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. 2020 Jan 13;36(4):979–985. doi: 10.1021/acs.langmuir.9b03570

Structural Arrest and Phase Transition in Glassy Nanocellulose Colloids

Guang Chu †,‡,*, Gleb Vasilyev †, Dan Qu †, Shengwei Deng §, Long Bai ‡, Orlando J Rojas ‡,∥,*, Eyal Zussman †,*
PMCID: PMC7704027  PMID: 31927969

Abstract

graphic file with name la9b03570_0005.jpg

From drying blood to oil paint, the developing of a glassy phase from colloids is observed on a daily basis. Colloidal glass is solid soft matter that consists of two intertwined phases: a random packed particle network and a fluid solvent. By dispersing charged rod-like cellulose nanoparticles into a water–ethylene glycol cosolvent, here we demonstrate a new kind of colloidal glass with a high liquid crystalline order, namely, two general superstructures with nematic and cholesteric packing states are preserved and jammed inside the glass matrix. During the glass formation process, structural arrest and phase transition occur simultaneously at high particle concentrations, yielding solid-like behavior as well as a frozen liquid crystal texture that is because of caging of the charged colloids through neighboring long-ranged repulsive interactions.

Introduction

Colloidal suspensions are ubiquitous substances in our everyday life, inks, paints, and dairy products being some of the many examples.1 Controlling the assembly of colloids holds great promise in the synthesis of their superstructures and results in bulk colloidal materials with a variety of new functions. During the colloidal assembly process, the suspension experiences a dramatic growth in viscosity as the particle concentration increases.2 Above a certain concentration, the suspension becomes solid-like and is said to be a “colloidal glass”.3−5 Structurally, such a system resembles a liquid, yet the within-flow motion is restrained to the extent that the colloids’ arrangement can be essentially considered as locked. Therefore, comparing with regular glassy materials which are produced by temperature shifts, the direct link between colloidal suspension and colloidal glass is the particle concentration. In colloidal glass, particles are randomly jammed in a network that is stabilized by several interactions, for example, long-ranged electrostatic forces between charged particles as well as short-ranged van der Waals force occurring by the fluctuating electric dipole moments of the particles.6 These forces lead to structural arrest of the colloidal particles inside the matrix, also described as caging of each individual particle by its neighboring ones.7−9

Apart from concentration, the shape of the suspended particles plays another important role in the formation of colloidal glass.6 The simplest colloidal particles that can form a glass phase is hard-spheres. Indeed, most of the studies on colloidal glasses, both experimental and theoretical, are concerned with hard-sphere systems,4,5,10 whereas colloidal particles with strong anisotropy can provide additional complexity in modulating the structure and phase transition process in comparison to spherical colloids. Thus, anisotropic particles can be used to better understand the interplay between steric interactions and entropy, which both influencing the glass transition in colloids that may give rise to a diversity of new glassy states, for example, a liquid crystal (LC) glass. For lyotropic colloidal suspension, anisotropic colloid exhibits a glass transition at high concentrations; meanwhile, the colloids fall into an LC phase as the particle arrangement is locked and jammed in the glassy matrix.11,12 Previous studies on drying rod-like colloidal boehmite and fd-virus suspensions demonstrated a glass transition within the nematic region, in which the particles are packed in order without further LC ordering transitions.13−15 These evaporation-induced glass transition processes are out-of-equilibrium, and typically show strong temporal and spatial variations in the glass matrix.

Cellulose nanocrystals (CNCs) are twisted and negatively charged nanorods, most commonly derived from plant-sourced materials.16 When CNCs are dispersed into water or specific organic solvents, it will form a stable colloidal suspension and self-assemble into a cholesteric phase at high particle concentrations.17−22 Unlike other colloidal LCs, the cholesteric CNCs remain ordered upon evaporation and further lock the helicoid arrangement into solid films. Hence, the increased particle concentration leads to structural arrest in the glass transition process.23−27 However, the glassy state of liquid crystalline CNCs typically occurs at a narrow concentration range and quickly evolves into a casted film through solvent evaporation.12 It is therefore not surprising that CNC colloidal glass induced by evaporative drying is kinetically metastable and difficult for steady-state research and utilization. Recently, Xu et al. found that the colloidal glass transition process of CNCs was influenced by adding salt and increasing the particle concentration.28 Bertsch et al. further demonstrated an ion-induced CNC colloidal glass which contained nematic domains.29 However, a stable CNC-derived colloidal glass with cholesteric LC ordering and without added salt has never been reported. In this paper, we present a general method to prepare stable colloidal LC glasses by selective solvent removal from CNCs suspended in a binary water–ethylene glycol (EG) solvent. During the evaporation process, the suspension first displays a two-phase coexistence region and then transforms from an isotropic–cholesteric fluid state into a nematic–cholesteric colloidal glass, undergoing a combination of LC phase transition and glass formation. Because of the percolation of negative-charged CNC nanorods, the colloidal glass forms into a caged network, which is stabilized by surrounding long-ranged repulsive electrostatic interactions. Optical and rheological tests indicate that the LC texture is frozen inside the glassy matrix and exhibits a solid-like behavior. We believed that the current selective solvent-removing method could be extended to other anisotropic aqueous colloidal systems to induce the LC glass transition upon increasing particle concentration.

Experimental Section

Materials and Apparatus

All chemicals were used as received without further purification. EG (99.8%, anhydrous) was purchased from Sigma-Aldrich. Deionized water (18 MΩ) was obtained from a Millipore-purified water system. CNC powder was obtained from the U.S. Forest Products Laboratory at the University of Maine. The CNCs were prepared by controlled sulfuric acid hydrolysis and freeze-drying into solid powders.

Polarized optical microscopy (POM) images were obtained on an Olympus BX51-P microscope with images taken by polarizers in a perpendicular arrangement to verify to the anisotropy of the composite samples. A high-resolution DP71 camera (Olympus, resolution of 5760 × 3600 pixels) was used to record the images of the glass sample. The resulting POM images were analyzed using ImageJ to acquire the pixel fluctuations in the helical pitch region. Transmission electron microscopy (TEM) was conducted on a FEI Tecnai G2S-Twin with a field emission gun operating at 200 kV. The zeta potential of the CNC suspension was measured using a Malvern Zetasizer Nano-ZS90. Laser diffraction of the glass samples was conducted on a home-made laser system with a collimated monochromatic incident laser at the wavelength of 530 nm. A discovery DHR-2 rotational rheometer (TA Instruments, USA) was used to characterize the rheological properties of the suspension under steady-state shear flow. All rheological measurements were performed at room temperature (25 °C).

Preparation of a Two-Phase CNC Water–EG Suspension and Colloidal LC Glass

In a typical experiment, 0.5 g of CNC powder was dispersed in 6.64 g of water–EG cosolvent with varying mass ratios (see Table S1) and stirred overnight to generate a homogenous mixture. After that, the mixture was sonicated for 2 min in an ice bath with the power input of 60% (VCX-750, Sonics & Materials. Inc) and then sealed for 1 week to get full equilibrium with a two-phase separation.

The preparation of colloidal LC glass was based on selective evaporation of water from the two-phased CNC water–EG suspension. In a typical experiment, a two-phased CNC water–EG suspension (7 wt %, water–EG mass ratio of 1:1) was slowly evaporated at room temperature for 2 months to fully remove the water content inside the mixture. During the evaporation process, the concentration of the suspension was tracked by measuring the weight loss of water at a constant time interval (5 days). The glass transition stage occurs at the CNC concentration of 10 wt %; further evaporation led to vitrification of the sample with upper nematic and bottom cholesteric ordering. The resulting colloidal LC glass was preserved and sealed in glass vials for further use.

Results and Discussion

The colloidal system, CNCs dispersed in a miscible water–EG cosolvent, was tested for varying mass ratios (Supporting Information, Table S1). The CNC dimensions corresponded to 250 nm in length and 20 nm in width (Supporting Information, Figure S1), with a typical rod-like morphology (aspect ratio or length/width of 12.5). This high aspect ratio of CNC promotes the formation of an LC phase as well as an arrested glassy state.30Figure 1a shows the phase diagram of aqueous CNC suspensions of different concentrations after equilibrium for 3 days. At low CNC concentrations (<3.0 wt %), the resulting suspension is stable, homogeneous, and totally isotropic. Further increase in the concentration leads to a clear isotropic–anisotropic phase transition (Figure 1a, inset), with upper isotropic and bottom anisotropic cholesteric ordering. It should be noted that the volume fraction of the isotropic phase decreases with increasing concentration and finally disappears when the suspension concentration is beyond a second threshold value (10 wt %). The choice of solvents allows control of the CNC phase transition. Unlike other organic solvents (e.g., dimethyl sulfoxide, dimethylformamide, and toluene),31,32 nonvolatile EG limits phase separation even at relatively high CNC mass fractions (Figure 1b). However, as the CNC concentration increases, the optical texture of the colloids changes from isotropic to fully nematic with strong birefringence, implying the formation of an LC phase (Figure S2). Meanwhile, the viscosity of the suspension increases nonlinearly with CNC concentration and finally undergoes a glass transition above the critical concentration (Figures 1c and S3), giving rise to colloidal glass. This transition occurs at a mass fraction of 7.0 wt %, much higher than the threshold for phase separation in pure water and is explained by the percolation of the repulsive CNC nanoparticles. The surface charge (the zeta potentials of CNCs in water and CNCs in EG are −51 and −38 mV, respectively) induces long-range electrostatic repulsion that leads to a caged particle network during the glass transition whereby each CNC nanorod is trapped within the potential landscape formed by neighboring particles.11 Based on the DLVO (Derjaguin−Landau−Verwey−Overbeek) theory, when the CNC particles are dispersed in EG, the decrease of zeta potential can induce the decrease of the repulsive double layer forces between CNCs, which therefore leads to the formation of a highly packed colloidal glass phase.33 Besides, the intermolecular hydrogen bonding also plays an important role in the CNC phase transition process. When CNCs are dispersed in pure EG, no cholesteric phase separation occurs, which is due to the strong intermolecular hydrogen bonding (because EG has two −OH groups, both of which can form hydrogen bonds, see Figure S4) between neighboring EG molecules. As a result, the suspension is more viscous and first falls into a glassy state before the phase separation.

Figure 1.

Figure 1

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(a) Calculated ratio of the anisotropic phase for suspensions of varying CNC concentrations. The inset corresponds to a photograph of an aqueous suspension at 7 wt % CNCs displaying two separated phases. (b) Photographs of the CNC–EG suspension with varying concentrations. (c) Viscosity as a function of concentration for the CNC–EG suspension, which is measured at the shear stress of 30 Pa. Inset is the photograph of the CNC–EG suspension at the concentration of 6 and 7 wt %, respectively, which demonstrates the glass transition. (d) Photographs of the CNC water–EG suspension with varying mass fractions of water and EG (the CNC concentration is fixed at 7 wt %). (e) Fluctuation of helical pitch as a function of EG contents for the phase-separated CNC water–EG suspension. The inset is a POM image and schematic illustration of cholesteric CNCs. (f) Apparent viscosity of the upper and bottom phases of CNCs suspended in water–EG as a function of EG content.

Miscible solvents can be used to match the particle density and minimize the gravitational effect so as to adjust the colloidal diffusion and sedimentation during the glass transition process.34,35 In order to prepare the precursor for cholesteric liquid crystalline colloidal glass, we used water–EG cosolvents with varying mass ratios at a fixed CNC concentration of 7.0 wt % (Table S1). Adding water could effectively interfere with the hydrogen bonding network in EG and decrease the strength of intermolecular hydrogen bonding (see Figure S4). After equilibrium for 1 week, the CNC suspension in the binary solvent at a low EG content (<50%) separates into two coexisting phases (the corresponding zeta penitential of CNC in water–EG cosolvent (1:1) is −42 mV), upper isotropic and bottom cholesteric phases (Figure 1d). However, as the EG content increases, these homogenous suspensions display no phase separation, showing nematic birefringent texture under POM, similar to the observed images for pure EG at high CNC concentrations (Figure S5). POM imaging of the cholesteric phase indicates a periodic fingerprint texture with two adjacent lines at a given separation (half pitch, Figure 1e). The helical pitch is found to be nearly constant as the EG mass fraction increases from 0 to 50%, implying that EG has little impact on the formation of the cholesteric CNC phase. Moreover, as the EG mass fraction in the water–EG suspension increases, the system becomes more viscous (Figure 1f). After reaching a critical point (mass EG/water ratio = 9:1), the suspension exhibits glassy behavior and no longer flows. Compared with the pure aqueous CNC suspension, the observed viscosity growth with EG addition is due to the increase of the CNC volume fraction (the density of EG is higher than water; thus, the more the amount of EG is, the higher the CNC volume fraction inside the mixed suspension) as well as the strength growth of intermolecular hydrogen bonding between water–EG network, which results in a colloidal glass transition.

Based on the observations so far, we conclude that CNCs exhibit a glass transition with nematic ordering at high EG content. Note that preparing a colloidal glass with cholesteric ordering depends on the annealing time. Cholesteric CNC LC glass results from the phase-separated water–EG precursor (mass ratio 1:1, 7 wt % CNC). After annealing in an open condition for 2 months, the suspension becomes highly concentrated by selective evaporation of water, yielding CNCs at a calculated concentration of 13 wt % in EG (Figure 2a). The final CNC–EG mixture exhibits glassy behavior with two separated phases, implying that the LC texture is preserved in the CNC–EG colloidal glass and displays a high mechanical strength and a self-supporting structure (Figure 2a, inset). In contrast, the fast water evaporation of the same precursor placed in an oven (60 °C) induces thermal convection, which disrupts the two-phase structure, resulting in remixing of the separated phases (Figure S6). After evaporation, the volume fraction of the cholesteric ordered LC glass is 0.412, similar to the volume fraction of its initial suspension counterpart (0.422), suggesting that the two-phase suspension was simultaneously contracted during the glass transition process. Besides, a weak iridescent color is observed in the bottom cholesteric LC glass because of the light scattering from the crystalline colloidal array, whereas the upper phase remains relatively clear (Figure 2b). Laser diffraction of the cholesteric colloidal glass shows periodic ring patterns that fit the Bragg equation, whereas the upper glass phase only shows an asymmetrical diffraction spot, implying an anisotropic feature of the upper colloidal glass. When we put the glassy samples under cross-polarized light, a more detailed structural information emerges. In the case of the nematic LC glass, a distorted Schlieren texture was observed (Figures 2c and S7). For the bottom LC glass, a large area of fingerprint texture is observed, characteristic of cholesteric ordering (Figure 2d). The measured helical pitch is 5.6 μm, much smaller than that in the initial LC suspension (10.3 μm). This phenomenon, that is, the reduced helical pitch upon increasing CNC concentration, is due to the decreasing of electrostatic repulsion between CNC particles, which allows the adjacent rods to approach each other more closely.

Figure 2.

Figure 2

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(a) Normalized evaporation curve for a mixed CNC water–EG suspension at different time scales, showing glass transition at 10 wt % and a fully LC glassy state at 13 wt %, respectively. (b) Photograph of the phase-separated LC glass with upper clear appearance and bottom iridescence because of Bragg light diffraction (left). Photographs of laser diffraction patterns obtained from nematic and cholesteric phases of LC glass, respectively (right). (c) POM image of the nematic LC glass with a typical Schlieren texture around a bubble. (d) POM image of the cholesteric LC glass with a large area of periodic fingerprint texture. Inset is the image analysis of the fingerprint texture which shows the fluctuation in the helical pitch.

The phase diagram for CNC nanorods dispersed in EG is shown in Figure 3a as a function of concentration (c). It is apparent that below the first critical concentration, c1 = 3 wt %, the suspension is in an isotropic liquid state. An increased particle concentration forces the system into an LC state with nematic ordering (3 wt % < c2 < 6 wt %) and exhibits a gradual viscosity growth. However, despite the nematic arrangement of CNCs, further increase of concentration considerably enhances the probability of close particle collision, inducing percolation of the charged nanorods and block the particle movement, jamming and limiting their reorganization (c3 > 6 wt %). As a consequence, the fluid phase turns into a gel-like glassy state with permanent particle ordering that is arrested during the glass transition. As the time scales required to reach an equilibrated helical superstructure are longer than the time scales required for glass formation,12 the CNC particles are therefore directly locked and jammed in the nematic glassy state, without further self-reorganizing into a higher-ordered cholesteric phase. Thus, the CNC nanoparticles in pure EG are kinetically trapped in the nematic LC glass regime before the cholesteric LC phase has time to fully develop. However, cholesteric LC glass is still obtained at high concentrations (c4 = 13 wt %), just by a two-step phase transition process (Figure 3b).

Figure 3.

Figure 3

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(a) Phase diagram of CNCs dispersed in pure EG that exhibits both glass transition and structural arrest as a function of concentration. Note that the existence of the LC glassy state requires high concentrations of CNCs with close particle encounters. (b) Schematic illustrations of LC glass formation with bottom cholesteric and upper nematic phases, respectively. During the selective drying process, the water molecules from the bulk phase diffuse to the liquid–vapor interface and then further evaporate, resulting in an increased colloidal particle concentration and freezing of LC ordering into the glassy matrix.

The formation of a CNC cholesteric helix structure over micrometre-scaled distances is quite slow in the water–EG cosolvent. During equilibrium, the homogeneous suspension usually takes a week to fully separate into a two-phase heterogeneous regime with an upper isotropic and bottom cholesteric CNC orientation. Removing the solvent from the colloidal suspension through evaporation is a crucial process, which can result in structural arrest of the various nonequilibrium colloidal states.21,36 The liquid–vapor interface is located at the upper phase, where the CNC concentration increases rapidly as water evaporates, and thus undergoes earlier glass transition.12 Further down into the bulk, the sample remains in a fluid state. In order to reach the glass transition threshold, water molecules in the bottom phase are diffusing to the upper phase and further evaporate, whereas the nonevaporating EG remains in the suspension. Thus, the two-phase CNC suspension continuously decreases in volume and increases in the particle concentration, eventually reaching an equilibrium stage where the CNC particles are jammed and locked in the glassy matrix with arrangements that depend on the initial state of the suspension.37 Besides, during the entire drying process, the upper phase of the suspension is always wet because of the replenishment, via diffusion, of water molecules from the interior to the liquid–vapor interface. This water gradient in the two-phase suspension might lead to a directional (upward) water flow that is effective in aligning the isotropic phase into a nematic state until the particles interact with each other through long-ranged repulsive forces and no substantial further evaporation takes place.12 In the end, we speculate that selective water evaporation from the two-phase CNC suspension leads to a phase transition and glass formation at the same time, thereby giving rise to a heterogeneous LC glass with upper nematic and bottom cholesteric states.

The classification of an LC glass as a solid depends on the time scale and applied forces. At the glass transition stage, when the sample is placed horizontally over a long equilibration time, a gravity-induced glass flow develops, pushing the system to an out-of-equilibrium state (Figure 4a). Here, rheological measurements are useful to quantify how the colloidal LC glass responds to the given stress.38Figure 4b shows the steady-state flow curves of the mixed water–EG CNC suspension (mass ratio 1:1, 7 wt %) and evaporated LC glass at varying CNC concentrations. In the case of the initial CNC suspension, the viscosities of both the bottom cholesteric phase and the upper isotropic counterpart decrease slowly with a plateau profile at low shear rates and then drop more pronouncedly at high shear rates, which are attributed to the shear thinning behavior and revealing the alignment of CNC nanorods along the shear field.39 However, applying shear stress to the LC glass at a CNC concentration of 10 wt % leads to changes in its microstructure and breaks up the caging effect between neighboring particles, namely, two shear thinning regions are observed at increasing shear rates. The first shear thinning region, with gradual reduction of the apparent viscosity at low shear rates, is ascribed to the distortion of the cages formed by ordered CNCs. The second shear thinning region, at intermediate and high shear rates, is due to the alignment of LC domains which are destroyed at high shear rates.40 However, for LC glass at a concentration of 13 wt %, the viscosity of nematic and cholesteric ordered glasses decrease exponentially with increasing shear rates (η = γm–1, where η and γ are the viscosity and shear rate, respectively, and m is the power law exponent with its value less than 1, showing monotonous shear thinning behavior in the whole region and indicating full vitrification of the sample. The shear effects on LC glass and its corresponding suspension are also described by the response of shear stress-shear rate and viscosity-shear stress (Figures S8 and S9). Two shear thinning regions are observed along the increasing of the shear rate for an initial mixed CNC suspension, but a plumb viscosity drop with preserving the generated stress almost constant for the LC glass, demonstrating the solid-like behavior of LC glass and pseudoplastic fluid behavior of its initial mixed suspension.

Figure 4.

Figure 4

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(a) Photographs of the gravity-induced flowing of LC glass (10 wt %) at varying times, showing both solid-like and fluid behaviors. (b) Evolution of the apparent shear viscosity with shear rate for the mixed CNC suspension and LC glass with nematic and cholesteric ordering, respectively. (c–e) Storage modulus (G′, filled symbols) and loss modulus (G″, open symbols) of the mixed CNC suspension (7 wt %) and corresponding LC glass (10 and 13 wt %, respectively) in relation to the angular frequency.

Both colloidal suspensions and colloidal glasses are viscoelastic; therefore, their rheological properties depend on the measured frequency.41 Thus, dynamic frequency sweeps were performed to inquire into the viscoelastic differences during the transition from the mixed CNC suspension to LC glass (Figure 4c–e). The storage modulus (G′) reflects the material ability to store elastic energy during deformation, whereas the loss modulus (G″) characterizes energy dissipation, and these two moduli in general depend on the frequency. As expected for the CNC suspension with either isotropic or cholesteric ordering, the G″ was dominant and greater than G′, and both moduli increased with frequency, characteristics of a viscoelastic liquid (Figure 4c). For colloids at glass transition with a concentration of 10 wt %, the upper nematic phase exhibits a frequency-dependent viscoelastic behavior with G′ and G″ values that are almost identical at low frequencies, whereas at high frequencies the value of G′ is larger than G″. However, the frequency-dependent G′ and G″ in the bottom cholesteric phase undergoes a crossover at 0.35 rad/s, showing liquid-like viscous behavior (G′ < G″) at low frequencies. At high frequencies, a solid-like behavior (G′ > G″) is dominant (Figure 4d), revealing the formation of a robust three-dimensional caged network inside the glassy matrix. In the case of LC glass, at a CNC concentration of 13 wt %, G′ and G″ are frequency-independent with high absolute values in nematic and cholesteric LC glass, exhibiting G′ > G″ over a large range of frequencies, characteristic of a solid-like behavior with high mechanical strength (Figure 4e). In addition, the corresponding tangent of the phase angle (tan δ = G″/G′) of these samples also supports the transition noted with increasing concentration, for example, from a fluid suspension to a solid colloidal LC glass (Figure S10).

Conclusions

To conclude, we have demonstrated a charged colloidal LC glass with nematic and cholesteric arrangement through selective solvent removal from a two-phase separated CNC water–EG suspension. Water molecules evaporate during the drying process, whereas the cosolvent EG remains in suspension, resulting in an increased particle concentration. Therefore, as evaporation continues, the water content in the suspension decreases and eventually it undergoes a glass transition with both particle structural arrest and freezing LC texture within the glassy state. The obtained colloidal LC glass not only maintains a characteristic long-range arrangement but also exhibits the solid-like behavior of colloidal glass, which can be ascribed to a complex soft-matter material that features novel properties. Finally, we believe that the present finding of LC glass can be further used as colloidal ink for 3D printing, which can allow designing of novel hierarchical structures with the desired mechanical and optical anisotropy.

Acknowledgments

E.Z. and G.C. acknowledge the financial support of the Winograd Chair of Fluid Mechanics and Heat Transfer at Technion, the Russell Berrie Nanotechnology Institute (RBNI) and the Israel Science Foundation (ISF grant no. 286/15). G.C. and O.J.R. acknowledge funding support from the FinnCERES flagship program and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Advanced grant agreement no. 788489, “BioElCell”).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.langmuir.9b03570.

  • Additional experimental details and figures (e.g., photographs, POM images and rheology data) (PDF)

Author Contributions

G.C. prepared the LC glass samples and carried out the POM, TEM, and laser diffraction measurements. G.V. carried out the rheology measurement. G.C., O.J.R., and E.Z. designed and led the project. The paper was written through contributions of all the authors. All the authors have given approval to the final version of the paper.

The authors declare no competing financial interest.

Supplementary Material

la9b03570_si_001.pdf (724.8KB, pdf)

References

  1. Mewis J.; Wagner N. J.. Colloidal Suspension Rheology; Cambridge University Press, 2012. [Google Scholar]
  2. Weeks E. R. Introduction to the colloidal glass transition. ACS Macro Lett. 2017, 6, 27–34. 10.1021/acsmacrolett.6b00826. [DOI] [PubMed] [Google Scholar]
  3. Lindsay H. M.; Chaikin P. M. Elastic properties of colloidal crystals and glasses. J. Chem. Phys. 1982, 76, 3774–3781. 10.1063/1.443417. [DOI] [Google Scholar]
  4. Pusey P. N.; Van Megen W. Phase behaviour of concentrated suspensions of nearly hard colloidal spheres. Nature 1986, 320, 340–342. 10.1038/320340a0. [DOI] [Google Scholar]
  5. Pusey P. N.; van Megen W. Observation of a glass transition in suspensions of spherical colloidal particles. Phys. Rev. Lett. 1987, 59, 2083. 10.1103/physrevlett.59.2083. [DOI] [PubMed] [Google Scholar]
  6. Hunter G. L.; Weeks E. R. The physics of the colloidal glass transition. Rep. Prog. Phys. 2012, 75, 066501. 10.1088/0034-4885/75/6/066501. [DOI] [PubMed] [Google Scholar]
  7. Negi A. S.; Osuji C. O. Time-resolved viscoelastic properties during structural arrest and aging of a colloidal glass. Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys. 2010, 82, 031404. 10.1103/physreve.82.031404. [DOI] [PubMed] [Google Scholar]
  8. Puertas A. M.; Fuchs M.; Cates M. E. Comparative simulation study of colloidal gels and glasses. Phys. Rev. Lett. 2002, 88, 098301. 10.1103/physrevlett.88.098301. [DOI] [PubMed] [Google Scholar]
  9. Weeks E. R.; Weitz D. Properties of cage rearrangements observed near the colloidal glass transition. Phys. Rev. Lett. 2002, 89, 095704. 10.1103/physrevlett.89.095704. [DOI] [PubMed] [Google Scholar]
  10. Mason T. G.; Weitz D. A. Linear viscoelasticity of colloidal hard sphere suspensions near the glass transition. Phys. Rev. Lett. 1995, 75, 2770. 10.1103/physrevlett.75.2770. [DOI] [PubMed] [Google Scholar]
  11. Xu Y.; Atrens A. D.; Stokes J. R. Liquid crystal hydroglass formed via phase separation of nanocellulose colloidal rods. Soft Matter 2019, 15, 1716–1720. 10.1039/c8sm02288g. [DOI] [PubMed] [Google Scholar]
  12. 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 10.1038/am.2013.69. [DOI] [Google Scholar]
  13. Kang K.; Dhont J. Glass transition in suspensions of charged rods: structural arrest and texture dynamics. Phys. Rev. Lett. 2013, 110, 015901. 10.1103/physrevlett.110.015901. [DOI] [PubMed] [Google Scholar]
  14. 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. 10.1021/la970376z. [DOI] [Google Scholar]
  15. Kang K. Glass transition of repulsive charged rods (fd-viruses). Soft Matter 2014, 10, 3311–3324. 10.1039/c3sm53131g. [DOI] [PubMed] [Google Scholar]
  16. Habibi Y.; Lucia L. A.; Rojas O. J. Cellulose nanocrystals: chemistry, self-assembly, and applications. Chem. Rev. 2010, 110, 3479–3500. 10.1021/cr900339w. [DOI] [PubMed] [Google Scholar]
  17. 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, 2076–2082. 10.1021/la950133b. [DOI] [Google Scholar]
  18. Bruckner J. R.; Kuhnhold A.; Honorato-Rios C.; Schilling T.; Lagerwall J. P. F. Enhancing self-assembly in cellulose nanocrystal suspensions using high-permittivity solvents. Langmuir 2016, 32, 9854–9862. 10.1021/acs.langmuir.6b02647. [DOI] [PubMed] [Google Scholar]
  19. Chu G.; Vasilyev G.; Vilensky R.; Boaz M.; Zhang R.; Martin P.; Dahan N.; Deng S.; Zussman E. Controlled Assembly of Nanocellulose-Stabilized Emulsions with Periodic Liquid Crystal-in-Liquid Crystal Organization. Langmuir 2018, 34, 13263–13273. 10.1021/acs.langmuir.8b02163. [DOI] [PubMed] [Google Scholar]
  20. Chu G.; Vilensky R.; Vasilyev G.; Deng S.; Qu D.; Xu Y.; Zussman E. Structural Transition in Liquid Crystal Bubbles Generated from Fluidic Nanocellulose Colloids. Angew. Chem. 2017, 129, 8877–8881. 10.1002/ange.201703869. [DOI] [PubMed] [Google Scholar]
  21. Chu G.; Vilensky R.; Vasilyev G.; Martin P.; Zhang R.; Zussman E. Structure evolution and drying dynamics in sliding cholesteric cellulose nanocrystals. J. Phys. Chem. Lett. 2018, 9, 1845–1851. 10.1021/acs.jpclett.8b00670. [DOI] [PubMed] [Google Scholar]
  22. 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, 170–172. 10.1016/s0141-8130(05)80008-x. [DOI] [PubMed] [Google Scholar]
  23. Revol J. F.; Godbout L.; Gray D. Solid self-assembled films of cellulose with chiral nematic order and optically variable properties. J. Pulp Pap. Sci. 1998, 24, 146–149. [Google Scholar]
  24. Shopsowitz K. E.; Qi H.; Hamad W. Y.; MacLachlan M. J. Free-standing mesoporous silica films with tunable chiral nematic structures. Nature 2010, 468, 422–425. 10.1038/nature09540. [DOI] [PubMed] [Google Scholar]
  25. Chu G.; Yin H.; Jiang H.; Qu D.; Shi Y.; Ding D.; Xu Y. Ultrafast Optical Modulation of Rationally Engineered Photonic-Plasmonic Coupling in Self-Assembled Nanocrystalline Cellulose/Silver Hybrid Material. J. Phys. Chem. C 2016, 120, 27541–27547. 10.1021/acs.jpcc.6b09052. [DOI] [Google Scholar]
  26. Chu G.; Camposeo A.; Vilensky R.; Vasilyev G.; Martin P.; Pisignano D.; Zussman E. Printing Flowers? Custom-Tailored Photonic Cellulose Films with Engineered Surface Topography. Matter 2019, 1, 988–1000. 10.1016/j.matt.2019.05.005. [DOI] [Google Scholar]
  27. Chu G.; Qu D.; Camposeo A.; Pisignano D.; Zussman E. When Nanocellulose Meets Diffraction Grating: Freestanding Photonic Paper with Programmable Optical Coupling. Mater. Horiz. 2020, 10.1039/C9MH01485C. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Xu Y.; Atrens A. D.; Stokes J. R. ″Liquid, gel and soft glass″ phase transitions and rheology of nanocrystalline cellulose suspensions as a function of concentration and salinity. Soft Matter 2018, 14, 1953–1963. 10.1039/c7sm02470c. [DOI] [PubMed] [Google Scholar]
  29. Bertsch P.; Sánchez-Ferrer A.; Bagnani M.; Isabettini S.; Kohlbrecher J.; Mezzenga R.; Fischer P. Ion-induced formation of nanocrystalline cellulose colloidal glasses containing nematic domains. Langmuir 2019, 35, 4117–4124. 10.1021/acs.langmuir.9b00281. [DOI] [PubMed] [Google Scholar]
  30. Nordenström M.; Fall A.; Nyström G.; Wagberg L. Formation of colloidal nanocellulose glasses and gels. Langmuir 2017, 33, 9772–9780. 10.1021/acs.langmuir.7b01832. [DOI] [PubMed] [Google Scholar]
  31. Viet D.; Beck-Candanedo S.; Gray D. G. Dispersion of cellulose nanocrystals in polar organic solvents. Cellulose 2007, 14, 109–113. 10.1007/s10570-006-9093-9. [DOI] [Google Scholar]
  32. Frka-Petesic B.; Radavidson H.; Jean B.; Heux L. Dynamically controlled iridescence of cholesteric cellulose nanocrystal suspensions using electric fields. Adv. Mater. 2017, 29, 1606208. 10.1002/adma.201606208. [DOI] [PubMed] [Google Scholar]
  33. Oguzlu H.; Danumah C.; Boluk Y. Colloidal behavior of aqueous cellulose nanocrystal suspensions. Curr. Opin. Colloid Interface Sci. 2017, 29, 46–56. 10.1016/j.cocis.2017.02.002. [DOI] [Google Scholar]
  34. Zhu J.; Li M.; Rogers R.; Meyer W.; Ottewill R.; Russel W.; Chaikin P. Crystallization of hard-sphere colloids in microgravity. Nature 1997, 387, 883–885. 10.1038/43141. [DOI] [Google Scholar]
  35. Simeonova N. B.; Kegel W. K. Gravity-induced aging in glasses of colloidal hard spheres. Phys. Rev. Lett. 2004, 93, 035701. 10.1103/physrevlett.93.035701. [DOI] [PubMed] [Google Scholar]
  36. Chu G.; Zussman E. From chaos to order: evaporative assembly and collective behavior in drying liquid crystal droplets. J. Phys. Chem. Lett. 2018, 9, 4795–4801. 10.1021/acs.jpclett.8b01866. [DOI] [PubMed] [Google Scholar]
  37. Mu X.; Gray D. G. Formation of chiral nematic films from cellulose nanocrystal suspensions is a two-stage process. Langmuir 2014, 30, 9256–9260. 10.1021/la501741r. [DOI] [PubMed] [Google Scholar]
  38. Pham K. N.; Petekidis G.; Vlassopoulos D.; Egelhaaf S. U.; Poon W. C. K.; Pusey P. N. Yielding behavior of repulsion- and attraction-dominated colloidal glasses. J. Rheol. 2008, 52, 649–676. 10.1122/1.2838255. [DOI] [Google Scholar]
  39. Ureña-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. 10.1021/ma201649f. [DOI] [Google Scholar]
  40. Shafeiei-Sabet S.; Hamad W. Y.; Hatzikiriakos S. G. Influence of degree of sulfation on the rheology of cellulose nanocrystal suspensions. Rheol. Acta 2013, 52, 741–751. 10.1007/s00397-013-0722-6. [DOI] [Google Scholar]
  41. Mattsson J.; Wyss H. M.; Fernandez-Nieves A.; Miyazaki K.; Hu Z.; Reichman D. R.; Weitz D. A. Soft colloids make strong glasses. Nature 2009, 462, 83–86. 10.1038/nature08457. [DOI] [PubMed] [Google Scholar]

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