Relationship between the Morphology, Nanostructure, and Strength Properties of Aquivion® Type Perfluorinated Proton-Conducting Membranes Prepared by Casting from Solution

Orientational uniaxial stretching of proton conducting perfluorinated membranes

“…Our method for the synthesis of membrane copolymers of the Aquivion ® -type with or without using a modifying additive (5% perfluorinated hydrocarbon С 6 -С 10 ) allows the directed regulation of the chemical composition of the copolymer (in the range of equivalent weights EW = 700-1200 g mol À1 SO 3 H), which determines the electrochemical and mechanical properties of the membranes. 24,31,32 Aquivion ® -type membranes were produced from the obtained copolymers using two ways. According to the first method, the powder of the copolymer in the sulfonyl fluoride form was pressed in pre-prepared aluminum molds, providing a required film thickness of the membrane material.…”

“…Pressing modes were selected in the temperature range 250-300 C and pressure 23-25 MPa, taking into account the molecular characteristics of the copolymer (melt flow index (MFI) 0.01-0.6 g (10 min) À1 ) and the chemical composition of the copolymer (EW according to FTIR, EW FTIR = 660-990 g mol À1 ). The obtained films of the copolymer in the sulfonyl fluoride form were converted into sulfonic acid form of membranes using an optimized technology for the complete hydrolysis of all sulfonyl fluoride groups, similarly to Rolfi et al 33 According to the second method, membranes were obtained by casting from 2% to 3% solutions in DMF of copolymers of the Aquivion ® -type in sulfonic alkaline form, followed by heating and annealing to remove the solvent, according to the procedure described in Primachenko et al 24 Thus several membrane samples with different EW were prepared, named Sh-1, Sh-2, Sh-3, …, where "Sh" is a short for a term "short," meaning "short side chain. "…”

“…This is reflected in the electrochemical and mechanical properties of the original non-stretched membranes, giving an advantage to cast membranes over pressed ones. 24 We have investigated the effect of the composition of the copolymer (EW) on the electrochemical characteristics, structure, and morphology of oriented membranes. Comparison of the proton conductivity of oriented membranes of the Aquivion ® -type obtained by pressing (Table 1) shows that at the similar stretching degree of 300%, membrane with a higher EW-Sh-4 demonstrates an almost double relative increase in the value of proton conductivity compared to a membrane with lower EW-Sh-1 (37.9% for Sh-4 and 16% for Sh-1 in relation to the non-stretched membrane).…”

“…Similar conditions for the formation of optimal properties of Aquivion ® -type membranes obtained by casting from a solution in dimethylformamide (DMF) were confirmed by our data. 24 Among various methods for improving the mechanical properties of perfluorinated membranes, the method of orientational uniaxial stretching of membranes is of special interest. 25,26 Stretching can increase the crystallinity of the membrane, as well as change the morphology of the water-conducting channels, leading to a simplification (straightening) of proton transfer paths in the membrane and an increase in the proton conductivity of the membranes along the stretching direction.…”

State of the art and prospects in the development of proton‐conducting perfluorinated membranes with short side chains: A review

“…The influence of preparation conditions of Aquivion‐type membranes obtained by casting from N,N‐dimethylformamide solution on membrane morphology was studied 120 . The work on rationally selecting and controlling the conditions of solvent evaporation and the subsequent annealing resulted in producing the membranes with excellent physical‐mechanical properties and high proton conductivity at the optimal regime of preparation.…”