Entropy-driven synthesis of super-soft, ultra-stretchable yet highly-tough low-topology-entropy silicone elastomers for on-skin wearable electronics

On-skin wearable electronics require substrate materials that are simultaneously ultra-soft, highly stretchable and mechanically robust – properties that conventional addition-cured silicone elastomers (SEs) cannot reconcile due to their inhomogeneously crosslinked, high-topology-entropy (HTE) networks. Here, we report an entropy-driven, multi-step strategy that transforms a commercial vinyl-functional polydimethylsiloxane (PDMS-V)/multi-hydride-functional polydimethylsiloxane (PDMS-H) blend into a low-topology-entropy silicone elastomer (LTE-SE). By sequentially swelling the precursors in non-volatile PDMS oil and volatile petroleum ether, polysiloxane coils were first entropically extended and then recoiled, while crosslinks were ‘frozen’ at nearly equidistant positions. The resulting solvent-free network exhibited an initial modulus of 0.24 MPa (≈8.4 times softer than the HTE control), an elongation at break of 1150% (≈3.5 times higher) and a toughness of 24 MJ m⁻³ (≈2.7 times higher). Beyond intrinsic mechanical gains, the ultra-soft PDMS oil-swelling SE enabled one-step, three-dimensional encapsulation of millimetre-scale electronics and remained soft, stretchable and electrically insulating. Functional fillers, such as TiO₂ nanoparticles, were dispersed without compromising softness, yielding a stretchable device that simultaneously senses, blocks and alerts against harmful UV radiation on the skin. This work establishes network-entropy engineering as a general route to reconcile the classical softness–strength dilemma of SEs and expands their application horizon in next-generation on-skin wearable electronics. An entropy-driven oil-swelling/solvent-recoil strategy that converts conventional PDMS into a low-topology-entropy silicone network with simultaneously ultra-soft, >1000% stretchable and highly tough performance features is successfully developed for 3D soft encapsulation of on-skin wearable electronics. • Entropy-driven multistep strategy unlocks super-soft (< 0.3 MPa), ultra-stretchable (> 1100%) yet highly tough (24 MJ m⁻³) silicone elastomers, breaking the long-standing softness-versus-strength trade-off in PDMS networks. • Low-topology-entropy (LTE) network formed via sequential “nonvolatile oil swelling/ in-situ hydrosilylation → Using volatile solvent to replace nonvolatile oil via solvent exchange → recoiling chain segments via the removal of solvent by air drying” delivers homogeneous crosslinkage, uniform strand lengths and high entanglement density. • Ultralow Young’s modulus and stretchable silicone elastomer (SE) matrix enables single-step 3-D soft encapsulation of millimetre-scale rigid electronics, retaining electrical insulation and mechanical integrity, ideal for skin-mounted circuits. • TiO₂-nanoparticle hybridisation functionalizes SEs and adds simultaneous UV shielding (≈ 98% at 365 nm), real-time sensing and audible alarm within the same stretchable patch, demonstrating facile, application-specific functionalisation of the ultrasoft platform. • Network-entropy engineering offers a general, scalable route to reconcile mechanical, electrical and functional demands of next-generation on-skin wearable electronics, soft robotics, and extreme-environment protective devices.