Exclusion and Trapping of Carbon Nanostructures in Nonisotropic

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B: Liquids, Chemical and Dynamical Processes in Solution, Spectroscopy in Solution

Exclusion and Trapping of Carbon Nanostructures in Non-Isotropic Suspensions of Cellulose Nanostructures Orit Mendelson, Guang Chu, Efrat Ziv, Yael Levi-Kalisman, Gleb Vasilyev, Eyal Zussman, and Rachel Yerushalmi-Rozen J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.9b02227 • Publication Date (Web): 02 Apr 2019 Downloaded from http://pubs.acs.org on April 2, 2019

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The Journal of Physical Chemistry

Exclusion and Trapping of Carbon Nanostructures in Non-Isotropic Suspensions of Cellulose Nanostructures Orit Mendelson1,2, Guang Chu3, Efrat Ziv2, Yael Levi-Kalisman4, Gleb Vasilyev3, Eyal Zussman3, Rachel Yerushalmi – Rozen2,5* 1. Department of Chemistry, Nuclear Research Center-Negev, Beer-Sheva, 84190, Israel. 2. Department of Chemical Engineering, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel. 3. NanoEngineering Group, Faculty of Mechanical Engineering, Technion – Israel Institute of Technology, 32000 Haifa, Israel. 4. The Center for Nanoscience and Nanotechnology, and The Institute of Life Sciences at The Hebrew University of Jerusalem, Israel 5. The Ilse Katz Institute for Nanoscience and Technology, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel.

Corresponding author: Rachel Yerushalmi – Rozen [email protected], 972-86461272

Abstract Incorporation of carbon nanotubes (CNTs) into liquid crystalline (LC) phases of cellulose nanostructures (CNCs) may be used for preparation of hybrids with novel optical, electrical and mechanical properties. Here we investigated the effect of nanoparticle diameter, geometry, aspect ratio and flexibility on the exclusion of dispersed carbon nanostructures (CNS) from the chiral nematic phase (N*) of the CNCs. While CNS are nicely dispersed in isotropic suspensions of CNCs, we observe that fullerenes, carbon black and CNT are depleted from the N* phase. This observation is surprising as theoretical predictions and previous observations of nanoparticles indicate that nanometric inclusions would be incorporated within the N* phase. Cryo1 ACS Paragon Plus Environment

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TEM imaging reveals that the dispersed CNS induce miss- orientation of the CNCs irrespective of their geometry and size. Rheological measurements suggest that about 10% of the CNCs are affected by the CNS. The multi-particle nature of the interaction may be the origin of the non-size selective exclusion of the CNS. Re-entrant behavior is observed at high CNCs concentrations (about 13 wt%) where a (nematic) gel-like phase kinetically traps the CNS. These phases exhibit non-Newtonian flow behavior, and birefringence, offering a pathway for preparation of non-isotropic CNCs-CNTs composites and thin films via liquid processing.

Introduction Suspensions comprising more than one type of nanostructures (NS) can serve as “colloidal inks” for additive manufacturing and layer-by-layer deposition of multifunctional nanocomposites1. Novel combinations of optical,34,4 electrical and mechanical properties were demonstrated in engineered materials. Yet, mismatch in physical characteristics such as the aspect ratio, rigidity or size, may lead to uncontrolled entropy-driven self-assembly, spatial organization or macroscopic phase separation6,7 into coexisting liquid phases. Two types of nanostructures, currently at the focus of materials engineering, are cellulose nanocrystals (CNCs)8,9 and carbon nanotubes (CNTs)9. It was demonstrated that both single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) can be dispersed by CNCs in aqueous media, at low CNCs concentrations (below the isotropic-chiral nematic transition)1011. Dispersion of CNTs by CNCs alleviates the need for chemical functionalization of the CNTs or utilization of surfactants10,12,13 offering efficient pathway for preparation of CNCs-CNTs hybrids and composites.

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Here we characterize the behavior of hydrophobic, non-charged carbonaceous nanostructures (CNs) in CNCs dispersions all the way from the dilute, isotropic regime through the chiral nematic phase (N*) and up to the gel-phase of the CNCs. While the nanostructures are of similar chemical composition, they differ in their geometry (spherical C60 fullerenes and Carbon Black (CB) vs. cylindrical CNTs), typical diameter (nanomteric sized fullerenes and CNTs vs. colloidal CB) and in the persistence length (SWNTs (30-170 m)14 vs. MWNTs (about 200 nm, due to local defects)). Sonication of the CNs in aqueous suspensions of CNCs results in the formation of stable dispersions in which the CNCs comprise the majority phase. As was reported before1110, we observe that the different CNs can be dispersed at low CNCs concentrations (1wt%) forming colloidal inks. The dispersions are stable and long lived. Surprisingly, we find that unlike previous reports on size mismatch of inclusions and the related depletion interactions in other systems6,15,16, all the CNs studied here, irrespective of size and geometry, are depleted from the N* phase of the CNCs (here observed above 4.2wt%). Cryo-TEM imaging and rheological measurements indicate that a significant fraction of the CNCs are involved in the dispersion of the CNs. The multi-particle nature of the interaction may be the origin of the observed exclusion of the CNs from the LC phase of the CNCs. Re-entrant behavior is observed at high CNCs concentrations (about 13wt%) where a (nematic) gel-like phase kinetically traps the CNs. The latter is used for preparation of CNCsCNTs dispersions with non-Newtonian flow behavior and thin films hybrids that exhibit iridescence. Experimental Section Materials: CNCs suspensions: Cellulose nanocrystals were extracted from pulp by controlled sulfuric acid-catalyzed hydrolysis. 20 g of milled pulp was hydrolyzed in 3 ACS Paragon Plus Environment


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200 mL of H2SO4 (1g pulp/10 ml H2SO4) aqueous solution (64wt%) under vigorous stirring at 45 °C for 60 min. The pulp slurry was diluted with cold deionized water (about ten times the volume of the acid solution used) to stop the hydrolysis and allowed to subside overnight. The clear top layer was decanted and the remaining cloudy layer was centrifuged. The supernatant was decanted and the resulting thick white slurry was washed three times with deionized water. Finally, the white thick suspension was placed into a Millipore ultraﬁltration cell (model 8400) to wash the cellulose with deionized water until the pH of suspension was stable at a range of 3-5.5. The cut-off value of the membrane is 3 kDa (Ultrafiltration Discs, Millipore). The thick pulp slurry from the Millipore cell was diluted to the desired concentration with constant stirring, and the concentration was measured. The suspensions were sonicated for complete suspension and prevention of aggregation of the CNCs. The dimensions of the CNCs are 5-20 nm width and 200-300 nm length. Zeta potential measurements of sonicated suspensions from different batches (3 wt%) show values of -50 ±5 mV. CNCs powder: was purchased from University of Maine Process Development Center, USA (www.flp.fs.us). The CNCs were extracted from wood pulp using sulfuric acid hydrolysis. The dimensions of the CNCs are 5-20 nm width and 150-200 nm length. Zeta potential measurements of suspensions (3wt%) prepared by sonication of the freeze dried powder in water show values of -55 ±5 mV. Table 1: Carbonaceous NS Diameter, d and Supplier length, l d ~ 1.2 nm SWNTs

Sigma-Aldrich (cat. 805033) l ~ 3-5 µm


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MWNTs –

d ~ 6-10 nm Nanothinx S.A. Inc. Greece

NTX4

l ˃ 10 µm

Carbon black

Cabot Corp

C60

SES research Houston, TX (99.95%

fullerenes*

purity cat. No. 600-9950)

d ~ 50-100 nm

d ~ 1 nm

Preparation: CNs dispersions were prepared by sonicating (2h, 50Watt, 43kHz) 2 mg of MWNTs, SWNTs or CB powders and C60 fullerenes (Table 1) in 4 mL of a suspension containing CNCs (1-7wt% at pH = 2-3). The resulting dispersions were centrifuged at 4500 rpm for 20 min. The dispersions were stable for several months, and precipitation was not observed. Highly concentrated dispersions were prepared by dispersing the CNTs or CB in 1wt% of CNCs, then adding powder of CNCs to the suspensions to a final concentration of 13wt%. The suspensions were stirred for 2h. Characterization: Cryogenic transmission electron microscopy (Cryo-TEM) was applied for direct imaging of the nanostructure of suspended CNCs, and CNCs-CNs dispersions. Samples were prepared by applying a 3 L drop to a glow discharge treated TEM grid (300 mesh Cu Lacey substrate, Ted Pella, Ltd.). The excess liquid was blotted and the specimen was vitrified by rapid plunging into liquid ethane pre-cooled by liquid nitrogen using a vitrification robot system (Vitrobot mark IV, FEI). The rapid cooling results in physical fixation of the liquid state and allows examination of the dispersion in the high vacuum of the electron microscope at cryogenic temperature, which prevents the formation of either cubic- or hexagonal ice. The vitrified samples were examined at -177 °C using FEI Tecnai 12 G2 TWIN TEM operated at 120 kV and equipped with a 5 ACS Paragon Plus Environment


Gatan model 626 cold stage. The images were recorded by a 4Kx4K FEI Eagle CCD camera in low dose mode. TIA (Tecnai Imaging & Analysis) software was used to record the images. Zeta potential measurements: The zeta potential and the average particle size were measured by analyzing 3wt% CNCs in water using the Zetasizer Nano ZS (Malvern Instruments Ltd.). Polarized optical microscopy (POM): Images of CNCs suspensions and CNCs-CNs dispersions were taken using a polarized light microscope (Leica DM400M), equipped with a CCD camera (Leica DFC450C). Raman Spectroscopy: Raman scattering spectra were obtained using a Jobin-Yvon LabRam HR 800 micro-Raman system, equipped with a Synapse CCD detector and excitation source of Argon laser (= 532nm, 3mW, spot size of about 1µm, exposure time of 30 s). In most of the measurements the laser power was reduced by 10 using ND filter. Rheological measurements: Discovery DHR-2 rotational rheometer (TA Instruments, USA) was used to characterize the rheological properties of the suspensions and dispersions under steady-state and oscillatory shear deformations. Controled rate and strain amplitude were applied, respectively. Parallel-plate geometry, with a diameter of 40 mm and a gap of 0.35 mm, was used. All rheological measurements were performed at 25 °C.

Results and Discussion Aqueous suspensions (1-13wt%) of electrostatically stabilized sulfuric acid-hydrolyzed CNCs were prepared and studied. Figure 1a presents the percentage of the nematic phase along the biphasic Isotropic-Nemaic line obtained from visual inspection of the 6 ACS Paragon Plus Environment

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suspensions. Above a threshold concentration of 4.2 wt% (2.7 vol%) a transition from randomly oriented colloidal suspension to a biphasic regime of coexisting isotropicchiral nematic (I-N*) phases takes place. The fraction of the nematic phase increases (monotonically) with CNCs concentration up to a jammed gel phase (~ 12 wt%). Representative POM images of suspensions at concentrations around 3 wt% (2 vol%) (Figure 1b) reveal the nucleation of droplets (tactoids) of the chiral nematic phase below the I-N* transition17. Fingerprint texture is observed via POM in the lower, chiral nematic phase of 7 wt% (4.6 vol%) suspensions (Figure 1c)) while the upper phase is isotropic (Figure 1d)). Further increase in the CNCs concentration up to 13 wt% (8.7 vol%) reveals a non-isotropic gel phase (SI, Figure S1).

Figure 1: a) A diagram presenting the volume ratio of the nematic phase along the biphasic I-N* line. The inset presents an image of a CNCs suspension at the biphasic regime taken between crossed polarizers. POM images (crossed polarizers configuration) of CNCs suspensions b) 1%wt c) lower (N*) phase and d) upper (I) phase of 7wt% suspensions. The scale bar is 50 microns (b-d).

With CNCs length of about 300 nm (±50) and diameter of about 20 nm (±10) the volume fraction at the transition is =0.03, one order of magnitude lower than the 7 ACS Paragon Plus Environment


prediction suggested by the relation φ = 4.5D/L=0.3 derived from the Onsager model 18,19.

This value is similar to previous reports20, and can be attributed to electrostatic

repulsion21,22. We note here that the polydispersity in CNCs dimensions and the variability in the measured zeta potential is high and thus the threshold concentration may change slightly from batch to batch. In a series of experiments CNs were sonicated in suspensions of CNCs of different concentrations (1 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 8 wt%). We observe that up to the I-N* transition of the native suspensions the CNs are well dispersed, and the resulting dispersions are black and ink-like. The dispersions are stable, and macroscopic aggregation is not observed even after weeks of incubation at ambient conditions (Figure 2a). In CNCs suspension residing at the biphasic region, the CNs are preferentially suspended in the isotropic phase (Figure 2b, c, upper phase), and depleted from the N* phase (Figure 2b, c, lower phase) of the CNCs. The phase diagram follows closely that of the native CNCs (Figure 2f), demonstrated by representative POM images at 5.5 wt% dispersions (Figure 2d,e, upper and lower phase, respectively), with a similar pitch value of ~15 m.


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Figure 2. Optical images of dispersions of 0.5 mg/ml of MWNTs, SWNTs, and CB prepared using a) 1.0 wt% CNCs and b) 5.5 wt% CNCs. SWNT in c) 1 wt%, 4 wt%, 5 wt% and 6 wt% suspensions of CNCs. POM images of d) the upper phase e) the lower phase, of the 5.5wt% CNCs dispersion of MWNTs presented in b) f) An overlay of the ratio of the N*-I phases as a function of CNCs concentration in the presence of dispersed SWNTs (black squares) and native CNCs (open triangles). Raman scattering spectra were used to investigate the mutual interaction between SWNTs and for quantitative analysis of the CNCs-SWNTs ratio.

Figure 3. Raman scattering of dried powders of a) SWNTs b) CNCs c), d) dispersions of SWNTs (1 mg/ml) in 6 wt% CNCs dried (air, room temperature) by deposition of a small volume from each phase on a glass slide c) upper d) lower phase. The Raman spectra of SWNTs and CNCs, presented in Figures 3a and 3b, respectively, are typical to the pristine materials: For the SWNTs, sharp peaks are observed at Raman shifts of ∼1595 cm-1 due to the tangential stretching mode (G-band) and a broader band around ∼2662 cm-1 (G'-band), arises from an overtone of the disorder induce mode around 1337 cm-1 (D-band)23. Raman spectra of dried CNCs-CNTs dispersions are 9 ACS Paragon Plus Environment


presented in Figure 3c,d. The peaks of the upper phase are slightly shifted (by 2–7 cm1)

to higher wavenumbers (Figure 3c). The ratio between the D-band and the G-band

intensities is ~0.25, equal to the ratio obtained for the pristine SWNTs. The latter indicates that the interaction between the suspended SWNTs and the CNCs does not modify the sp2 hybridization of the pristine SWNTs. The Raman spectrum of the lower phase (Figure 3d) is dominated by the typical peaks of the CNCs. The relative fraction of SWNTs to CNCs as evaluated from the signals ratio at ~1592 cm-1 (SWNTs G-band) to ~1097 cm-1 CNCs feature, is ~6.6 (SWNTs to CNCs) for the upper phase and ~0.8 (SWNTs to CNCs) in the lower phase. These values clearly indicate that the SWNTs are depleted from the lower (N*) phase and enriched in the upper (isotropic) phase. Similar results (not shown) were obtained for MWNTs. The microstructure of the dispersions was investigated using cryo-TEM. In Figure 4 we present images taken from vitrified 1 wt% CNCs dispersions of SWNTs (Figure 4a,b) and MWNTs (Figure 4c).

Figure 4. Cryo-TEM images of 1 wt% CNCs suspensions of: a,b) SWNTs (0.5 mg/ml). Blue lines in the insets (which are low magnifications of the images) outline individual SWNTs. c) MWNTs (0.5 mg/ml). Black arrows point at suspended MWNTs. Scale bars = 200 nm


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Cryo-TEM images of dispersed SWNTs (Figure 4a,b) reveal that CNCs align along the semi-rigid SWNTs (highlighted by blue lines in the inset images). Due to the smaller diameter (about 1 nm) of the SWNTs they are hardly noticeable in the cryo-TEM image of the CNCs. In contrast, the suspended MWNTs are clearly visible as can be seen in Figure 4c. The dispersing CNCs seem to crowd in the vicinity of suspended MWNTs (and CB, Figure S2).

Figure 5 Cryo-TEM images of the upper phase of 5.5 wt% CNCs suspensions containing a) SWNTs b) MWNTs. The lower phase of 5.5 wt% CNCs-MWNTs dispersion at two magnifications c) and d). Cryo-TEM images of suspensions at concentrations in the biphasic regime (above 4.2 wt% (volume fraction of φ = 0.027) show randomly oriented CNCs in the upper phase 11 ACS Paragon Plus Environment


(Figure 5a,b). While dispersed SWNTs are hard to observe in the presence of concentrated CNCs (Figure 5a) MWNTs are clearly seen (Figure 5b, and Figure S3 in the SI). The cryo-TEM images of the lower phase of the dispersions (the white looking phase in Figures 2,3) show what may seem to be clusters of oriented CNCs, with typical dimensions of about 500 nm. The cryo-TEM images (Figures 4, 5 and S3) indicate that CNCs do not align with either the MWNTs or CB, but stack along the SWNTs, as was reported before11. In Figure 6 we present a schematic illustration of the interaction between the MWNTs and the CNCs at the biphasic regime.

Figure 6. A sketch showing MWNTs (black curved lines) dispersed in randomly oriented CNCs (green rods) in the isotropic phase (left). In the biphasic region (right), MWNTs are depleted from the chiral-nematic (N*) phase and enriched the isotropic phase. We observe that the CNCs-CNs interactions do not follow the expected behavior: previous reports indicate that the criteria for inclusion (or exclusion) of nanostructures within the chiral nematic (N*) phase of the CNCs is their size, where particles larger than the inter-CNCs distance (25 to 50 nm, depending on the concentration of the 12 ACS Paragon Plus Environment

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suspension24) should be excluded and particles of smaller diameter are expected to be incorporated into the N* phase. If that should be the criteria we would expect that C60 fullerenes (Figure S4 in the SI) that are spherical, monodisperse nanostructures with a diameter of 1nm25 would be incorporated in the N* and CB (with a typical diameter of 50 nm) would be incorporated at the low concentrations of the N*. However, we find here that none of the investigated CNs is incorporated into the N*. So what is the origin of CNs enrichment in the isotropic phase of the CNCs suspensions? If we assume that dispersion of CNs by CNCs involves interaction of more than a few CNCs with each CNs (as observed in the cryo-TEM images) the effective disruption of the CNCs packing due to the presence of dispersed CNs becomes a non-local effect, not directly related to the size of the individual CNs, but rather to the CNs-CNCs aggregates. This conjecture is supported by the flow behavior of the dispersions described below. A different behavior is observed in the highly concentrated CNCs suspensions. In Figure 7a we present dispersions at CNCs concentrations of 13 wt%. The samples were prepared by dispersing the CNTs (or CB) in 1 wt% of CNCs adding CNCs (powder) to the suspensions to a final concentration of 13 wt%. As can be seen in Figure 7a, a single phase of black ink-like dispersion is obtained. Typical POM images (crossed polarizers configuration) show the disappearance of the fingerprint texture, and the appearance of birefringent (liquid) nematic phase (Figure 7c), similar to the behavior of the native CNCs (Figure S1 in the SI). The dispersion is stable and does not phase separate for weeks, probably as jamming of the CNCs results in kinetic stabilization of the dispersed CNTs in the viscous dispersion (see rheological characterization below). The dispersion can be dried to form birefringent films (Figure 7 bottom of a and b). As can be seen in the image the dried film is composed of random domains of LC phases, probably due



to the evaporation of the water and freezing of the non-equilibrium organization of the film. In the case of the fullerenes, mixing the two phases and fast drying of the fullereneladen suspension shows the formation of iridescent films. The absence of particle aggregates at the contact line (also known as the “coffee- stain” effect26) indicates that mesoscopic fullerene aggregation does not take place upon drying, probably due to gelation of the CNCs (Figure S4 of the SI).

Figure 7. Concentrated suspensios of CNCs prepared by addition of CNCs powder to a dispersion of a) SWNTs (0.5 mg/ml in 1 wt% CNCs suspensions) b) MWNTs (0.5 mg/ml in 1 wt% CNCs suspension). Birefringent films formed by drying the dispersions are shown below a and b. c) POM images of 0.5mg/ml of SWNTs and CB in 13%wt of CNCs suspensions. The scale bar is 1 cm. d) A cartoon presenting the re-entrant behavior of dispersed CNTs in suspensions of CNCs.

In Figures 8 and 9 we present rheological investigation of the flow behavior of dispersions of CNs in CNCs suspensions. Flow curves of dilute, isotropic (1 wt%) CNCs suspensions (Figure 8a) demonstrate almost Newtonian behavior. Slight decrease of viscosity with shear rate may be ascribed to orientation of the particles under the action of the strong shear field27. The viscosity of the dispersions (CNCsSWNTs or CNCs-CB) is somewhat lower than the viscosity of the CNCs suspensions. As the viscosity in diluted concentration regime scales with the volume fraction of the 14 ACS Paragon Plus Environment

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suspended particles according to the Einstein equation28, this observation indicates a reduction in the fraction of suspended (dispersed) objects, probably due to the formation of aggregates comprising CNCs and CNs. This assumption is supported by the cryoTEM images (Figure 4a and Figure S2), where CNCs are seen to align along the SWNTs and accumulate around CB aggregates. Quantitative estimation (see the SI) would suggest that about 10wt% of the CNCs take part in the dispersion of the CNs. The effect of the CNs on the flow behavior of concentrated (13 wt%) CNCs gel-like suspensions (Figure 8b) is qualitatively different. Namely, the presence of CNTs increases significantly the viscosity in comparison with the viscosity of pure CNCs suspension, and even more so in the CB dispersions. In particular, in the region of low shear rates an increase of 2.5-fold in the viscosity was measured for CNCs-SWNTs dispersions and 6.5-fold for CNCs-CB dispersions.

Figure 8. Flow curves of a) 1 wt% and b) 13 wt% CNCs suspensions containing carbonaceous particles (SWNTs or CB) at 25°C.

The results of frequency sweep tests (Figure 9a) of CNCs suspensions (13 wt%) demonstrate solid-like behavior with G’ > G”, where G’ is the storage modulus and G’’ the loss modulus. The storage modulus of the suspensions is weakly dependent on the oscillation frequency in the region of the frequencies applied and thus can be considered 15 ACS Paragon Plus Environment


a plateau. Comparison of the measured storage moduli (G’) enables us to compare between the colloidal structures of the dispersions, as the plateau value is reciprocally proportional to mesh size of the transient network formed in a suspension29. As the lowest value is measured in CNCs suspensions, and the highest in CNCs-CB dispersions, one may conclude that mesh size formed in the native concentrated gellike CNCs suspensions is decreased in CB dispersions. At the same time, the loss moduli of the dispersions do not differ significantly in the region of intermediate and high frequencies. The degree of solid-like behavior can be quantified by the value of tangent delta, tan δ = G”/G’. It is clearly seen (Figure 9b) that suspensions of pure CNCs exhibit the highest tan δ value while suspension containing CB the lowest indicating an increased contribution of the elastic component (G’). In addition, it should be noted that the static structures formed in CB dispersions (Figure S2) recover after shearing, as indicated by the storage modulus (Figure S5). The latter reaches the initial value after the structure was destroyed under the action of high amplitude oscillations and a downward strain run (from high to low strain amplitude) is applied. In contrast, the storage modulus of both pure CNCs and CNCs-SWNTs suspensions do not reach this level and remain lower revealing incomplete structure recovery. For the CNCs suspension this effect is more pronounced.


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Figure 9. (a) Dynamic moduli G’ (filled shapes) and G” (empty shapes) and (b) tan δ vs. frequency for 13 wt% CNCs suspensions containing carbonaceous particles.

Conclusions Hybrid materials produced via co-processing of two types (or more) of nanostructures are at the focus of current materials engineering, as they may exhibit new combinations of mechanical, optical and thermal properties30,31. In this study we investigated the behavior of carbon nanotubes and spherical nanostructures (carbon black and fullerenes) dispersed by CNCs. Common knowledge derived from colloidal suspensions would suggest that the phase behavior of the CNCs-CNS dispersions should be dominated by the geometry, flexibility and size mismatch between the nanostructures32. Following this line of thought we would expect that the elastic (entropic) penalty of inclusion of the C60 fullerenes (spherical, diameter = 1nm) or the SWNTs (rigid, elongated, diameter about 1 nm) would be minor and these CNs would be incorporated into the nematic phase of the CNCs without a significant free energy penalty. The observed exclusion of all the CNs investigated here from the N* phase of the CNCs, is thus surprising. Cryo-TEM imaging and characterization of the flow behavior of the dispersions reveals that a large number of CNCs (about 10 wt%) interact with the CNS and thus the disruption of the CNCs phase is non-local. The long- range effect of the carbonaceous inclusions, that may result from the hydrophobic interaction between the CNs and the CNCs, introduces a much larger distortion than would be expected from the size (geometrical dimensions) of the individual CNs. At concentrated CNCs (13 wt%) suspensions, prepared by addition of CNCs powder to a stable dispersion of CNTs in the dilute CNCs phase, a re-entrant behavior is observed, and the CNTs are trapped within the nematic (N) phase, forming a black ink-like gel-like phase. A similar effect is observed in dispersions of CB that exhibit non-Newtonian flow 17 ACS Paragon Plus Environment


behavior. We suggest that the latter transition is related to kinetic trapping of the dispersed CNTs within the suspended CNCs as was reported before for both CNCs and CNTs33,34. Thin films prepared from the hybrids exhibit birefringence, offering a pathway for preparation of non-isotropic CNCs-CNTs composites and thin films via liquid processing.

Supporting Information: POM images of the LC phase of CNCs, Cryo-TEM images of CNTs-CNCs and CB-CNCs dispersions, and rheological measurements.

Acknowledgment R.Y.-R. holds the Stanley D. and Nikki Waxberg professorial chair in Advanced Materials. The support of the Israel Science Foundation (ISF grant 193-18) is acknowledged.

References 1. Farahani, R. D.; Dube, M.; Therriault, D. Three-Dimensional Printing of Multifunctional Nanocomposites: Manufacturing Techniques and Applications. Adv. Mater. 2016, 28 (28), 5794-5821. 2. Hou, K.; Ali, W.; Lv, J.; Guo, J.; Shi, L.; Han, B.; Wang, X.; Tang, Z. Optically Active Inverse Opal Photonic Crystals. J. Am. Chem. Soc. 2018, 140 (48), 16446–16449. 3. Zhu, Y.; Wang, H.; Wan, K.; Guo, J.; He, C.; Yu, Y.; Zhao, L.; Zhang, Y.; Lv, J.; Shi, L.; et al. Enantioseparation of Au20(PP3)4Cl4 Clusters with Intrinsically Chiral Cores. Angew. Chem. Int. Ed. 2018, 57, 9059– 9063.


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