Abstract
One of the central challenges in soft matter mechanics is to achieve reversible and programmable modulation of viscoelasticity in polymer-based elastomers at small strains, which is crucial for precision engineering and advanced functional devices. Conventional approaches are constrained by irreversibility and lack of dynamic control. In this study, it is demonstrated that ultrasonic vibration (19-22 kHz) enables dynamic, reversible, and tunable modulation of the mechanical response in such materials. Uniaxial compression experiments combined with constitutive and inverse modeling reveal a reversible transition from viscoelastic, dissipative behavior to an elastic-dominated, stable state. The standard linear solid (SLS) model links macroscopic mechanical changes to molecular-level dynamics, such as chain alignment and mobility. Experimentally, ultrasonic vibration suppresses viscoelastic relaxation and energy dissipation, induces negative hysteresis, and enables tunable, reversible hardening, all strongly dependent on vibration frequency and power. Quantitatively, a typical 20% increase in the instantaneous elastic modulus and over 80% reduction in the delayed elastic modulus and viscosity are achieved under ultrasonic vibration. These results clarify the mechanism by which ultrasonic vibration regulates viscoelasticity and provide practical guidance for designing adaptive polymer systems in applications such as ultrasonic-assisted polishing, soft robotics, and flexible electronics.