Cholesteric Liquid Crystal Phase Research Articles

Cholesteric liquid crystal phase variations within nanotubes: an in-depth analysis of the influences of twist radius and molecular pitch

ABSTRACT This study investigates the self-assembly and phase transitions of cholesteric liquid crystals (CLCs) when confined in nanotubes, specifically focusing on the variations in their molecular structures. A dissipative particle dynamics method was used to investigate how the changes in helix radius ( r LC ) and pitch ( P ) affect the behaviour of the LCs. For pitches of 24, 12, and 6, the orientation order parameter ( P 2 ) showed distinct trends during cooling. Smaller helix radii resulted in isotropic to nematic to smectic phase transitions, whereas larger radii resulted in a novel smectic phase with spiral structures (Sm s ). Circumferential local-order parameters ( P 2 r and P 2 z ) were introduced to better characterise the phases, and a disordered spiral-structure phase (Sm s 2 ) with local perturbations was observed. The transitions between isotropic, nematic, and smectic phases, highlighting the influence of the pitch and helix radius, were observed from the phase diagrams. Smaller pitches and radii prevented the formation of stable structures; however, specific combinations induced characteristic spiral structures in the smectic phase. These results provide new insights into the self-assembly of confined CLCs, which have potential applications in the design of photonic devices and LC-based sensors. This study advances our understanding of phase control in quasi-one-dimensional systems and highlights the importance of molecular variations in liquid crystal behaviour.

Cholesteric Liquid Crystals with Thermally Stable Reflection Color from Mixtures of Completely Etherified Ethyl Cellulose Derivative and Methacrylic Acid.

Cellulose derivatives have attracted attention as environmentally friendly materials that can exhibit a cholesteric liquid crystal (CLC) phase with visible light reflection. Previous reports have shown that the chemical structures and the degrees of substitution of cellulose derivatives have significant influence on their reflection properties. Although many studies have been reported on CLC using ethyl cellulose (EC) derivatives in which the hydroxy groups are esterified, there have been no studies on EC derivatives with etherified side chains. In this article, we optimized the Williamson ether synthesis to introduce pentyl ether groups in the EC side chain. The degree of substitution with pentyl ether group (DSPe), confirmed via 1H-NMR spectroscopic measurements, was controlled using the solvent and the base concentration in this synthesis. All the etherified EC derivatives were soluble in methacrylic acid (MAA), allowing for the preparation of lyotropic CLCs with visible reflection. Although the reflection peak of lyotropic CLCs generally varies with temperature, the reflection peak of lyotropic CLCs of completely etherified EC derivatives with MAA could almost be preserved in the temperature range from 30 to 110 °C even without the aid of any crosslinking. Such thermal stability of the reflection peak of CLCs may be greatly advantageous for fabricating new photonic devices with eco-friendliness.

Testing different supervised machine learning architectures for the classification of liquid crystals

ABSTRACTDifferent convolutional neural network (CNN) and inception network architectures were trained for the classification of isotropic, nematic, cholesteric and smectic liquid crystal phase textures to test the prediction accuracy for each one of these models. Varying the number of layers and inception blocks, as well as the regularisation, and application to different phase transitions and classification tasks, it is shown that in general the architecture of an inception network with two blocks leads to the best classification results. Regularisation, such as image flipping, and dropout layers additionally somewhat increase the classification accuracy. Even for simple tasks like the isotropic-nematic transition, which is of importance for applications in the automatic readout of sensors, convolutional neural networks need more than one layer. Care must be taken to not apply architectures of too large complexity, as this will again reduce the classification accuracy due to overfitting. Architecture complexity needs to be adjusted to the given classification task

Bioinspired Photonic Materials from Cellulose: Fabrication, Optical Analysis, and Applications.

Polysaccharides are a class of biopolymers that are widely exploited in living organisms for a diversity of applications, ranging from structural reinforcement to energy storage. Among the numerous types of polysaccharides found in the natural world, cellulose is the most abundant and widespread, as it is found in virtually all plants. Cellulose is typically organized into nanoscale crystalline fibrils within the cell wall to give structural integrity to plant tissue. However, in several species, such fibrils are organized into helicoidal nanostructures with a periodicity comparable to visible light (i.e., in the range 250-450 nm), resulting in structural coloration. As such, when taking bioinspiration as a design principle, it is clear that helicoidal cellulose architectures are a promising approach to developing sustainable photonic materials. Different forms of cellulose-derived materials have been shown to produce structural color by exploiting self-assembly processes. For example, crystalline nanoparticles of cellulose can be extracted from natural sources, such as cotton or wood, by strong acid hydrolysis. Such "cellulose nanocrystals" (CNCs) have been shown to form colloidal suspensions in water that can spontaneously self-organize into a cholesteric liquid crystal phase, mimicking the natural helicoidal architecture. Upon drying, this nanoscale ordering can be retained into the solid state, enabling the specific reflection of visible light. Using this approach, colors from across the entire visible spectrum can be produced, alongside striking visual effects such as iridescence or a metallic shine. Similarly, polymeric cellulose derivatives can also organize into a cholesteric liquid crystal. In particular, edible hydroxypropyl cellulose (HPC) is known to produce colorful mesophases at high concentrations in water (ca. 60-70 wt %). This solution state behavior allows for interesting visual effects such as mechanochromism (enabling its use in low-cost colorimetric pressure or strain sensors), while trapping the structure into the solid state enables the production of structurally colored films, particles and 3D printed objects. In this article, we summarize the state-of-the-art for CNC and HPC-based photonic materials, encompassing the underlying self-assembly processes, strategies to design their photonic response, and current approaches to translate this burgeoning green technology toward commercial application in a wide range of sectors, from packaging to cosmetics and food. This overview is supported by a summary of the analytical techniques required to characterize these photonic materials and approaches to model their optical response. Finally, we present several unresolved scientific questions and outstanding technical challenges that the wider community should seek to address to develop these sustainable photonic materials.

Nematic to Cholesteric Transformation in the Cellulose Nanocrystal Droplet Phase

Nucleation, growth, and transformation of chirality in nanomaterial systems is a growing research topic with broad interest in tunable and configurable chiroptical materials. Similar to other one-dimensional nanomaterials, cellulose nanocrystals (CNCs), which are nanorods of naturally abundant biopolymer cellulose, display chiral or cholesteric liquid crystal (LC) phases in the form of tactoids. However, the nucleation and growth of the cholesteric CNC tactoids to equilibrium chiral structures and their morphological transformations are yet to be critically assessed. We noticed that the onset of liquid crystal formation in CNC suspensions is characterized by the nucleation of a nematic tactoid that grows in volume and spontaneously transforms into a cholesteric tactoid. The cholesteric tactoids merge with the neighboring tactoids to form bulk cholesteric mesophases with various configurational palettes. We applied scaling laws from the energy functional theory and found suitable agreement with the morphological transformation of the tactoid droplets monitored for their fine structure and orientation by quantitative polarized light imaging.

Fluorination Enables Dual Ferroelectricity in Both Solid- and Liquid-Crystal Phases.

Ferroelectric materials are a special type of polar substances, including solids or liquid crystals. However, obtaining a material to be ferroelectric in both its solid crystal (SC) and liquid crystal (LC) phases is a great challenge. Moreover, although cholesteric LCs inherently possess the advantage of high fluidity, their ferroelectricity remains unknown. Here, through the reasonable H/F substitution on the fourth position of the phenyl group of the parent nonferroelectric dihydrocholesteryl benzoate, we designed ferroelectric dihydrocholesteryl 4-fluorobenzoate (4-F-BDC), which shows ferroelectricity in both SC and cholesteric LC phases. The fluorination induces a lower symmetric polar P1 space group and a new solid-to-solid phase transition in 4-F-BDC. Beneficial from fluorination, the SC and cholesteric LC phases of 4-F-BDC show clear ferroelectricity, as confirmed by well-shaped polarization-voltage hysteresis loops. The dual ferroelectricity in both SC and cholesteric LC phases of a single material was rarely found. This work offers a viable case for the exploration of the interplay between ferroelectric SC and LC phases and provides an efficient approach for designing ferroelectrics with dual ferroelectricity and cholesteric ferroelectric liquid crystals.

Liquid crystalline matrix-induced viscoelastic mechanical stimulation modulates activation and phenotypes of macrophage.

Accumulating evidence indicates that the mechanical microenvironment exerts profound influences on inflammation and immune modulation, which are likely to be key factors in successful tissue regeneration. The elastic modulus (Em) of the matrix may be a useful adjustable property to control macrophage activation and the overall inflammatory response. This study constituted a series of Em-tunable liquid crystalline cell model (HpCEs) resembling the viscoelastic characteristic of ECM and explored how mechanical microenvironment induced by liquid crystalline soft matter matrix affected macrophage activation and phenotypes. We have shown that HpCEs prepared in this work exhibited typical cholesteric liquid crystal phase and distinct viscoelastic rheological characteristics. All liquid crystalline HpCE matrices facilitated macrophages growth and maintained cell activity. Macrophages in lower-Em HpCE matrices were more likely to polarize toward the pro-inflammatory M1 phenotype. Conversely, the higher-Em HpCEs induced macrophages into an elongated shape and upregulated M2-related markers. Furthermore, the higher-Em HpCEs (HpCE-O1, HpCE-H2, HpCE-H1) could coax sequential polarization states of RAW264.7 from a classically activated "M1" state toward alternatively activated "M2" state in middle and later stage of cell culture (within 3-7 days in this work), suggesting that the HpCE-based strategies could manipulate the local immune microenvironment and promote the dominance of the pro-inflammatory signals in early stages, while M2 macrophages in later stages. The liquid crystalline soft mode fabricated in this work maybe offer a new design guideline for in vitro cell models and applications.

Molecular engineering of the polymer stabilizing network to enhance the electro-optic response of cholesteric liquid crystals

The selective reflection of the cholesteric liquid crystal (CLC) phase in the planar orientation can be tuned or broadened by the incorporation of polymer stabilizing networks (PSCLC).

Kinetic arrest during the drying of cellulose nanocrystal films from aqueous suspensions analogous to the freezing of thermal motions

A comprehensive understanding of controlling the iridescence of cellulose films by manipulating the alignment and helical pitch of cellulose nanocrystals (CNCs) is required to advance cellulose photonics and its optoelectronic applications. Aqueous suspensions of CNCs exhibit a cholesteric liquid crystal (LC) phase with structural color; however, attaining a uniformly colored film is extremely difficult. Presumably, because multiple interrelated factors influence the CNC molecular alignment and helical pitch, existing models are not necessarily conclusive and remain a subject of debate. To eventually achieve homogeneously colored films, we compare aqueous CNC suspensions as a lyotropic liquid LC with thermotropic ones, and we spectroscopically confirm that the coloration of CNC droplets originates from the periodic CNC structure. The suspension drying process significantly influences the quality of iridescence of CNC films. Rapidly drying a droplet of a CNC suspension forms a concentric rainbow film, with red edges and a blue center, typical of the coffee-ring effect observed in air-dried films. By contrast, slow drying under controlled humidity, which reduces capillary flow, provides higher uniformity and a large blue area. Orbitally shaking films while drying under high humidity further improves the uniformity. Therefore, the evaporation rate significantly influences the thermodynamically stabilized helical pitch of CNCs, which determines the structural color. We qualitatively model the kinetic arrest induced by the rapid evaporation of lyotropic LCs in a manner equivalent to that induced by the rate of temperature change in thermotropic LCs and other materials.

Effective Chiral Interactions between Nonchiral Rigid Macromolecules in a Chiral Solvent and the Induced Cholesteric Liquid Crystal Phase

It has been shown that a nonchiral anisotropic macromolecule embedded in a chiral dielectric solvent possesses an effective optical activity proportional to the optical activity of the solvent. As a result, there exists an effective chiral interaction between the macromolecules, which creates a torque acting on the primary axes of the two interacting molecules. A general expression for the effective chiral interaction potential has been derived in terms of the effective polarizability and the effective gyration tensor of the macromolecule in the chiral solvent. Explicit expressions for the components of the effective polarizability and the gyration have been obtained using the model of a hard rod filled with anisotropic dielectric and embedded into the isotropic chiral dielectric medium. The theory predicts the formation of the cholesteric helical structure in the nematic polymer liquid crystal phase induced by a chiral solvent.

Research on Circularly Polarized Luminescent and Clustering-Triggered Emission Properties of Cholesteryl Benzoate

Circularly polarized luminescence (CPL) materials have attracted intensive attention due to their exceptional photophysical properties. However, it has been rarely reported in the field of nontraditional luminescence. It is of great significance to construct circularly polarized luminescent materials with atypical luminescent groups without traditional conjugated structures. Cholesteryl benzoate is a classical cholesteric liquid crystal, and we coincidentally find that it shows clustering-triggered emission behavior in recent studies, which means that cholesteryl benzoate can emit circularly polarized light at the cholesteric liquid crystal phase. Therefore, we synthesized cholesteryl benzoate and studied its photophysical properties in detail. The findings show that cholesteryl benzoate shows triggered emission behavior. The research results suggest that the emission behavior of cholesteric benzoate shows concentration-enhanced emission, aggregation-induced emission (AIE), excitation wavelength dependence, and low-temperature phosphorescence luminescence characteristics. The solid-state circularly polarized luminescence (CPL) property of cholesteryl benzoate quenched by the cholesteric phase was also studied, and the measured luminescence asymmetry factor (glum) could achieve −2.6 × 10–3. In addition, we also simulated the luminescence mechanism of cholesteryl benzoate by theoretical calculation.

Peculiarities of focal conic structure formed near the cholesteric-isotropic phase transition.

Focal conic structure formed near the transition from the cholesteric liquid crystal phase into isotropic liquid is studied in planar cells with a combination of optical methods. Employing a procedure with slow variation of temperature, we manage to obtain regions of periodic focal conic structure with two-dimensional square ordering in the plane of the cell. Using ordered samples and materials with selective reflection in the visible spectral range, we obtain spectral and microscopic optical data which deepen our knowledge of the focal conic structure.

(Digital Presentation) Electrochemical Polymerization of Thiophene in Cholesteric Liquid Crystal with Vitamins

Vitamins are natural compounds which is important for biological reactions. Vitamin C (ascorbic acid) is a water-soluble substance, while Vitamin E (tocopherol) is a soluble material in organic solvents. Further, antioxidant action can affect for metabolism in biological system. Vitamin E has three asymmetric centers in the molecular structure. In the liquid crystal technology, nematic liquid crystal is simple and high fluidity similar to isotopic liquid. Addition of small amount of chiral compounds to nematic liquid crystal can induce cholesteric liquid crystal. This is another chiral and helical version of nematic liquid crystal. In this study, we employed vitamin E as a chiral inducer to nematic liquid crystal for formation of helical liquid crystal system. Electrochemical polymerization is a convenient method for preparation of electroactive polymer deposited on an electrode in the form of thin film. Electrochemical polymerization in LC provides some interesting phenomena. First, electrochemical polymerization in liquid crystal allows the resultant to imprint morphology of molecular aggregation structure from molecular level to macroscopic level of liquid crystal. Second, electrochemical polymerization produces electroactive polymer with dynamically color change upon electrochemical redox process, which character can be applied for electrochemical driven display. Third, electrochemical charge and discharge provides voltaic storage function for the resultant polymer. Thus, electrochemical technique and polymer chemistry, such a brilliant combination produces electro-optic character. Recently, electrochemical polymerization in helical liquid crystal system has been performed. The electrochemical polymerization employs cholesteric liquid crystal as an electrolyte for polymerization. Cholesteric liquid crystal can be prepared by mix of nematic liquid crystal and chiral compounds. We employ synthetic compound as a chiral inducer. Here, we use vitamin E as chiral inducer to nematic liquid crystal preparation of cholesteric liquid crystal electrolyte solution for electrochemical polymerization. Observation of optical texture of the cholesteric liquid crystal electrolyte containing tetrabutylammonium perchlorate (TBAP) as a supporting salt showed fingerprint texture, which is characteristic of cholesteric liquid crystal.Next, electrochemical polymerization in cholesteric liquid crystal induced by vitamin E was carried out. We employed constant voltage electrochemical polymerization to ITO (indium–tin-oxide) coated glass slides were sandwiched via insulator tetrafluoroethylene as a spacer, and the choleretic liquid crystal electrolyte contained monomer (2,2′-bithiophene) was charged with pipette before application of voltage for electrochemical polymerization. The entire polymerization cell was heated to change the liquid crystal to isotropic phase. Then, gradually cooled to room temperature, and the isotopic phase was changed to cholesteric liquid crystal phase with iridescence. After confirming the electrolyte showed liquid crystal phase, constant voltage of 6 V across the sandwiched cell for 60 min was applied. Then, the polymerization cell was de-assembled and washed wish a large volume of organic solvent to remove the liquid crystal electrolyte solution, oligomer, and residual monomer. The polymer film thus prepared was deposited on cathode. This is quite interesting phenomena because electrochemical polymerization is generally occurred at the anode with oxidation. However, this result indicates that electrochemical polymerization in liquid crystal at cathode is possible. Cathodic electrochemical polymerization has been reported for dibromo aromatic compound or unsaturated aliphatic compounds. However, cathodic electrochemical polymerization of aromatic compounds with no halogen group has been few reported.The polymer shows electronic optical transition in visible range due to development of p-conjugated system and absorption at long wave lengths due to doping band accompany by generation on polaron (radical cation). The electrochemical character of the resultant polymer was examined using cyclic voltammetry (CV). The CV measurements were achieved in a monomer-free 0.1-M TBAP−acetonitrile solution at the scan rates of 10 mVs−1. The potential was calculated using a reference of silver/silver ion (Ag/Ag+) electrode. The oxidation and reduction signals are observed during the oxidation and reduction processes. The result showed the resultant polymer has good redox property. The resultant polymer shows no CD signal from short to long wavelengths, indicating no optical activity. However, the polymer shows the similar optical texture to that of liquid crystal electrolyte under the polarizing optical microscopy observations, implying the fingerprint texture of the polymer as macroscopic transcription of the liquid crystal structure may not contribute optical active property. Transcription from liquid crystal environment may not always occurs from molecular level to macroscopic level in the polymerization in liquid crystal. The polymer prepared in this study has no hierarchal structure from molecular level to the higher level, indicating macroscopic morphological imprinting in the polymerization is not essential condition for imprinting from the molecular level.

Rheological Properties of Cholesteric Liquid Crystal with Visible Reflection from an Etherified Hydroxypropyl Cellulose Derivative.

Optical properties of hydroxypropyl cellulose (HPC) derivatives have been widely investigated for their ability to exhibit cholesteric liquid crystal (CLC) phase. However, there are only a limited number of studies on their rheological properties even though they are quite important for the applications of such HPC derivatives to the versatile CLC photonic devices. In this article, we report on the optical and rheological properties of an HPC derivative possessing pentyl ether groups in the side-chains. The etherified HPC derivative exhibited thermotropic CLC phase with light reflection in the temperature range between 25 °C and 120 °C. After the HPC derivative was heated once at isotropic phase, followed by being cooled to the CLC phase, the reflection peak could not be observed, even at the CLC phase. At this stage, the HPC derivative exhibited solid-like rheological responses compared to that of sheared at a constant shear rate of 1.0 s−1. Such differences in the optical and rheological properties of the HPC derivative can be ascribed to the difference in CLC orientation state. From the rheological results, the etherified HPC derivative showed liquid-like behavior rather than the esterified HPC derivatives. This evidence provides a promising clue for fabricating high-quality CLC devices by the facile CLC orientation.

Dual-Cross-linked Liquid Crystal Hydrogels with Controllable Viscoelasticity for Regulating Cell Behaviors.

The liquid crystal properties and viscoelasticity of the natural bone extracellular matrix (ECM) play a decisive role in guiding cell behavior, conducting cell signals, and regulating mineralization. Here, we develop a facile approach for preparing a novel polysaccharide hydrogel with liquid crystal properties and viscoelasticity similar to those of natural bone ECM. First, a series of chitin whisker/chitosan (CHW/CS) hydrogels were prepared by chemical cross-linking with genipin, in which CHW can self-assemble to form cholesteric liquid crystals under ultrasonic treatment and CS chains can enter into the gaps between the helical layers of the CHW cholesteric liquid crystal phase to endow morphological stability and good mechanical properties. Subsequently, the obtained chemically cross-linked liquid crystal hydrogels were immersed into the desired concentration of the NaCl solution to form physical cross-linking. Due to the Hofmeister effect, the as-prepared dual-cross-linked liquid crystal hydrogels showed an enhanced modulus, viscoelasticity similar to that of natural ECM with relatively fast stress relaxation behavior, and fold surface morphology. Compared to both CHW/CS hydrogels without liquid crystal properties and CHW/CS liquid crystal hydrogels without further physical cross-linking, the dual-cross-linked CHW/CS liquid crystal hydrogels are more favorable for the adhesion, proliferation, and osteogenic differentiation of bone marrow mesenchymal stem cells. This approach could inspire the design of hydrogels mimicking the liquid crystal properties and viscoelasticity of natural bone ECM for bone repair.

Thermal and optical properties of amphitropic liquid crystals derived from cholesterol and cinnamic acid

ABSTRACT In this paper, we firstly demonstrate the synthesis of chiral amphitropic liquid crystals derived from cholesterol as well as their thermal and optical properties. Chiral monomeric cholesteryl-4-(6-acryloyloxyhexyloxy) cinnamate (CCM) derived from cholesterol and cinnamic acid has been synthesised showing amphitropic liquid crystal phases. The synthesised CCM exhibits oily streak textures under a polarised optical microscope (POM), corresponding to cholesteric liquid crystal phase formed after heating over 120°C and after being treated with organic solvents such as dichloromethane, chloroform, tetrahydrofuran and toluene. Both the thermotropic and lyotropic cholesteric liquid crystals exhibit selective light reflection, and the wavelength of the reflected light falls in the visible light region showing colourful appearances. The results suggest that CCM could be used for the development of sensors for both temperature and solvents. Homopolymer (Poly-CCM) was synthesised via free radical polymerisation. The synthesised polymer did not exhibit any mesomorphic behaviour either by heating or being treated with solvents. These results indicate that the long chain hydrocarbons and sidechains of CCM were disturbed and restricted after polymerisation leading to the loss of liquid crystalline properties. However, cholesteric construction of monomeric CCM was fixed via UV-polymerisation. The synthesised Poly-CCM film shows Bragg reflection significantly.

Chiral shape fluctuations and the origin of chirality in cholesteric phases of DNA origamis.

Lyotropic cholesteric liquid crystal phases are ubiquitously observed in biological and synthetic polymer solutions, characterized by a complex interplay between thermal fluctuations and entropic and enthalpic forces. The elucidation of the link between microscopic features and macroscopic chiral structure, and of the relative roles of these competing contributions on phase organization, remains a topical issue. Here, we provide theoretical evidence of a previously unidentified mechanism of chirality amplification in lyotropic liquid crystals, whereby phase chirality is governed by fluctuation-stabilized helical deformations in the conformations of their constituent molecules. Our results compare favorably to recent experimental studies of DNA origami assemblies and demonstrate the influence of intramolecular mechanics on chiral supramolecular order, with potential implications for a broad class of experimentally relevant colloidal systems.

Electrically Induced Splitting of the Selective Reflection in Polymer Stabilized Cholesteric Liquid Crystals

AbstractElectrical reconfiguration of the cholesteric liquid crystal phase is subject to extensive prior research. Here, a distinctive composition that allows the typically singular selective reflection to be split into two distinct and tunable selective reflections with an electric field is reported. The distinctive electro‐optic phenomena (reflection notch splitting) are shown to be composition dependent and enabled by the introduction of appreciable amounts of side chain liquid crystalline mesogens. Functional opportunities enabled by the distinguished control of the two reflection elements are demonstrated, including spectrally variant polarization filters.

Vapor treatment, liquid crystal formation, magnetic orientation, and crystallization (VLMC) to form helical polyisocyanides with oriented crystal‐like structure

AbstractWe describe a four‐step process [solvent vapor treatment, liquid crystal formation, magnetic orientation, and crystallization (VLMC)] for producing oriented helical polyisocyanides with crystal‐like structure. We synthesized a series of ortho‐alkyl groups substituted with poly(phenyl isocyanide), and characterized the polymer structure using polarizing optical microscopy, scanning electron microscopy, and X‐ray diffraction. The results demonstrated that the polymer has a crystal‐like structure and the sample forms cholesteric liquid crystal phase. Vapor treatment of polymer films under a magnetic field produced an aligned fiber structure at the submicron level and demonstrated magnetic alignment and formation of a solvent vapor‐induced polymer crystal. These results demonstrated formation of a polymer with a one‐handed helical structure, formation of a liquid crystal and polymer crystal via solvent vapor treatment, and magnetic alignment of a textile‐like polymer crystal domain.

Γ-convergence of a mean-field model of a chiral doped nematic liquid crystal to the Oseen–Frank description of cholesterics

Systems of elongated molecules, doped with small amounts of molecules lacking mirror symmetry can form macroscopically twisted cholesteric liquid crystal phases. The aim of this work is to rigorously derive the Oseen–Frank model of cholesterics from a more fundamental model concerned with pairwise molecular interactions. A non-local mean-field model of the two-species nematic host/chiral dopant mixture is proposed, and it is shown that Oseen–Frank’s elastic free energy for cholesteric liquid crystals can be obtained in a simultaneously large-domain and dilute-dopant asymptotic regime. By techniques of -convergence, it is shown that in the asymptotic limit, dopant–dopant interactions are negligable, the Frank constants and nematic host order parameter are unperturbed by the presence of dopant, but the mirror asymmetry of the dopant–host interaction leads to a macroscopically twisted ground state. The constant of proportionality between the helical wavenumber and dopant concentration, the helical twisting power (HTP), can be explicitly found through such an analysis, with a nonlinear temperature dependence. Depending on the relative strengths of the host–host and host–dopant interactions, it is shown that HTP may increase or decrease with temperature.