Macroscopic and microscopic insights regarding organization of nematic liquid crystalline phase assisted by in situ grown gold nanoparticles

Liquid crystals (LCs), the fourth state of matter, have been the subject of immense scientific interest and extensively studied research over the last few decades, not only due to their potential applications in modern science and technology but also as an ideal candidate system for understanding the mechanism of living cells,¹ the property of self-organization,² and their role as a tunable solvent.³ The fascinating properties of liquid crystals, such as having order and mobility at molecular, supramolecular, and macroscopic levels;^4,5 the existence of all kinds of supramolecular interactions, including van der Waals, dipolar, quadrupolar, charge transfer, metal coordination, etc.;⁶ and their extreme sensitivity to small external perturbations such as light, electric, and magnetic fields, etc.,⁷ make them unique and, therefore, domains of liquid crystal span across multiple disciplines of pure and applied science.⁴ 

A relatively new and emerging field that has received increasing attention over recent years is liquid crystal nanoscience,⁸ which primarily deals with cooperative phenomena between liquid crystals and nanomaterials.⁹ The alignment and assembly of nanomaterials can be achieved in LC phases, as LC provides good support for nanomaterials being anisotropic mediums and also induces minimum distortion. Using the inherent intriguing properties of LC, researchers found it a suitable template for synthesizing nanomaterials in multiple dimensions and organizing them into well-defined superstructures.¹⁰ However, studies in this direction mostly involve multiple steps that require separate synthesis of NPs, their functionalization, and doping in LC domains. In such processes, instead of enriching the physicochemical properties, destabilization of LC domains owing to the chemisorption of LC domains on the NPs is often reported.¹¹ To address the issue, the most effective and viable approach is that the template used for the assembly of NPs can also provide active sites for reducing NP precursors so that formation and assembly of NPs can be performed in a single step and thereby chemisorption can be reduced considerably. However, not a great deal of attention had been put forward for such in situ growth and assembly. In the literature, some of the work in this direction includes the in situ synthesis and assembly of AuNPs embedded in glass-forming LCs by Mallia and co-workers,⁷ where attention has been given to the morphology control of AuNPs over enrichment in the physicochemical properties of the LC medium. Similarly, the work by Antharjanam and Prasad,¹² although they investigated the effect of in situ grown AgNPs on the phase ordering of nematic liquid crystal MBBA, the same system on which we are working, did not provide any microscopic insight into the macroscopic organization of the LC phase. It is worthwhile to mention that the microscopic description behind phase ordering of LC on a macroscopic scale was not studied with any rigor and, therefore, we reasoned that attention is necessary to address such a description for a complete understanding of phase ordering at the molecular level. This is, so far, the first approach where NP assisted phase ordering in LC is studied from both macroscopic and microscopic levels with equal emphasis.

In this article, we have prescribed a new approach to synthesizing AuNPs inside a well-known nematic liquid crystalline material MBBA [N-(4-methoxybenzylidene)-4-butylaniline], which acts as a template as well as a reducing agent to reduce the Au precursor HAuCl₄, 3H₂O. This one-step, in situ synthesis does not require any external stabilizer or capping unit, and synthesized AuNPs stabilize within the NLC matrix to form the MBBA−AuNP composite. The synthesized AuNPs were characterized by various microscopic and spectroscopic tools, which confirm the formation of AuNPs within the NLC matrix. The most important outcome that has emerged from our study is the organization of the NLC phase during NP production, which is manifested through ordered texture evolution, significant enhancement in concomitant thermal properties, and modulation in the electronic properties in the MBBA−AuNP composite compared to MBBA alone. These macroscopic phase orderings are well corroborated with our findings from the microscopic scale, where we were trying to analyze such organization at the molecular level. We firmly believe that the present study will open up new possibilities regarding understanding the LC–NP interaction.

All the reagents, nematic liquid crystal MBBA [N-(4-methoxybenzylidene)-4-butylaniline], hydrated gold-III chloride (HAuCl₄, 3 H₂O), and methanol were all procured from Sigma-Aldrich and used without any further purification. For the preparation of AuNPs, homogeneous solutions of MBBA and methanol are mixed with various concentrations of hydrated gold-III chloride. The resultant solution almost immediately changes its color from pale yellow to light brown and eventually dark brown, indicative of the formation of AuNPs inside the MBBA matrix (see Fig. S1 in the supplementary material). In our synthesis scheme, AuNPs are produced with or without heat treatment, as we observed an immediate change in color after the incorporation of Au salt, despite using optimal heat treatment up to 60 °C for our synthesis.

The morphology of the AuNPs was investigated through Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). TEM was employed using a FEI Tecnai G2 F30 ST microscope operating at 300 kV equipped with a GATAN Orius SC1000B CCD camera. EDX elemental analysis was performed using an EDS detector (EDAX Inc.). A carbon coated Cu grid (300 mesh) was used for TEM sample preparation using the drop casting method and dried properly before being used as a sample. SEM investigations were performed using the Quanta 200 FEG scanning electron microscope from FEI Co. (Netherlands), which is operated at an accelerating voltage between 200 V and 30 kV in both low and high vacuum modes. The conjugated product was drop-casted on a Si (111) wafer; methanol was allowed to evaporate from the sample and form a film. This film was inserted directly into the experimental chamber for measurement.

UV–Visible (UV–Vis) spectroscopy was employed as a characterization tool for synthesized AuNPs through its characteristic Surface Plasmon Resonance (SPR) peak and also to investigate the role of AuNPs on the optical properties of MBBA. UV–Vis spectroscopy was employed using a Perkin-Elmer Scan Lambda 750 spectrometer in transmission mode. Standard quartz cuvettes of dimension (4.5 × 12.5 × 12.5 mm³) and an optical path length of 10 mm were used for this purpose. This measurement was performed in the solution phase for both the MBBA and MBBA–AuNP composites.

X-ray Photoelectron Spectroscopy (XPS) was undertaken as a tool for characterizing AuNPs through the observation of their characteristic binding energy peaks as well as the coordination between MBBA and AuNP. XPS was performed using an Al K_α monochromatic x-ray source (1486.60 eV) from VG SCIENTA, which is also equipped with VG SCIENTA R400WAL electron energy analyzer with a total experimental energy resolution better than 0.6 eV at room temperature. The analysis chamber has a base pressure lower than 8 × 10⁻¹¹ mbar. The sample preparation was performed similar to the method described for SEM.

X-ray Diffraction (XRD) was employed for the characterization of AuNPs through monitoring the diffraction peaks of Au and also to understand AuNP induced phase ordering in MBBA. This was performed using a Rigaku SmartLab (Rigaku Corporation, Tokyo, Japan) five circle diffractometer with a Cu rotating anode generator delivering 1.30 kW x-ray power at Cu K_α radiation of wavelength 0.154 nm. The preparation of the sample for XRD measurement was performed similarly to SEM.

Optical Polarization Microscopy (OPM) was employed in order to investigate the texture evolution in the MBBA–AuNP conjugate system and compare it with a neat MBBA and MBBA–methanol mixture. OPM was performed using an IX 70, Olympus, Japan polarization microscope equipped with a 10× objective lens and a CCD camera (640 × 480 pixel²). The microscope is equipped with a locally made heating stage. For obtaining the OPM images for the neat MBBA and MBBA–methanol solutions, a sandwich film between two glass coverslips was taken. For the MBBA–AuNP conjugated product, the sample preparation was performed similar to the method described for SEM.

Differential Scanning Calorimetry (DSC) measurements were performed for the thermal property analysis of the conjugated product and the neat MBBA. This was carried out using a NETZCSH 204 F1 calorimeter with a scanning rate of 10 °C/min in a nitrogen atmosphere at a flow rate of 20 ml/min. Standard aluminum crucibles were used for sample loading. For MBBA, a neat liquid sample was used. For the conjugated product, methanol was allowed to evaporate from the sample and then dried to form a brown powder. This powder was then used as a sample for the MBBA–AuNP conjugated product.

Imine (C=N) nitrogen in MBBA is capable of donating its non-bonded electrons and thus can act as an active site for reducing Au salt to produce AuNPs and, therefore, form an MBBA–AuNP conjugated product. We explore the possibility of AuNPs being coordinated around an imine bond. To test this possibility, we have incorporated FTIR spectroscopy on both pristine MBBA and its coordinated product with AuNP obtained from 80 mol. % of precursor concentration around imine stretch. In Fig. 1, we summarize the results obtained from FTIR spectroscopy. The imine stretch frequency of MBBA, which appears at 1625 cm⁻¹¹³ is found to be absent completely in the MBBA–AuNP conjugated product, which confirms the coordination of AuNPs around the imine site of MBBA. The coordination between MBBA and AuNP was further confirmed by XPS spectroscopy. Figure 1(b) shows the XPS survey spectrum of the MBBA–AuNP conjugated product, where distinct peaks from the precursor (Au and Cl peaks of HAuCl₄) and reducing agent (C, N, and O peaks of MBBA) are clearly visible. For better clarity, high resolution XPS spectra of O1s, N1s, and C1s are shown separately (see Fig. S4 in the supplementary material). This is a clear indication of the attachment of AuNPs to MBBA.

The synthesized AuNPs inside MBBA were characterized by TEM, XRD, XPS, and UV–Vis spectroscopy. In Fig. 2(a), we have shown a TEM image of the AuNPs synthesized using 10 mol. % of precursor concentration relative to MBBA after 10 min of reaction. AuNPs with mostly spherical or nearly spherical morphologies with an average diameter of 6–7 nm were observed in this process. With a significant increase in the precursor concentration to 80 mol. %, the size of the AuNPs also increases concomitantly (please see the supplementary material). AuNPs with a facetted spherical morphology and an average size between 150 and 200 nm are observed (Fig. S2), which is much higher compared to the size obtained from 10 mol. %. The gradual increase in the size of the NPs is expected as more nucleation centers are produced in the solution phase with increasing salt concentrations. On a larger scale, the SEM image also exhibits an abundance of faceted spherical shapes with a scarcity of anisotropic AuNPs such as prisms, hexagons, trapezoidal, and rectangular plates. The majority of the AuNPs being in equilibrium spherical shape over anisotropic shape is indicative of the fact that growth is controlled thermodynamically rather than kinetically. This can be attributed to the minimization of surface free energy in the equilibrium shape. After a long time of evolution, we have also seen that the AuNPs maintain their spherical morphologies, and this signifies that the shape anisotropy of the template (as MBBA has a rod like structure) has no role in controlling the shape of the AuNPs as the later tends to grow according to the process maintaining the thermodynamic equilibrium. These spherical NPs will stabilize in the MBBA matrix and eventually enhance the physicochemical properties of MBBA, as we will see in the forthcoming section. Antharjanam and Prasad had also reported stabilization of isotropic AgNPs within MBBA even at a very high concentration of precursor (80 mol. %).¹² It must be worth mentioning that while physical dispersion allows only a small concentration of NP doping in the liquid crystal matrix,^21,22 the in situ growth technique permits much larger concentrations of NPs to be stabilized inside the LC matrix. In fact, Edamana et al. have also shown that a NP concentration of ≥40 mol. % is required for enhancing the thermo-physical properties of LC.¹² 

Figure 2(b) shows the HRTEM image of a single AuNP, and the lattice spacing was calculated to be 2.30 nm, which is nearly equal to the lattice spacing of the (111) plane of Au. The elemental analysis was performed by EDX as shown in Fig. 2(c), which also indicates the formation of AuNPs inside the MBBA matrix. The existence of the Cu peak was due to the Cu grid used for the TEM measurements. Figure 2(d) demonstrates the XRD spectrum of the MBBA–AuNP composite, which shows five well-resolved diffraction peaks at 2θ = 38.2^◦, 44.4^◦, 64.6^◦, 77.4^◦, and 81.80 corresponding to the Bragg reflections from the (111), (200), (220), (311), and (222) planes for the FCC phase of Au.¹⁴ The calculated lattice constant for Au using Bragg’s law, taking the (111) peak as a reference, is 4.08 Å, which is in good agreement with the reported data for pure Au. The XPS spectra of the MBBA–AuNP conjugated product as shown in Fig. 2(e) also exhibit the characteristic peak doublets at 84 and 88.4 eV, corresponding to the 4f_7/2 and 4f_5/2 peaks suggestive of the formation of Au⁰ in the matrix.¹⁵ In addition to that, the UV–visible spectra of the MBBA–AuNP conjugate system (80 mol. % precursor concentration) exhibit the characteristic surface plasmon resonance (SPR) peak of Au around 510 nm [Fig. 2(f)], which confirms the formation of Au⁽⁰⁾ in the matrix. The SPR peak is found to shift to a higher wavelength with increasing reaction time, indicating an increase in the size of the AuNPs due to the increased nucleation with time.

During AuNP production inside the MBBA matrix, we observed a significant change in the phase ordering of MBBA, which is manifested through a distinct change in the optical texture and modulation in the thermal as well as optical properties of MBBA. For studying the texture evolution, we have incorporated a detailed optical polarization microscopy (OPM) experiment on pristine MBBA, MBBA–methanol mixture, and MBBA–AuNP conjugated products at different weight percentages of Au precursor to substantiate AuNP induced phase ordering in MBBA. In Fig. 3, we summarize the results obtained from OPM study. Figure 3(a) shows the OPM image of MBBA, which exhibits its characteristic thread-like (Nematic schlieren) texture, which is also retained in its mixture with methanol [Fig. 3(b)], suggesting that methanol plays no role in the transformation of the texture of MBBA. For the a MBBA–AuNP conjugate, we have performed a systematic study with a gradual increase in precursor concentration to examine the effect of AuNPs on the texture evolution of MBBA. At lower salt concentrations (2 and 5 mol. %), no apparent texture transformation is detected, as shown in Figs. 3(c) and 3(d) at room temperature. Although the nematicity of MBBA is lost at these concentrations, it appears to be a mixed phase of MBBA + AuNP with spherical droplets, as no apparent texture evolution is perceived. Upon heating to 320 K, the isotropic phase of the mixture (at 5 mol% Au Salt concentration) is obtained, as shown in Fig. 3(e). Upon increasing the precursor concentration to 10 mol. %, no noticeable texture evolution can be seen [supplementary material Fig. S3(a)]. However, from 20 mol. % and above, we observe a substantial change in the texture [as shown in supplementary material Figs. S3(b) and S3(c)] as compared to previous concentrations. Here we can observe grass root like morphology at room temperature, and the density of these grass roots increases considerably with precursor concentration, as evident from these images. Such textures, although unique, do not represent any known conventional LC phase. We anticipated that since such textures are evolving at room temperature, increasing the temperature would lead to a transition in textures. However, no such definite conventional LC phase evolves even after increasing temperature. Although thermal stability at 40 mol. % concentration definitely increases as the isotropic temperature detected at this concentration is around 340 K [as indicated in Fig. S3(d)], at a still higher concentration of 60 mol. % and around 345 K, smectic like textures are observed [Fig. S3(e)]. Figure 3(f) shows the OPM image of the texture obtained from 80 mol. % at room temperature, which ultimately turns into focal conic textures of smectic mesophase at around 350 K [Figs. 3(g) and 3(h)]. Figure 3(i) shows the isotropic phase of the same mixture at 362 K.

Having confirmed the AuNP induced phase ordering in MBBA, we next proceed to investigate the thermal properties of the MBBA–AuNP conjugated product, which will provide a valuable insight into the thermal stability of the conjugated product and can be compared with neat MBBA. For that, we have employed DSC on neat MBBA and MBBA–AuNP conjugated products at different Au precursor concentrations of 40, 50, and 80 mol. %. The reason for choosing these concentrations is that above 40 mol. % precursor concentration, a substantial change in the phase ordering is manifested by our OPM study. Figure 4(a) shows the DSC thermograms (heat flow vs temperature) of neat MBBA and composites at the said concentrations. Characteristic N–I transition of MBBA, which appears at TN-I = 314.20 K [as shown in the inset of Fig. 4(a)] with calculated enthalpy ΔHN-I = 1.30 J/g. In comparison, with increasing precursor concentrations, the isotropic temperature of the conjugate products progressively shifts toward a higher temperature with a concomitant increase in enthalpy. At 80 mol. %, the composite undergoes a substantial increase in the isotropic temperature to TN-I = 356 K and an associated change in enthalpy, ΔHN-I = 76.50 J/g. The inherent broadness in the peak associated with the isotropization in the MBBA–AuNP conjugated product is possibly due to the complex thermodynamical process involved with it as the system passes through multiple phases; i.e., nematic → smectic → isotropic. Nonetheless, the stabilization of the nematic LC phase at a higher temperature during the conjugation process is unambiguous.

The conjugation process also brings out an alternation in the optical properties of MBBA, as investigated by UV–Vis spectroscopy. Pristine MBBA exhibits its characteristic double hump absorption peaks at around 281 and 322 nm with nearly equal intensity [Fig. 4(b)]. The former being attributed to the π–π* and later being attributed to the n–π* transition. In conjugated products, we have observed the triplet splitting of the π–π* transition with peaks fit to 270, 280, and 291 nm, suggesting that new electronic energy levels are created [Fig. 4(c)]. The n–π* transition peak intensity also reduces considerably in the conjugated product, suggesting that the conjugation process leads to a decrease in the non-bonding character of the electron. The cartoon depicting the energy levels and various transitions in MBBA and MBBA–AgNP conjugates is shown in Fig. 4(d).

The combined study of OPM, XRD, and DSC clearly indicates AuNP induced phase ordering in MBBA. We believe that such macroscopic ordering should be inherited from the microscopic level and, therefore, we urge that a detailed investigation be necessary to understand the molecular insight into the macroscopic organization of the mesophase. For that, we have undertaken detailed Fourier Transform Infrared (FTIR) spectroscopy, which non-invasively provides a deeper insight into interaction at the molecular level. For the sake of visual clarity, we have shown the FTIR spectra region wise for both MBBA and MBBA–AuNP composites so that a clear comparison can be made.

In Fig. 5(a), the FTIR spectra of MBBA and MBBA–AuNP conjugate obtained from 80 mol. % of salt concentration are shown from 700 to 900 cm⁻¹. In this region, pristine MBBA exhibits two characteristic peaks at 836 and 888 cm⁻¹, which correspond to the out-of-plane (oop) distortion vibration of benzene rings.¹⁶ In our earlier work, we have shown that because of these oop distortion vibrations, there are plenty of conformal states that exist in MBBA, and due to this, any particular conformation is difficult to achieve, which leads to the lack of positional ordering in MBBA.¹⁶ However, if by some means such oop vibrations are minimized, then the in-plane arrangement of benzene rings with C=N and C–N can be possible, and MBBA can achieve a particular conformational state. This was reported in our earlier works by introducing room temperature ionic liquids and polar solvents in MBBA.^17–18 In our present work, we have also seen that the introduction of AuNPs in MBBA (MBBA–AuNP conjugated product) can greatly affect these oop vibrations. As shown in Fig. 5(a), one of the vibrations gets eliminated (the peak at 888 cm⁻¹), and the other significantly gets reduced in intensity (the peak at 836 cm⁻¹). This clearly manifests toward significant minimization of oop vibrations that will lead to a particular conformation in MBBA by aligning the benzene rings in the plane with –C=N and leading to positional ordering.

In Fig. 5(b), FTIR spectra from 1400 to 1500 cm⁻¹ are shown for both samples. In this region, frequencies correspond to CH3 and CH2 deformation for MBBA and appear at 1422, 1441, and 1465 cm⁻¹.¹³ As compared to the MBBA–AuNP composite, most of the deformation frequencies are found to be absent. This is another molecular signature of bringing ordering into MBBA by AuNPs. The FTIR spectra between 2800 and 3000 cm⁻¹ [Fig. 5(c)] for MBBA exhibit peaks at 2856, 2871, 2930, and 2956 cm⁻¹, which are attributed to the CH3 and CH2 asymmetric and symmetric stretch frequencies,¹³ which are either found to be completely absent in the MBBA–AuNP composite or, if present, have undergone significant lowering in frequencies. The N–H stretch frequencies in the MBBA–AgNP composite, as shown in Fig. 5(d), also undergo significant lowering in frequency compared to MBBA (3374 and 3452 cm⁻¹ in neat MBBA to 3117 and 3156 cm⁻¹ in MBBA–AgNP conjugate). This also indicates the role of AuNP in arresting the conformations of the MBBA rendering the organization process.

To have more insight, we have undertaken low angle XRD on the MBBA–AuNP conjugate, anticipating from our OPM observations that we could get some signature of the positionally ordered (only in 1-Dimension) smectic phase. In Fig. 5(e), the XRD spectrum of MBBA–AuNP conjugate is shown for 20, 50, and 80 mol. % of the Au precursor concentration. As can be seen, at 20 mol. % concentration, the curve is flat, and no signature of any positional ordering can be spotted. At 50 mol. % concentration, a small but prominent peak at 2θ = 4.80° can be observed, which gets significantly intensified at 80 mol. % concentration, showing some positional ordering for the emerged smectic like mesophase. This is in good corroboration with our observation from OPM, as in lower concentrations we do not observe any phase ordering despite the change in texture. At the said angle (2θ = 4.80°), the substrate (Si111 in our case) and AuNPs do not exhibit any characteristic peaks. As for the nematic phase, the existence of a diffuse (broad) peak in between 2θ = 15°–20° through WAXS measurement, indicating a fluid like correlation, was reported by various authors.^19,20 In comparison, the peak at 2θ = 4.80° is sharp, as are the narrow wide angle maxima. The existence of such a sharp peak attributable to the positionally ordered layered arrangement of the smectic phase had already been reported in earlier work.¹⁹ Using Bragg’s law, taking λ = 0.154 nm for Cu Kα radiation for first order diffraction (n = 1), the calculated “d” value was obtained to be 18.40 Å. The molecular length of MBBA is around 19 Å,²³ which is exactly equal to the spacing between the layers. This indicates a parallel arrangement of the molecules within the layers. Therefore, the combined study of FTIR and XRD gives us valuable microscopic insight into the AuNP assisted organization of the nematic phase of MBBA. A cartoon representing the minimization of out-of-plane distortion vibrations of the benzene rings of MBBA in the presence of AuNPs, as confirmed by our FTIR data, leading to the in-plane arrangement of the benzene rings in conjunction with the C=N and C–N bonds so that the ordered mesophase of MBBA can take one particular conformation is shown in Fig. 5(f).

In summary, a novel and systematic approach to understand the organization of the nematic liquid crystalline phase of MBBA in the presence of AuNPs grown in situ in a single step without requiring any separate reducing, stabilizing, or capping units is put forward. The role duality of MBBA, which acts as a template as well as a reducing agent by donating the non-bonded imine electrons to reduce Au precursor, has been exploited. As compared to the physical dispersion of NPs into the LC matrix, where larger concentrations of NPs can lead to phase segregation, this process allows the adherence of AuNPs into the LC medium even at much higher concentrations. In fact, the modulation of the physicochemical properties of LC medium by AuNPs only gets affected at higher precursor concentrations, as confirmed by our study. The morphologies of AuNPs are nearly isotropic, with faceting at the edges suggesting that the shapes are thermodynamically controlled rather than kinetically, and the shape of the template MBBA (an elongated rod-like structure) has no effect on the morphology control of AuNPs. The size of the AuNPs increases substantially with precursor concentration, suggesting a nucleation driven process, and the absence of any capping unit for controlling the size is the key factor for abrupt growth. The pronounced effect of these AuNPs on the morphological, thermophysical, and electronic properties of the LC medium was thoroughly investigated. A systematic investigation of the texture evolution of the LC matrix in the presence of AuNPs was performed from low to high concentrations of precursor over a wide range of temperatures. While a low concentration (2–10 mol. %) of AuNP does not seem to have a significant impact on the evolution of texture, from above 20 mol. %, a gradual change in the texture was detected, and around 60 mol. % and above, the focal conic fan like texture of Smectic mesophase was seen. This change from the nematic to the smectic phase corroborated well with our findings from DSC, where a gradual increase in the isotropization temperature and associated enthalpy were identified with increasing precursor concentration. At 80 mol. %, a nearly 40 K increase in the isotropic temperature and a 60 fold enhancement in the associated enthalpy compared to neat MBBA were recorded, indicating the stabilization of the newly emerged mesophase at a higher temperature. The effects of AuNPs are also observed on the electronic properties of MBBA, where we found newly emerged electronic energy levels around the π-π* transition and a significant reduction in the intensity of the n-π* transition, which manifests the decrease in the non-bonding character of imine electrons and conjugation between MBBA–AuNP. The organization on a macroscopic scale is well supported by our microscopic observations, which provide deeper insight at a molecular level, which helps to understand the process better. Through our FTIR observations, it is clear that the decrease in the out-of-plane distortion vibrations of the benzene rings of MBBA in the presence of AuNPs significantly reduces the numbers of various conformational states in MBBA, and one particular conformation is achieved by in-plane alignment of benzene rings in conjunction with C=N and C–N bond rendering the organization process. Besides, the notable absence of various deformation bands and the decrease in stretch frequencies provide support for facilitating the organization process. To this end, the XRD study unambiguously reflects the existence of a prominent peak at the lower angle, which is the signature of smectic like ordering, and also provides specific information about the molecular arrangement within the smectic layers. In addition, the non-existence of such peaks at lower AuNP concentrations (20 mol. %) and prominent peaks at higher AuNP concentrations (50 and 80 mol. %) clearly reflects that the emergence of the smectic mesophase due to organization is facilitated at higher AuNP concentrations only. Therefore, a clear correspondence between macroscopic and microscopic observations is established from our study. Our study encompasses a new approach to tuning liquid crystalline order by nanoparticles, as it was previously performed by introducing electric or magnetic fields, surface effects, etc., and LC-NP interaction was only realized through the external incorporation of NPs into LC material. In those cases, chemisorption often leads to the destabilization of the LC network, and ordering is not achieved. Contrary to that, in situ growth of NPs inside the LC matrix can be a viable approach where we can achieve ordering with enhanced physical properties. We envisage that our approach could find its place in understanding the organization of the soft matter systems.

The supplementary material contains photographs of the MBBA–methanol mixture before and after the addition of Au precursor, SEM and TEM images of the AuNPs at 80 mol. % Au precursor concentration, OPM images of the textures obtained at different Au precursor concentrations, and high resolution XPS images around O1s, N1s, and C1s.

The author would like to acknowledge the Department of Atomic Energy (DAE, India) and the Director of the Saha Institute of Nuclear Physics (SINP) for their institutional support. The author would like to acknowledge Dr. Rajendra Prasad Giri for XRD and Dr. Ashish Kundu for XPS measurements.

The authors have no conflicts to disclose.

K. Dan: Conceptualization (equal). B. Satpati: Data curation (supporting). A. Datta: Supervision (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.