Nanoconfinement of Hydrophobic Domains Facilitates Strong Mesoscale Networks in Silk-Inspired Materials

Recombinant silks call for efficient sequence designs that maximize mechanical performance at a low molecular weight, which requires hydrophobic blocks to form nanoconfined crystals for cooperativity. Yet, it remains unclear how manipulating crystal size by drawing and tuning hydrophobic block length influences morphology. We address this question with molecular simulations that vary the hydrophobic block length in silk-like copolymers while fixing total chain length and hydrophobic/hydrophilic block ratios. We find that block length controls domain morphology and strength and toughness peak at a critical value of block length. A graph-based analysis, idealizing crystals as nodes and amorphous bridges as edges, indicates enhanced toughness when interdomain connectivity is both sufficient and evenly distributed, which is only possible when crystals are nanoscopic and strong. Distributed-connectivity through nanoconfinement emerges as a design rule that maximizes strength and toughness in molecular-weight-constrained recombinant silks, copolymers, and semicrystalline polymers.