Abstract
The microporous polyvinylidene fluoride (PVDF) membranes were prepared by the solvent evaporation method using 50 wt.% of different pore-forming additives: poly(1-ethyl-3-vinylimidazolium tetrafluoroborate) (PIL-BF4), polyethylene glycol 3000 (PEG-3K) and 40000 (PEG-40K), dibutyl phthalate (DBP). The influence of used additive on morphology, porosity, degree of crystallinity, tensile properties, electrolyte uptake and ionic conductivity of the membranes were investigated. The maximum electrolyte uptake of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) was 184 wt.% for the membrane prepared with PEG-40K, however, the membrane was fragile and unsuitable for practical use. The remaining membranes showed approximately the same porosity (45‒48%) and electrolyte uptakes (169‒175%). At the same time, the membranes significantly differed in mechanical properties and ionic conductivity. The membrane prepared with PIL-BF4, unlike others, has a sponge-like structure and demonstrated high mechanical properties, namely tensile strength is 17.7 MPa and fracture strain is 132.5%. Bucky gel actuators were fabricated using membranes prepared with different additives. The blocking force of the actuators based on membranes with different additives decreased in the sequence of PIL-BF4, DBP and PEG. The actuator based on the membrane prepared with PIL-BF4 demonstrates a blocking force of 5.7 mN and a deformation of 1.35 % at 3 V DC.
Highlights
Polyvinylidene fluoride (PVDF) and its comonomers are of the most studied and common polymers for membrane manufacturing
The membranes prepared with polyethylene glycol (PEG) and dibutyl phthalate (DBP) have interconnected spherulite structure and the radius of the spherical fragments depends on the additive
Microporous PVDF membranes were prepared via dry-cast technique from DMF solution using different pore-forming additives, namely PILBF4, DBP, PEG-3K and PEG-40K
Summary
Polyvinylidene fluoride (PVDF) and its comonomers are of the most studied and common polymers for membrane manufacturing. A polymer gel electrolyte (PGE) is prepared by dry PVDF membrane saturation in the electrolyte. The high ionic conductivity, thermal and chemical stability, a wide electrochemical window are the unique properties of ionic liquids (ILs), making them a good alternative to aqueous or solid electrolytes to prepare PGEs. Polymer gel electrolytes based on IL demonstrate room temperature conductivity above 10-3 S/cm, which is enough for practical use [25]. We demonstrated the effectiveness of using poly(1-ethyl-3-vinylimidazolium tetrafluoroborate) (PIL-BF4) as a pore-forming additive for the manufacture of a durable and highly porous PVDF membrane [28]. This study is focused on the comparison of different additives as a pore-former on the structure, mechanical and electrochemical properties of PVDF membranes, and the influence of the membrane properties on bucky-gel actuators performance
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