Sulfonic SiO2 nanocolloid doped perfluorosulfonic acid films with enhanced water uptake and inner channel for IPMC actuators

Abstract

This study provides a facile and effective strategy to fabricate sulfonic SiO2 nanocolloid (HSO3–SiO2) doped perfluorosulfonic acid (PFSA) films with enhanced water uptake and inner channel for high-performance and cost-effective ionic exchange polymer metal composite (IPMC) actuators. A commercial precursor of mercaptopropyl trimethoxysilane was hydrolyzed to form thiol functionalized SiO2 nanocolloids (SH–SiO2, ∼25 nm in diameter), which were further oxidized into sulfonic SiO2 nanocolloids (HSO3–SiO2, ∼14 nm in diameter). Both SiO2 nanocolloids were used as additives to dope PFSA film for fabricating IPMC-used matrix films. Due to difference of compatibility, the SH–SiO2 nanocolloids take phase separation in the cocrystallization course, and aggregate into huge, regular spherical particles with a mean diameter of ∼690 μm; while the HSO3–SiO2 nanocolloids are completely compatible with PFSA, forming a very homogeneous hybrid matrix film. Related physiochemical investigations by analytical tools revealed that, the resultant HSO3–SiO2 hybrid film shows better IPMC-related properties compared to the SH–SiO2 hybrid film: 1.59 folds in water uptake, and 2.37 folds in ion exchanging capacity, thus contains an increased number of cations and possesses larger and better interconnected inner channels for IPMC bending. Consequently, the HSO3–SiO2 hybrid IPMC actuator exhibits remarkably higher levels of actuation behaviours such as higher force output, higher displacement output, and longer stable working time, which could be used as a valuable artificial muscle for flexible actuators or displacement/vibration sensors at low cost.