Water is not just a universal solvent that is unaffected by its interactions. New publications from North Carolina State University show that water can change its solubility characteristics depending on what it interacts with. Specifically, when water interacts with cellulose, it can be layered to control the chemical reactions within and the physical properties of the material. The work has implications for more sustainable and efficient design of cellulose-based products.
“Cellulose is the most abundant biopolymer in the world and is used in applications ranging from bandages to electronics,” says Lucian Lucia, professor of chemistry and forestry biomaterials at NC State and corresponding author of a new study in Matter. “But cellulose processing has been done mostly by trial and error, and some of them use incredibly aggressive chemicals. To find better ways to process cellulose, we need to understand its more fundamental interactions, for example with water.”
To do so, he worked with his colleague Jim Martin, a professor of chemistry at NC State who studies the fundamental properties of water as a solvent.
“Water has the uncanny ability to change characteristics depending on what it encounters, giving it a wide range of solubility characteristics,” says Martin. Martin is the author of an op-ed in Matter that accompanies Lucia’s study.
“We change the nature of the water by what we dissolve in it and by the concentrations of those solutes in the water,” says Martin. “Think about the continuity between Kool-Aid and hard candy. It starts with sugar. In Kool-Aid, the sugar dissolves completely. As you remove the water, you get caramel, then hard candy, and then back to crystalline sugar.” “.
“We know that water is critical to the way cellulose is deposited,” says Lucia. “So in this study we investigate how it targets and plays a reactive role in mitigating or harnessing the chemistry.”
The researchers physically manipulated different types of wood fibers and observed how the water attached itself and other molecules within the resulting structures. They saw that at lower water contents, the distribution of water and the resulting molecular interactions between the water and the fibers create bridging structures within the material that cause it to lose flexibility.
In fact, they found that water can “hide” within the cellulose network, forming strong hydrogen bonds. This bond, in turn, dictates the tension or clearance of the bridge structures.
“The water forms shells around the fibers that can be stacked, like a nesting Russian doll,” says Martin. “The fewer layers or plies, the harder the fibers. But when you add more layers, the connection between the fibers gets further apart and the material becomes softer.”
The researchers hope to explore the variety of forms of water bonding within these structures in future work.
“Studying these interactions at the molecular level paves the way toward manipulating water in cellulose to design better products and processes,” says Lucian. “Understanding what’s going on from fundamental principles allows us to design approaches that harness the properties of water for everything from drug delivery to electronics design.”
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