Tianzi Huang

Tunable morphologies from charged block copolymers

The bulk morphologies formed by a new class of charged block copolymers, 75 vol % fluorinated polyisoprene (FPI) – 25 vol% sulfonated polystyrene (PSS) with 50% sulfonation, are characterized, and the fundamental underlying forces that promote the self-assembly processes are elucidated. The results show how the bulk morphologies are substantially different from their uncharged diblock counterparts (PS-PI) and also how morphology can be tuned with volume fraction of the charged block and the casting solvent. A physical understanding based on the underlying strong electrostatic interactions between the charged block and counterions is obtained using Monte Carlo (MC) and Molecular Dynamics (MD) simulations. The 75/25 FPI-PSS shows hexagonal morphologies with the minority blocks (PSS) forming the continuous phase due to charge percolation and the FPI blocks arranged in hexagonal cylinders. Some long-range order can be sustained even if lipophobicity is increased (addition of water), albeit with lower dimensional structures. However, thermal annealing provides sufficient energy to disrupt the percolated charges and promotes aggregation of ionic sites which leads to a disordered system. Diverse and atypical morphologies are readily accessible by simply changing the number distribution of the charges on the PSS block.

Effect of solvents and thermal annealing on the morphology development of a novel block copolymer ionomer: a case study of sulfonated polystyrene-block-fluorinated polyisoprene; J. Polym. Eng. 2013, 33, 49–59

No abstract available.

Effect of solvents and thermal annealing on the morphology development of a novel block copolymer ionomer: a case study of sulfonated polystyrene-block-fluorinated polyisoprene

Abstract The morphologies of sulfonated polystyrene-block-fluorinated polyisoprene (s-PS-b-f-PI) were studied as functions of different kinds of solvents and thermal annealing, using transmission electron microscope microscopy (TEM), small angle X-ray scattering (SAXS) and intermediate angle X-ray diffraction (IMAXD). The film of the block copolymer ionomer with an acid form [sulfonated PS-b-fluorinated PI (sH-PS-b-f-PI)], which was cast from anhydrous tetrahydrofuran (THF), developed a well-ordered cylindrical morphology of the f-PI domains in the sH-PS matrix. The morphology was explained by the solubility parameter and the Bjerrum length. The morphology changed to that of a no long-range ordered structure, through thermal annealing. The result was different from the usual behavior of uncharged diblock copolymers and could have been due to the ionic cluster formation. The solution casting films of the block copolymer ionomer with a cesium neutralized form (sCs-PS-b-f-PI) were obtained from the mixed solvent of THF/water (98/2, wt/wt) and DMSO. The ionic cluster formation in the film cast from the mixed solvent was hardly changed by annealing. The promotion of the ionic cluster formation by annealing was clearly observed in the film cast from DMSO. However, hindrance of microphase separation by the promotion of the ionic cluster formation was not confirmed in this study.