Subscriber access provided by University of South Dakota
Article
Characterization of Concentration-Dependent Gelation Behavior of Aqueous TEMPO-Cellulose Nanocrystal Dispersions Using Dynamic Light Scattering Yaxin Zhou, Shuji Fujisawa, Tsuguyuki Saito, and Akira Isogai Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.8b01689 • Publication Date (Web): 17 Dec 2018 Downloaded from http://pubs.acs.org on December 18, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Biomacromolecules
1
Characterization of Concentration-Dependent Gelation
2
Behavior of Aqueous TEMPO-Cellulose Nanocrystal
3
Dispersions Using Dynamic Light Scattering
4 5
Yaxin Zhou,† Shuji Fujisawa,† Tsuguyuki Saito,† and Akira Isogai*,†
6 7
†
8
University of Tokyo, Tokyo 113-8657, Japan
Department of Biomaterials Science, Graduate School of Agricultural and Life Sciences, The
9 10
ABSTRACT: Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) with high and
11
low aspect ratios, respectively, were prepared from wood cellulose by catalytic oxidation with
12
2,2,6,6-tetramethylpiperidine-1-oxyl
13
Cavitation-induced force was used to prepare TEMPO-CNCs from aqueous suspensions of
14
TEMPO-oxidized celluloses. Aqueous dispersions of the TEMPO-CNF and TEMPO-CNCs
15
with different solid concentrations were prepared by dilution or condensation. Dynamic light
16
scattering (DLS) was used to determine the solid concentrations at the transition points from
17
the dilute to semi-dilute regions and from the semi-dilute to dense gel regions in the aqueous
18
TEMPO-CNF and TEMPO-CNC dispersions. All the DLS data corresponded well to the fitting
19
curves of the normalized time-correlation functions. The solid concentration at the gelation
20
point increased from 0.40% w/v for the TEMPO-CNF dispersions to 1.71 % w/v for the
21
TEMPO-CNC dispersions, and the aspect ratio decreased from 134 to 57, respectively. The
22
solid concentrations of the TEMPO-CNF and TEMPO-CNC dispersions at the gelation point
(TEMPO)
and
subsequent
ACS Paragon Plus Environment
sonication
in
water.
1
Biomacromolecules 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 28
23
calculated using effective-medium theory based on their aspect ratios corresponded well with
24
those experimentally determined by DLS.
25 26
KEYWORDS: Cellulose nanocrystal, TEMPO-CNC, Dynamic light scattering, Gelation point,
27
Effective-medium theory
28 29
INTRODUCTION
30
Nanocelluloses are prepared from plant cellulose fibers and bacterial, tunicate, and algal
31
celluloses by mechanical disintegration in water with or without chemical or enzymatic
32
pretreatment. Cellulose molecules in terrestrial and vascular plant cell walls form crystalline
33
cellulose microfibrils with small widths of ~3 nm and lengths over several microns as the
34
smallest elements.1,2 Nanocelluloses with widths of 3–100 nm are prepared from plant
35
cellulose fibers with widths of 20–40 µm and lengths of 1–3 mm by downsizing, with their
36
nanostructures originating from the cellulose microfibrils. Plant nanocelluloses are roughly
37
categorized as either cellulose nanofibrils (CNFs) or cellulose nanocrystals (CNCs) depending
38
on their lengths; CNFs have lengths >300 nm and CNCs have lengths 2 nm were different between SBKP-120 and
430
MCC-60, each sample had a highly positive and constant V value at the distances >2 nm in
431
pure water. Moreover, both SBKP-120 and MCC-60 had positive (or repulsive) potential
432
energies at the distances >0.07–0.09 nm and >0.24–0.27 nm for the crossed and parallel
433
orientations, respectively. These results indicate that electrostatic repulsions owing to the
434
anionic sodium carboxylate groups densely present on TEMPO-CNC surfaces always work
435
between the TEMPO-CNC elements in water.
436
It has been reported that TEMPO-CNFs form small clusters in aqueous dispersions.32 In each
437
cluster, some TEMPO-CNF elements have nematic-ordered and self-assembled structures
438
owing to close packing. These structures result in the formation of birefringence for the
439
aqueous dispersions and nano-layered and plywood-like dense structures in cast-dried
440
TEMPO-CNF films. The nematic-ordered structures are formed for the TEMPO-CNF/water
441
dispersions
442
surface-charged TEMPO-CNF elements.32 In the case of TEMPO-CNCs, therefore, the
443
concentration-dependent aggregation may occur between the clusters (not nano-elements) in
because
electrostatic
repulsions
efficiently
ACS Paragon Plus Environment
work
between
the
highly
19
Biomacromolecules
444
water, different from the conventional CNCs or other nanocelluloses.15,17,43,44 This is probably
445
the reason why the gelation points of TEMPO-CNCs obtained in Figure 6 and Table 2 are
446
primarily governed by their morphologies and concentrations in water rather than their surface
447
charges. Further studies are, however, needed to clarify the detailed gelation or
448
concentration-dependent aggregation mechanism of TEMPO-CNCs in water.
450 451 452 453 454 455
Interaction potential energy V (kT)
449 10.0
a
5.0 2.5 0.0 -2.5 -5.0
0
5
456 457 458 459 460 461 462
SBKP-120 in pure-water MCC-60 in pure water
7.5
10
15
20
25
Distance from solid surface (nm) Interaction potential energy V (kT)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 20 of 28
200
b
SBKP-120 in pure water MCC-60 in pure water
150 100 50 0 -50 -100
0
5
10
15
20
25
Distance from solid surface (nm)
463 464 465 466
Figure 7. Interaction potential energy V between two cylindrical TEMPO-CNCs in parallel (a)
467
and crossed (b) orientations, calculated using the DLVO theory,45 and sizes and carboxylate
ACS Paragon Plus Environment
20
Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
468
Biomacromolecules
contents (Table 1 in the main manuscript) of SBKP-120 and MCC-60.
469 470
CONCLUSION
471
The solid concentrations of aqueous dispersions of TEMPO-CNCs with lengths
