# Nanoparticles Confined in Liquid Crystalline Coatings with Smectic Focal-Conic Textures: Implications for Precise Nanoparticle Positioning

Camille Nour Mahyaoui, Claire Emilie Goldmann, Emmanuel Garre, Sandrine

Mariot, Ivan Dozov, Claire Meyer, Patrick Davidson

<figure><img src="image_1.png" /></figure>

## To cite this version:

Camille Nour Mahyaoui, Claire Emilie Goldmann, Emmanuel Garre, Sandrine Mariot, Ivan Dozov, et al.. Nanoparticles Confined in Liquid Crystalline Coatings with Smectic Focal-Conic Textures: Implications for Precise Nanoparticle Positioning. ACS Applied Nano Materials, 2025, 8 (10), pp.5207-5217. 10.1021/acsanm.5c00356. hal-04959041

HAL Id: hal-04959041

https://hal.science/hal-04959041v1

Submitted on 20 Feb 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
Nanoparticles Confined in Liquid Crystalline
Coatings with Smectic Focal-Conic Textures:
Implications for Precise Nanoparticle Positioning

Camille Nour Mahyaoui,ᵃ,ᵇ,ᶜ* Claire Emilie Goldmann,ª Emmanuel Garre,ᵇ Sandrine Mariot,ª

Ivan Dozov,ª Claire Meyer,ᶜ Patrick Davidsonª*

ªLaboratoire de Physique des Solides, Université Paris Saclay, CNRS, Orsay, 91405, France

ᵇSurface du Verre et Interfaces, Saint Gobain/CNRS, Aubervilliers, 93300, France

ᶜPhysique des Systèmes Complexes, Université de Picardie Jules Verne, Amiens, 80039, France.

* Corresponding authors:

Dr Camille N. Mahyaoui

Camille.Mahyaoui@saint-gobain.com

Dr. Patrick Davidson

patrick.davidson@universite-paris-saclay.fr

Keywords: nanoparticles; gold; quantum dots; liquid crystal; smectic; nematic; coating;
confinement
ABSTRACT.

Composite systems prepared by dispersing mineral particles in molecular liquid crystals (LCs) have attracted much interest due to the prospects of improving the LC properties thanks to the particles and of precisely positioning the particles on a substrate thanks to the spontaneous organization of the LC. However, to achieve these goals, the strong tendency of particles to aggregate in LCs must be mitigated. We describe a simple and inexpensive process to prepare thin (≈4 µm) coatings consisting of metallic (gold) or semiconducting (quantum dots) nanoparticles (NPs), of ≈5 nm diameter, dispersed in the common smectic LC 8CB. Thanks to the regular lattice of focal conic domains (FCDs) that appears under hybrid anchoring conditions, nanoparticle aggregation is limited to the micrometer scale, allowing us to fabricate large-area (≈100 cm²) homogeneous NP/8CB coatings. Polarized-light, dark-field, fluorescence, and confocal optical microscopies, together with atomic force microscopy, were used to determine the location of the NPs in the coatings. These techniques revealed that most of the NPs cluster at the coating top surface, forming small (1 µm) aggregates located not only at defect lines but also at the center of each FCD. Moreover, after several months, the NPs adsorb onto the polymer-coated substrate to form a honeycomb lattice. Furthermore, upon heating in the nematic phase, the NPs aggregate in regularly spaced lines. These observations show that the issue of NP localization in LC coatings is more complex than previously thought. Because our process for preparing nanocomposite coatings is robust to variations in both substrate type (glass or silicon wafer) and NP type and size, it could be used for applications that require a macroscopically homogeneous distribution of metallic or semiconducting particles that are precisely positioned on a substrate, such as the fast parallel screening of pesticides or biological markers by surface-enhanced Raman scattering.
# 1. INTRODUCTION

Composite materials composed of inorganic particles dispersed in small organic liquid-crystalline (LC) molecules have been studied for many years with the general purpose of improving the physical properties of the LCs or precisely controlling the positions and orientations of the particles thanks to the LC organization.¹⁻⁷ For example, as recently demonstrated, the latter feature provides nanostructured materials suitable for applications in the detection of banned pesticides, at very low levels, by surface-enhanced Raman scattering (SERS).⁸ Among these LC composite systems, the nematic ones have been much more studied than the smectic ones because of their applications in electro-optical devices, such as displays.⁹⁻¹² In this research field, particles larger than one micron have attracted much attention because they can be studied individually by optical microscopy. For these large particles, the nature, planar or homeotropic, of the LC director at the particle surface is extremely important in determining the director field around the particles, the possible presence of topological defects in this field, the defect-mediated interactions between the particles, and thus ultimately the stability of the particle dispersion in the LC phase.¹³⁻¹⁹

In contrast to the case of large particles in nematic phases, relatively few studies have dealt so far with the case of nanoparticles (NPs) dispersed in smectic molecular liquid crystals.²⁰⁻³² Moreover, most of these studies deal with the influence of NP doping on the physical properties of the LC. However, the prospect of precisely controlling the positions of metallic or semiconducting NPs in a coating is highly desirable for various applications based on the plasmonic or fluorescent particle properties. Yet, NP aggregation in liquid crystals is notoriously difficult to avoid and often results in large disordered aggregates that span the entire sample.
For particles of very small size (i.e. a few nm), comparable to that of an LC molecule (≈ 2 nm), the issue of director anchoring at the particle surface is much less relevant than for large particles, but entropic terms related to the NP distribution should be considered.³³,³⁴ The main advantage of using LC smectic textures is that they naturally provide ways to achieve the important goal of accurately positioning NPs on a substrate, which can be done in two ways. In a top-down approach, substrates are patterned by lithography or stamping to create textures made of topological defects that trap the particles.³⁵,³⁶ But this approach is somewhat cumbersome and expensive, and it is difficult to scale up to the very large areas required for industrial applications. In a bottom-up approach, one possible strategy is to take advantage of the defect textures that spontaneously appear in smectic films subjected to conflicting anchoring conditions. This happens, for example, in LC coatings (or electro-optical cells) where the bottom and top surfaces impose homogeneous planar and homeotropic anchoring, respectively (the so-called “hybrid anchoring”). For very small thicknesses (one micrometer or less), linear defects appear and have been used to confine and align gold nanospheres and CdSe nanorods.³⁷⁻⁴¹ Gold nanoparticles (AuNPs) have also been confined and organized in the periodic lattice of dislocations that occurs in wedge cells.⁴²,⁴³ Large AuNPs, 100 – 500 nm in diameter, initially deposited on the substrate and covered by the smectic liquid crystal, have been shown to migrate through defect lines from the bottom of the LC film to its top surface under the influence of an anchoring-induced lifting force.⁴⁴ In general, it is now widely believed that nanoparticles aggregate within the topological defect cores of the liquid crystalline matrix.

Here, we describe a very simple procedure to prepare macroscopically homogeneous NP-doped smectic coatings by a bottom-up approach (Figure 1). We have used the common liquid crystal 8CB (see Experimental Part), which has the following mesophase sequence: SmA 32.4°C N
39.5°C I, to prepare ≈ 4 µm thick coatings under hybrid anchoring conditions. The resulting smectic textures are already fairly well documented in the literature.⁴⁵,⁴⁶ When the anchoring polymer layer on the substrate is not rubbed, the smectic textures consist of toroidal focal conic domains (TFCDs), each organized around a circular singular defect line parallel to the substrate and a perpendicular straight line.⁴⁷,⁴⁸ When the anchoring polymer layer is rubbed (which is mostly the case in our work), the symmetry of the texture is reduced and the TFCDs are replaced by elliptic-hyperbolic focal conic domains (EHFCDs, see Figure 2a, below). In these domains, the smectic layers follow Dupin's cyclides, which are organized with respect to elliptical and hyperbolic defect lines.⁴⁹,⁵⁰,⁴⁸,⁴⁵ In smectic films thicker than about 1 µm, the EHFCDs are densely packed on a quasi-hexagonal lattice with a period of several micrometers that increases with film thickness. Note that this texture has recently been exploited by the Saint-Gobain industrial group to design a new operating principle of “smart windows”.⁵¹,⁵² Therefore, instead of the TFCD texture, we used the EHFCD texture, whose anisotropy also adds new functionalities. Following a very simple procedure described in detail in the Experimental Part, we have prepared large (up to ≈ 100 cm²), macroscopically uniform, NP/8CB nanocomposite coatings with this EHFCD texture, using gold and quantum dot (QD) nanoparticles a few nanometers in diameter. The versatility and robustness of the procedure has been demonstrated by varying the nature and size of the NPs, and the nature of the substrate. Finally, by exploiting the respective optical properties of AuNPs and QDs, we combined polarizing, dark-field, and confocal optical microscopies, together with atomic force microscopy (AFM), to determine the location of the NPs within the defect texture and its evolution upon aging, and found that this issue is more complex than previously considered.
<figure><img src="image_3.png" /></figure>

Figure 1. Schematic representation of the procedure used to prepare nanoparticle-doped smectic coatings. Left: Components of the initial solution of 8CB liquid crystal and either gold or quantum dot nanoparticles in toluene. Middle: Spin coating of this solution onto a glass slide covered with a brushed PVA (polyvinyl alcohol) layer. Right: Magnification of the nanostructured smectic matrix.

## 2. MATERIALS AND METHODS

### 2.1. Materials.

The 8CB (4-octyl-4-biphenylcarbonitrile, CAS number: 52709-84-9) liquid crystal was purchased from Tokyo Chemical Industry and was used without further purification. For confocal optical microscopy experiments, 8CB was doped with the fluorophore BTBP (N,N'-bis(2,5-dit-butylphenyl)-3,4,9,10-perylenedicarboximide, CAS number: 83054-80-2) purchased from Sigma-Aldrich. This rod-like guest molecule is known to align along the director field of the host liquid crystal.⁵³ Precise volumes of a solution of BTBP in toluene and of a solution of QD nanoparticles in toluene were added to 8CB to obtain a mixture of 8CB containing 0.01 wt% BTBP and 0.05 wt% QDs after toluene evaporation.
Gold nanoparticles (AuNPs) were synthesized, using the Stucky synthesis, according to a well-documented procedure.⁵⁴,⁵⁵ Several batches of AuNPs were prepared, differing in the average NP diameter, which ranged from 3 to 6 nm. Since the 6 nm AuNPs were the easiest to observe, they were used in most cases, unless otherwise specified. The AuNPs were coated with a hexadecanethiol ligand brush and dispersed in toluene. Their size polydispersity (12.7% was measured by x-ray scattering.

Two different kinds of CdSe/ZnS quantum dots (QDs) were purchased as dry powders from PlasmaChem GmbH (ref: PL-QD-O-Kit) with average particle diameters of 2.7 nm and 6.5 nm, respectively. The former (resp. the latter) has an emission wavelength of 540 nm (resp. 630 nm) and both have a broad excitation band in the UV range. Both kinds of QDs are coated with a trioctylphosphine oxide ligand brush and dispersed in toluene. Their size polydispersity is around 20%, according to the supplier.

## 2.2. Sample preparation.

Samples were investigated both as coatings and in electro-optical cells.

A typical preparation of LC/NP coatings consists of the following steps: standard microscope glass slides were first washed with a 2 v/v%RBS® 25 solution, then rinsed with distilled water, and dried under a nitrogen stream.

Silicon wafers (WAFERS2, thickness 280 µm, Neyco) were also used and treated in the same way as glass slides.

All substrates were stored in a laminar flow hood to avoid contamination by dust particles, and all subsequent steps were carried out under the hood. A polymer anchoring layer was then deposited on the glass slides, as follows. A 9.1 wt% aqueous solution of poly(vinyl alcohol) (PVA,
Mowiol®49-8, M<sub>w</sub> = 27,000 g/mol, CAS : 9002-89-5) in distilled water was prepared by heating at 90°C for 1h under stirring. This solution (at 60-70°C) was deposited on the glass slides by spin-coating (60 s, 4000 rpm), resulting in a uniform PVA planar anchoring layer of 400 – 500 nm thickness. To achieve homogeneous (rather than degenerate) planar anchoring, unless otherwise specified, the samples were brushed using a benchtop brushing machine (Holmarc, HO-IAD-BTR-01) with a roller rotation speed of 500 rpm and a sample stage translation speed of 1 mm/s.

The NPs were dispersed in toluene and the dispersions were placed in an ultrasonic bath (Elma, Elmasonic P) at room temperature for 15 min. The dispersions in toluene were then mixed with 8CB to achieve a typical NP volume fraction of 0.01 vol% in the coatings. This corresponds to a gold core weight fraction of ≈ 0.2 wt% for AuNP/8CB mixtures and a CdSe/ZnS core weight fraction of ≈ 0.05 wt% for QD/8CB mixtures. The nanoparticle concentrations chosen for this study represent a compromise between the two requirements of sufficient nanoparticle doping and the avoidance of the macroscopic nanoparticle aggregation that occurs at higher concentrations.

The mixture was homogenized using a vortexer during 1-2 minutes.

The dispersion of 8CB and NPs in toluene was then deposited on top of the alignment layer by a second spin-coating step (60 s, 1000 rpm, deposited volume: 100 µL). The thickness of the NP/8CB nanocomposite film could be conveniently controlled by adjusting the volume ratio of 8CB/toluene dispersion (vol<sub>8CB</sub>/vol<sub>tol</sub>). The film thickness roughly follows a linear dependence, ranging from about 2 µm for vol<sub>8CB</sub>/vol<sub>tol</sub> = 0.5 to about 10 µm for vol<sub>8CB</sub>/vol<sub>tol</sub> = 5. Note that the choice of coating thickness determines the period of the quasi-hexagonal lattice of EHFCDs.<sup>56</sup> Coating thicknesses were measured using an optical profilometer (ZYGO, Newview 9000). The coatings presented in this article were prepared using vol<sub>8CB</sub>/vol<sub>tol</sub> = 1, leading to coating thicknesses of 3.6 ± 0.4 µm.
The NP/8CB coatings were then heated to the nematic phase (35°C) and slowly cooled to room temperature at 0.1°C/min to obtain uniform FCD smectic textures.

Samples were also prepared in electro-optical cells of 8 µm sample thickness, purchased from INSTEC (Boulder, Co, USA; ref: S100A080uHAN), providing hybrid anchoring conditions. Samples in cells could be placed in a beaker, set in an ultrasonic bath, and heated to the isotropic phase (45-50 °C) to suppress any prior NP aggregation.

**2.3. Optical microscopy.**

All samples were first examined by polarized-light microscopy (POM), using an Olympus BX51 upright microscope, equipped with an Olympus LED light source, an Olympus U-POC-2 (NA: 0.9) condenser, and two different objectives (Olympus LMPLFLN 50X, NA = 0.5; MPlanFL N 100X BD, NA = 0.9). Since gold particles and aggregates can often be detected by dark-field (DF) microscopy, all AuNP/8CB samples were also observed with the same microscope under DF illumination conditions in reflection.

The influence of temperature and annealing on the coatings and cells was investigated using an
Instec HCS302XY heating stage driven by a computer-interfaced mK2000B controller.

All QD/8CB samples were observed not only by POM in transmission, but also by fluorescence microscopy using another Olympus BX51 upright microscope, equipped with an Olympus fluorescence LED source (CoolLED pE-300lite). Two different Olympus fluorescence cubes were used, depending on the QD emission wavelengths: a FITC cube was used for the 2.7 nm diameter QDs, whereas a TRITC cube was used for the 6.5 nm diameter QDs. A 40X objective (Olympus PLCN40XPH, NA 0.65) was used for these observations.
All microscopy images were acquired using sCMEX20 Euromex cameras equipped with CMOS sensors. The POM and DF microscopy images of AuNP/8CB samples, and the POM and fluorescence microscopy images of QD/8CB samples, were compared by thresholding and superposition using the skimage library for thresholding and home-made routines written in Python. Fast Fourier Transforms of some of the images were also performed using Python routines.

Additional observations of some QD/8CB coatings were made using a Leica (DMI6000B-CS) inverted confocal optical microscope equipped with an oil immersion objective (HC PL APO CS2; 63X, NA = 1.4). The microscope was controlled by Leica computer software (LAS X 3.5.7.23225). The excitation laser wavelength was 405 nm and the z-step was 300 nm. For these observations, coatings were prepared on glass coverslips of 150 µm thickness, and the BTBP fluorophore described above was added to 8CB. Since the excitation laser is linearly polarized and the fluorescence intensity is maximum when the long axis of the fluorophore is parallel to the light polarization, the director field can be mapped.⁵⁷

## 2.4. Atomic force microscopy (AFM).

The microscopic structure of the nanocomposite coatings was directly characterized by AFM (Bruker, ICON), in tapping mode, at room temperature. No further sample treatment was required.

## 2.5. X-ray scattering.

Some x-ray scattering experiments were carried out to investigate the aggregation state of the AuNPs dispersed in toluene and in AuNP/8CB nanocomposites. Two different setups were used, which have already been described in detail.⁵⁸,⁵⁹ The first one, is a home-made scattering setup equipped with a rotating anode generator, whereas the second one is the Swing high-flux beamline
of the Soleil synchrotron radiation facility (St-Aubin, France). In both cases, $q$ is the scattering vector modulus, $q = 4\pi\sin\theta/\lambda$, where $\lambda$ is the wavelength ($\lambda_{MoK\alpha} = 0.71$ Å for the first setup and $\lambda = 0.77$ Å for the second) and $2\theta$ is the scattering angle. AuNP dispersions in toluene were filled into cylindrical 1 mm diameter Lindemann glass x-ray capillaries (Glas-Technik & Konstruktion, Germany), while AuNP/8CB nanocomposite coatings were deposited on 280 nm thick silicon wafers using the procedure described above. All scattering patterns were recorded in transmission geometry.

# 3. RESULTS AND DISCUSSION

## 3.1. Preparation of uniform NP-doped 8CB coatings and cells.

Nanoparticle-doped 8CB films, typically 3-4 µm thick and 4 cm² in area, deposited on rubbed PVA-coated glass slides, have been prepared by a simple spin-coating process (see Experimental Part for more details). As expected, these films show by polarized optical microscopy (POM) a quasi-hexagonal lattice of EHFCDs (Figure 2), which has already been investigated in detail.⁴⁵ The comparison of pure 8CB and AuNP/8CB liquid crystalline coatings, using POM, shows no significant difference in their textures (Figure 2a,c), even at high magnification. Therefore, the EHFCD lattice is not altered at all by the presence of AuNPs at the concentration used here (0.2 wt%). Nevertheless, differences can be found by dark-field (DF) microscopy (Figure 2b,d). DF images of pure 8CB films show a very weak signal, most likely due to light scattered by the cores of the elliptical and hyperbolic line defects. In contrast, DF images of AuNP/8CB samples show an additional stronger signal that must be related to the presence of the nanoparticles. This DF signal depends on the observation conditions and may also vary from sample to sample. In particular, small AuNP aggregates of about 1 µm in size can be clearly observed if care is taken to
focus on the top surface of the film. Many AuNP/8CB samples also show the DF signal as a regular pattern of fairly uniform “symmetrical commas” (Figure 2e), strongly reminiscent of optical caustics. In fact, the aspect of the DF signal depends on the exact position of the focusing plane within the sample (Figure SI1), and the commas may result from the propagation of the DF signal of AuNPs, well dispersed or aggregated, through the EHFCD texture. (Indeed, the presence of a small proportion of dispersed AuNPs and very small aggregates cannot be detected by DF optical microscopy.) Image thresholding of Figure 2d and superposition on Figure 2c, shown in Figure 2f, confirms that the small AuNP aggregates are precisely positioned with respect to the EHFCD lattice. This particle ordering is observed over the entire field of view (Figure 2g) and its good quality is illustrated by the Fourier transform (Figure 2h) of the DF image.
<figure><img src="image_4.png" /><figcaption>Figure 2. Optical microscopy images of pure and AuNP-doped 8CB coatings in the SmA phase at room temperature. (a) POM image and (b) DF image of a pure 8CB coating; (c) POM image and (d) DF image of an AuNP-doped 8CB coating (0.2 wt% AuNP); (e) DF image of another AuNP-</figcaption></figure>
doped 8CB coating (0.2 wt% AuNP); (f) superposition of the images in (c) and (d) showing the location (in red) of the small AuNP aggregates with respect to the EHFCD texture; (g) larger scale DF image of an AuNP-doped 8CB coating (0.2 wt% AuNP) showing the homogeneity of the sample; (h) Fourier transform of the image in (g). (r is the rubbing direction and the white cross represents the directions of the crossed polarizer and analyzer.)

Similar samples were prepared by filling AuNP/8CB mixtures into 8 µm thick electro-optical cells providing hybrid anchoring conditions (see Experimental Part for more details). After mild sonication at 45°C, the AuNP aggregates appear upon slow cooling from the nematic phase and get trapped in the EHFCDs (Figure SI2) within two degrees below the N/SmA transition. Further cooling of the sample in the SmA phase does not result in any further change in the aggregation state of the AuNPs. This is in stark contrast to the behavior of samples heated in the isotropic phase (Figure SI3), where the aggregates grow slowly, most likely due to van der Waals attractive interactions, until they span the entire microscope field of view. Consequently, care should be taken to avoid heating the samples to the isotropic phase.

These observations demonstrate that the smectic A layers in EHFCDs prevent the growth of macroscopic NP aggregates by effectively acting as physical barriers that prevent aggregate diffusion. Although the nanoparticles used in this study are small enough that the LC anchoring effects could be neglected, this assumption may not hold in the case of their aggregates. In particular, aggregate diffusion along the director would involve the dynamic reorganization of the ligands and LC molecules to match the smectic layered structure with its periodic alternation of aliphatic chains and mesogenic cores. Further modeling of this mechanism requires assumptions
about the aggregate morphology and the anchoring type and strength that need to be supported by
new detailed experimental evidence, which is beyond the scope of this paper.

The aggregation of AuNPs in doped 8CB coatings at the microscopic scale was also confirmed
by X-ray scattering (Figure SI4). The scattering from a fresh dispersion of AuNPs in toluene can
be simply fitted by the form factor of isolated polydisperse spherical nanoparticles. In contrast, the
scattering from AuNPs in the doped 8CB coatings shows a structure factor peak due to the dense
packing of the nanoparticles in the aggregates. Gold nanoparticle aggregation is also confirmed by
the analysis of the extinction spectroscopy spectra of the hybrid coatings, which show the related
classical shift of the plasmon resonance frequency (Figure SI5).

At this stage, the reason why the nanoparticles aggregate in 8CB remains unclear. For spherical
nanoparticles, steric (i.e., hard sphere) interactions would favor either uniform dispersion at low
volume fractions, as used here, or crystallization or glassy states, but at much higher volume
fractions. Topological defects are certainly important because their cores are more disordered than
the bulk liquid crystal, so the system should minimize its free energy by confining the nanoparticles
tightly in the defect cores where they least disturb the smectic structure, which is the most widely
accepted scenario in this research field. However, our AFM data (described below) show that the
nanoparticles are confined not only to the defect cores, but also to other regions of the EHFCDs,
and in particular to the top surface of the coatings. Van der Waals attractions are another type of
interaction that certainly also matters, especially for gold nanoparticles dispersed in an apolar
solvent. In fact, even simple solutions of our gold nanoparticles in toluene eventually aggregate
after a few months of aging. Therefore, elucidating the mechanism of nanoparticle aggregation in
8CB will clearly require further experimental and modeling efforts.
The nematic phase under hybrid anchoring conditions usually shows a simple director field, except in the vicinity of the N/SmA transition, where it undergoes the classical Cladis-Torza instability, which is driven by the divergence of the bend and twist elastic constants.⁶⁰ This instability gives rise to a complex periodic 3-dimensional distortion of the director field, which is readily observed by POM (Figure 3a) as alternating thick and thin stripes running parallel to the rubbing direction, and has recently been theoretically revisited.⁶¹ In the N phase, away from the phase transition, AuNPs at low concentration are hardly detectable by DF microscopy. However, somewhat surprisingly, close to the transition, this technique reveals that the Cladis-Torza modulation can trap AuNP aggregates (Figure 3b) and confine them in ≈ 5 µm spaced lines parallel to the rubbing direction, coinciding with the thick stripes (Figure 3c). Since no periodic order can be detected along this direction (Figure 3d), the NP confinement is only 1-dimensional. In the absence of smectic layers, this observation of AuNP confinement provides indirect evidence that the director modulation induced by the Cladis-Torza instability must be inhomogeneous (as suggested by POM), with line defects (or linear regions of highly distorted director fields) oriented parallel to the planar anchoring direction. Although the depth of field of the microscope objective is not much smaller than the coating thickness, the AuNPs appear to be located at the bottom of the nematic coating. Assuming that the AuNPs should cluster in the distorted regions of the sample, this observation would confirm the theoretical prediction that the distorted regions are located at the bottom of the sample, away from the top surface where strong homeotropic anchoring prevails.⁶¹ Provided that the N-SmA transition is crossed slowly (≈ 0.1°C/min), the stripes associated with the Cladis-Torza instability fragment periodically and the EHFCD texture leading to AuNP patterning is recovered in an almost reversible manner.
<figure><img src="image_5.png" /><figcaption>Figure 3. (a) POM and (b) DF microscopy images of an AuNP-doped 8CB sample filled in an 8 µm thick electro-optical cell in the N phase at 32.55°C; (c) superposition of the images in (a) and (b) showing the location of the small AuNP aggregates with respect to the striped texture created by the Cladis-Torza instability; (d) Fourier transform of the image in (b).</figcaption></figure>

Doped QD/8CB nanocomposite coatings of a few micrometers thickness have been prepared (see Experimental Part) using the same procedure as for the AuNP/8CB coatings described above. POM observations (Figure 4a,c) show that the EHFCD lattice of the coatings is also preserved after doping with QDs at this low concentration (≈ 0.05 wt%). A major advantage of QDs is their fluorescence properties, which allowed us to identify their positions in the smectic texture. Two different kinds of QDs were used, which differ in core diameter and therefore in emission wavelength. The smaller ones (diameter 2.7 nm) emit at 540 nm (green), whereas the larger ones (diameter 6.5 nm) emit at 630 nm (red). Fluorescence microscopy images (Figure 4b,d) show small QD aggregates, each confined within a single EHFCD for the larger QDs or a few adjacent EHFCDs for the smaller QDs. Comparison of high magnification POM and fluorescence
microscopy images (Figure 4e,f) demonstrates that most EHFCDs host a small QD aggregate at their center and that few aggregates are found elsewhere, mostly at the EHFCD lattice defects. In addition, a weak uniform fluorescence background is present in the fluorescence images, especially for 6.5 nm diameter QDs (Figure 4d,f). This could indicate that a small fraction of QDs are not aggregated but well dispersed in the bulk of the coating. Nevertheless, the overall behavior of the QD/8CB coatings is essentially the same as that of the AuNP/8CB coatings, illustrating the general character of both our sample preparation procedure and the micro-segregation of the nanocomposite coatings.
<figure><img src="image_6.png" /><figcaption>Figure 4. POM and fluorescence microscopy images of QD-doped 8CB coatings in the SmA phase at room temperature. (a) POM and (b) fluorescence images of a QD-doped 8CB coating (0.05 wt% QD, QD diameter: 2.7 nm); (c) POM and (d) fluorescence images of a QD-doped 8CB coating (0.05 wt% QD, QD diameter: 6.5 nm); (e) same conditions as (d) but at higher magnification; (f) image superposition showing the location of the small QD aggregates with respect to the EHFCD texture.</figcaption></figure>
## 3.2. Detailed investigation of NP localization in NP/8CB nanocomposite coatings.

To determine more precisely the localization of the AuNPs within the samples, AuNP/8CB coatings were examined by atomic force microscopy (AFM). Figure 5a-h compares optical microscopy and AFM images of both pure and doped 8CB coatings, acquired respectively on the same samples. The AFM images of the surface of pure 8CB coatings, in both height and phase modes, reveal a cellular organization due to the EHFCD lattice. The top surface of the sample, visualized in height mode, shows a relief distorted by the underlying EHFCD lattice observed by POM. In particular, the region where the hyperbolic line ends at the top surface corresponds to a depression ≈ 50 nm deep. The phase mode AFM images show a weak contrast, with a similar aspect, corresponding to small variations in the viscoelastic properties due to the EHFCD texture. The AFM images of AuNP/8CB coatings differ from those of pure 8CB coatings in that they show the micron-sized AuNP aggregates decorating the top surface of the EHFCDs. The AuNP aggregate signal is observed not only in height mode, but also more easily in phase mode, indicating that the aggregates have mechanical properties that are very different from those of the LC matrix. Indeed, all the bright areas observed in Figure 5h represent AuNP aggregates which rarely look point-like and spherical, since there is no reason why they should be compact and smooth, rather than irregular. Detailed quantitative image analysis of both optical and atomic force microscopy images (Figure SI6) showed that less than 5% of the EHFCDs are not decorated with nanoparticles, but up to 20% of the micronic aggregates are located between the EHFCDs, often in lattice defects.
<figure><img src="image_7.png" /><figcaption>Figure 5. Comparison of optical microscopy and AFM images of pure (top row) and AuNP-doped (bottom row) 8CB coatings in the SmA phase at room temperature. (a) POM image, (b) DF image, (c) height mode AFM image, and (d) phase mode AFM image of a pure 8CB coating (the H-labeled black arrows in (c,d) point to the traces of the hyperbolic lines at the coating free surface); (e) POM image, (f) DF image, (g) height mode AFM image, and (h) phase mode AFM image of an AuNP-doped 8CB coating (0.2 wt% AuNP). (r is the rubbing direction and the white cross represents the directions of the crossed polarizer and analyzer.) In (f), (g), and (h), the white circles enclose an AuNP aggregate. (Note that the optical microscopy and AFM images were acquired from different parts of the samples.)</figcaption></figure>

Other AFM images were taken at lower (Figure 6a) and higher magnification, at the scale of a single (representative) EHFCD (Figure 6b,c). These images show that the AuNP aggregates are most frequently located at two distinct positions in each EHFCD: at the center of the domain and near the hyperbola. A cut of the AFM image along the rubbing direction, through the AuNP aggregates (Figure 6d), shows the relief of the EHFCD surface, with the jagged appearance of the AuNP aggregates. By subtracting the smooth variation of the EHFCD, the surface of the AuNP
aggregates can be characterized (Figure 6e). The aggregates appear as rather flat rafts, a few micrometers wide and 30 nm thick floating at the surface of the EHFCDs. Similar AFM results (Figure SI7) have also been obtained with AuNP/8CB coatings deposited on unrubbed polymer-coated glass substrates giving rise to the TFCD texture, showing that these observations are not specific of the EHFCD texture. In fact, the presence of large irregular AuNP aggregates floating on the surface of 8CB coatings, albeit in the absence of an EHFCD lattice, has already been reported in the literature.⁶² The fact that the nanoparticle micronic aggregates are located at the top surface of the coatings could be due to the same anchoring-based upward force experienced by large particles doped in smectic liquid crystals.⁴⁴ More detailed characterization of the aggregate morphology is required to confirm this assumption theoretically.
<figure><img src="image_8.png" /><figcaption>Figure 6. AFM images of AuNP-doped 8CB coatings (0.2 wt% AuNP) under the same conditions as in Figure 5. (a) Image acquired in height mode, at lower magnification, showing that the AuNPs most frequently cluster at two distinct locations at the top of each EHFCD; (b) phase mode and (c) height mode AFM images at higher magnification. The white dashed line contour shows the boundaries of a single EHFCD domain and the solid arrows point to the two distinct locations of AuNPs within the EHFCD; (d) blue line: sample height profile along the blue horizontal cut shown in (c), red line: polynomial fit of the LC height profile (excluding the aggregates) along the same cut; (e) subtraction of the fitted LC height profile from the topographic data, showing only the contribution of the small AuNP aggregates. (Note the very different scales along the x and z axes.)</figcaption></figure>
<figure><img src="image_9.png" /></figure>

Figure 7 Polarizing fluorescence confocal microscopy of QD-doped 8CB coatings (0.05 wt% QDs, QD diameter: 6.5 nm) in the SmA phase at room temperature. (a) 3-dimensional representation of the sample where the QDs are shown in red and the z-axis is the normal to the substrate and the x-axis is the rubbing direction; (b), (c), and (d) are planar sections through the volume shown in (a) with orientations indicated by the (x,y,z) trihedron. In (b), the arrows point to a QD aggregate at the top of the coating and to a population of QDs on the substrate. In (c), P is the polarization direction of the excitation laser. The gray scale is related to the orientation of the LC director with respect to the laser polarization.

The localization of the NP aggregates in the bulk of the nanocomposite coatings can be more conveniently studied by using confocal microscopy of the QDs, which allows 3-dimensional exploration of the samples (Figure 7a). This exploration confirms the previous conclusions that most of the NP aggregates are located at the top surface of the coating, at the centers of the EHFCDs and sometimes also close to the hyperbolic lines. However, closer inspection of the data, particularly of the vertical sections through the coatings (as in Figure 7b,d), shows that a significant
proportion of the aggregates lie, possibly adsorbed, on the (polymer-coated) glass substrate at the bottom surface of the coating.

The adsorption of AuNP aggregates on the glass substrates of AuNP/8CB coatings was also observed by DF microscopy. For this purpose, the samples were heated in the isotropic phase to suppress the small DF signal of the elliptical and hyperbolic lines. Then, a faint, slightly distorted, honeycomb lattice made of adsorbed AuNPs appears (Figure 8) as a background to the small NP aggregates at the top surface. Although these small aggregates drift along with any flow occurring in the sample and slowly percolate throughout the sample, the adsorbed NP lattice remains fixed. This adsorbed lattice seems to result from the decoration by AuNPs of the projections on the substrate plane of close-packed portions of the elliptical defect lines. The DF signal of the honeycomb lattice grows regularly with sample aging time over months, indicating that the proportion of adsorbed AuNPs increases very slowly but steadily. The formation of this adsorbed lattice could be due to the slow sedimentation of micron-sized aggregates under the influence of gravity. It is worth noting that these observations seem to contradict previous reports of upward migration of silica particles from the bottom to the top of smectic films.⁴⁴ However, in that case, the particles are much larger (100 – 500 nm diameter) than the present ones, so that liquid crystal anchoring at the particle surface is important and indeed leads to an upward force on the particles that can overcome the effect of gravity.
<figure><img src="image_10.png" /><figcaption>Figure 8. DF microscopy study of the time evolution of AuNP-doped 8CB coatings (0.2 wt% AuNP) stored at room temperature, but observed at 45°C in the isotropic phase. Images were captured (a) 4, (b) 31, (c) 51, (d) 66, (e) 99, and (f) 179 days after the preparation of the coatings. The rubbing direction r is shown in (a), the yellow dashed lines in (d) show the borders of the EHFCDs, and the red segment in (d) shows the cut used to calculate the evolution over time of the DF signal intensity of a segment of the honeycomb lattice. (g) Time dependence of the intensity contrast of the honeycomb lattice with respect to the image background. (The data point in blue does not belong to this sample series, but was taken several months earlier.)</figcaption></figure>
4. CONCLUSION AND PERSPECTIVES

A very simple and inexpensive process has been developed for the preparation of macroscopically uniform nanoparticle-doped LC coatings under hybrid anchoring conditions that create a well-ordered lattice of focal conic domains which trap the nanoparticles and prevent the formation of large aggregates. This provides a simple way to position small NP aggregates at the nodes of a 2-dimensional quasi-hexagonal lattice, with a period of a few micrometers that can be tuned by adjusting the coating thickness. These nanoparticle-based coatings may find sensing applications for the fast parallel detection of markers in biomedical testing and of pollutants, as recently demonstrated.⁸ The precise positioning of the nanoparticle aggregates over large areas is an important advantage in this perspective. In contrast to previous work, there is no need to functionalize the nanoparticles with LC ligands,⁶³⁻⁶⁷ to use a sublimable liquid crystal,²⁴ or to apply an electric field.⁶⁸ Moreover, the bottom-up nature of the process is a clear advantage over more expensive and complex top-down patterning techniques, such as microlithography²⁷ or photoalignment.⁶⁹ In particular, it should be easier to scale up and adapt to industrial production processes. Furthermore, this method is robust with respect to variations in NP type (AuNPs or QDs) and size, in the 2.5 – 6 nm range (Figure SI8), and in substrate type (glass slides or silicon wafers, Figure SI9). It can be applied equally to rubbed or unrubbed anchoring layers, leading to EHFCDs or TFCDs (Figure SI7), respectively. In addition, the process, still using spin-coating, has been easily upscaled to prepare much larger uniform coatings of ≈ 100 cm² area (Figure SI10), which is a significant improvement over the few-mm² area samples reported in the literature to date. For industrial applications, the sample size should still be further scaled up to ≈ 1 m², which could be achieved by using a different coating technique, such as dip coating or blade coating. In addition, the coatings should be prepared in a clean room to get rid of the small proportion of
imperfections that are related to the presence of small dust particles and that currently affect the sample homogeneity. Still from an application perspective, it is also worth noting that the liquid crystal used here is 8CB, which is one of the cheapest and most widely available commercial liquid crystals. However, since its clearing point is low (39.5°C) and the mechanical properties of the coatings should be improved, even at room temperature, the FCD lattice should be fixed, for example by polymerizing a molecular additive under UV light, as is commonly done to prepare polymer-stabilized liquid crystals.⁵¹,⁷⁰ To broaden the application range of this process, another approach would be to get rid of the liquid crystal altogether after the nanoparticle patterning by washing it away. Using different techniques, several attempts have been made to achieve this goal, but they remained unsuccessful because the quality of the nanoparticle patterning could not be maintained during this step, which requires additional effort.

From a more fundamental point of view, our detailed study using optical microscopy (POM, DF, and confocal), complemented by an AFM investigation, has shown that the localization of the NPs is more complex than previously thought (Figure 9). Micron-sized NP aggregates are located at the surface of the LC coating in each EHFCD, not only at the hyperbola but also at the center of the EHFCD. Moreover, a weak fluorescent background for QDs and the peculiar shape of the DF signal of AuNPs also suggest the presence of isolated NPs in the bulk of the LC films. It should be emphasized again here that the presence of the SmA layers, despite their fluid-like character, seems to prevent the NP aggregates from growing and coalescing, which calls for measurements of the diffusion coefficients of such nanoparticles in SmA phases.
<figure><img src="image_11.png" /><figcaption>Figure 9. Tentative schematic representation of the localization of the nanoparticles within the EHFCD lattice. (a) 3-dimensional sketch showing the hyperbolic (in green) and the elliptical (in red) lines, several smectic layers as blue surfaces, the substrate in dark gray, and the nanoparticles in red. (b) Representation of the nanoparticles adsorbed on the substrate, forming a distorted honeycomb lattice patterned by the elliptical defect lines.</figcaption></figure>

However, over months, NP aggregates tend to sediment and adsorb on the PVA-coated substrate, following the elliptical line defects of the FCDs to form an original distorted honeycomb lattice. Such sedimentation seems to contradict previous studies⁴⁴ reporting an upward migration of particles from the substrate to the top surface of the sample. This discrepancy could be explained
by the large difference in NP size, which determines whether LC anchoring at the particle surface
is relevant or not.

Finally, in the nematic phase, close to the N/SmA transition, the Cladis-Torza periodic instability
occurs, giving rise to NP lines. This instability can therefore be used to confine the NPs on a 1-
dimensional lattice, with a period of a few microns, instead of the 2-dimensional lattice of the
smectic EHFCDs. However, the preservation of this 1-dimensional lattice at room temperature for
applications requires its fixation by photopolymerization, as discussed above.⁵¹,⁷⁰

**Supporting Information.** Supporting figures of: influence of focalization on DF images; gradual formation of AuNP aggregates; DF image of large AuNP aggregates in the isotropic phase; x-ray scattering of fresh AuNP dispersions in toluene and in AuNP/8CB coatings; extinction spectroscopy spectra of the hybrid coatings; quantitative image analysis of both optical and atomic force microscopy images; AFM images of unrubbed AuNP/8CB coatings; influence of AuNP diameter on the DF images; DF images of coatings on silicon wafers; DF images of a homogeneous large-area AuNP/8CB coating.

**Author Contributions.**

C.N.M. and P.D. designed the project, C.N.M. performed the experiments, analyzed the data, and
prepared the figures. C.G. synthesized the gold nanoparticles, E.G. supervised the sample
preparation procedures, and S.M. supervised the confocal microscopy investigation. C.N.M. and
P.D. wrote the first draft of the manuscript, which was edited and revised by all authors.
## Funding Sources.

This work was funded by the Agence Nationale Recherche et Technologie, Saint-Gobain Research Paris, and the Agence Nationale de la Recherche (grant number ANR-23-CE24-0006-03, project DISPLAY).

## ACKNOWLEDGMENT

We thank Axel Fouques and Hervé Montigaud for helpful discussions, Thomas Bizien for assistance with the use of the SWING beamline, and acknowledge SOLEIL for provision of synchrotron radiation facilities (under the approved proposal # 20221057) and the LPS-Plateforme Morpheus (Université Paris-Saclay, CNRS) for x-ray scattering experiments. This work was funded by a joint Ph.D. grant from Agence Nationale Recherche et Technologie and Saint-Gobain Research Paris. The authors thank the Agence Nationale de la Recherche (grant number ANR-23-CE24-0006-03, project DISPLAY) for financial support.
REFERENCES

(1) Hegmann, T.; Qi, H.; Marx, V. M. Nanoparticles in Liquid Crystals: Synthesis, Self-Assembly, Defect Formation and Potential Applications. *J. Inorg. Organomet. P.* **2007**, *17* (3), 483–508. https://doi.org/10.1007/s10904-007-9140-5.

(2) Mirzaei, J.; Reznikov, M.; Hegmann, T. Quantum Dots as Liquid Crystal Dopants. *J. Mater. Chem.* **2012**, *22* (42), 22350–22365. https://doi.org/10.1039/c2jm33274d.

(3) Smalyukh, I. I. Liquid Crystal Colloids. In *Annu. Rev. Conden. Ma. P.*; Sachdev, S., Marchetti, M. C., Eds.; Annual Reviews: Palo Alto, 2018; Vol. 9, pp 207–226. https://doi.org/10.1146/annurev-conmatphys-033117-054102.

(4) Lavrentovich, O. D. Transport of Particles in Liquid Crystals. *Soft Matter* **2014**, *10* (9), 1264–1283. https://doi.org/10.1039/c3sm51628h.

(5) Dierking, I. From Colloids in Liquid Crystals to Colloidal Liquid Crystals. *Liq. Cryst.* **2019**, *46* (13–14), 2057–2074. https://doi.org/10.1080/02678292.2019.1641755.

(6) Lagerwall, J. P. F.; Scalia, G. Carbon Nanotubes in Liquid Crystals. *J. Mater. Chem.* **2008**, *18* (25), 2890–2898. https://doi.org/10.1039/b802707b.

(7) Mitov, M.; Portet, C.; Bourgerette, C.; Snoeck, E.; Verelst, M. Long-Range Structuring of Nanoparticles by Mimicry of a Cholesteric Liquid Crystal. *Nat. Mater.* **2002**, *1* (4), 229–231. https://doi.org/10.1038/nmat772.

(8) Kim, D. S.; Honglawan, A.; Yang, S.; Yoon, D. K. Arrangement and SERS Applications of Nanoparticle Clusters Using Liquid Crystalline Template. *ACS Appl. Mater. Inter.* **2017**, *9* (8), 7787–7792. https://doi.org/10.1021/acsami.6b15343.

(9) Reznikov, Y.; Buchnev, O.; Tereshchenko, O.; Reshetnyak, V.; Glushchenko, A.; West, J. Ferroelectric Nematic Suspension. *Appl. Phys. Lett.* **2003**, *82* (12), 1917–1919. https://doi.org/10.1063/1.1560871.

(10) Stark, H. Physics of Colloidal Dispersions in Nematic Liquid Crystals. *Phys. Rep.* **2001**, *351* (6), 387–474. https://doi.org/10.1016/S0370-1573(00)00144-7.

(11) Mertelj, A.; Lisjak, D. Ferromagnetic Nematic Liquid Crystals. *Liq. Cryst. Rev.* **2017**, *5* (1). https://doi.org/10.1080/21680396.2017.1304835.

(12) Khatua, S.; Manna, P.; Chang, W.-S.; Tcherniak, A.; Friedlander, E.; Zubarev, E. R.; Link, S. Plasmonic Nanoparticles-Liquid Crystal Composites. *J. Phys. Chem. C* **2010**, *114* (16), 7251–7257. https://doi.org/10.1021/jp907923v.

(13) Poulin, P.; Stark, H.; Lubensky, T. C.; Weitz, D. A. Novel Colloidal Interactions in Anisotropic Fluids. *Science* **1997**, *275* (5307), 1770–1773. https://doi.org/10.1126/science.275.5307.1770.

(14) Lapointe, C. P.; Mason, T. G.; Smalyukh, I. I. Shape-Controlled Colloidal Interactions in Nematic Liquid Crystals. *Science* **2009**, *326* (5956), 1083–1086. https://doi.org/10.1126/science.1176587.

(15) Musevic, I.; Skarabot, M.; Tkalec, U.; Ravnik, M.; Zumer, S. Two-Dimensional Nematic Colloidal Crystals Self-Assembled by Topological Defects. *Science* **2006**, *313* (5789), 954–958. https://doi.org/10.1126/science.1129660.

(16) Li, Y.; Prince, E.; Cho, S.; Salari, A.; Golestani, Y. M.; Lavrentovich, O. D.; Kumacheva, E. Periodic Assembly of Nanoparticle Arrays in Disclinations of Cholesteric Liquid Crystals. *P. Natl. Acad. Sci. U. S. A.* **2017**, *114* (9), 2137–2142. https://doi.org/10.1073/pnas.1615006114.
(17) Meeker, S. P.; Poon, W. C. K.; Crain, J.; Terentjev, E. M. Colloid-Liquid-Crystal Composites: An Unusual Soft Solid. *Phys. Rev. E* **2000**, *61* (6), R6083–R6086.
https://doi.org/10.1103/PhysRevE.61.R6083.

(18) Bai, Y.; Abbott, N. L. Recent Advances in Colloidal and Interfacial Phenomena Involving Liquid Crystals. *Langmuir* **2011**, *27* (10), 5719–5738. https://doi.org/10.1021/la103301d.

(19) Rahimi, M.; Roberts, T. F.; Armas-Perez, J. C.; Wang, X.; Bukusoglu, E.; Abbott, N. L.; de Pablo, J. J. Nanoparticle Self-Assembly at the Interface of Liquid Crystal Droplets. *P. Natl. Acad. Sci. U. S. A.* **2015**, *112* (17), 5297–5302. https://doi.org/10.1073/pnas.1422785112.

(20) Stamatoiu, O.; Mirzaei, J.; Feng, X.; Hegmann, T. Nanoparticles in Liquid Crystals and Liquid Crystalline Nanoparticles. In *Liquid Crystals: Materials Design and Self-assembly*; Tschierske, C., Ed.; Springer-Verlag Berlin: Berlin, 2012; Vol. 318, pp 331–393.
https://doi.org/10.1007/128_2011_233.

(21) Pratibha, R.; Park, W.; Smalyukh, I. I. Colloidal Gold Nanosphere Dispersions in Smectic Liquid Crystals and Thin Nanoparticle-Decorated Smectic Films. *J. Appl. Phys.* **2010**, *107* (6), 063511. https://doi.org/10.1063/1.3330678.

(22) Atata, S. B.; Lelidis, I. Exploring Quantum Dots Size Impact at Phase Diagram and Electrooptical Properties in 8CB Liquid Crystal Soft-Nanocomposites. *Nanomaterials-Basel* **2023**, *13* (22), 2980. https://doi.org/10.3390/nano13222980.

(23) Kyrou, C.; Ambrozic, M.; Tsiourvas, D.; Kralj, S.; Atata, S. B.; Lelidis, I. Effect of Quantum Dots on the Phase Behavior and Order of 8CB Liquid Crystal. *J. Mol. Liq.* **2023**, *387*, 122568.
https://doi.org/10.1016/j.molliq.2023.122568.

(24) Kim, D. S.; Honglawan, A.; Kim, K.; Kim, M. H.; Jeong, S.; Yang, S.; Yoon, D. K. Fabrication of Periodic Nanoparticle Clusters Using a Soft Lithographic Template. *J. Mater. Chem. C* **2015**, *3* (18), 4598–4602. https://doi.org/10.1039/c5tc00687b.

(25) Rzoska, S. J.; Starzonek, S.; Drozd-Rzoska, A.; Czuprynski, K.; Chmiel, K.; Gaura, G.; Michulec, A.; Szczypek, B.; Walas, W. Impact of BaTiO₃ Nanoparticles on Pretransitional Effects in Liquid Crystalline Dodecylcyanobiphenyl. *Phys. Rev. E* **2016**, *93* (2), 020701.
https://doi.org/10.1103/PhysRevE.93.020701.

(26) Singh, U. B.; Pandey, M. B.; Dhar, R.; Verma, R.; Kumar, S. Effect of Dispersion of CdSe Quantum Dots on Phase Transition, Electrical and Electro-Optical Properties of 4PP4OB. *Liq. Cryst.* **2016**, *43* (8), 1075–1082. https://doi.org/10.1080/02678292.2016.1159344.

(27) Lee, E.; Xia, Y.; Ferrier, R. C.; Kim, H.-N.; Gharbi, M. A.; Stebe, K. J.; Kamien, R. D.; Composto, R. J.; Yang, S. Fine Golden Rings: Tunable Surface Plasmon Resonance from Assembled Nanorods in Topological Defects of Liquid Crystals. *Adv. Mater.* **2016**, *28* (14), 2731–2736. https://doi.org/10.1002/adma.201506084.

(28) Meienberg, K.; Malinina, T.; Nguyen, Z.; Park, C. S.; Glaser, M. A.; Clark, N. A.; Maclennan, J. E. Nanoparticle Aggregation and Fractal Growth in Fluid Smectic Membranes. *Mol. Cryst.* *Liq.* *Cryst.* **2015**, *611* (1), 14–20.
https://doi.org/10.1080/15421406.2015.1027990.

(29) de Melo, P. B.; Nunes, A. M.; Omena, L.; do Nascimento, S. M. S.; da Silva, M. G. A.; Meneghetti, M. R.; de Oliveira, I. N. Thermo-Optical Properties and Nonlinear Optical Response of Smectic Liquid Crystals Containing Gold Nanoparticles. *Phys. Rev. E* **2015**, *92* (4), 042504. https://doi.org/10.1103/PhysRevE.92.042504.

(30) Lorenz, A.; Agra-Kooijman, D. M.; Zimmermann, N.; Kitzerow, H.-S.; Evans, D. R.; Kumar, S. Bilayers in Nanoparticle-Doped Polar Mesogens. *Phys. Rev. E* **2013**, *88* (6), 062505.
https://doi.org/10.1103/PhysRevE.88.062505.
(31) Martinez-Miranda, L. J.; McCarthy, K.; Kurihara, L. K.; Harry, J. J.; Noel, A. Effect of the Surface Coating on the Magnetic Nanoparticle Smectic-A Liquid Crystal Interaction. *Appl. Phys. Lett.* **2006**, *89* (16), 161917. https://doi.org/10.1063/1.2359430.

(32) Singh, D. P.; Duponchel, B.; Kondratenko, K.; Boussoualem, Y.; Pujar, G. H.; Inamdar, S. R.; Douali, R.; Daoudi, A. Phase Contraction, Fluorescence Quenching and Formation of Topological Defects in Chiral Smectic C Matrix by Cd<sub>0.15</sub>Zn<sub>0.85</sub>S/ZnS Core/Shell Quantum Dots Dispersion: Faster Electro-Optic Response for Gadget Displays. *Liq. Cryst.* **2020**, *47* (11), 1638–1654. https://doi.org/10.1080/02678292.2020.1754939.

(33) Voloschenko, D.; Pishnyak, O. P.; Shiyanovskii, S. V.; Lavrentovich, O. D. Effect of Director Distortions on Morphologies of Phase Separation in Liquid Crystals. *Phys. Rev. E* **2002**, *65* (6), 060701. https://doi.org/10.1103/PhysRevE.65.060701.

(34) Blanc, C.; Coursault, D.; Lacaze, E. Ordering Nano- and Microparticles Assemblies with Liquid Crystals. *Liq. Cryst. Rev.* **2013**, *1* (2), 83–109. https://doi.org/10.1080/21680396.2013.818515.

(35) Yoon, D. K.; Choi, M. C.; Kim, Y. H.; Kim, M. W.; Lavrentovich, O. D.; Jung, H.-T. Internal Structure Visualization and Lithographic Use of Periodic Toroidal Holes in Liquid Crystals. *Nat. Mater.* **2007**, *6* (11), 866–870. https://doi.org/10.1038/nmat2029.

(36) Ok, J. M.; Kim, Y. H.; Lee, T. Y.; Yoo, H.-W.; Kwon, K.; Jung, W.-B.; Kim, S.-H.; Jung, H.-T. Controlling Smectic Liquid Crystal Defect Patterns by Physical Stamping-Assisted Domain Separation and Their Use as Templates for Quantum Dot Cluster Arrays. *Langmuir* **2016**, *32* (50), 13418–13426. https://doi.org/10.1021/acs.langmuir.6b03355.

(37) Coursault, D.; Grand, J.; Zappone, B.; Ayeb, H.; Levi, G.; Felidj, N.; Lacaze, E. Linear Self-Assembly of Nanoparticles Within Liquid Crystal Defect Arrays. *Adv. Mater.* **2012**, *24* (11), 1461–1465. https://doi.org/10.1002/adma.201103791.

(38) Coursault, D.; Blach, J.-F.; Grand, J.; Coati, A.; Vlad, A.; Zappone, B.; Babonneau, D.; Levi, G.; Felidj, N.; Donnio, B.; Gallani, J.-L.; Alba, M.; Garreau, Y.; Borensztein, Y.; Goldmann, M.; Lacaze, E. Tailoring Anisotropic Interactions between Soft Nanospheres Using Dense Arrays of Smectic Liquid Crystal Edge Dislocations. *ACS Nano* **2015**, *9* (12), 11678–11689. https://doi.org/10.1021/acsnano.5b02538.

(39) Rozic, B.; Fresnais, J.; Molinaro, C.; Calxte, J.; Umadevi, S.; Lau-Truong, S.; Felidj, N.; Kraus, T.; Charra, F.; Dupuis, V.; Hegmann, T.; Fiorini-Debuisscher, C.; Gallas, B.; Lacaze, E. Oriented Gold Nanorods and Gold Nanorod Chains within Smectic Liquid Crystal Topological Defects. *ACS Nano* **2017**, *11* (7), 6728–6738. https://doi.org/10.1021/acsnano.7b01132.

(40) Do, S.-P.; Missaoui, A.; Coati, A.; Coursault, D.; Jeridi, H.; Resta, A.; Goubet, N.; Wojcik, M. M.; Choux, A.; Royer, S.; Briand, E.; Donnio, B.; Gallani, J. L.; Pansu, B.; Lhuillier, E.; Garreau, Y.; Babonneau, D.; Goldmann, M.; Constantin, D.; Gallas, B.; Croset, B.; Lacaze, E. From Chains to Monolayers: Nanoparticle Assembly Driven by Smectic Topological Defects. *Nano Lett.* **2020**, *20* (3), 1598–1606. https://doi.org/10.1021/acs.nanolett.9b04347.

(41) Jeridi, H.; Niyonzima, J. de D.; Sakr, C.; Missaoui, A.; Shahini, S.; Vlad, A.; Coati, A.; Goubet, N.; Royer, S.; Vickridge, I.; Goldmann, M.; Constantin, D.; Garreau, Y.; Babonneau, D.; Croset, B.; Gallas, B.; Lhuillier, E.; Lacaze, E. Unique Orientation of 1D and 2D Nanoparticle Assemblies Confined in Smectic Topological Defects. *Soft Matter* **2022**, *18* (25), 4792–4802. https://doi.org/10.1039/d2sm00376g.

(42) Milette, J.; Relaix, S.; Lavigne, C.; Toader, V.; Cowling, S. J.; Saez, I. M.; Lennox, R. B.; Goodby, J. W.; Reven, L. Reversible Long-Range Patterning of Gold Nanoparticles by
Smectic Liquid Crystals. *Soft Matter* **2012**, *8* (24), 6593–6598.
https://doi.org/10.1039/c2sm25445j.

(43) Oswald, P.; Milette, J.; Relaix, S.; Reven, L.; Dequidt, A.; Lejcek, L. Alloy Hardening of a Smectic A Liquid Crystal Doped with Gold Nanoparticles. *Europhys. Lett.* **2013**, *103* (4), 46004. https://doi.org/10.1209/0295-5075/103/46004.

(44) Honglawan, A.; Kim, D. S.; Beller, D. A.; Yoon, D. K.; Gharbi, M. A.; Stebe, K. J.; Kamien, R. D.; Yang, S. Synergistic Assembly of Nanoparticles in Smectic Liquid Crystals. *Soft Matter* **2015**, *11* (37), 7367–7375. https://doi.org/10.1039/c5sm01458a.

(45) Zappone, B.; Meyer, C.; Bruno, L.; Lacaze, E. Periodic Lattices of Frustrated Focal Conic Defect Domains in Smectic Liquid Crystal Films. *Soft Matter* **2012**, *8* (16), 4318–4326. https://doi.org/10.1039/c2sm07207f.

(46) Zappone, B.; Lacaze, E. One-Dimensional Patterns and Topological Defects in Smectic Liquid Crystal Films. *Liq. Cryst. Rev.* **2023**, *11* (1–2), 1–18. https://doi.org/10.1080/21680396.2022.2076748.

(47) Bidaux, R.; Boccara, N.; Sarma, G.; Deseze, L.; Degennes, P.; Parodi, O. Statistical Properties of Focal Conic Textures in Smectic Liquid-Crystals. *J. Phys.-Paris* **1973**, *34* (7), 661–672. https://doi.org/10.1051/jphys:01973003407066100.

(48) Kleman, M.; Lavrentovich, O. D. Liquids with Conics. *Liq. Cryst.* **2009**, *36* (10–11), 1085–1099. https://doi.org/10.1080/02678290902814718.

(49) Grandjean, F.; Friedel, G. Observations Géométriques Sur Les Liquides à Coniques Focales. *B. Mineral.* **1910**, 409–465.

(50) Fournier, J.; Durand, G. Focal Conic Faceting in Smectic-a Liquid-Crystals. *J. Phys. II* **1991**, *1* (7), 845–870.

(51) Boniello, G.; Vilchez, V.; Garre, E.; Mondiot, F. Making Smectic Defect Patterns Electrically Reversible and Dynamically Tunable Using In Situ Polymer-Templated Nematic Liquid Crystals. *Macromol. Rapid Comm.* **2021**, *42* (11), 2100087. https://doi.org/10.1002/marc.202100087.

(52) Mondiot, F. Dispositif electrocommandable a diffusion variable par cristaux liquides et son procede. WO2020065038A1, April 2, 2020. https://patents.google.com/patent/WO2020065038A1/fr?inventor=mondiot&oq=mondiot (accessed 2024-10-07).

(53) Nowicka, K.; Bielejewska, N.; Kuczynski, W.; Knapkiewicz, M.; Hoffmann, J. Exploration of Liquid Crystal Structures Using Fluorescent Confocal Polarizing Microscopy. *Phase Transit.* **2014**, *87* (10–11), 1073–1079. https://doi.org/10.1080/01411594.2014.953950.

(54) Zheng, N.; Fan, J.; Stucky, G. D. One-Step One-Phase Synthesis of Monodisperse Noble-Metallic Nanoparticles and Their Colloidal Crystals. *J. Am. Chem. Soc.* **2006**, *128* (20), 6550–6551. https://doi.org/10.1021/ja0604717.

(55) Goldmann, C.; Moretti, C.; Mahler, B.; Abecassis, B.; Emperor-Clerc, M.; Pansu, B. Precise Size Control of Hydrophobic Gold Nanoparticles in the 2-5 Nm Range. *Chem. Commun.* **2021**, *57* (93), 12512–12515. https://doi.org/10.1039/d1cc05351e.

(56) Guo, W.; Bahr, C. Influence of Anchoring Strength on Focal Conic Domains in Smectic Films. *Phys. Rev. E* **2009**, *79* (1), 011707. https://doi.org/10.1103/PhysRevE.79.011707.

(57) Smalyukh, I. I.; Shiyanovskii, S. V.; Lavrentovich, O. D. Three-Dimensional Imaging of Orientational Order by Fluorescence Confocal Polarizing Microscopy. *Chem. Phys. Lett.* **2001**, *336* (1–2), 88–96. https://doi.org/10.1016/S0009-2614(00)01471-8.
(58) Tache, O.; Rouziere, S.; Joly, P.; Amara, M.; Fleury, B.; Thill, A.; Launois, P.; Spalla, O.; Abecassis, B. MOMAC: A SAXS/WAXS Laboratory Instrument Dedicated to Nanomaterials. *J. Appl. Crystallogr.* **2016**, *49*, 1624–1631.
https://doi.org/10.1107/S1600576716012127.

(59) Cherni, L.; El Rifaii, K.; Wensink, H. H.; Chevrier, S. M.; Goldmann, C.; Michot, L. J.; Davidson, P.; Gabriel, J.-C. P. Crystalline Restacking of 2D-Materials from Their Nanosheets Suspensions. *Nanoscale* **2023**, *15* (45), 18359–18367. https://doi.org/10.1039/d3nr04885c.

(60) Cladis, P.; Torza, S. Growth of a Smectic-a from a Bent Nematic Phase and Smectic Light Valve. *J. Appl. Phys.* **1975**, *46* (2), 584–599. https://doi.org/10.1063/1.321663.

(61) Gim, M.-J.; Beller, D. A.; Yoon, D. K. Morphogenesis of Liquid Crystal Topological Defects during the Nematic-Smectic A Phase Transition. *Nat. Commun.* **2017**, *8*, 1–9.
https://doi.org/10.1038/ncomms15453.

(62) Gharbi, I.; Palacio-Betancur, V.; Ayeb, H.; Demaille, D.; de Pablo, J. J.; Kamien, R. D.; Lacaze, E. Liquid Crystal Films as Active Substrates for Nanoparticle Control. *ACS Appl. Nano Mater.* **2021**, *4* (7), 6700–6708. https://doi.org/10.1021/acsnanm.1c00680.

(63) Cseh, L.; Mehl, G. H. Structure-Property Relationships in Nematic Gold Nanoparticles. *J. Mater. Chem.* **2007**, *17* (4), 311–315. https://doi.org/10.1039/b614046g.

(64) Saliba, S.; Coppel, Y.; Davidson, P.; Mingotaud, C.; Chaudret, B.; Kahn, M. L.; Marty, J. D. Liquid Crystal Based on Hybrid Zinc Oxide Nanoparticles. *J. Mater. Chem.*, 2011, 21, 6821–6823.

(65) Nealon, G. L.; Greget, R.; Dominguez, C.; Nagy, Z. T.; Guillon, D.; Gallani, J.-L.; Donnio, B. Liquid-Crystalline Nanoparticles: Hybrid Design and Mesophase Structures. *Beilstein J. Org. Chem.* **2012**, *8*, 349–370. https://doi.org/10.3762/bjoc.8.39.

(66) Riahinasab, S. T.; Keshavarz, A.; Melton, C. N.; Elbaradei, A.; Warren, G.; Selinger, R. L. B.; Stokes, B. J.; Hirst, L. S. Nanoparticle-Based Hollow Microstructures Formed by Two-Stage Nematic Nucleation and Phase Separation. *Nat. Commun.* **2019**, *10*, 894.
https://doi.org/10.1038/s41467-019-08702-3.

(67) Lewandowski, W.; Constantin, D.; Walicka, K.; Pociecha, D.; Mieczkowski, J.; Gorecka, E. Smectic Mesophases of Functionalized Silver and Gold Nanoparticles with Anisotropic Plasmonic Properties. *Chem. Commun.* **2013**, *49* (71), 7845–7847.
https://doi.org/10.1039/c3cc43166e.

(68) Suh, A.; Ahn, H.; Shin, T. J.; Yoon, D. K. Controllable Liquid Crystal Defect Arrays Induced by an In-Plane Electric Field and Their Lithographic Applications. *J. Mater. Chem. C* **2019**, *7* (6), 1713–1719. https://doi.org/10.1039/c8tc06042h.

(69) Wu, S.-B.; Ma, L.-L.; Chen, P.; Cao, H.-M.; Ge, S.-J.; Yuan, R.; Hu, W.; Lu, Y.-Q. Smectic Defect Engineering Enabled by Programmable Photoalignment. *Adv. Opt. Mater.* **2020**, *8* (17), 2000593. https://doi.org/10.1002/adom.202000593.

(70) Mahyaoui, C. N.; Mondiot, F.; Dozov, I.; Davidson, P.; Meyer, C. Influence of Polymerisation Parameters on the Electro-Optical Properties of Polymer-Stabilised Liquid Crystals for Smart Glass Application. *Liq. Cryst.* **2024**. https://doi.org/10.1080/02678292.2024.2374952.
ToC Graphic

<figure><img src="image_12.png" /></figure>