Molecular orientation in dry and hydrated cellulose fibers: a coherent anti-Stokes Raman scattering microscopy study.
Coherent anti-Stokes Raman scattering (CARS) microscopy is combined with spontaneous Raman scattering microspectroscopy and second harmonic generation (SHG) microscopy to interrogate the molecular alignment in dry and hydrated cellulose fibers. Two types of cellulose were investigated: natural cellulose I in cotton fibers and regenerated cellulose II in rayon fibers. On the basis of the orientation of the methylene symmetric stretching vibration, the molecular alignment of cellulose microfibrils is found to be conserved on the micrometer scale. Whereas the molecular orientation in cotton shows modest variability along the fiber, the alignment of the cellulose units in rayon is highly consistent throughout the fiber. The ordered alignment is retained upon fiber hydration. Upon hydration of the cellulose fibers, an anisotropic electronic contribution is observed, which indicates an ordered incorporation of water molecules into the fiber structure. The third-order and second-order electronic polarizability of cellulose I are directed along the axis of the polyglucan chain. No second-order optical response is observed in cellulose II, supporting the antiparallel arrangement of the polyglucan chains in regenerated cellulose.
Zimmerley
Maxwell
M
Department of Chemistry, University of California, Irvine, California 92697, USA.
Younger
Rebecca
R
Valenton
Tiffany
T
Oertel
David C
DC
Ward
Jimmie L
JL
Potma
Eric O
EO
D002482:Cellulose / Q000737:chemistry*; D032561:Cotton Fiber; D004583:Electrons; D008853:Microscopy / Q000379:methods*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D014867:Water / Q000737:chemistry*
D014867:Water; D002482:Cellulose; C012024:rayon, purified