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Mao Y, Bleuel M, Lyu Y, Zhang X, Henderson D, Wang H, Briber RM. Phase Separation and Stack Alignment in Aqueous Cellulose Nanocrystal Suspension under Weak Magnetic Field. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:8042-8051. [PMID: 29957957 DOI: 10.1021/acs.langmuir.8b01452] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Isotropic-nematic (I-N) transitions in cellulose nanocrystal (CNC) suspension and self-assembled structures in the isotropic and nematic phases were investigated using scattering and microscopy methods. A CNC suspension with a mass fraction of 7.4% spontaneously phase separated into an isotropic phase of 6.9% in the top layer and a nematic phase of 7.9% in the bottom layer. In both the phases, the CNC particles formed stacks with an interparticle distance being of ≈37 nm. One-dimensional small-angle neutron scattering (SANS) profiles due to both phases could be fitted using a stacking model considering finite particle sizes. SANS and atomic force microscopy studies indicate that the nematic phase in the bottom layer contains more populations of larger particles. A weak magnetic field of ≈0.5 T was able to induce a preferred orientation of CNC stacks in the nematic phase, with the stack normals being aligned with the field (perpendicular to the long axis of CNC particles). The Hermans orientation parameter, ⟨ P2⟩, was ≈0.5 for the nematic phase; it remained unchanged during the relaxation process of ≈10 h. The fraction of oriented CNC populations decreased during the relaxation; dramatic decrease occurred in the first 3 h. The top layer remained isotropic in the weak field. Polarized microscopy studies revealed that the nematic phase was chiral. Adjacent particles in a stack form a twisting angle of ≈0.6 °, resulting in a helix pitch distance of ≈22 μm.
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Affiliation(s)
- Yimin Mao
- Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg , Maryland 20899 , United States
| | - Markus Bleuel
- Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg , Maryland 20899 , United States
| | - Yadong Lyu
- Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg , Maryland 20899 , United States
| | - Xin Zhang
- Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States
| | - Doug Henderson
- Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States
| | - Howard Wang
- Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States
| | - Robert M Briber
- Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States
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