Aperiodic “bricks and mortar” mesophase: a new equilibrium state of soft matter and application as a stiff thermoplastic elastomer

A new thermodynamically stable, aperiodic “bricks-and-mortar” (B&M) cellular mesophase structure is reported in PS1-b-(PI-b-PS2)3 miktoarm copolymer and PS homopolymer blends [PS1, long polystyrene; PI, poly(isoprene); PS2, short polystyrene], where PS comprises discrete hard “bricks” and PI the continuous soft “mortar”. The mesophase is unique in its extreme domain volume fractions, its lack of positional order, and quasi-long-range orientational order. On the basis of this unusual mesophase structure, a series of PS-based thermoplastic elastomers are realized, combining rigidity from an exceptionally high content of discrete glassy PS domains (up to 82 wt %) and high extensibility with recoverable elasticity from a low content of continuous rubbery PI (down to 18 wt %). The new elastomers show sharp yielding behavior while maintaining good elasticity at large strains. Tensile-SAXS experiments reveal that voiding plays an important role for the mechanical behavior and voids can open/close reversibly with/without loading. Plastic deformation only results in a slight loss of recoverable elasticity.

Shi, W., Hamilton, A. L., Delaney, K. T., Fredrickson, G. H., Kramer, E. J., Ntaras, C., Avgeropoulos, A., Lynd, N. A., Demassieux, Q. and Creton, C.
Macromolecules
Volume: 48
Number: 15
Pages: 5378–5384
Date: July, 2015
ICB Affiliated Authors: Glenn H Fredrickson