Structure and Properties of Sulfonated Pentablock Terpolymer Films as a Function of Wet–Dry Cycles

Abstract

The structure and properties of poly(tert-butylstyrene-b-hydrogenated isoprene-b-sulfonated styrene-b-hydrogenated isoprene-b-tert-butylstyrene) (tBS-HI-SS-HI-tBS) films were investigated as a function of "wet−dry cycles", where one "cycle" is defined as a 24 h soak in deionized water followed by a 24 h drying period in air. Films were characterized with a variety of complementary measurements that include X-ray scattering, infrared spectroscopy, water uptake, impedance spectroscopy, and tensile tests. We find that cycling drives a structural transition toward increasingly interconnected SS domains, which is favorable for water and ion transport. However, cycling can also induce mechanical deformations that reduce ductility, swelling, and water uptake. The significance of this trade-off is illustrated by comparing the properties for two film thicknesses as a function of cycle number: The ductility of thinner films (15 μm) is lost after four cycles, an effect that is correlated with the appearance of macroscale buckles, and the extent of swelling is also reduced. Therefore, the transport properties reflect a balance between the increased SS domain interactions and reduced water content. The ductility in thick films (30 μm) also declines with cycling, but to a lesser extent, and these systems retain their ability to swell through six cycles. Therefore, the transition to a network-like SS structure enhances both water uptake and transport. These systematic studies demonstrate that successive wet−dry cycles can lead to complex changes in the performance of amphiphilic block copolymer films, which may complicate their design for applications in water treatment or protonconducting layers in electrochemical devices.

Block Copolymer Membranes

“…[28] The morphology is important. The cyclic hydration of NexarÔ films promotes a transition to a more interconnected network of sulfonated domains [29] that favors the water transport. By choosing the right solvents to cast NexarÔ films, the water transport can be several times increased.…”

Highways for water molecules: Interplay between nanostructure and water vapor transport in block copolymer membranes

“…Nexar™, commercially available sulfonated pentablock copolymers, are an interesting class of block copolymers that maintain a good balance between mechanical properties and membrane performance [28][29][30]. Nexar™ with a high degree of sulfonation maintains its mechanical integrity in the hydrated state because of the glassy end blocks [29,[31][32][33][34]. The middle sulfonated block can create water-selective channels, while the two end blocks (tert-butyl styrene and ethylene-co-propylene) provide good mechanical stability and chain flexibility, respectively (Fig.…”

Sulfonated Pentablock Copolymer Membranes and Graphene Oxide Addition for Efficient Removal of Metal Ions from Water

“…The absorption peaks at 1169 and 1200 cm −1 of s-PBC can be attributed to asymmetric stretching of SO 2 in the sulfonic groups. Furthermore, three other absorption peaks at 2858, 2924 and 2958 cm −1 are observed and ascribed to asymmetric and symmetric CH stretching [ 26 , 27 ]. The peaks at 1645 cm −1 and in the region between 3000 and 3600 cm −1 , related to water molecules inside the polymer, are less intense but still evident for the materials in the dry state, showing their high affinity for water [ 28 ].…”