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Article

Cholesteric Liquid Crystal Polymer Network Patterns with a Golden Structural Color

by
Qingyan Zeng
,
Wei Liu
,
Yi Li
and
Yonggang Yang
*
State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, Department of Polymer Science and Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
*
Author to whom correspondence should be addressed.
Chemistry 2025, 7(3), 93; https://doi.org/10.3390/chemistry7030093
Submission received: 29 April 2025 / Revised: 30 May 2025 / Accepted: 2 June 2025 / Published: 3 June 2025
(This article belongs to the Section Supramolecular Chemistry)
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Abstract

:
Cholesteric liquid crystal polymer network (CLCN) films with composite structural colors have potential applications in decoration and anti-counterfeiting. Herein, a thermochromic acrylate-based cholesteric liquid crystal mixture was prepared. The structural color of CLCN films can be controlled by the photopolymerization temperature. Based on the oxygen inhibition of the acrylate group, CLCN films with double reflection bands were prepared using a two-step photopolymerization method. The distance between these two reflection bands was controlled by the polymerization temperatures of these two steps. Since golden colors are the most attractive for decoration, herein, colorful patterns with a golden structural color were prepared by controlling the polymerization temperatures.

1. Introduction

Cholesteric liquid crystal (CLC) structures are ubiquitous in plants and animals [1,2,3,4,5], and their helical structure endows them with distinctive optical properties, including selective Bragg reflection. In accordance with the Bragg equation [6,7,8,9,10,11,12,13], the reflection wavelength at the maximum (λ) is given by λ = n × P (n, the average refractive index), and the reflection bandwidth Δλ is given by Δλ = Δn × P (Δn = ne − no, where ne and no are the extraordinary and ordinary indices, respectively), where P is the helical pitch of the CLC. The helical supramolecular structure in CLC self-assembly produces structural colors that can be regulated by adjusting the helical pitch of CLC [14]. For thermochromic and photochromic CLCs, their helical pitches can be adjusted by changing the temperature and light dose, respectively [15,16].
Broadband reflective materials with a CLC structure have been found in beetles [17]. The helical pitch of the CLC structure in the dorsal cuticle of golden beetles exhibits variation with depth, demonstrating a strong reflection in the green–yellow–orange region, as well as in the infrared region. Jewel scarabs exhibit vibrant light reflections ranging from bright green to metallic silver-colored, indicating selective and broadband reflections. The metallic silver-colored portion of the cuticle exhibits a CLC structure with a pitch distribution ranging from 150 to 540 nm and a reflectance spectrum occurring between 450 and 1000 nm. Because the entire wavelength range is reflected, the color of a broadband reflector is also less dependent on direction. The wider the bandwidth range is, the closer the cuticle is to pure gold or silver (mirror-like) [18].
Due to the low viscosity of small-molecule CLC, the CLC pitch is typically homogeneous [19]. And the birefringence of CLC materials is generally less than 0.3 [20,21]. Based on Bragg’s law, the bandwidths of selectively reflected lights are typically less than 150 nm. It has been demonstrated that the reflection bandwidth can be increased by adjusting the pitch distribution of CLC [22,23,24,25,26,27,28]. Acrylate-type CLC mixtures polymerize under UV irradiation to form cholesteric liquid crystal polymer networks (CLCNs) [29]. Composite CLCN films with a broad reflection band can be simply prepared by overlapping CLCN films with a single helical pitch [30]. Polymer-stabilized cholesteric liquid crystal (PSCLC) and CLCN films have been prepared by the diffusion of less reactive or non-reactive compounds during the preparation process [22,31]. However, these methods are constrained by the need for LC cells, limiting their large-scale preparation. In this study, we overcome this barrier through a two-step photopolymerization approach leveraging oxygen inhibition and temperature modulation. This enables the independent control of broadband reflection within a single film, compatible with patterning and large-scale applications. Similarly, based on oxygen inhibition and molecular diffusion, a two-step photopolymerization method for the preparation of a CLCN film with double reflection bands was developed [32,33].
Acrylate-type monomers can be polymerized under light with a weak intensity, with the protection of inert gases such as nitrogen and argon. However, polymerization in air is hindered by oxygen inhibition due to free-radical polymerization [34]. The wavelengths of the reflection bands were controlled by two polymerization temperatures. Although the obtained composite colored CLCN films can be applied for decoration and as optical filters, research on this method is still limited. Herein, CLCN films with a broad reflection band or double ones were prepared by carefully controlling polymerization temperatures. Patterns with a golden color were prepared, which were suitably applied for decoration.

2. Materials and Methods

2.1. Chemical Reagents and Instruments

(R)-1,2-Propanediol and Irgacure 907 were purchased from 9 Ding Chemistry Co., Ltd. (Shanghai, China). Tetrahydrofuran (THF) was purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. (Shanghai, China). Dicyclohexylcarbodimide (DCC) and 4-dimethylaminopyridine (DMAP) were purchased from Adamas Chemical Co., Ltd. (Shanghai, China). Cyclohexanone, cyclopentanone, and ethanol were obtained from Chinasun Specialty Products Co., Ltd (Shanghai, China). LC242 and rubbing-oriented poly(ethylene terephthalate) (PET) films were provided by Wuxi Wanli Adhesive Material Co., Ltd. (Wuxi, China). 4-(4-(6-(Acryloyloxy)hexoxy)benzoyloxy)benzoic acid was synthesized according to the literature [35].
The 1H NMR spectrum was recorded using an INOVA-400 spectrometer (Varian Inc., Palo Alto, CA, USA) in CDCl3 using tetramethylsilane (TMS) as an internal standard. The FT-IR spectra were measured using a Nicolet 6700 spectrometer (NICOLET, Waltham, MA, USA) at a 2.0 cm−1 resolution by averaging over 32 scans. The mass spectrum (MS) was measured with an Ultraflextreme MALDI TOF/TOF spectroscope (BRUKER, Billerica, MA, USA). The elemental analysis was performed using a Vario EL III instrument (Elementar Analysensysteme GmbH, Langenselbold, Germany). Polarized optical microscopy (POM) images were taken using a CPV-900C polarization microscope (Shanghai Optical Instrument Factory, Shanghai, China) fitted with a Linkam LTS420 hot stage (LINKAM, Tadworth, Surrey, UK). The differential scanning calorimetry (DSC) measurement was conducted using a TA-Q200 (TA Instruments, New Castle, DE, USA) under nitrogen at 10 °C min−1. Field-emission scanning electron microscopy (FE-SEM) images were obtained using a Hitachi Regulus-8230 (HITACHI, Tokyo, Japan) operating at 5.0 kV. CLCN films were freeze-fractured in liquid nitrogen to expose the cross-sections. Multiple periodicities were measured across the FE-SEM images using software (Operation, ver. 3.7) with a calibrated scale bar. Before taking the FE-SEM images, platinum was spattered on the surfaces of the samples. The circular dichroism (CD) spectra were measured using a JASCO 815 spectrometer (JASCO, Tokyo, Japan). The diffuse reflectance UV−Vis−NIR (DRUV−Vis−NIR) spectrum was recorded using an UV−Vis−NIR spectrophotometer (UV1900i, SHIMADZU, Kyoto, Japan). Error limits were estimated as follows: band width, 1.00 ± 0.20 nm; wavelength accuracy, ±0.3 nm (D2/Hg), ±0.5 nm in the range of 190–1000 nm; wavelength repeatability, ≤0.1 nm (D2/Hg), ≤0.2 nm in the range of 190–1000 nm; photometric accuracy, ±0.3%; and photometric repeatability, ≤0.1%. Since the repeatability and accuracy of the wavelength and photometry were high, the UV–Vis spectra shown in this manuscript should be highly accurate. The optical activity of (R)-C6P was characterized by using the Automatic Polarimeter (Autopol IV) produced by RUDOLF Co., Ltd. (Hackettstown, NJ, USA). The photopolymerization was carried out using a high-pressure Hg lamp (MINHIO 4012–20, 1.0 kW) produced by MINHIO Intelligent Equipment Co., Ltd. (Shenzhen, China). The light intensities of UVV (>390 nm), UVA (320–390 nm), UVB (280–320 nm), and UVC (<280 nm) were measured to be 75.4, 96.0, 87.2, and 0 mW cm−2, respectively. The UV LED series equipment (UVSF81T, 260 mW cm−2, output power) was produced by FUTANSI Electronic Technology Co., Ltd. (Shanghai, China).

2.2. Preparation of the CLCN Films with Single Reflection Band

A typical preparation procedure was as follows. An LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 55.6/37.0/4.6/2.8) mixture was dissolved in a mixture of cyclohexanone/cyclopentanone (v/v, 4/1) with a solid content of 20 wt%. The solution was coated on the surface of a rubbing-oriented PET film by using a 20 μm Mayer bar. Then, the solvents were removed by heating at 120 °C for 5 min. Finally, the CLCN film was obtained by photopolymerization at 30 °C and under the irradiation of the high-pressure Hg lamp for 10.0 s. The other CLCN films were prepared by changing the concentration of CA-iso.

2.3. Preparation of the Broadband Reflective CLCN Films

A typical preparation procedure was as follows. A CLC mixture-coated PET film was prepared as described above. Photopolymerization was carried out at 60 °C and under the irradiation of the 365 nm UV lamp (5.2 mW cm−2) for 1.0 s and then at 55 °C and under the irradiation of the high-pressure Hg lamp for 10.0 s. The other CLCN films were prepared by changing the concentration of CA-iso.

2.4. Preparation of the CLCN Film with a Flower Pattern

A CLC mixture was prepared at the LC242/(R)-C6P/CA-iso/Irgacure 907 weight ratio of 55.6/37.0/4.6/2.8. The CLC mixture-coated PET film was prepared as described above. Photopolymerization was carried out at 58 °C and under the irradiation of the 365 nm UV lamp (5.2 mW cm−2) for 1.0 s. A photomask was used to expose the shape of a flower. Photopolymerization was carried out under the irradiation of the 365 nm UV lamp (260 mW cm−2) for 10.0 s at 30 °C. After removing the photomask, photopolymerization was carried out under the irradiation of the high-pressure Hg lamp for 10.0 s at 48 °C.

2.5. Preparation of the CLCN Film with a Cloud Pattern by Screen Printing

A mixture with the LC242/(R)-C6P/CA-iso/Irgacure 907 weight ratio of 55.6/37.0/4.6/2.8 was dissolved in a mixture of cyclohexanone/cyclopentanone (v/v, 4/1) to form a solution with 50 wt% of solid content. Then, the solution was coated on the PET film and glass and stainless steel surfaces by screen printing. The solvents were removed at 120 °C for 5.0 min. Photopolymerization was carried out at 64 °C and under the irradiation of the 365 nm UV lamp (5.2 mW cm−2) for 1.0 s and then at 60 °C and under the irradiation of the high-pressure Hg lamp for 10.0 s.

2.6. DSC Curves of (R)-C6P and CLC Mixture

DSC measurements were conducted on the solid samples of (R)-C6P and an LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 55.6/37.0/4.6/2.8) mixture, which were performed using about 5 mg of (R)-C6P or the CLC mixture with cooling and heating rates of 10 °C min−1. The measurements were cycled between −50 and 100 °C three times.

2.7. CD Spectra of (R)-C6P and CLC Mixture

(R)-C6P or the LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 55.6/37.0/4.6/2.8) mixture were dissolved in a mixture of cyclohexanone/cyclopentanone (v/v, 4/1) with a solid content of 20 wt%. Then, the solutions were coated on the surface of the rubbing-oriented PET film using a 20-μm Mayer bar. After removing the solvents at 120 °C for 5 min, the CD spectra were taken at different temperatures. The CD and UV–Vis spectra of the (R)-C6P solution in THF were taken at a concentration of 1.0 × 10−2 M and 25 °C using a 2.0 mm cell.

3. Results and Discussion

3.1. CLCN Films with Single Reflection Band

The chemical structures of the liquid crystals, chiral dopant, and photoinitiator are illustrated in Figure 1a. The synthetic procedure for (R)-C6P is shown in Scheme S1, Supporting Information (Figure S1). During the cooling process, a marbled texture and a Grandjean one were observed in the polarized optical microscopy (POM) images at 60.0 and 45.0 °C, respectively (Figure 1b,c). Both nematic and cholesteric structures were identified. A similar compound was synthesized using (S)-1,2-propanediol. Two cholesteric phases with different handedness were identified at different temperatures [36]. And the nematic phase was formed between these two cholesteric phases. Differential scanning calorimetry (DSC) revealed a phase transition sequence of I 69.2 °C N 57.3 °C Ch 40.1 °C Cr (I, isotropic state; N, nematic phase; Ch, cholesteric phase; Cr, Crystal) (Figure S2). The CD spectra of (R)-C6P were recorded at different temperatures (Figure S3). The negative signals indicated a right-handed helical supramolecular structure. With increasing temperature, the CD signal shifted to a long wavelength. When the temperature reached 65 and 70 °C, only one negative signal was identified at 332 nm, which originated from the chiral stacking of the aromatic rings of neighboring (R)-C6P molecules. For the CD spectrum of the (R)-C6P solution in THF (1.0 × 10−2 M), one positive CD signal was identified at 302 nm, and two negative CD signals were identified at 276 and 231 nm (Figure S4). No CD signals originated from the stacking of neighboring molecules were identified. Since (R)-C6P is thermochromic, it is possible to prepare a thermochromic CLC mixture using it.
The reactive liquid crystal monomer diacrylate LC242 exhibited a nematic phase between 70 and 120 °C (Figure 1a) [37]. The chiral dopant CA-iso is generally used for the preparation of CLC mixtures with right-handedness [38]. Irgacure 907 is a photoinitiator for radical polymerization. For the CLC mixture prepared at the LC242/(R)-C6P/CA-iso/Irgacure 907 weight ratio of 55.6/37.0/4.6/2.8, a Grandjean texture was identified in the POM image taken at 50 °C during the cooling process, indicating an enantiotropic cholesteric phase (Figure S5). The DSC characterization indicated a phase transition sequence of Tg −22.4 °C Ch 66.3 °C I 58.5 °C Ch −26.7 °C Tg (Tg, glass transition temperature) (Figure S6). The existence of the glass transition temperature should be driven by the high viscosity of the CLC mixture. CLCN films with a single reflection band were prepared according to the approach shown in Scheme 1. After the solution of a CLC mixture was coated on the surface of a rubbing-oriented PET film using a Mayer bar, the solvents were removed at a hot temperature. Then, a CLC film with a uniform helical pitch was obtained at 30 °C. After the CLC mixture was irradiated under the irradiation of the high-pressure Hg lamp (1.0 kW), a CLCN film with single helical pitch was obtained. Herein, a series of CLCN films were prepared by systematically adjusting the CA-iso concentration (Figure 1d). With increasing the CA-iso concentration from 3.0 to 4.6 wt%, the Bragg reflection band shifted from 617 to 445 nm. The cross-sectional FE-SEM images of the CLCN films at the CA-iso concentrations of 4.2 and 3.4 wt % are shown in Figure S7. The helical pitches of them were 310 and 370 nm, respectively. Based on the Bragg equation, the average refractive indices of the CLCN films were about 1.50.
The CD spectra of the LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 55.6/37.0/4.6/2.8) mixture were taken at different temperatures (Figure 1e,f). The negative CD signals indicated a right-handed helical supramolecular structure (Figure 1e). With increasing the temperature from 30 to 68 °C, the CD band shifted from 434 to 769 nm, and the intensity decreased. This redshift should have been driven by the thermochroism of (R)-C6P which was shown in the CD spectra taken at different temperatures (Figure S3). When the temperature reached 72 °C, the mixture came into an isotropic state. Then, no CD signals were identified at the long wavelength. For the CD spectrum taken at 68 °C, a positive signal was identified at 323 nm, indicating a chiral stacking of the aromatic rings. The thermochromism of (R)-C6P may be driven by the temperature dependency of molecular conformation [39,40]. Based on this thermochromic behavior, a series of CLCN films were prepared by changing the polymerization temperature. With increasing polymerization temperature from 40 to 64 °C, the Bragg reflection band of the CLCN film shifted from 467 to 650 nm (Figure 1g). Comparing the reflection bands before and after polymerization (Figure S8), the slightly blue shift should have been driven by the polymerization shrinkage. This shrinkage has been found in many polymerization systems [41,42].

3.2. CLCN Films with a Broad Reflection Band or Double Reflection Bands

A two-step polymerization approach was performed for the preparation of these films (Scheme 1). The spacing between the two reflection bands was controlled by the difference between the two polymerization temperatures. Namely, when the temperature difference was small, the CLCN films with a broad reflection band were obtained. And when the temperature difference was large, the CLCN films with double reflection bands were obtained. In the first polymerization step, the CLC mixture was irradiated for 1.0 s using a 365 nm LED lamp (5.2 mW cm−2) at a certain temperature. Due to oxygen inhibition, only the acrylates near the PET surface were polymerized. Since the acrylates near the air were not polymerized, the helical pitch of the CLC mixture at the top section changed with changes in the temperature. In the second polymerization step, the film was cured under the high-pressure Hg lamp (1.0 kW) for 10 s at a lower temperature. Comparing the LED and high-pressure Hg lamps, the high-pressure Hg lamp had strong UVB (87.2 mW cm−2) light which was proposed to drive a high photopolymerization rate. Due to the high intensity of the UV light, the oxygen inhibition was overcome. Then, the helical pitch of the top section of the film was fixed. Based on the temperature dependency of the helical pitch of the CLC mixture, the helical pitches of the CLCN film could be controlled by tuning the polymerization temperatures.
A series of CLCN films with a broad reflection band were prepared by changing the CA-iso concentration and keeping the polymerization temperatures of the first and second steps at 60 and 55 °C, respectively (Figure 2a). Multi-reflection bands should be formed by the partial overlap of two reflection bands [43]. With decreasing the CA-iso concentration from 6.2 to 4.0 wt%, the reflection band redshifted, and the full width at half maximum intensity increased (Figure 2c). Cross-sectional FE-SEM images of the CLCN films prepared at the CA-iso concentrations of 5.3 and 4.0 wt% are shown in Figure 3. Each CLCN film possessed two helical pitches. Therefore, the broad reflection band was formed by the overlapping of two reflection bands.
CLCN films were also prepared using the LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 55.6/37.0/4.6/2.8) mixture and by changing the polymerization temperature of the first step from 45 to 60 °C and keeping the polymerization temperature of the second step at 40 °C (Figure 2b). For the CLCN films with double reflection bands, with increasing the polymerization temperature from 50 to 60 °C, the reflection band at the longer wavelength redshifted from 567 to 683 nm (Figure 2d). However, the reflection band at the shorter wavelength was kept at 464 nm which was controlled by the polymerization temperature of 40 °C. For the CLCN film prepared at 45 and 40 °C, due to the overlapping of the two reflection bands, one broad reflection band was identified at 515 nm. Therefore, the golden structural color could be obtained simply by controlling the polymerization temperatures of the two steps.
For a better understanding of the formation of the structure, the FT-IR spectra of the LC242/(R)-/CA-iso/Irgacure 907 (w/w/w/w, 55.6/37.0/4.6/2.8) mixture were taken during the CLCN film preparation process (Figure S9). The absorption bands of the C=O bond were identified at 1750 and 1718 cm−1, and the absorption bands of the C=C bonds of the acrylates were identified at 1633, 1408, and 810 cm−1 [44]. After the irradiation of the LED lamp, the intensity of the absorption bands at 1633, 1408, and 810 cm−1 decreased sharply, indicating the partial polymerization of the acrylate group. After the irradiation of the Hg lamp, the intensity of the absorption band of the C=C bond decreased further, indicating that most of the acrylate groups had been polymerized.
FE-SEM analysis was employed to quantitatively evaluate the oxygen inhibition effect on the photopolymerization of CLC mixture (Figure S10). After the first polymerization step, unreacted compounds were removed by washing with acetone. A CLCN film with a thickness of 1.5 μm was identified on the PET substrate (Figure S10a). For the CLCN film prepared through the two-step polymerization approach, the thickness was about 3.5 μm, revealing that the thickness of oxygen inhibition layer was approximately 2.0 μm (Figure S10b). These experimental observations provide direct evidence for the spatial penetration depth of molecular oxygen.

3.3. CLCN Film with Flower Pattern or Cloud Pattern

A CLCN film with a golden flower pattern was prepared using the LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 55.6/37.0/4.6/2.8) mixture and a photomask (Figure 4). The flower area was prepared through the two-step approach at 58 and 48 °C. And the background was prepared through the same approach at 58 and 30 °C. The spectrum of the flower area showed two reflection bands at 515 and 635 nm, and that of the background showed two reflection bands at 450 and 635 nm. The distance between the two reflection bands were simply controlled by the polymerization temperatures. Both the pink and golden structural colors are attractive for decoration.
Based on the Bragg reflection equation, the wavelength of the reflection band relies on the angle between the incidence light and the normal line of the liquid crystal plane. Herein, two CLCN patterns were prepared through one- and two-step approaches, respectively (Figure 5a,c). For the cloud pattern prepared through the one-step approach, a reflection band with a bandwidth of 100 nm was identified at 640 nm (Figure S11). With changing the view angle from 0 to 60 °, the color changed from red to green (Figure 5a,b), and the reflection band shifted to 518 nm (Figure S11a). For the cloud pattern with a bandwidth of 200 nm (Figure S11b), with changing the view angle from 0 to 60 °, the color changed from red to golden (Figure 5c,d). Such CLCN films have great potential for decorative and anti-counterfeiting applications.

4. Conclusions

A photopolymerizable thermochromic CLC mixture was prepared using diacrylates and a chiral dopant. Based on oxygen inhibition, the CLCN films with double helical pitches were prepared on the PET film surface through a two-step photopolymerization approach. The distance between two reflection bands was controlled by the polymerization temperatures of these two steps. Then, the CLCN films with composite structural colors were prepared. Herein, CLCN patterns with a golden structural color were prepared, which could be applied for decoration and anti-counterfeiting. This work paves the way for the next-generation smart optical systems combining broadband reflection with dynamic color modulation and promising applications in decorative coatings, security labeling, and other photonic devices.

Supplementary Materials

The following supplementary information can be downloaded at: https://www.mdpi.com/article/10.3390/chemistry7030093/s1. Synthesis and characterization of (R)-C6P. Scheme S1: Synthetic route for (R)-C6P. Figure S1: 1H NMR spectrum of (R)-C6P. Figure S2: DSC curves of (R)-C6P. Figure S3: CD spectra of (R)-C6P taken at different temperatures. Figure S4. CD and UV–Vis spectra of the (R)-C6P solution in THF taken at a concentration of 1.0 × 10−2 M and 25 °C. Figure S5: POM images of the LC242/(R)-C6P/CA-iso/Irgacure 907 mixture during the cooling process at 50 °C (scale bar: 50 μm). Figure S6: DSC curves of the LC242/(R)-C6P/CA-iso/Irgacure 907 mixture. Figure S7: Cross-sectional FE-SEM images of the CLCN films prepared at 30 °C using (a) the LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 55.8/37.5/4.2/2.8) and (b) the LC242/(R)-C6P/CA-iso/Irgacure 907 (w/w/w/w, 56.3/37.5/3.4/2.8) mixtures. Figure S8: The maximum reflection wavelengths of CLC films at different temperatures. Figure S9: FT-IR spectra of the CLC mixture and CLCN film. Figure S10. Cross-sectional FE-SEM images of the CLCN films. Figure S11: UV–Vis spectra of the CLCN films taken at different incident angles of light. (a) The cloud pattern with a narrow reflection band. (b) The cloud pattern with a broad reflection band.

Author Contributions

Conceptualization, Y.Y.; investigation, Q.Z. and Y.Y.; writing—original draft preparation, Q.Z., Y.L. and W.L.; writing—review and editing, W.L. and Y.Y.; supervision, Y.Y.; project administration, Y.L. and Y.Y.; funding acquisition, Y.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (52273212), Jiangsu Engineering Laboratory of Novel Functional Polymeric Materials, Jiangsu Key Laboratory of Advanced Functional Polymer Materials, and the Key Laboratory of Polymeric Materials Design and Synthesis for Biomedical Function.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials, and further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Chemical structures of the compounds in the CLC mixture, POM images of (R)-C6P taken at (b) 60 and (c) 45 °C during the cooling process (scale bar: 20 μm), (d) UV–Vis spectra of the CLCN films prepared under the irradiation of the high-pressure Hg lamp (1.0 kW) and at different CA-iso concentrations, (e,f) CD spectra of the CLC mixture taken at different temperatures, and (g) UV–Vis spectra of the CLCN films prepared under the irradiation of the high-pressure Hg lamp (1.0 kW) and at different temperatures.
Figure 1. (a) Chemical structures of the compounds in the CLC mixture, POM images of (R)-C6P taken at (b) 60 and (c) 45 °C during the cooling process (scale bar: 20 μm), (d) UV–Vis spectra of the CLCN films prepared under the irradiation of the high-pressure Hg lamp (1.0 kW) and at different CA-iso concentrations, (e,f) CD spectra of the CLC mixture taken at different temperatures, and (g) UV–Vis spectra of the CLCN films prepared under the irradiation of the high-pressure Hg lamp (1.0 kW) and at different temperatures.
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Scheme 1. Schematic representation of the preparation of the CLCN film with single and double helical pitches through the one- and two-step polymerization approaches, respectively. The pink bars/ovals are the liquid crystals and those for the formation of the CLCN structure with the helical pitch of P1, and the blue bars/ovals are the cross-linked liquid crystals within the CLCN film with the helical pitch of P2.
Scheme 1. Schematic representation of the preparation of the CLCN film with single and double helical pitches through the one- and two-step polymerization approaches, respectively. The pink bars/ovals are the liquid crystals and those for the formation of the CLCN structure with the helical pitch of P1, and the blue bars/ovals are the cross-linked liquid crystals within the CLCN film with the helical pitch of P2.
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Figure 2. (a) Photographs and (c) UV–Vis spectra of the CLCN films prepared by changing the CA-iso concentration (the polymerization temperatures of the first and second steps were 60 and 55 °C, respectively). (b) Photographs and (d) UV–Vis spectra of the CLCN films prepared by changing the polymerization temperature of the first step and keeping that of the second step at 40 °C.
Figure 2. (a) Photographs and (c) UV–Vis spectra of the CLCN films prepared by changing the CA-iso concentration (the polymerization temperatures of the first and second steps were 60 and 55 °C, respectively). (b) Photographs and (d) UV–Vis spectra of the CLCN films prepared by changing the polymerization temperature of the first step and keeping that of the second step at 40 °C.
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Figure 3. Cross-sectional FE-SEM images of the CLCN films prepared at 60 and 55 °C with different concentrations of CA-iso of (a) 5.3 wt% and (b) 4.0 wt%.
Figure 3. Cross-sectional FE-SEM images of the CLCN films prepared at 60 and 55 °C with different concentrations of CA-iso of (a) 5.3 wt% and (b) 4.0 wt%.
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Figure 4. UV–Vis spectra of the CLCN film with a golden flower pattern (Step 1/Step 2 polymerization: flower: 58/40 °C; background: 58/30 °C). Inset: A photograph of the CLCN film (scale bar: 1.0 cm).
Figure 4. UV–Vis spectra of the CLCN film with a golden flower pattern (Step 1/Step 2 polymerization: flower: 58/40 °C; background: 58/30 °C). Inset: A photograph of the CLCN film (scale bar: 1.0 cm).
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Figure 5. Photographs of the cloud pattern with a narrow reflection band taken in (a) the vertical and (b) oblique directions and those of the cloud pattern with a broad reflection band taken in (c) the vertical and (d) oblique directions (scale bar: 1.0 cm).
Figure 5. Photographs of the cloud pattern with a narrow reflection band taken in (a) the vertical and (b) oblique directions and those of the cloud pattern with a broad reflection band taken in (c) the vertical and (d) oblique directions (scale bar: 1.0 cm).
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Zeng, Q.; Liu, W.; Li, Y.; Yang, Y. Cholesteric Liquid Crystal Polymer Network Patterns with a Golden Structural Color. Chemistry 2025, 7, 93. https://doi.org/10.3390/chemistry7030093

AMA Style

Zeng Q, Liu W, Li Y, Yang Y. Cholesteric Liquid Crystal Polymer Network Patterns with a Golden Structural Color. Chemistry. 2025; 7(3):93. https://doi.org/10.3390/chemistry7030093

Chicago/Turabian Style

Zeng, Qingyan, Wei Liu, Yi Li, and Yonggang Yang. 2025. "Cholesteric Liquid Crystal Polymer Network Patterns with a Golden Structural Color" Chemistry 7, no. 3: 93. https://doi.org/10.3390/chemistry7030093

APA Style

Zeng, Q., Liu, W., Li, Y., & Yang, Y. (2025). Cholesteric Liquid Crystal Polymer Network Patterns with a Golden Structural Color. Chemistry, 7(3), 93. https://doi.org/10.3390/chemistry7030093

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