Quantifying the Contribution of Intrachain Conformational Locking to Covalent Hydrogel Mechanics

In covalently cross-linked hydrogel networks, physical associations and interchain entanglements are commonly treated as noncovalent cross-links contributing to network mechanics. Here, we propose that, beyond these interchain effects, a mechanically relevant contribution may arise from conformational locking within polymer strands between adjacent chemical cross-linking points. Using a solvent-exchange strategy in chemically cross-linked poly(acrylic acid) hydrogels, we selectively suppress weak interactions without altering the covalent network topology, enabling isolation of these local intrachain constraints. Weak interactions can stabilize locally folded conformations within cross-link-to-cross-link segments, temporarily sequestering portions of load-bearing strands and reducing their mechanical participation under small deformation. This effect is termed intrachain conformational locking (InCL). Although the fraction of InCL is small, their systematic modulation can lead to measurable changes in macroscopic mechanical responses. An Ω-chain model is introduced to rationalize how the release of InCL-associated hidden length contributes to network deformation.