  The phase behavior of polydisperse ABA triblock copolymers is studied using
dissipative particle dynamics simulations, focusing on the emergence and
property of bicontinuous structures. Bicontinuous structures are characterized
by two separate, intermeshed nanoscopic domains extending throughout the
material. The connectivity of polymeric bicontinuous structures makes them
highly desirable for many applications. For conventional monodisperse diblock
and triblock copolymers, regular bicontinuous structures (i.e., gyroid and
Fddd) can be formed over a narrow composition window of ~3%. We demonstrate
that the composition window for the formation of bicontinuous structures can be
regulated by designed polydispersity distributions of ABA triblock copolymers.
In particular, introducing polydispersity in both A and B blocks can lead to a
significant enhancement of the composition window of bicontinuous structures
with both continuous A and B domains. The mechanism of the bicontinuous
structure enhancement is elucidated from the distribution of the long and short
blocks. Furthermore, it is shown that the polymeric bicontinuous structures
from polydisperse ABA triblock copolymers possess good continuity throughout
the sample, making them ideal candidates for advanced applications.
