“Bilayer-folded lamellar mesophase induced by random polymer sequence” by Minjoong Shin, Hayeon Kim, Geonhyeong Park, Jongmin Park, Hyungju Ahn, Dong Ki Yoon, Eunji Lee, and Myungeun Seo was published in Nature Communications. This work was done in collaboration with Dr. Hyungju Ahn at Pohang Accelerator Laboratory, the Eunji Lee group at Gwangju Institute of Science and Technology (GIST), and the Dong Ki Yoon group at KAIST.

Flipping a coin with a constant bias creates a discrete probability distribution named after Jacob Bernoulli. The Bernoulli distribution arises with the monomer composition as the bias in the random copolymerization of two monomers. Each monomer addition is sequentially encoded and connected randomly in the polymer chain sequence. At the equimolar composition of monomers A and B, finding B next to A in the sequence should be the most likely (50%). However, A-rich local sequences can appear with considerable probabilities: the random sequence can be very heterogeneous. 

We found that an amphiphilic random copolymer composed of hydrophilic and hydrophobic monomers forms a unique lyotropic mesophase in the concentrated aqueous solution. This new phase is identified as a bilayer-folded lamellar morphology, where the micellar bilayer forms by association of the hydrophobic alkyl chains, folds periodically, and stacks further. While this strongly resembles chain-folded lamellae found in crystalline polymers, bilayer folding in a thermodynamically stable manner has not been reported to our knowledge. 

We believe this periodic folding is due to the sequence matching problem of the random sequence, in which the number of possible sequences grows exponentially with the degree of polymerization. We hypothesized that the resulting local curvature mismatches, different from the ensemble-averaged interfacial curvature, can be stabilized by forming recurrent hinges. The mesophase is characterized as an anisotropically alignable birefringent hydrogel with structural hierarchy across multiple length scales. Check out more details at the following link:

https://www.nature.com/articles/s41467-022-30122-z

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