Shear-Induced Breakup of Cellulose Nanocrystal Aggregates

Subscriber access provided by GAZI UNIV

Article

Shear-induced Breakup of Cellulose Nanocrystal Aggregates Hua-Neng Xu, Yi-You Tang, and Xiao Kun Ouyang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b03807 • Publication Date (Web): 12 Dec 2016 Downloaded from http://pubs.acs.org on December 15, 2016

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 free 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 accessible to all readers and 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.

Langmuir 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 35

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

Langmuir

Shear-induced Breakup of Cellulose Nanocrystal Aggregates Hua-Neng Xu,1, 2* Yi-You Tang 2 and Xiao-Kun Ouyang 3 1

State Key Laboratory of Food Science and Technology, Jiangnan University, 1800 Lihu

Avenue, Wuxi, Jiangsu 214122, People’s Republic of China 2

School of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi,

Jiangsu 214122, People’s Republic of China 3

School of Food and Pharmacy, Zhejiang Ocean University, Zhoushan 316022, People’s

Republic of China * To whom correspondence should be addressed. E-mail: [email protected]

ABSTRACT The flow properties of two kinds of cellulose nanocrystal (CNC) rods with different aspect ratios and similar zeta potentials in aqueous suspension have been investigated. The aqueous CNC suspensions undergo a direct transition from dilute solution to colloidal glass instead of phase separation with increasing CNC concentration. The viscosity profile shows a single shear thinning behavior over the whole range of shear rates investigated. The shear thinning behavior becomes stronger with increasing CNC concentration. The viscosity is much higher for the unsonicated compared to the sonicated suspensions. The CNC rods appear arrested without alignment with increasing shear rate from the small-angle light scattering (SALS) patterns. The arrested glass state results from electric double layers surrounding the CNC rods, which give rise to long-ranged repulsive interactions. For the first time we demonstrate that, within a narrow range of CNC concentrations, a shear-induced breakup process of the CNC

ACS Paragon Plus Environment

Langmuir

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

aggregates exists when the shear rate is over a critical value and the process are reversible in the sense that the aggregates can be reform. We discuss the competition between the shear-induced breakup and the concentration-driven aggregation based on the experimental observations. The generated aggregate structure during breakup is characterized by a fractal dimension of 2.41. Furthermore, we determine two important variables, the breakup rate and the characteristic aggregate size, and derive analytical expressions for their evolution during the breakup process. The model predictions are in quantitative agreement with the experimental results.

INTRODUCTION Recently, cellulose nanocrystal (CNC) has become the focus of investigations as a nanomaterial, due to its specific physical properties and high aspect ratio. CNC rods are commonly isolated from cellulose materials by using acid hydrolysis, where their size and surface properties depend on the cellulose source and hydrolysis conditions. Controlling the self-assembly of CNC rods in aqueous suspension and the resulted microstructures are of fundamental importance to produce novel materials with desirable mechanical and optical properties.1-3 Aqueous CNC suspensions were known to exhibit phase separation and form a liquid crystalline phase above a critical concentration, owing to the CNC anisotropic shape.4, 5 The formation and characteristics of liquid crystalline domains depend on the concentration, dimension and surface charge density of the CNC rods,6-8 and also on the ionic strength of the medium.9-11. The reported common feature was that, at a low concentration, the CNC rods are oriented randomly in the suspensions


Page 2 of 35

Page 3 of 35

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

Langmuir

which is called isotropic phase; however, when increased to at a critical concentration, the CNC suspensions become biphasic-a liquid crystalline phase formed in equilibrium with the isotropic phase. It was also found that the surface modifications on the CNC rods led to their aqueous suspensions with unexpected gelling properties, which apparently inhibited the formation of liquid-crystalline phases.12, 13 It is instructive to compare the phase behavior of CNC suspensions with that of other anisotropic charged particles. The phase diagrams of some charged particles, such as boehmite rods,14-16 chitin nanocrystal,17 carbon nanotubes,18 and fd virus particles,19, 20 have been studied in detail. These suspensions exhibit a rich state diagram, including fluid, liquid-crystalline phases, and some dynamically arrested or nonergodic states including gel and glass. The formation of liquid crystalline phases in the suspensions can be explained by Onsager’s theory as driven by the excluded-volume effect.

21

The

excluded-volume contribution to the entropy can overweigh the loss of orientational entropy of the system at sufficiently high concentration. The nonergodic states range from soft glassy phases dominated by interparticle repulsions to colloidal gels stabilized by attractive interactions.22 The effect of charges can be minimized by the addition of salt, inducing an attraction between the particles. A similar situation can be produced in suspensions where the addition of polymer is used to produce an interparticle attraction.23-25 Because the range and depth of the interactions can be tuned by various factors including temperature, polymer size and concentration, and salt concentration, an intriguing metastable states can be realized. Recently, direct liquid-to-glass transitions in colloid particle suspensions were reported at low ionic strengths.14-16, 18-20 The structural particle arrest is found to be due to caging of the charged particles in the potential setup


Langmuir

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

by their neighbors through long-ranged electrostatic interactions. Although the sensitive balance between glass formation and liquid crystal self-assembly was discussed,3, 26-29 the predictions of phase diagrams for CNC rods are not always realized due to the intricacies of the dynamics of phase transitions. The steady shear behavior of aqueous CNC suspensions has been studied in some detail.28-35 The shear flow on the CNC suspensions can alter their microstructure through deformation and orientation of their constitutive elements. Due to the formation of liquid crystalline domains in the system, the flow curve of the CNC suspensions was often characterized by three different flow regimes and two plateaus.33 One plateau at low shear rates was corresponded to the flow of isotropic, and the other at high shear rates was related to the flow of oriented suspensions. The understanding of flow behavior of the CNC suspensions can significantly benefit from simultaneous measurements of their macroscopic rheological properties and their microscopic structure and dynamics. Recently, rheology-small angle neutron scattering, X-ray scattering and light scattering (SANS, SAXS and SALS) have been used to acquire the information on the size and morphology of CNC rods in aqueous suspensions under flow. 36-39 The utilization of small angle scattering with simultaneously rheological characterization can allow for real time analysis of the structure formation of the CNC rods and their correlation with changes in viscosity. While the studies gave some important structural information on the flow behavior of the CNC rods, it is clear that more data on the length scale between a single CNC rod and its aggregated state are essential to expand the understanding on the CNC self-assembly behavior. When colloidal particles are exposed to shear stress, their trajectories change and


Page 4 of 35

Page 5 of 35

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

Langmuir

different aggregate structures may be formed. Shear-induced aggregation of colloidal particles is always accompanied by some particle rearrangements within the aggregates through breakup events. While the breakup of colloidal aggregates has been studied in the literature through both experiments and simulations,40-44 quantifying the aggregate breakup process still remains challenging because of the need for reducing the experimental and computational cost. Recently, a semianalytical model to investigate the mechanical stability and breakup of colloidal aggregates has been constructed.45 By characterizing colloidal interactions, collective stress transmission inside the aggregate, hydrodynamic interactions, fractal structure, and microscopic convective-diffusive dynamics of the bonded particles in the aggregate, the model can be used to predict the breakup rate as well as the stable fragment sizes. Following this approach to the breakup of colloidal aggregates, here we have investigated a shear-induced breakup behavior of two kinds of CNC rods (CNC1 and CNC2) with different aspect ratios and similar zeta potentials. For charged CNC rods, it has been reported that the electrostatic interactions between them play an important role in the critical concentrations of liquid crystal phase formation, and also the microstructure and rheology of the CNC suspensions.33-35 In particular, the importance of surface charge of CNC rods and ionic strength of the system has been explored. However, to our knowledge, the effect of the shape (aspect ratio) of CNC rods, which governs their flexibility in aqueous suspensions, on the microstructure and rheology of the CNC suspensions is not up to now well understood. In this study, the surface charge density of the CNC rods is nearly unchanged and only an increase in aspect ratio of the CNC rods can contribute to modifying their arrangement in aqueous suspension. We probe the


Langmuir

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

microstructure formation and evolution of the CNC aggregates in aqueous suspension with increasing CNC concentration by means of small-angle light scattering during rheological characterization (rheo-SALS). It should be noted that the use of such techniques with lower scattering vectors (SAXS or SANS) is not applicable to probe the CNC aggregates because they generally only allow for dimensions below 200 nm to be probed in direct space and are thereby limited to individual CNC rods. The CNC aggregates are larger objects that require measurements at scattering vectors falling in the Q range of light scattering. It seems that the CNC aggregates are more suitably probed by small-angle light scattering (SALS) techniques.

EXPERIMENTAL SECTION Materials Sulphuric acid (H2SO4) were purchased from Sinopharm Chemical Reagent CO., Ltd, and used without further purification. A commercial cotton microcrystalline cellulose (MCC) was purchased from Sangon Biotech (Shanghai) Co.,Ltd., with a particle size about 100 µm. Ultrapure Milli-Q water with a resistivity 18.2 MΩ was used.

Preparation and characterization of CNC rods Two kinds of CNC rods (CNC1 and CNC2) were produced from MCC by sulfuric acid hydrolysis for 2 and 1 h, respectively. Firstly, the MCC powders were added into 60 wt % sulfuric acid for hydrolysis at 45°C. Then, 10-fold deionized water was added to stop hydrolysis, and the resulting suspension was centrifuged at 25°C and 5000 rpm for 10 min to remove excess acid. After the centrifugation, the precipitate was collected and dialyzed with membranes against deionized water for several days until the pH of the


Page 6 of 35

Page 7 of 35

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

Langmuir

water from successive washes stayed constant. The suspension was concentrated by immersing the dialysis tube in polyethylene glycol 20000 to get a stock suspension. The stock suspension was diluted to produce suspensions with different concentrations. The suspension was then sonicated with a high-intensity ultrasonic probe (Xinzhi Co., China, JY92-IIN, 20 kHz) continuously in an ice bath for 5 min at 60% of the maximum power for the disruption of potential CNC aggregates, since the surface charge of CNC rods is highly sensitive to heat and an increase in temperature can cause de-esterification of the sulfate groups on the CNC surface. Morphology of the CNC rods was analyzed using a JEOL JEM-2100 transmission electron microscope (TEM) at 80 kV acceleration voltage. Drops of diluted CNC suspensions were deposited on a TEM grid immediately after sonication and dried under ambient conditions. Image J software was used to measure the physical dimensions of CNC rods. Malvern Instruments Zetasizer (Nano ZS) was used to measure the zeta potential of the CNC rods. The electrophoretic mobility of the CNC rods under the influence of an external oscillating electrical field was measured and converted to zeta-potential by the instrument software. In the conversion of electrophoretic mobility to zeta potential, we assume that the CNC rods are uniformly charged and that the electric field is too low to align them.46 Consequently, the measured mobility can be treated as an orientationally averaged mobility.

Rheology-Small angle light scattering (Rheo-SALS) measurement Aqueous suspensions with CNC concentrations ranging from 1.0 to 6.0 wt% were analyzed. The rheological properties and microstructure of the CNC suspensions were


Langmuir

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

investigated by rheo-SALS. Rheology and SALS data were collected simultaneously using an AR-G2 rheometer (TA Instruments, New Castle, DE) with the commercially available SALS attachment. The experimental apparatus has already been described elsewhere.47, 48 A transparent, quartz parallel-plate configuration (40 mm diameter) with a 1 mm gap was used for all rheology tests. The measurements were made at shear rates from 0.1 to 1000 s-1, at temperature of 25 oC. A single viscosity and scattering pattern are reported per measured shear rate. A He-Ne laser (λ= 635 nm) was used and SALS images were recorded for each of the samples. The accessible range of scattering vectors q is from 1.38 to 6.10 µm-1, where q = (4π n0 / λ )sin(θ / 2) depends on the distance between sample and screen, θ is the scattering angle, n0 is the refractive index of water, and λ is the wavelength of the laser. The SALS images were analyzed using ImageJ with standard protocols for subtracting the background and removing the beam stop from the raw images.49, 50 The normalized mean intensity is defined as the ratio of the average intensity of the image (after removal of the beam stop) to the intensity if all pixels in the image were saturated (a value of 255 for the 8-bit camera used). The characteristic length (ac) of the CNC aggregates was determined using Debye-Bueche plots (I-0.5 vs q2).51, 52 A linear fit to the data plotted in the Debye-Bueche format was calculated in the flow or vorticity direction using the method of least squares. The slope and intercept of the linear fit were used to calculate a characteristic length [ac = (slope/intercept)0.5] for the CNC aggregates at various conditions. In addition, the distortion of the CNC aggregates was characterized by an aspect ratio, which was determined by taking the ratio of the characteristic length values in the flow and vorticity directions.


Page 8 of 35

Page 9 of 35

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

Langmuir

Furthermore, assuming that the produced aggregates behave as fractal-like objects, the fractal dimension of the aggregates (df) was estimated from the structure factor measured by small-angle light scattering (SALS).53-55 The measured scattered light intensity, I(q), can be expressed as I (q ) = I (0) P ( q ) S ( q ) , where I(0) is the zero-angle intensity, P(q) is the form factor (due to primary particles), S(q) is the structure factor (due to the arrangement of primary particles within the aggregates). Therefore, by analyzing S(q) versus q in the range of q values using a double logarithmic plot results in a straight line with the slope equal to -df.

RESULTS AND DISCUSSION The physicochemical properties of the CNC rods are summarized in Table 1, and their TEM micrographs are displayed in Figure 1. The CNC exhibits a needle-like shape with individual rods and rod bundles (Figure 1). Particularly, the average length and width of the rods are 218.1 ± 25.3/8.2 ± 3.5 and 452.8 ± 33.2/10.1 ± 3.3 nm for CNC1 and CNC2, respectively. Here the CNC rods are longer than those reported (70-300 nm).3 The apparent difference in length may arise from cotton sources and hydrolysis conditions such as time, temperature, and acid concentration. It is obvious that, with an increase of hydrolysis time from 1 to 2 h, both the length and width of the CNC rods are reduced. This can be explained by the fact that the crystalline region within MCC is more able to withstand attack by sulfuric acid than the amorphous region. For CNC2 rods, the hydrolysis reaction was restricted to a relatively short time so that the acid could degrade only the amorphous regions in cellulose, leaving behind the crystalline ones. However, with increasing hydrolysis time, sulfuric acid can remove the amorphous component and


Langmuir

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 10 of 35

partly damage the crystalline regions of the MCC, resulting in a decrease in both length and width. Compared with the change in width, the decrease in length is more evident.

Table 1. Length, width, aspect ratio and zeta potential of CNC1 and CNC2 rods CNC1

CNC2

CNC rods sonication

no sonication

sonication

no sonication

length, L (nm)

218.1 ± 25.3

219.5 ± 24.8

452.8 ± 33.2

453.1 ± 34.6

width, W (nm)

8.2 ± 3.5

8.2± 3.6

10.1 ± 3.3

10.1± 3.2

aspect ratio, L/W

26.6

26.8

44.8

44.9

zeta potential (mV)

-34.6 ± 4.2

-29.5 ± 5.7

-34.4 ± 5.6

-29.8 ± 5.2


Page 11 of 35

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

Langmuir

(a)

(b) Figure 1. TEM images of (a) CNC1 rods and (b) CNC2 rods.


Langmuir

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

Thus, the aspect ratio values of the CNC1 and CNC2 rods are calculated and summarized in Table 1. The CNC1 has an aspect ratio value of 26.6, and CNC2 has a relatively higher aspect value of 44.8. During the sulfuric acid hydrolysis process, negatively charged sulfate groups were introduced on the surface of CNC rods, which led to a considerable change in the zeta potential. The zeta potentials of CNC1 and CNC2 suspensions have the values of -34.6 ± 4.2 and -34.4 ± 5.6 mV, respectively. It shows that the further hydrolysis after 1 h did not affect the surface charge density of sulfate ester groups on the CNC rods. To further study the effect of sonication on the dimension and zeta potential of CNC rods, measurements have been performed on samples unsonicated, and the data are summarized in Table 1. The dimension of CNC rods in an unsonicated suspension is practically the same as that for the one sonicated, i.e., no change in the dimension of individual CNC rods during sonication is observed. This result is consistent with the work presented by Shafiei-Sabet et al.33 The sonication-induced increase in surface charge of the CNC rods is further supported by the increase in zeta potential seen in the suspensions (Table 1). It suggests that sonication can affect the surface charge of the CNC rods and release some ions into the surrounding media, which in turn can affect the stabilization of suspension. 33 It was reported that, with increasing CNC concentration the CNC suspensions undergo a transition from an isotropic phase to a biphasic structure of isotropic and liquid crystalline, and finally to a gel-like structure.9-11 However, in our case, with increasing CNC concentration the suspensions turns into a colloidal glass directly without spontaneous phase separation observed. Noticeably, the aqueous CNC1 suspension of 7.0 wt% does not flow when turning the sample bottle upside down (Figure 2). Similar


Page 12 of 35

Page 13 of 35

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

Langmuir

kinetic arrest without phase separation was experimentally found to take place directly from the isotropic liquid state at low particle concentration.18 The CNC rods exhibit strongly negatively charged surface properties due to the presence of hydroxyl and sulfate groups (Table 1). The possible formation mechanism can be explained as a result of each rod being trapped in an electrostatic cage by neighboring rod repulsion as the rods approach and their double layers overlap with an increase of concentration. Although increasing CNC concentration may lead to ordered liquid crystal phases, it also considerably enhances the probability of close rod encounters. Microscopically, the motion of a CNC rod is thus blocked or confined by the neighboring rods, making the suspension freeze. Here, the high aspect ratio of CNC rods has important roles in triggering the glass transition before any liquid crystalline ordering.

Figure 2. Photograph of CNC1 suspensions with increasing CNC concentration (1.0~7.0 wt%) for 48 h after preparation.

The dependence of steady shear viscosity on shear rate at 25°C for the suspensions with CNC concentrations from 1.0 to 6.0 wt% is shown in Figure 3. For both the CNC suspensions, the viscosity gradually increases as the CNC concentration increases, which may be due to the growth in collision possibility of the CNC rods. However, the viscosity


Langmuir

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 14 of 35

monotonically decreases as the shear rate increases over the whole investigated ranges, exhibiting a typical single-region shear-thinning behavior. The reported three-region shear-thinning behavior is not found for the CNC suspensions at any concentration level. The shear-thinning phenomenon becomes more significant as the CNC concentration increases. In comparison to the CNC1 suspensions, the CNC2 suspensions display more marked shear-thinning behavior and much higher viscosity at the same concentration. To make a comparative evaluation, the plots of viscosity versus shear-rate are fitted to a power law model as follows.

η = K γ n -1

(1)

where η is the viscosity, γ is the shear rate, K is the consistency coefficient, and n is the rate index. The viscosity of the CNC suspensions can be well fitted by the model (Figure 3), and the power law coefficients for each sample are shown in Table 2. It is shown that the degree of shear-thinning (as given by the flow index n) increases with increasing concentration.


Page 15 of 35

100 1% CNC1 2% CNC1 3% CNC1

10

5% CNC1

Viscosity (Pa.s)

6% CNC1 MODEL

1

0.1

0.01

1E-3 0.1

1

10

Shear rate (1/s)

100

1000

(a) 100

1% CNC2 2% CNC2 3% CNC2 5% CNC2 6% CNC2 MODEL

10

Viscosity (Pa.s)

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

Langmuir

1

0.1

0.01 0.1

1

10

Shear rate(1/s)

100

1000

(b) Figure 3. Steady shear viscosity versus shear rate for aqueous suspensions of (a) CNC1 and (b) CNC2 with various concentrations at 25oC. The continuous lines correspond to the best fit of power law model for each concentration.


Langmuir

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 16 of 35

Table 2. Consistency and rate index of CNC suspensions behaving as power law fluids CNC concentration (wt %)

K

n

CNC1

0.007

0.94

CNC2

0.09

0.91

CNC1

0.02

0.89

CNC2

0.18

0.86

CNC1

0.11

0.71

CNC2

0.36

0.86

CNC1

1.28

0.44

CNC2

4.24

0.45

CNC1

5.76

0.27

CNC2

9.42

0.33

1.0

2.0

3.0

5.0

6.0

The information on the microstructures of the CNC aggregates is probed by two-dimensional SALS images (Figure 4). On a microscopic length scale, all the CNC suspensions show isotropic ring patterns at low or high concentrations, which suggest the formation of nearly spherical aggregates (i.e., they do not have a preferential orientation after shear). There is no noticeable orientation observed in the images even in the case of 1000 s-1. It should be noted that, within the narrow concentration regime of 2.0 and 3.0 wt%, there is a progressive decrease in the areas of intense scattering appears with increasing shear rate. We specifically take into account a competition between the shear-induced breakup and the concentration-driven aggregation of the CNC suspensions. At a low concentration, the CNC rods are disordered and more random in the suspensions


Page 17 of 35

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

Langmuir

with a strong resistance to flow, and as a result a nearly circular aggregate on the micrometer scale is formed. At higher concentrations, the rods approach and their double layers overlap so that they are being trapped by their neighbors through long-ranged electrostatic interactions. Some physical constraints between the CNC rods could be easily created due to their large aspect ratio even at a low concentration. Alternatively, the high shear force might cause a breakup of the entangled CNC aggregates. With a further increase of CNC concentration, the aggregates become significantly denser and the physical constraints are stronger, and the rods’ movements are prohibited to such an extent that they can better withstand the shear stresses. As a result, the breakup can only happen in terms of a cage around each individual CNC rod that is formed by its neighbors within a narrow concentration regime.


Langmuir

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

(a)

(b) Figure 4. SALS images for aqueous suspensions of (a) CNC1 and (b) CNC2 as a function of shear rate. The flow direction is from left to right in all images.


Page 18 of 35

Page 19 of 35

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

Langmuir

To investigate the effect of sonication on the rheological behavior of CNC suspensions, the shear viscosity for 3.0 wt% CNC suspensions unsonicated as a function of shear rate has been measured and compared to that of the sonicated. The results are shown in Figure 5. The suspensions exhibit shear-thinning over the shear rate range investigated. A decrease in viscosity is observed after sonication, which is more significant in the low shear rate region. It indicates that sonciation can break the large aggregates into smaller pieces in the suspensions, which consequently causes a decrease in viscosity.

33

According to Eq. (1), we can estimate the shear energy per unit volume (E) as 56

E = ∫ σ(t ) γ (t )dt = ∫ K γ n +1dt

(2)

where σ is the shear stress, γ is the shear rate, t is the shear time, K is the consistency coefficient, and n is the rate index. The energy of shear breakup for CNC1 and CNC2 is 3.39 and 19.17J/mL, respectively. Compared to the shear energy, the ultrasonic energy (1140 J/mL) is high enough to breakup the aggregate structure and disperses the individual CNC rods.


Langmuir

10

CNC1 sonication CNC1 no sonication CNC2 sonication CNC2 no sonication

1

Viscosity (Pa.s).

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 35

0.1

0.01 0.1

1

10

100

1000

Shear rate (1/s)

Figure 5. Steady state viscosity versus shear rate for 3.0 wt% CNC suspensions unsonicated and sonicated as a function of shear rate.


Page 21 of 35

To obtain a further understanding and explore the breakup process, a shear-recovery experiment was carried out. As shown in Figure 6, the shear rate first increases 0.1 to 1000 s-1 and then decreases to the starting point in the same way. In addition, a set of scattering images, which provide information about the microstructure of the aggregates during the shear periods are shown as inserts. It is found that there is no hysteresis observed in the flow curve and SALS images for the reverse measurements. The absence of hysteresis suggests that structural changes during breakup are almost reversible, and the destructed aggregates can recover in a short time.

CNC1 increasing

1

CNC1 decreasing CNC2 increasing CNC2 decreasing

Viscosity (Pa.s).

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

Langmuir

0.1

0.01

0.001 0.1

1

10

100

1000

Shear rate (1/s)

Figure 6. Shear and recovery of 2.0 wt% CNC1 and CNC2 suspensions as a function of shear rate. Arrows correspond to the location of reported SALS images.


Langmuir

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 22 of 35

In order to estimate the restructuring of the CNC aggregates under shear flow and its effect on the breakup process, we introduce a proxy for estimating the local breakup rate from light scattering data. Following the respective size of the aggregate under the breakup conditions, the proxy to the breakup rate (KR), defined as the inverse of the characteristic time of the stress controlling the breakup, can be expressed as 43 KR = (

ac 0 − ac )γ ac 0

(3)

where ac0 is the size of the aggregate before breakup, ac denotes the characteristic size of the aggregate after breakup, and γ refers to the shear rate. It can be seen that the evaluated breakup rate follows a power law with respect to the applied shear rate, as shown in Figure 7. In addition, independent of the aspect ratio, a slope of 1.391 is found for the aggregates. From the curves of small angle light scattering we extract the fractal dimension (df) for the aggregates which equals to 2.41 ± 0.04. The obtained scaling is in close agreement with values obtained using Stokesian dynamics with exponents equal to 1.37 for aggregates with a df of 1.8 and equal to 1.58 for aggregates with a df of 2.7, respectively.44


Page 23 of 35

10000

Slope=1.391

1000 Breakup rate (1/s)

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

Langmuir

100 CNC1 CNC2 10

1 1

10

100

1000

10000

Shear rate (1/s)

Figure 7. Breakup rate versus shear rate for CNC aggregates with a fractal dimension of 2.41 during breakup process.

The interesting characteristic of the CNC aggregates under shear flow is the characteristic size in relation to the shear rate at which they breakup. When the breakup process is at steady state, the aggregation and breakup rates become equal and the aggregate size becomes constant with time. We define the characteristic size as that of the largest aggregate which does not breakup under defined shear conditions. Hence, the aggregates smaller than the characteristic size may not break up on the time scale of observation due to the energy barrier, whereas the aggregates larger than the characteristic size are unstable and break up instantaneously. The breakup becomes a fast process beyond the characteristic size due to the vanishing of the activation energy


Langmuir

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 24 of 35

barrier.45, 57 It was found that a power law dependence of the characteristic aggregate size versus the shear rate at the breakup location can be expressed as 45 ac : γ

−

1 d f +α ( d f )

: γp

(4)

where p is the scaling exponent, and α (df) is given by Eq. (5). α = −2.06491d f − 0.0180344 / (3 − d f ) + 4.98585

(5)

As the characteristic size of the aggregates decreases with increasing shear rate, we consider the rotational Peclet number of the CNC rods, which gives the ratio of the timescale of diffusive transport over the timescale of convective transport caused by shear. The rotational Peclet number (Per) is defined by 58, 59 Per =

γ Dr

=

8πη 0γ a 3 3k BT (ln 2rp − 0.5)

(6)

where γ is the shear rate, Dr is the rotary Brownian diffusion coefficient, η0 is the viscosity of the solvent, a is the length of rod, kB is the Boltzman’s constant, T is the temperature, and rp is the aspect ratio of rod. It is apparent that the degree of breakup increases with the increase of aspect ratio at equivalent shear rates. The method that we try to account for the effects of aspect ratio on breakup is to renormalize the suspending medium viscosity with the suspension viscosity.60 Here, according to Eq. (1), we obtain a dressed Peclet number (Per*) as: Per* = Per

η 8π Ka 3γ n = η 0 3k BT (ln 2 rp − 0.5)

(7)

According to Eq. (4), it is possible to find a correlation between the characteristic size and the dressed Peclet number at which the experiments were performed. Based on Eq. (4) and Eq. (7), we extend an analysis for the characteristic size of aggregate as a function of


Page 25 of 35

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

Langmuir

the dressed Peclet number as: p * n

ac : γ : ( Pe ) p

(8)

Eq. (8) shows a power law dependence of the characteristic size of aggregates on the dressed Peclet number, with the scaling exponent value depending on the aggregate fractal dimension and the index of shear-thinning. For the CNC aggregates with df of 2.41, we obtain p = -0.418, which corresponds to p/n = -0.470 and -0.486 for CNC1 and CNC2, respectively. In Figure 8, the normalized characteristic length (ac/a) of the CNC aggregates is presented by points on a double-logarithmic scale plot against the corresponding dressed Peclet number, whereas the scaling obtained by fitting the parameters p and n, is presented by lines. A good agreement can be clearly seen, which means that the CNC aggregates with different aspect ratio tend to breakup approximately in the same manner. On the other hand, the increase in viscosity (due to higher CNC concentration or aspect ratio) causes the dressed Peclet number to be higher, which means that the effective hydrodynamic stress acting on the aggregates is larger, and hence the degree of breakup increases with the increase of aspect ratio at equivalent shear rates.


Langmuir

100

CNC1 CNC2

a c/a

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 26 of 35

10 Slope=-0.47 Slope=-0.486

1 0.1

1

10

100 Pe

1000

10000

*

Figure 8. Normalized characteristic length (ac/a) versus dressed Peclet number for CNC aggregates with a fractal dimension of 2.41 during breakup process.


Page 27 of 35

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

Langmuir

CONCLUSION The aqueous CNC suspensions undergo a direct transition from dilute solution to colloidal glass instead of phase separation with increasing CNC concentration. Electrostatic repulsive interactions and excluded-volume effects of the CNC rods seem to play a major role in the sol-glass transition. Sonication does not change the rod size, while decreasing the viscosity of the suspensions. The viscosity profile of the CNC suspensions shows a single shear thinning behavior over the whole range of shear rates investigated. The shear thinning behavior becomes stronger with increasing CNC concentration. The reversible shear-induced breakup process of the CNC aggregates over a critical shear rate is witnessed by the rheo-SALS. We suggest that the CNC rods have a strong glass formation capacity, which have a strong resistance to flow under shear force, and therefore the competition between shear-induced breakup and concentration-driven aggregation exists. We describe the breakup behavior through two important variables, the breakup rate and the characteristic size of aggregates. It is found that the CNC aggregates tend to breakup approximately in the same manner and have the same fractal dimension of 2.41. The breakup rate shows a power law dependence on the shear rate, and the normalized characteristic length of the CNC aggregates shows a power law dependence on the dressed Peclet number, with the scaling exponent value depending on the aggregate fractal dimension and the shear-thinning index.


27

Langmuir

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 28 of 35

ACKNOWLEDGMENTS The work is supported by the National Natural Science Foundation of China (No. 21576116 and 21476212), Program of "Collaborative innovation center of food safety and quality control in Jiangsu Province ", and the Nantong science and Technology Bureau (MS22015041).

REFERENCES (1) Habibi, Y.; Lucia, L. A.; Rojas, O. J. Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications. Chem. Rev. 2010, 110, 3479-3500. (2) Kelly, J. A.; Shopsowitz, K. E.; Ahn, J. M.; Hamad, W. Y.; MacLachlan, M. J. Chiral Nematic Stained Glass: Controlling the Optical Properties of Nanocrystalline Cellulose-Templated Materials. Langmuir 2012, 28 (50), 17256-17262. (3) Lagerwall, J. P. F.; Schütz, C.; Salajkova, M.; Noh, J.; Hyun Park, J.; Scalia, G.; Bergström, L. Cellulose Nanocrystal-Based Materials: from Liquid Crystal Self-assembly and Glass Formation to Multifunctional Thin Films. NPG Asia Mater.

2014, 6, e80. (4) Revol, J. F.; Bradford, H.; Giasson, J.; Marchessault, R. H.; Gray, D. G. Helicoidal Self-Ordering of Cellulose Microfibrils in Aqueous Suspension. Int. J. Biol. Macromol. 1992, 14 (3), 170−172. (5) Revol, J. F.; Godbout, L.; Dong, X.M.; Gray, D.G.; Chanzy, H.; Maret, G. Chiral Nematic Suspensions of Cellulose Crystallites; Phase Separation and Magnetic Field Orientation. Liq. Cryst. 1994, 16, 127-134. (6) Hirai, A.; Inui, O.; Horii, F.; Tsuji, M. Phase Separation Behavior in Aqueous


28

Page 29 of 35

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

Langmuir

Suspensions of Bacterial Cellulose Nanocrystals Prepared by Sulfuric Acid Treatment. Langmuir 2009, 25, 497-502. (7) Fall, A. B.; Lindström, S. B.; Sundman, O.; Ödberg, L.; Wågberg, L. Colloidal Stability of Aqueous Nanofibrillated Cellulose Dispersions. Langmuir 2011, 27, 11332-11338. (8) Cherhal, F.; Cousin, F.; Capron, I. Influence of Charge Density and Ionic Strength on the Aggregation Process of Cellulose Nanocrystals in Aqueous Suspension, as Revealed by Small-Angle Neutron Scattering. Langmuir 2015, 31, 5596-5602. (9) Dong, X. M.; Kimura, T.; Revol, J.-F.; Gray, D. G. Effects of Ionic Strength on the Isotropic-Chiral Nematic Phase Transition of Suspensions of Cellulose Crystallites. Langmuir 1996, 12 (8), 2076-2082. (10) Dong, X. M.; Gray, D. G. Effect of Counterions on Ordered Phase Formation in Suspensions of Charged Rodlike Cellulose Crystallites. Langmuir 1997, 13 (8), 2404-2409. (11) Araki, J.; Kuga, S. Effect of Trace Electrolyte on Liquid Crystal Type of Cellulose Microcrystals. Langmuir 2001, 17 (15), 4493-4496. (12) Hasani, M.; Cranston, E.D.; Westmana, G.; Gray, D. G. Cationic Surface Functionalization of Cellulose Nanocrystals. Soft Matter 2008, 4, 2238-2244. (13) Lu, Ang.; Hemraz, U.; Khalili, Z.; Boluk, Y. Unique Viscoelastic Behaviors of Colloidal Nanocrystalline Cellulose Aqueous Suspensions. Cellulose 2014, 21, 1239-1250. (14) Buining, P. A.; Philipse, A. P.; Lekkerkerker, H. N. W. Phase Behavior of Aqueous Dispersions of Colloidal Boehmite Rods. Langmuir 1994, 10, 2106-2114.


29

Langmuir

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 30 of 35

(15) Wierenga, A.; Philipse, A. P.; Lekkerkerker, H. N. W.; Boger, D. V. Aqueous Dispersions of Colloidal Boehmite: Structure, Dynamics, and Yield Stress of Rod Gels. Langmuir 1998, 14, 55-65. (16) van Bruggen, M. P. B.; Lekkerkerker, H. N. W. Metastability and Multistability: Gelation and Liquid Crystal Formation in Suspensions of Colloidal Rods. Langmuir

2002, 18, 7141-7145. (17) Tzoumaki, M. V.; Moschakis, T.; Biliaderis, C. G. Metastability of Nematic Gels Made of Aqueous Chitin Nanocrystal Dispersions. Biomacromolecules 2010, 11, 175-181. (18) Hough, L.; Islam, M.; Janmey, P.; Yodh, A. Viscoelasticity of Single Wall Carbon Nanotube Suspensions. Phys. Rev. Lett. 2004, 93, 168102. (19) Kang, K.; Dhont, J. K. G. Structural Arrest and Texture Dynamics in Suspensions of Charged Colloidal Rods. Soft Matter 2013, 9, 4401-4411. (20) Kang, K.; Dhont, J. K. G. Glass Transition in Suspensions of Charged Rods: Structural Arrest and Texture Dynamics. Phys. Rev. Lett. 2013, 110, 015901. (21) Onsager, L.; Ann, N. Y. The Effects of Shape on the Interaction of Colloidal Particles. Acad. Sci. 1949, 51, 627-659. (22) Tanaka, H.; Meunier, J.; Bonn, D. Nonergodic States of Charged Colloidal Suspensions: Repulsive and Attractive Glasses and Gels. Phys. Rev. E 2004, 69, 031404. (23) Poon, W. C. K.; Haw, M. D. Mesoscopic Structure Formation in Aggregation and Gelation. Adv. Colloid Interface Sci. 1997, 73, 71-126. (24) Poon, W. C. K.; Pirie, A. D.; Pusey, P. N. Gelation in Colloid-Polymer Mixtures.


30

Page 31 of 35

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

Langmuir

Faraday Discuss. 1995, 101, 65-76. (25) Anderson, V. J.; Lekkerkerker, H. N. W. Insights into Phase Transition Kinetics from Colloid Science. Nature 2002, 416, 811-815. (26) Boluk, Y.; Zhao, L.; Incani, V. Dispersions of Nanocrystalline Cellulose in Aqueous Polymer Solutions: Structure Formation of Colloidal Rods. Langmuir 2012, 28, 6114-6123. (27) Hu, Z.; Cranston, E. D.; Ng, R.; Pelton, R. Tuning Cellulose Nanocrystal Gelation with Polysaccharides and Surfactants. Langmuir 2014, 30, 2684-2692. (28) Li, M.-C.; Wu, Q.; Song, K.; Lee, S.; Qing, Y.; Wu, Y. Cellulose Nanoparticles: Structure-Morphology-Rheology Relationships. ACS Sustainable Chem. Eng. 2015, 3, 821-832. (29) Martoia, F.; Dumont, P. J. J.; Orgeas, L. Micro-mechanics of Electrostatically Stabilized Suspensions of Cellulose Nanofibrils under Steady State Shear Flow. Soft Matter 2016, 12, 1721-1735. (30) Araki, J.; Wada, M.; Kuga, S.; Okano, T. Flow Properties of Microcrystalline Cellulose Suspension Prepared by Acid Treatment of Native Cellulose. Colloids Surf., A 1998, 142 (1), 75-82. (31) Bercea, M.; Navard, P. Shear Dynamics of Aqueous Suspensions of Cellulose Whiskers. Macromolecules 2000, 33, 6011-6016. (32) Urena-Benavides, E. E.; Ao, G.; Davis, V. A.; Kitchens, C. L. Rheology and Phase Behavior of Lyotropic Cellulose Nanocrystal Suspensions. Macromolecules 2011, 44, 8990-8998. (33) Shafiei-Sabet, S.; Hamad, W. Y.; Hatzikiriakos, S. G. Rheology of Nanocrystalline


31

Langmuir

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 32 of 35

Cellulose Aqueous Suspensions. Langmuir 2012, 28, 17124-17133. (34) Qiao, C.; Chen, G.; Zhang, J.; Yao, J. Structure and Rheological Properties of Cellulose Nanocrystals Suspension. Food Hydrocolloids 2016, 55, 19-25. (35) Shafiei-Sabet, S.; Hamad, W. Y.; Hatzikiriakos, S. G. Ionic Strength Effects on the Microstructure and Shear Rheology of Cellulose Nanocrystal Suspensions. Cellulose

2014, 21, 3347-3359. (36) Orts, W.; Godbout, L.; Marchessault, R. H.; Revol, J. F. Enhanced Ordering of Liquid Crystalline Suspensions of Cellulose Microfibrils: A Small Angle Neutron Scattering Study. Macromolecules 1998, 31, 5717-5725. (37) Ebeling, T.; Paillet, M.; Borsali, R.; Diat, O.; Dufresne, A.; Cavaille, J. Y.; Chanzy, H. Shear-Induced Orientation Phenomena in Suspensions of Cellulose Microcrystals, Revealed by Small Angle X-ray Scattering. Langmuir 1999, 15 (19), 6123-6126. (38) Schütz, C.; Agthe, M.; Fall, A. B.; Gordeyeva, K.; Guccini, V.; Salajková, M.; Plivelic, T. S.; Lagerwall, J. P. F.; Salazar-Alvarez, G.; Bergström, L. Rod Packing in Chiral Nematic Cellulose Nanocrystal Dispersions Studied by Small-angle X-ray Scattering and Laser Diffraction. Langmuir 2015, 31 (23), 6507-6513. (39) Qi, W.; Xu, H. N.; Zhang, L. The Aggregation Behavior of Cellulose Micro/Nanoparticles in Aqueous Media. RSC Adv. 2015, 5, 8770-8777. (40) Soos, M.; Ehrl, L.; Bäbler, M. U.; Morbidelli, M. Aggregate Breakup in a Contracting Nozzle. Langmuir 2010, 26, 10-18. (41) Zaccone, A.; Soos, M.; Lattuada, M.; Wu, H.; Babler, M. U.; Morbidelli, M., Breakup of Dense Colloidal Aggregates under Hydrodynamic Stresses. Phys. Rev. E

2009, 79, 061401.


32

Page 33 of 35

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

Langmuir

(42) Harshe, Y. M.; Lattuada, M.; Soos, M. Experimental and Modeling Study of Breakage and Restructuring of Open and Dense Colloidal Aggregates. Langmuir 2011, 27, 5739-5752. (43) Saha, D.; Soos, M.; Luethi, B.; Holzner, M.; Liberzon, A.; Babler, M. U.; Kinzelbach, W. Experimental Characterization of Breakage Rate of Colloidal Aggregates in Axisymmetric Extensional Flow. Langmuir 2014, 30, 14385-14395. (44) Harshe, Y. M.; Lattuada, M. Breakage Rate of Colloidal Aggregates in Shear Flow through Stokesian Dynamics. Langmuir 2012, 28, 283-292. (45) Conchuir, B. O.; Zaccone, A. Mechanism of Flow-induced Biomolecular and Colloidal Aggregate Breakup. Phys. Rev. E 2013, 87, 032310. (46) van der Zande, B. M. I.; Koper, G. J. M.; Lekkerkerker, H. N. W. Alignment of Rod-Shaped Gold Particles by Electric Fields J. Phys. Chem. B 1999, 103, 5754-5760. (47) Baravian, C.; Caton, F.; Dillet, J. Steady Light Diffusion Application to Rheology: A New Tool for the Characterization of Concentrated Suspensions. Rheol. Acta 2004, 43, 427-432. (48) Christophe, B.; Julien, M.; François, C.; Alain, D. Characterization of Dynamical Emulsification Process in Concentrated Conditions. AIChE J. 2007, 53, 1994-2000. (49) Kline, S. R. Reduction and analysis of SANS and USANS data using IGOR Pro. J. Appl. Crystallogr. 2006, 39, 895-900. (50) TA Instruments. AR Series Small Angle Light-Scattering (SALS) Accessory Manual. TA Instruments: Newark, DE, 2008. (51) Walker, L. M.; Kernick III, W. A.; Wagner, N. J. In Situ Analysis of the Defect


33

Langmuir

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 34 of 35

Texture in Liquid Crystal Polymer Solutions under Shear. Macromolecules 1997, 30, 508-514. (52) Xu, H. N.; Ma, S. F.; Chen, W. Unique Role of β-cyclodextrin in Modifying Aggregation of Triton X-114 in Aqueous Solutions. Soft Matter 2012, 8, 3856-3863. (53) Kerker, M. The Scattering of Light. Academic Press: New York, 1969. (54) Jones, A. R. Lights Scattering for Particle Characterization. Prog. Energy Combust. Sci. 1999, 25, 1-53. (55) Sorensen, C. M. Light Scattering by Fractal Aggregates: A review. Aerosol Sci. Technol. 2001, 35, 648-687. (56) Agrawal, A.; Yu, H. Y.; Srivastava, S.; Choudhury, S.; Narayanan, S.; Archer, L. A. Dynamics and Yielding of Binary Self-Suspended Nanoparticle Fluids. Soft Matter

2015, 11, 5224-5234. (57) Mura, F., Zaccone, A. Effects of Shear Flow on Phase Nucleation and Crystallization. Phys. Rev. E 2016, 93, 042803. (58) Russel, W. B.; Saville, D. A.; Schowalter, W. R. Colloidal dispersions. Cambridge: University Press, 1991. (59) Kinloch, I. A.; Roberts, S. A.; Windle, A. H. A Rheological Study of Concentrated Aqueous Nanotube Dispersions. Polymer 2002, 43, 7483-7491. (60) Egres, R. G.; Nettesheim, F.; Wagner, N. J. Rheo-SANS Investigation of Acicular-precipitated Calcium Carbonate Colloidal Suspensions through the Shear Thickening Transition. J. Rheol. 2006, 50, 685-709.


34

Page 35 of 35

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

Langmuir

Table of Content Graphic


35

Shear-Induced Breakup of Cellulose Nanocrystal Aggregates

Recommend Documents