Rationalizing the Phase Behavior of Triblock Copolymers through Experiments and Molecular Simulations

In this paper, we develop a new coarse-grained
model, under the
MARTINI framework, for Pluronic block copolymers that is able to describe
the self-assembly mechanism and reproduce experimental micelle sizes
and shapes. Previous MARTINI-type Pluronic models were unable to produce
realistic micelles in aqueous solution, and thus our model represents
a marked improvement over existing approaches. We then applied this
model to understand the effects of polymer structure on the cloud
point temperature measured experimentally for a series of Pluronics,
including both normal and reverse copolymers. It was observed that
high polyoxypropylene glycol content leads to dominant hydrophobic
interactions and a lower cloud point temperature, while high hydrophilic
polyoxyethylene glycol content shields the micelles against aggregation
and hence leads to a higher cloud point temperature. As the concentration
increases, the effect of polymer architecture (normal versus reverse)
starts to dominate, with reverse Pluronics showing a lower cloud point
temperature. This was shown to be due to the increased formation of
cross-links between neighboring micelles in these systems, which promote
micelle aggregation. Our results shed new light on these fascinating
systems and open the door to increased control of their thermal responsive
behavior.