Quantifying Structure-Property Relationships in Ferroelectric Polymers Toward High-Performance Soft Robots

Owing to their excellent electromechanical (EM) response, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))-based ferroelectric polymers (FEPs) are extensively utilized in soft actuators. Currently, the strain (S₃₃) of FEPs is mostly identified as electrostriction and described by S₃₃ = Q₃₃P². Wherein, Q₃₃ represents the electrostriction coefficient, P is polarization, and Q₃₃ is mainly derived from data fitting. However, this approach fails to establish a connection between the composition and structure of FEPs, hindering the design of FEPs with higher EM response performance. This study introduces an effective model that quantitatively correlates the structural parameter interplanar spacing (d) to the EM response, namely Q₃₃ = 100(Δd/d₀+1) × Q_33(s), where d₀ = 4.31 Å, Q_33(s) = -0.54 m⁴/C² are from single P(VDF-TrFE). Guided by this model, we tailored the electrical properties and d of FEPs by incorporating 1,5-Dihydroxy-2,2,3,3,4,4-Hexafluoropentane (HFPD), which results in a substantial improvement in the S₃₃ by up to 100%. The composite films show promising application in fabricating high-performance soft robots, including a biomimetic crawler (with a ultra-fast crawling speeds of 27 cm/s) and a biomimetic butterfly (with a thrust-to-weight ratio of 0.71). Overall, our findings offer new insights for designing FEPs with superior EM responses, potentially driving notable advancements in flexible actuators.