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. 2016 Aug 18;1(2):212-219.
doi: 10.1021/acsomega.6b00100. eCollection 2016 Aug 31.

Twist-Bend Stage in the Relaxation of Sheared Chiral Nematic Suspensions of Cellulose Nanocrystals

Derek G Gray  1 , Xiaoyue Mu  1
Affiliations

Twist-Bend Stage in the Relaxation of Sheared Chiral Nematic Suspensions of Cellulose Nanocrystals

Derek G Gray et al. ACS Omega. .

Abstract

Aqueous suspensions of cellulose nanocrystals (CNCs), prepared from natural cellulose by sulfuric acid hydrolysis, form stable chiral nematic suspensions above a critical CNC concentration. The chiral nematic organization may be preserved in films prepared from the suspensions by evaporation. However, shrinkage, gelation, and shear during film formation impair the optical properties of the dry film. In this article, we report an unusual behavior for a sample in which gelation occurred before the sample reached iridescent pitch values. In attempting to decouple changes in texture due to evaporation from those due to shear relaxation effects for this sample, we observed a transitory nematic-like texture that was induced by shear during the preparation of the sample for polarized light microscopy. We propose that the transition between chiral nematic and nematic structures involves a twist-bend-like intermediate and not an untwisting of the chiral nematic phase.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Phase composition as a function of concentration of CNCs in the suspension.
Figure 2
Figure 2
Overview of texture change with time for 9.6 wt % CNC suspension between a microscope slide and cover glass, viewed between crossed polars: (a) 5 min, (b) 30 min, (c) 60 min, (d) 110 min, (e) 170 min, (f) 330 min, and (g) 18 h. The spacer thickness is 185 μm. The same area of the sample is shown in each segment.
Figure 3
Figure 3
Texture change with time for 9.6 wt % CNC suspension between a microscope slide and cover glass, viewed between crossed polars: (a) immediately after preparation, (b) after 5 min, and (c) after 25 min.
Figure 4
Figure 4
Texture change with time for 9.6 wt % CNC suspension between a microscope slide and cover glass, viewed between crossed polars: (a) after 45 min, (b) after 75 min, and (c) after 105 min.
Figure 5
Figure 5
Texture change with time for 9.6 wt % CNC suspension between a microscope slide and cover glass, viewed between crossed polars with a 530 nm red plate after (a) 330 min and (b) 18 h.
Figure 6
Figure 6
Intermediate texture between crossed polars with a 530 nm red plate, 9.6 wt % CNC suspension after 155 min relaxation.
Figure 7
Figure 7
Sketch of possible relaxation routes from shear-induced nematic (a) and (e) to chiral nematic (c) structures. On the right, the transformation (e)–(d)–(c) occurs by twisting around the z axis. On the left, the transformation occurs via a twist–bend structure (b).
See this image and copyright information in PMC

References

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