Morphological details of cellulose nanofibers and their composites for Raman sensing application

This study investigated the morphologies of two bacterial and two wooden cellulose nanofiber (CNF) suspensions in water by using synchrotron X-ray scattering and scanning electron microscopy (SEM). The SEM analysis visually confirmed nanofibers. All small-angle X-ray scattering data were satisfactorily analyzed by using a three-phase elliptical cylinder model combined with blob contributions, thereby confirming all CNFs to consist of a core, an interfacial layer, and a solvated layer. The analysis further delivered detailed microstructure parameters beneficial for better utilization and applicability of CNFs. Moreover, the wide-angle X-ray scattering analysis confirmed all CNF suspensions retaining cellulose I_β structures. Furthermore, the CNFs were explored as potential matrix candidates for preparing high quality metal nanoparticle composites via redox reactions of metal sources in aqueous CNF solutions. The X-ray scattering and SEM analyses found that highly oblate silver (Ag) nanoparticles with rough surface were synthesized with a unimodal size distribution. The thin films of composites cast onto substrates were evaluated for Raman sensing performance by using methylene blue, a common Raman reporting analyte. Higher loading of Ag source in the redox reaction produced higher population of oblate Ag nanoparticles in a controlled size and distribution and led to excellent surface-enhanced Raman scattering performance.