Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin–Silica Nanoparticles Interface

Abstract

The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin–filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC-active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol-ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m−3) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin-based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin–filler interface.

Light‐Activated Stress Relaxation, Toughness Improvement, and Photoinduced Reversal of Physical Aging in Glassy Polymer Networks

“…[ 4,5 ] One highly efficient CAN chemistry is the reversible addition fragmentation chain transfer (RAFT) process [ 6,7 ] that has enabled applications including surface patterning, [ 8–10 ] self‐healing, [ 11 ] photoinduced shape shifting, [ 12 ] and toughening of thermosetting composites. [ 13–15 ] Despite its significant industrial potential, [ 4 ] the incorporation of dynamic covalent chemistry (DCC) into conventional thermosets has been largely limited to relaxation in the rubbery state at temperatures well above the glass transition temperature ( T g ). [ 16 ] Recently, progress has been made in designing thermosets that possess catalyst‐free, low‐temperature dynamic properties.…”

“…This level of stress relaxation in the glassy state is unprecedented for similar thermosets. Without the bond‐exchange process, typical glassy polymers normally relax 10–20% stress in their glassy state, [ 7,13,37 ] as evidenced in the control CuAAC systems where only 20–25% stress relaxation is observed. The presence of the RAFT moieties enhanced the stress relaxation by 2–4 times when compared with the corresponding control CuAAC system.…”

Regeneration of β‐Cyclodextrin Based Membrane by Photodynamic Disulfide Exchange — Steroid Hormone Removal from Water

“…Dynamic covalent chemistry based on reversible covalent bonding provides a versatile and powerful platform for dynamic manipulation and regeneration of surface properties. [ 31–33 ] Among them, disulfide bonds are of special interests as they can reversibly form and break under certain external stimuli such as light or pH. [ 34–36 ] We show that the photodynamic nature of disulfide bonds enables the UV induced release and reattachment of β‐CD ligands on the membrane surface after each adsorption cycle, thus conferring the affinity membrane with excellent regeneration properties ( Figure ).…”

Low‐shrinkage‐stress nanocomposite: An insight into shrinkage stress, antibacterial, and ion release properties

“…Previous efforts have been dedicated to improving the monomers and polymerization mechanisms. 11,12 The present study investigated a new resin system containing urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE) monomers. 13 UDMA, a high viscosity methacrylate-derivative monomer, has good mechanical performance and higher degree of conversion than Bisphenol A glycidyl dimethacrylate (Bis-GMA) or ethoxylated bisphenol A dimethacrylate (EBPADMA).…”