mechanical moduli, the interface between constituent materials is a primary locus for crack nucleation due to stress concentration. Herein, a novel adaptive interface (AI) is introduced to improve material mechanical performance by coupling moieties capable of Dynamic Covalent Chemistry (DCC) to the resin-filler interface as a means to induce interfacial stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with allyl sulfide or thioester containing silane that through DCC mechanisms can promote resin-filler bonding and localized interfacial stress relaxation. Employing this active, bond-exchanging interface imparts significant benefits to the composite performance; including improvements in toughness, polymerization shrinkage stress and enabling self-healing of interfaces during loading. In situ activation of DCC bonds in allyl sulfide based composites results in 70 % stress relaxation and three times higher fracture toughness relative to otherwise identical composites that possess similar silane structure, but without the DCC moiety. Similarly, active-thiol thioester exchange at the composite’s interface dramatically affects the fracture toughness of these materials, exhibiting significantly higher fracture toughness (4.4 MNm-3/2) than the control composite (2.7 MNm-3/2). This improvement in mechanical performance that results from the successful relaxation of interfacial stresses, is a platform technology that will broadly impact the field of polymeric composites.

Development of tougher polymer composites through interfacial stress relaxation

2019 Fall National Meeting

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