Controlling the Reflection Wavelength of Iridescent Solid Films of Nanocrystalline Cellulose

Beck, Stephanie; Bouchard, Jean; Berry, Richard

doi:10.1021/bm1010905

Cited by 337 publications

(293 citation statements)

References 17 publications

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“…To explore the relationship between the interbead separation, D, and P/2, we applied ultrasonic treatment at varying energy to the CNC suspension before its phase separation into an isotropic and Ch phases and in this manner achieved the variation in pitch of the Ch-CNC phase (30). Fig.…”

Section: Resultsmentioning

confidence: 99%

Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

Prince

Cho

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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An important goal of the modern soft matter science is to discover new self-assembly modalities to precisely control the placement of small particles in space. Spatial inhomogeneity of liquid crystals offers the capability to organize colloids in certain regions such as the cores of the topological defects. Here we report two selfassembly modes of nanoparticles in linear defects-disclinations in a lyotropic colloidal cholesteric liquid crystal: a continuous helicoidal thread and a periodic array of discrete beads. The beads form one-dimensional arrays with a periodicity that matches half a pitch of the cholesteric phase. The periodic assembly is governed by the anisotropic surface tension and elasticity at the interface of beads with the liquid crystal. This mode of self-assembly of nanoparticles in disclinations expands our ability to use topological defects in liquid crystals as templates for the organization of nanocolloids. colloidal liquid crystals | nanoparticle self-assembly | liquid crystal droplets | topological defects | anisotropic surface tension T he most extensively studied liquid crystalline phase, the socalled nematic, has been so named after the linear defectdisclinations that appear as flexible threads in optical microscopy textures; "thread" is "ν«μα" in Greek (1, 2). The disclinations represent singularities of the director that describes the local orientation of molecules. As one approaches the "core" of the defect, director deformation becomes so strong that the degree of orientational order varies in space. Disclinations can attract additives, e.g., colloidal particles (3-8) and even small molecules (9, 10). Such an attraction is energetically favored, as the strongly distorted disclination core region is replaced with the additive (4). The unique templating ability of disclinations has stimulated the exploration of their applications, such as the fabrication of optical materials (11), conductive microwires (12), soft magnets (13), and electrooptical devices (5,14,15).Disclinations in nematic liquid crystals are generally onedimensional structures, as the director pattern repeats itself along the line. When an additive is attracted to the disclination core, two possible morphologies are expected: (i) continuous thread-like assembly, or (ii) a linear array of discrete beads. The disclination-templated assemblies reported so far had a threadlike shape, as observed for polymers in the so-called blue phases (15) and for molecular amphiphiles at the cores of nematic disclinations (9, 10).Here, we report the templating behavior of disclinations in the chiral version of the nematic liquid crystal, the so-called cholesteric (Ch) phase. The local directorn in this phase undergoes helicoid twisting around a helical axisv while being perpendicular to this axis (1, 2). Continuous twist leads to a pseudolayered structure, with a well-defined pitch but no modulation of density. Experiments were performed for spherical Ch droplets, in which disclinations correspond to the equilibrium state, thus ensuring...

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Section: Resultsmentioning

confidence: 99%

Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

Prince

Cho

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Indeed, there is a need for studies that investigate helix formation in the fluid state and provide high-resolution data from this regime to complement the more numerous quantitative studies of dried films. 15,62,63 Studies on CNCs derived from filter paper 55 and from wood pulp, 64 as well as on bacterial CNCs, 30 show that the pitch p generally decreases as the particle concentration c is increased. The same type of concentration dependence of the pitch is observed for fd virus suspensions, except at high concentrations, where p increases with increasing c. 65 The latter behavior may be understood as a consequence of the suspension being close to a phase transition into a smectic phase.…”

Section: The Helix In Liquid Crystalline Cnc Suspensionsmentioning

confidence: 99%

Cellulose nanocrystal-based materials: from liquid crystal self-assembly and glass formation to multifunctional thin films

et al. 2014

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Cellulose nanocrystals (CNCs), produced by the acid hydrolysis of wood, cotton or other cellulose-rich sources, constitute a renewable nanosized raw material with a broad range of envisaged uses: for example, in composites, cosmetics and medical devices. The intriguing ability of CNCs to self-organize into a chiral nematic (cholesteric) liquid crystal phase with a helical arrangement has attracted significant interest, resulting in much research effort, as this arrangement gives dried CNC films a photonic band gap. The films thus acquire attractive optical properties, creating possibilities for use in applications such as security papers and mirrorless lasing. In this critical review, we discuss the sensitive balance between glass formation and liquid crystal self-assembly that governs the formation of the desired helical structure. We show that several as yet unclarified observations-some constituting severe obstacles for applications of CNCs-may result from competition between the two phenomena. Moreover, by comparison with the corresponding self-assembly processes of other rod-like nanoparticles, for example, carbon nanotubes and fd virus particles, we outline how further liquid crystal ordering phenomena may be expected from CNCs if the suspension parameters can be better controlled. Alternative interpretations of some unexpected phenomena are provided, and topics for future research are identified, as are new potential application strategies. NPG Asia Materials (2014) 6, e80; doi:10.1038/am.2013.69; published online 10 January 2014Keywords: cholesteric; gel; glass; liquid crystal; nanocellulose; photonic crystal; self-assembly INTRODUCTION Nanomaterials based on renewable resources are attracting rapidly growing interest, both from a fundamental scientific point of view and from the perspective of developing novel structural and functional macroscopic materials. 1,2 Using nature-based nanomaterials offers ecological advantages, and the extraordinary mechanical performance and/or photonic crystal character of biological composites such as bone, nacre, wood, beetle scales and butterfly wings is also an important inspiration for the development of new multifunctional materials. [3][4][5] However, full utilization of the intrinsic properties of nanosized starting materials requires the development of robust and versatile synthetic and processing routes to control assembly over several length scales. [6][7][8] Cellulose, one of the most versatile and widely found biopolymers in nature, has been used by humans for millennia as a building material, an energy source, a component of clothing and for storing and sharing knowledge and culture. Today, cellulose materials are used in a wide range of applications, and the paper and pulp industry

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“…If the helix is allowed to reach the short sub-micron range, this can be seen by the naked eye as vivid iridescent colors being reflected from the sample. Typically, this happens when the water of an aqueous suspension of the rods is allowed to evaporate, leaving a thin paper-like film that displays striking colors across the whole visible spectrum (Beck et al, 2011(Beck et al, , 2013Tabor et al, 2012;Gray, 2013;Dumanli et al, 2014;Kelly et al, 2014;Lagerwall et al, 2014;Mu and Gray, 2014;Park et al, 2014). Moreover, due to the helical internal structure, the reflected light is circularly polarized with the same handedness as the helix (Dumanli et al, 2014;Lagerwall et al, 2014;Park et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions

et al. 2016

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The cholesteric liquid crystal self-assembly of water-suspended cellulose nanocrystal (CNC) into a helical arrangement was observed already more than 20 years ago, and the phenomenon was used to produce iridescent solid films by evaporating the solvent or via sol-gel processing. Yet, it remains challenging to produce optically uniform films and to control the pitch reproducibly, reflecting the complexity of the three-stage drying process that is followed in preparing the films. An equilibrium liquid crystal phase formation stage is followed by a non-equilibrium kinetic arrest, which in turn is followed by structural collapse as the remaining solvent is evaporated. Here, we focus on the first of these stages, combining a set of systematic rheology and polarizing optics experiments with computer simulations to establish a detailed phase diagram of aqueous CNC suspensions with two different values of the surface charge, up to the concentration where kinetic arrest sets in. We also study the effect of varying ionic strength of the solvent. Within the cholesteric phase regime, we measure the equilibrium helical pitch as a function of the same parameters. We report a hitherto unnoticed change in character of the isotropic-cholesteric transition at increasing ionic strength, with a continuous weakening of the first-order character up to the point where phase coexistence is difficult to detect macroscopically due to substantial critical fluctuations.

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Controlling the Reflection Wavelength of Iridescent Solid Films of Nanocrystalline Cellulose

Cited by 337 publications

References 17 publications

Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

Cellulose nanocrystal-based materials: from liquid crystal self-assembly and glass formation to multifunctional thin films

Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions

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