Silicone Phase Behavior Resolves the Softness–Surface Functionality Trade‐Off in Emerging Stretchable Electronics

ABSTRACT Skin‐like stretchable electronics are constrained by a persistent trade‐off: ultrasoft silicone elastomers achieve exceptional mechanical compliance by incorporating low‐molecular‐weight softening species, but these same species migrate to the surface and interfere with plasma oxidation and functionalization. Removing these additives by solvent extraction typically diminishes softness and stretchability, whereas silicones that readily support plasma modification, such as polydimethylsiloxane (PDMS), are intrinsically stiffer and less compliant. This work shows that solvent extraction of the ultrasoft platinum‐cured silicone elastomer Mold Star surprisingly increases both extensibility and surface reactivity. Native Mold Star contains a dispersed low‐molecular‐weight phase that disrupts mechanical cohesion, passivates the surface, and obscures the nanoscale morphology of the elastomer. Extraction removes this phase, enabling robust plasma modification and metal adhesion. These changes fundamentally alter interfacial performance: e‐beam‐deposited gold delaminates, and electroless plating fails on native Mold Star, whereas extracted Mold Star supports adherent evaporated films and electroless Ni/Au coatings that remain conductive up to 80% strain. These findings establish control over the phase behavior of low‐molecular‐weight species as a powerful design principle for uniting softness and surface functionality in silicone elastomers for the next generation of electronic skins and bio‐integrated devices.