Discovery of Cellulose Surface Layer Conformation by Nonlinear Vibrational Spectroscopy

Area of Science:

• Biomass Science
• Materials Science
• Spectroscopy

Background:

• Cellulose structure and polymorphs, especially surface vs. bulk properties, remain incompletely understood.
• Distinguishing molecular structures of cellulose surface layers and crystalline core is crucial for biomass applications.

Purpose of the Study:

• To selectively characterize and differentiate the molecular structures of cellulose surface layers and crystalline core.
• To investigate conformational differences and hydrogen bonding networks within cellulose polymorphs.

Main Methods:

• Utilized Total Internal Reflection Sum Frequency Generation Vibrational Spectroscopy (TIR-SFG-VS) combined with conventional SFG-VS.
• Analyzed SFG spectra in C-H and O-H regions to probe molecular structures.

Main Results:

• Demonstrated selective characterization of surface layers and crystalline core of cellulose for the first time.
• Found Avicel surface layers to be essentially amorphous.
• Revealed crystalline surface layers in Iβ cellulose with distinct signatures compared to its crystalline core, highlighting differences in hydrogen bonding networks.

Conclusions:

• Spectroscopic observations provide transformative insights into cellulose structure.
• The study highlights significant structural and spectroscopic differences between cellulose surface and bulk crystalline regions.
• Findings advance the understanding of cellulosic biomass at a molecular level.