Studying Fundamentals of Water as a Solvent Could Lead to Greener Cellulose-Based Products

Water isn’t just a universal solvent that remains unaffected by its interactions. New publications from North Carolina State University show that water can change its solubility characteristics depending upon what it interacts with. Specifically, when water interacts with cellulose, it can stack in layered shells to control chemical reactions within, and physical properties of, the material. The work has implications for more sustainable and efficient design of cellulose-based products.

“Cellulose is the world’s most abundant biopolymer, and it’s used in applications that range from bandages to electronics,” says Lucian Lucia, professor of forest biomaterials and chemistry at NC State and corresponding author of a new study in Matter. “But cellulose processing has been mostly done by trial and error, and some of it utilizes incredibly harsh chemicals. To find better ways to process cellulose, we need to understand its most fundamental interactions – for example, with water.”

To do so, he worked with colleague Jim Martin, 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’s with, which gives it wide range of solubility characteristics,” Martin says. Martin is the author of an opinion piece in Matter that is a companion to Lucia’s study.

“We change the nature of water by what we dissolve in it, and by the concentrations of those solutes in water,” Martin says. “Think of the continuum between Kool-Aid and hard candy. You start with sugar. In Kool-Aid the sugar is completely dissolved. As you remove the water, you get taffy, then hard candy, then back to crystalline sugar.”

“We know that water is critical to how cellulose is laid down,” Lucia says. “So in this study we probed how it orients itself and plays a reactive role in mitigating or leveraging chemistry.”

The researchers physically manipulated different types of wood fibers and looked at how water bound to itself and other molecules within the resulting structures. They saw that at lower water contents, the water distribution and resulting molecular interactions between the water and the fibers create bridging structures within the material that cause it to lose flexibility.

In fact, they saw that the water can “hide” itself within the cellulose network, forming strong hydrogen bonds. This bonding in turn dictates the tightness or looseness of the bridging structures.

“The water forms shells around the fibers that can stack, like a nesting Russian doll,” Martin says. “The fewer shells, or layers, the harder the fibers. But when you add more layers, the connection between fibers grows farther away and the material becomes softer.”

The researchers hope to explore the variety of bonds water forms 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,” Lucian says. “Understanding what is happening from fundamental principles lets us design approaches that take advantage of water’s properties for everything from drug delivery to designing electronics.”

The research paper, “Computational and experimental insights into the molecular architecture of water-cellulose networks,” and the editorial piece, “Water under the influence of solutes: on the non-innocence of a universal solvent,” both appear in the May 3 edition of Matter. The work was supported in part by the National Science Foundation. Former NC State Ph.D. student Kandoker Samaher Salem is first author of the research paper. Co-authors include former NC State Ph.D. student Nelson Barrios, and current NC State faculty Hasan Jameel and Lokendra Pal.

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Note to editors: Abstracts follow.

“Computational and experimental insights into the molecular architecture of water-cellulose networks”

DOI: 10.1016/j.matt.2023.03.021

Authors: Kandoker Samaher Salem, Nelson Barrios, Hasan Jameel, Lokendra Pal, Lucian Lucia, North Carolina State University
Published: May 3, 2023 in Matter

Abstract:
The current perspective attempts to provide key insights into several major aspects of water solvation supported by several experimental and computational investigations. It is postulated that water is not just a common solvent from the framework of the molecular level, but in fact it can play the role of a co-reactant or induce an ‘‘organizational constraint’’ (e.g., crystallization) to regulate the rate of different chemical reactions. The focus of our perspective is to provide our insight into these phenomena; we will cast our net toward the formation of putative water molecules stackings around the three-dimensional network of the cellulose, the most abundant biomaterial on the planet, which is further mitigated by hydrogen bonding and water-cellulose molecular architecture on the morphology, properties, and chemical reactivity of micro- and nanocellulose. Our perspective also purviews the idea of water hydration shells present immediate to the hydrophilic surface of the cellulose that can help articulate water chemistry and the challenges it presents during drying.

“Water under the influence of solutes: on the non-innocence of a universal solvent”

Author: James Martin, North Carolina State University
Published: May 3, 2023 in Matter

Abstract: Water interactions with materials can dramatically change their properties. But the solute material also changes the properties of water. Here a Solvation Shell-Liquid Solvate (SSLS) model is presented that provides a molecular-based description of water interacting with sucrose and cellulose for which multiple types of water are identified. Bound water most significantly changes the specific material’s properties, whereas the hard-to-remove water, i.e., water that is significantly modified by the influence of the solute, is responsible for bulk properties such as the system’s liquidus. Both types of water are significantly distinct from classical descriptions that treat solvents as an inert medium. This model provides the molecular basis for the insights into the molecular architecture of water-cellulose networks described in a perspectives article, and further provides a framework that can generally be applied to diverse aqueous systems.