The linear chain of glucose molecules known as cellulose is held together by an acetal oxygen covalent link between the C1 of one glucose ring and the C4 of the next. The cellulose nanocrystals (CNC), created during the acid hydrolysis of cellulose, have lengths and widths of 100–300 nm and 3–10 nm, respectively. CNCs are bio-derived nanoparticles that can self-assemble in a colloidal solution into a left-handed chiral nematic (cholesteric) phase. The chemical chirality of the glucose repeating unit enables it to twist; however, the origin of chirality is still under debate [1]. Nature has created a wide range of materials and organized them so their structural colours can be seen. Since they never fade and offer no toxicity, structured colours are more eco-friendly than pigment.

The main cell walls of plants, algae, and oomycetes are structurally supported by the linear polysaccharide known as cellulose, a naturally abundant polymer [2]. It is a chemical molecule with a formula consisting of polysaccharides made up of hundreds or thousands of linked D-glucose units ^[3][4][5][3,4,5]. Nanomaterials have considerable applications in various fields, including health [6], electronics, biomaterials, and energy storage [7] and generation. Nano-sized cellulose can be found in the form of nano-fibrillated cellulose (NFC) (or interchangeably cellulose nanofibrils (CNF), CNCs, and bacterial cellulose (BC). These particles are favourable to a wide range of applications due to biocompatibility, degradability, and outstanding mechanical characteristics [8]. Other possible uses for cellulose include aerogels for tissue scaffolds, coverings(packaging goods), Pickering emulsion agents, water-filled hydrogels, and reinforcing agents in ceramic, polymer, and metal matrixes, to name a few [8]. Even though some nanoparticles, such as nanotubes (CNT) ^[9][10][9,10], have excellent mechanical qualities, their toxicity [11], greater manufacturing costs, and the importance of environmental tolerance are limiting their adoption within the industry. Another factor to consider is digestibility when it comes to health-directed practices; with similar agenda, biodegradability is another important advantage of CNC particles in biological applications where tuneable gradual degradation of the particles is required.

Acid hydrolysis transforms cellulose into CNCs, which are needle-shaped, rigid, negatively charged particles with a crystallinity of around 70% [8]; the majority of the mechanical delamination techniques used to manufacture CNF counters parts result in parts with decreased crystallinity and increased flexibility. Due to the fulfilment of the requirement of having one scale in nanometric scale (1–100 nm) and moving with the thermal motion of media molecule, these particles, when suspended, are Brownian colloids. The main objective of CNC research is to fully exploit the outstanding physical and chemical properties of CNC particles in many applications. CNC particles’ distinct mechanical qualities have led to their widespread application as reinforcing agents in a wide range of polymers, including polyvinyl alcohol (PVA) [12], polypropylene (PP) ^[13][14][13,14], polyethylene glycol ^[15][16][15,16] and many others, as a load-bearing element; it is noteworthy that CNC particles can also be employed on their own to make films and gels [17]. CNC particles can also function as liquid crystals or fibres due to their geometry, and their rod shape allows them to generate a variety of geometries as nanostructures, resulting in a wide array of features and functionalities. However, issues such as fine-tuning the interactions between CNC particles and polymer matrices, as well as achieving the agglomerate-free state of CNC particles in matrices, have remained challenging.

When the CNC concentration rises, the suspended undergoes an LC-to-gel transition ^[18][19][18,19]. Since the topology and mesostructure of the various CNC suspension states, including isotropic, biphasic, liquid crystalline, and liquid crystalline gel, differ fundamentally ^[20][21][20,21], they immediately affect the rheological properties of CNC solutions. TAccording to the literature study, the formation of liquid crystals affects rheology by causing the viscosity maximum to appear in the plot of viscosity versus concentration curve [22]. This is because liquid crystalline domains may be orientated easily ^{[18][23][24][25]}[18,23,24,25], the general flow pattern of CNC solutions during shearing, as well as the effects of dosage, charge density, sonication, and temperature levels, liquid crystal formation ^{[18][23][24][25]}[18,23,24,25], and viscosity, have all been examined for CNC suspensions. Some material will be emphasized under the pertinent headlines of these reports to organize and further explain these reports in the sections that follow. After addressing the application in manuscript parts regarding the liquid crystalline phase creation of CNCs and presenting a section on its processing and rheology, the foundations and techniques of liquid crystal structure tuning are also provided in a separate portion.

Researcher interest in chiral photonic crystals in biological systems has come from a range of disciplines; the wings of the Morpho butterfly [26], blue-skinned mandrill [27] and spotted parachute bird all feature structural colour ^[28][29][28,29] on their scales. When CNC is in its chiral condition, it may replicate nature’s periodic internal structure, which changes colour according to the viewing angle. Even though liquid crystal formation is connected to a state of suspension and gelation, details of the suspension, gelation, and colloidal behaviour have been omitted due to the current manuscript’s concision; these topics are covered in other references (refs) ^[8][29][8,29]. Table 1 provides an overview of varied yet focused on the main subject of chiral liquid crystalline phase formation and application formed on CNCs. Subjects include its chiral structure, left-handedness [1] and right-handedness [30], and methods of recognizing them using molecular dynamic simulations and microscopy [1], self-assembly, rheology ^{[31][32][33][34][35][36]}[31,32,33,34,35,36], using rheology to recognize states, the interaction of liquid crystalline state under magnetic and electric field [31] and its subsequent orientation, the effect of confinement on liquid crystalline, and finally its application and blend with other chemical additives [12]. This table is an introductory representation of research focused on CNC with distinct agendas.

Another contender for CNC, CNF can also form liquid crystalline phases; however, it is more challenging; even though at static conditions, CNF normally does not show birefringence in flow, it does like CNC [44]. Cellulose nanofibril (CNF) LC formation is more difficult due to the greater length of CNFs and their intrinsic proclivity to produce entanglements [45]. A high aspect ratio CNF can also encourage the development of glassy regimes before the isotropic to nematic LCs transition occurs. A similar effect occurs with CNTs, which researchers shorten by treating with superacid to cause LC formation

The cholesteric helix can be tuned to provide stimuli response materials that may match the complexity of biological systems, which is a big opportunity (may operate on moisture, heat, phase transition, etc.). Low-cost biodegradable optical sensors are made possible by implementing sustainable enhancements like CNC because the underlying nanostructure regulates how the reflected colour structurally responds to an external stimulus. It has been demonstrated that responsive materials can measure pressure in ^[46][202], detect humidity in ^[47][48][203,204], solvents in ^[46][202], ultraviolet (UV) light in ^[49][205], and temperature in ^[49][205].

For instance, CNCs-based films have an advantage over other inclusions with comparable properties because of their inherent sensitivity to water. Their low water resistance, which results in the loss of their prized iridescent colour even after being gently inflated by water, restricts their use in humid environments. However, because of their sensitivity to humidity, they make excellent humidity sensors. Recently, the co-assembly of CNC with oxidised starch and tannic acid was researched as a replacement for humidity variations to improve CNC’s solvent sensitivity. A full day of submersion in water did not affect the composite’s structural integrity, vibrant colour, or mechanical characteristics; cross-links were made possible using tannic acid ^[50][206]. Starch or tannic acid additions also kept the self-assembly mostly unaltered. As a result of the information provided here, the chirality sensitivity of CNCs is adjustable; that is, the degree of assembly with other substances, such as starch or tannic acid, can affect how sensitive the chirality is to humidity.

He et al. ^[51][207] produced CNC composite sheets that responded to moisture and mechanical stress using glycerol as a plasticiser. The structural colours of the films could have their chiral structures altered ^[51][207]. There was a reversible colour change when the film was exposed to relative humidity values between 16 and 98 percentBy altering its iridescent hue, the material can also monitor compression pressure quantitatively. In addition to responding to humidity and formaldehyde gas, films created using CNC technology can also change their structural colour and have gas detection capabilities ^[52][178]. At RHs of 43, 75, 86, and 99%, the maximum reflection wavelengths of CNC films were measured to be 360, 451, 513, and 525 nm, respectively. Due to their abundance of hydroxyl groups and porosity, CNC can also react to gas ^[53][208]. Formaldehyde gas concentration was varied to achieve maximum reflection wavelengths of 378, 404, and 470 nm, respectively, in order to evaluate the response of chiral structures to the gas.

CNCs can be utilised as solvent sensors since their chiral-optical properties can be altered in relation to solvents. Based on this, the researchers developed a unique technique for producing tuneable-colour mesoporous CNC films. Giese and colleagues ^[46][202] created mesoporous photonic cellulose (MPC) film by treating a composite of CNCs and a urea-formaldehyde (UF) resin with an alkaline solution. This allowed for quick and reversible structural colour changes in the visible light spectrum. They discovered that the peak reflection wavelength of the composite material was 430 nm in 100 percent ethanol but 840 nm in pure water. The colour will “redshift” when there is more water present. The synthetic cellulose films displayed excellent flexibility due to their reduced crystallinity (in comparison to the initial CNC films’ crystallinity) and the mesoporous structure produced by super-critical drying. Furthermore, the fast and reversible colour change this MPC film undergoes upon swelling makes it ideal for pressure sensing. These new active mesoporous cellulose materials could be useful for biosensing, functional membranes, tissue engineering, and chiral separation.

Instances of materials where PEG-induced “depletion affinity” has been acknowledged are DNA and lyotropic LC ^[54][55][209,210]. CNCs with asymmetric nematic structures can alter their optical properties by altering the PEG’s molecular weight ^[56][180]. As pure CNC films are delicate, several water-soluble polymers, such as poly(vinyl alcohol) [12], PEG, and polyurethane ^[57][181], have been added to increase the elasticity and good mechanical of the film. With these water-soluble polymers, the pitch size can also be changed. Due to depletion forces, PEG has two effects. First, it enhances the CNC film’s mechanical characteristics. Second, it alters the pitch size due to the effects of depletion.

However, the inclusion of polymers can also alter mechanical characteristics. By altering the polymer fraction, it is possible to change the depletion effect’s iridescent colours from red to blue. The concurrent improvement of mechanical properties enables a wide range of applications, including pressure sensors ^[58][113], humidity sensors, and anti-counterfeiting sheets ^[59][48]. For example, the reflectance spectra of pure CNC films show a peak at 242 nm, which rises to 361 nm when the PEG weight fraction reaches 30 wt%. Additionally, home furniture and other products can be created by altering the reflection spectrum ^[56][60][180,211] since the reflectance band grows when the PEG level exceeds 25 weight percent. The half-pitch diameter increases from 103 nm to 143 nm when the PEG weight percentage increases from 10% to 20%. Similar conduct was displayed in reference ^[56][180]. When the molecular weight of the non-adsorbing polymer rises, the pitch size can also change.

The creation of thin films on a Petri plate because of the evaporation of a tiny volume of an iridescent solution is the most basic demonstration of LC in confinement. Brilliant structural colours can still be created even when the thickness of such films is only a few orders of magnitude greater than the pitch length ^[61][62][212,213]. A planar orientation of the cholesteric nanostructure is easily produced in such thin-film confinement ^[63][214], even under quick-drying conditions when disclinations in the cholesteric order are supposed to be kinetically confined. The discontinuous pitch shift brought on by these disclinations becomes critical in very thin films (about 1–2 nm) and can produce an appealing colour mosaic ^[64][174]. According to some reports, confinement conceals translational order in smectic crystals ^[65][215] and turns the bulk isotropic-to-nematic transition into a continuous ordering from an isotropic to a nematic phase.

In addition, due to uneven film production on various surfaces, suspension can offer a variety of iridescent colours that can be adjusted. The effect of the substrate on the formation of the CNC cholesteric phase was investigated in ref. ^[66][216]. When CNC dispersion was dropped on the substrates, the influence of the substrate on the fading out of CNC suspension and its LC formation behaviour was investigated. On glass and stainless steel (SS), CNCs demonstrated initial contact angles of 37.83° and 57.32°, respectively. On the hydrophilic glass surfaces, the cholesteric phase self-assembled from the droplet’s bottom centre and diffused to the edges ^[67][217]. The iridescent coating films created on polystyrene (PS), SS, glass, Cu-Zn alloy, and Cu-Ni alloy exhibit distinctive “coffee rings” as a result of the edge-centre ordered drying procedure ^[68][125]. The study’s conclusions can be used to spray coat a variety of substrates, but more investigation is required to see whether the surfaces in question inherently display shimmering colour. When utilised as a stimulus-response material, developed iridescence may also be used to determine the surface’s composition. Additionally, coated components and a chemical resistance polymer can produce a vibrant, long-lasting coating, making this a suitable colouring technique for urban development.

Thermotropic LCs can act as a thermal switch and affect the average refractive index of periodic structures by being associated with the chiral structure of CNCs. This has already been done in silica films ^[69][218]. Thermotropic LCs can also undergo orientation due to temperature fluctuations. The film became colourless as the temperature increased because the thermotropic agent, originally nematic, changed into an isotropic state around 40 °C. On the other hand, films were iridescent at room temperature. As there was no indication of a reflection signal in the UV-vis spectra, these visual cues were coupled with the optical properties of LC-loaded films. In reference ^[70][219], the texture of the suspension of the CNC-grafted poly(N, N-dimethylamino ethyl methacrylate was also altered by temperature. This colour-changing technique has remained largely unexplored.

Pitch was measured using SEM on CNC film cross-sections and optical microscopy on CNC photonic films; the outcomes revealed a low-temperature dependency. The cholesteric stripe’s bright and dark margins were not equal, and their difference varied greatly with temperature and nematic phase. The change from one biaxial cholesteric to (calamitic cholesteric, discotic cholesteric and biaxial cholesteric), the crossovers between biaxial cholesteric and calamitic cholesteric as well as discotic cholesteric and biaxial cholesteric were seen using optical microscopy ^[71][220]. Changing the optical properties of photonic substances is a crucial objective in the creation of reflecting displays, screens, and sensors. The optical properties of photonic materials can be modified by adjusting their periodicity or refractive index contrast. Visitors that allow stimuli-induced changes in refractive index and hence fluid modulation of the optical properties of the composite may be present in a chiral nematic mesoporous host. As a result, temperature changes in CNC chiral structures can be programmed.

Due to its exceptional biocompatibility, adaptable surface chemistry, renewable and carbon-neutral nature, unsurpassed optical and mechanical capabilities, and great biocompatibility, nanocellulose is becoming increasingly popular [8]. AThis study’s objective is to present a current assessment of recent nanomaterial advancements is presented s and their prospective uses in soft robotics, energy storage, and medical research; therefore, the discussion on energy storage applications fits very well.

As cutting-edge technology (such as portable electronic gadgets, electric cars, and big intermittent battery systems) is integrated into our everyday lives, the need for sophisticated energy storage systems with high energy density, high power density, and extended lifespan has continued to rise ^[72][221]. Due to their lengthy lifespan, superior performance, and dependable stability, lithium ion batteries (LIBs) have been the most extensively used candidate systems in commercial electronic products ^[73][74][222,223]. Due to their extended cycle life, high specific power, and energy density, rechargeable lithium-ion batteries (LIBs) are also viable options for sustainable energy storage devices ^[75][76][224,225]. Since the introduction of commercial LIBs in 1991, carbonaceous materials have received a great deal of attention as candidate anode materials due to their respectable theoretical capacity (372 mAh·g⁻¹) ^[77][226], good electrical conductivity, and exceptional mechanical-chemical stability. Examples include graphite ^[78][79][227,228], CNT ^[80][229], and its associated composites ^[81][82][230,231]. At the same time, environmental concerns have sparked a lot of interest in adopting ecologically benign materials for Li/Na ion batteries sourced from sustainable resources such as ^[83][84][232,233] and ^[85][234]. The idea of employing carbon produced from fungi as an anode material for LIBs was put out by Tang et al. ^[86][235]. Several resources have been used as carbon sources and have shown outstanding electrochemical performances for Li/Na ion batteries. These resources include banana peels ^[87][236], packing peanuts ^[88][237], wheat ^[89][238], and numerous others ^[90][91][239,240]. The capacity of a battery is measured in milliamp hours (mAH). For example, if a battery has 250 mAH capacity and delivers 2 mA average current to a load, it should last 125 h.

However, the investigations have mostly concentrated on modifying carbon precursors or enhancing material composition. These material-oriented methodologies have not considered additional potential characteristics, such as electrode shape, dispersion, and alignment, that might impact the overall electrochemical kinetics and cycle stability of battery electrodes. For rechargeable energy storage devices, research into the implications of carbon precursors’ structural orientation (i.e., alignment)has thus far attracted little attention. Even if the fundamental elements that make up the electrode are the same, it is crucial to note that the architecture (or alignment) of materials can greatly alter the electrochemical kinetics and stability in energy storage applications ^[92][93][241,242]. For instance, Liu et al. looked at how three inorganic fillers with various alignments affected the ionic conductivity of composite polymer electrolytes ^[94][243]. Aligned inorganic nanowires (NW) have ten times higher ionic conductivity than randomly dispersed NWs. In this case, inorganic nanowires of different orientations were mainly utilized as fillers to improve the mobility of Li ions inside the polymer medium and to compensate for the drawbacks of polymer electrolytes. There is no evidence that the structural orientation of inorganic (or organic) components has a direct impact on the overall electrochemical performances of LIBs. To tackle the intriguing issues stated above, cellulose nanocrystals (CNCs) films with different structural orientations were utilized as carbon precursors for this experiment.

In a different study, the sol-gel technique was used to integrate Germanium (IV) oxide (GeO₂) onto chiral nematic CNCs. The procedure maintained the original arrangement of the chiral nematic CNC aerogels. It led to hybrid aerogels with a large proportion of randomly dispersed GeO₂ nanoparticles and concentrated regions up to 705 m²/g. Carbonizing the composite material produced a crystalline structure material with really no pressure collapse and good form restoration following release. By fusing the carbonaceous skeleton’s electrochemical double-layer capacitance with the pseudocapacitive contribution of the GeO₂ nanoparticles, materials with a maximum capacitance (Cp) of 113 F/g and high capacitance retention were created ^[95][244]. Similar to this, in work by Lizundia et al. ^[96][245], conductive polymers were applied to modified chiral nematic CNC sheets on polymerising pyrrole in place. The TEMPO-oxidation, acetylation, desulfation, and cationization processes did not affect the chiral structures. These innovative materials offer appealing possibilities for eco-friendly sensors and energy storage devices since they are simple to make. The chiral structure was unaffected by TEMPO oxidation, acetylation, desulfation, or cationization.

Synthetic chiral material created by nano-micro-sized matrices has aided chemical synthesis, chiral sensing, chiral catalysis, and metamaterial-based improved optical devices. Both hard template methods and soft template approaches are often used to create chiral substances. This method could be used to produce new chiral nanostructured materials. (1) Chiral material synthesis typically uses mesoporous hosts as hard templates to transfer their nanostructure to other materials. (2) Soft template method: material is created by partially removing the host template. The template uses techniques including hyper molecular aggregation, rapid self-assembly, and molecular evaporation. For nano-mesoporous materials, soft template creation is more flexible than hard template preparation. Chiral compounds based on cellulose have grown in prominence as chiral research shifts from the molecule to the nanoscale.

Template synthesis from nano colloidal LCs in limited shape can be used as a model for the organization of nanoparticles (chiral structure guides their assembly in 3-D space). In reference ^[97][201], 3-D confinement of cholesteric LC under two-dimensional containment was investigated. The phase-separated cholesteric shell was built with an isotropic inner thread parallel to the capillary’s long axis and a helicoidal axis parallel to the inner surface of the walls. The generated core-shell LCs might be used as optical waveguides since the geometry of the LCs changed as the amount of confinement increased. The structure was examined over time using POM, and it was discovered that an isotropic core had been precisely constructed after six hours. It took its core 168 h to begin to relax. The time-consuming nature of isotropic and cholesteric CNC rearranging was thus highlighted ^[97][201] The average pitch recorded in the core-shell structure of optical waveguides in ref. ^[97][201] after switching substrates to a glass capillary was about 9 micrometres, but the structure created in Teflon tubes was 5.8 micrometres under the same conditions. As a result, the pitch object served in the glass capillary was much larger than the one created in Teflon. The mismatch results from surface energy variations between the two surfaces.

In ref. ^[98][246], mesoporous black titanium dioxide (TiO_2-X) with the chiral nematic structure of core-shell nanorod was created utilising the templating method once more. Carbonized TiO₂/CNC helical materials were created by chiral depositing TiO₂ nanoparticles onto gelatine functionalized CNCs and calcinating to recover TiO_2-X copies after the carbon is removed. The black TiO₂ was composed of nanorods of chiral nematic crystalline-amorphous TiO₂ and had a mesoporous semiconducting structure. Highly porous nanocarbon networks support the chiral black TiO_2-X nanocrystals that make up the anode electrodes of lithium-ion batteries. In addition to the current efforts, these black TiO₂-_X materials and composites might be useful in fields including energy storage and catalysis. Using silica precursors and evaporation-induced self-assembly of CNC, reference ^[99][247] claims that nanocomposites containing chiral nematic structures can be created. Following the pyrolysis and etching of the silica, chiral nematic mesoporous carbon films are produced. Using a specific capacitance of 170 F·g⁻¹ at 230 mA·g⁻¹, mesoporous carbon sheets displayed nearly ideal capacitor behaviour in a symmetric capacitance with H₂SO₄ as the electrolyte. It has also been described in the literature ^[100][101][248,249] to produce energy storage devices employing cellulose filaments and other novel nanomaterials.

To facilitate different interactions with light, templating can also be used. Due to the scripting technique ^[36][102][36,250], the helical shape can be applied to a variety of media. Compared to a dried CNC film, the inorganic replica’s optical sensitivity may differ. While an optically isotropic material displays continuously shifting refractive indices due to rotation of the birefringent CNC rods, an amorphous inorganic film with a template exhibits recurrent discontinuous differences between the refractive indices of air and the substance. By introducing an index-matching fluid into the gaps and allowing it to evaporate, the reflection can be activated and deactivated ^[36][103][36,251]. If a thermotropic nematic was used to replace the gaps, the material’s absence from the gaps would cause its refractive index to change whenever an electric field is applied; a thermotropic nematic loses index matching, which causes the film to seem coloured. A birefringent matrix material lacked an index matching fluid, which prevents such ON/OFF switching of pho-tonic crystal characteristics even when the original dried CNC film is porous. Inorganic and air layer thicknesses, as well as their combined thickness (which establishes the local optical period), are likely to have a greater impact on the colours produced than visible light wavelengths. One potential use for transparent CNC-templated inorganic materials is cholesteric-based mirrorless lasing [36].

According to the sizes, structures, and surface chemical performances of lignocellulosic biomass, new materials and devices for energy storage should be researched. These materials and devices should use various biomass resources and their combinations as building blocks. According to reference [8], nanocellulose can be created from a wide range of sources and processes. For example, TEMPO-oxidized CNCs can be used with transparent conductors to create flexible and optically transparent electrodes ^[104][252]. Both forms of CNC contain negatively charged rod particles, and sulfuric acid hydrolysed CNC can be utilised as a template to make chiral nematic mesoporous electrode materials. Research into new materials and production techniques may lead to new opportunities in a range of applications. Even though supercapacitors and lithium-ion batteries (LIBs) have extensively used nanocellulose and its derivative materials ^[105][253], only a small number of research on the use of nanocellulose in sodium-ion and Li-S batteries has been published ^[106][107][254,255]. Additionally, several cutting-edge energy storage technologies, including Mg (Al, Mn)-ion batteries, have not received enough attention. Due to its physical robustness, adaptable structure, and surface/interface chemistry, nanocellulose and its derivatives are an environmentally friendly material alternative for rapidly developing energy storage devices.

The colour of films (produced with liquid crystalline CNCs) is produced by reflected light, which is determined by the wavelength and angle of incoming light. The material looks colourful to the human eye when the incoming light’s wavelength is in the visible range. The usage of the perfect films is constrained by their fragility and uneven structural makeup; therefore, an additional supplementary chemical is needed to address mechanical property weakness. This shortcoming is manageable considering the optical characteristics of the CNC chiral nematic LC that cannot be matched by other rod particles; inherent properties such as handedness, sensitivity to humidity, ability to be surface modified and mixed with other chemicals and wealth of information currently available in the literature. The CNC is also excellent for wettability control and adhesion because of its built-in periodic spirally structured LC structure. As mentioned in the energy storage usage, templating may enhance optical properties. In addition to other uses, novel materials have promise for chiral separation ^[108][256], enantioselective adsorption ^[109][257], catalysis ^[110][258], sensing, optoelectronics, and lithium-ion batteries ^[111][259].

Polymers and CNC have been used to boost the mechanical qualities of naturally inspired structures, as some accounts of this research were outlined earlier. For improved mechanical or optical qualities, the insertion of CNC films into larger laminar structures has been investigated ^[112][260]. Thin sandwiched structures with bright structural colour, improved mechanical characteristics, and shape memory capabilities were developed by incorporating CNC films into the polymer. Similar to the jewel beetle chrysin resplendent ^[47][203], CNC films may be built up on either side of a birefringent membrane to enable the simultaneous reflection of left- and right-handed circularly polarised light. A similar birefringent layer was produced for the sample optical mechanism by impregnating millimetre-scale planar gaps in CNC films with a nematic LC. This layer may be triggered by heat or electric fields to modify the reflected spectrum or its polarization state ^[113][261].

Additionally, CNCs sheets only reflect light with a left circular polarisation (LCP). The odd manner chiral cellulose nanorods self-assemble is what causes this property. It is possible to control the switch from right to left-handedness by adjusting the temperature or using an electric field ^[114][262]. This method might modify the optical characteristics of different chiral LC systems, which could be used as coatings, polarizers, and filters in optical devices. Using references and highlights, Table 3 presents some of the most important findings in the literature on the modification of optical characteristics of CNC pure and composite films.

Liquid crystal production can be considered a purifying technique since CNC can self-partition out of a mixture of colloids. In ref. ^[122][267] the co-assembly of CNCs and solid latex nanoparticles was investigated by the author; the nanoparticles were also fluorescently labelled, and co-assembly was investigated in both solution and solid films. The creation of two types of structures—CNC-rich layers with cholesteric structures and randomly distributed latex-rich layers—was demonstrated by the CNC-latex combination. These layers were arranged on the film’s plane, and a sizeable number of latex nanoparticles were dispersed in the cholesteric area of the CNC matrix. With the use of circular dichroism spectroscopy, the chiroptical properties of films were investigated. The CD spectra of a latex-free film revealed a positive single from the deliberate transmission of right-handed circularly polarized light by CNCs. With the addition of latex particles, the volume portion of the 0.31 positive CD signal remained constant, but the peak significantly grew, indicating a wider range of pitch values. The loss of cholesteric order and the 57% drop in signal were both correlated with the CNC percentage. The position maximum also remained constant, indicating that the addition of spherical latex particles did not affect the cholesteric domains.

Following findings from earlier studies on wood-sourced CNCs, measurements of the distance among fringe lines in fingerprint texture revealed that half pitch of domains increased from 14 ± 3 micrometres in latex-free CNC suspension to 2410 micrometres in the presence of latex particles ^[123][268]. Subsequent analysis of the fluorescence signal revealed that fluorescence intensity was 30% less cholesteric phase than in the isotropic phase, meaning there was a lower concentration of spherical particulates.

In films, the pitch of the organization is as follows phase decreased from 48 micrometre to 220 ± 80 nm for samples that contain latex particles while it changed to 220 ± 60 nm in samples with no latex particles, following the knowledge that assembly within cholesteric particles occurs primarily in suspension and not in the dried-out form. This is because films formed after drying will have lower pitch values. It was determined that excluded volume effects resulting from depletion pressures between latex spherical nanoparticles ^[124][125][269,270] were responsible for the creation of latex-rich “islands” in CNC-latex films. Due to depletion effects, the addition of tiny colloids to a solution of larger colloids can cause flocculation of the larger colloids; as a result, bigger latex nanoparticles may exhibit attraction in the presence of CNCs ^[126][127][271,272].

The author went on to infer that particle geometry regulates the assembly of a binary mixture of rods and spheres in the absence of interaction ^[128][273]. Phase separation between sphere- and rod-rich phases occurs in a liquid state, but at large sphere volume fractions, only one isotropic phase emerges ^[128][273]. If an application calls for such arrangements, having spheres within rod-rich phases is crucial in situations when it is intended to prevent rod particles from forming liquid crystalline phases, such as viruses.