(a) Random copolymerization of hydrophilic and hydrophobic monomers. Three binary sequences that can be generated by random copolymerization are given as examples for a copolymer consisting of 23 repeating units. (b) A random sequence can be drastically heterogeneous and contain hydrophilic- and hydrophobic-rich local sequences. When the chains associate in water via hydrophobic interaction, local sequence mismatches can take place for long chains, leading to folding because of the curvature instability. Image: KAIST.
(a) Random copolymerization of hydrophilic and hydrophobic monomers. Three binary sequences that can be generated by random copolymerization are given as examples for a copolymer consisting of 23 repeating units. (b) A random sequence can be drastically heterogeneous and contain hydrophilic- and hydrophobic-rich local sequences. When the chains associate in water via hydrophobic interaction, local sequence mismatches can take place for long chains, leading to folding because of the curvature instability. Image: KAIST.

Polymers are large molecules made up of repeating smaller molecules called monomers, and are found in nearly everything we use in our day-to-day lives. Polymers can be natural or synthetic. Natural polymers, also called biopolymers, include DNA, proteins, and materials like silk, gelatin and collagen. Synthetic polymers make up many different kinds of materials, particularly plastics, that are used in constructing everything from toys to industrial fiber cables to brake pads.

As polymers are formed through a process called polymerization, the monomers are connected together to form a chain. As the chain develops, the structure of the polymer determines its unique physical and chemical properties. Scientists are continually studying polymers: how they form, how they are structured and how they develop their unique properties. By understanding this information, scientists can develop new uses for polymers and create new materials for use in a wide variety of industries.

Now, in a paper in Nature Communications, Korean researchers report finding a new structure, which they term a bilayer-folded lamellar mesophase, in an aqueous solution of an amphiphilic copolymer.

“A new mesophase is an important discovery as it shows a new way for molecules to self-organize,” said Myungeun Seo in the Department of Chemistry at the Korea Advanced Institute of Science and Technology (KAIST). “We were particularly thrilled to identify this bilayer-folded lamellar phase because pure bilayer membranes are difficult to fold thermodynamically.”

The researchers think this mesophase structure arises from the sequence of monomers within the copolymer. The way the different monomers arrange themselves in the chain that makes up a copolymer is important and can have implications for what the copolymer can do. Many copolymers are random, which means that their structure is determined by how the monomers interact with each other.

In this case, the interaction between the hydrophobic monomers causes the copolymer chains to conceal the hydrophobic domain from water. As the structure gets more complex, the researchers found that a visible order develops that matches up pairs of monomers.

“While we tend to think random means disorder, here we showed that a periodic order can spontaneously arise from the random copolymer sequence based on their collective behavior,” said Seo. “We believe this comes from the sequence matching problem: finding a perfectly complementary pair for a long sequence is nearly impossible.”

This is what creates the unique structure of this newly discovered mesophase. The copolymer spontaneously folds and creates a multilamellar structure that is separated by water – multilamellar structure refers to plate-like folds where the folded layers stack on top of each other. The resulting mesophase is birefringent, meaning light refracts through it, and viscoelastic, which means that it is both viscous and elastic at the same time.

Looking ahead, the researchers hope to learn more about this new mesophase and figure out how to control the outcome. Once they understand more about the mesophase and how it is formed, it’s possible that new mesophases could be discovered as more sequences are researched.

“One of the obvious questions for us is how to control the folding frequency and adjust the folded height, which we are currently working to address. Ultimately, we want to understand how different multinary sequences can associate with another to create order and apply the knowledge to develop new materials,” said Seo.

This story is adapted from material from KAIST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.