We present a comprehensive study on the directed orientational self-assembly of anisotropic nanoparticles within nematic liquid crystal droplets, driven by tunable interfacial anchoring at the substrate–liquid crystal and liquid crystal–nanoparticle boundaries. This work demonstrates that nanoparticle alignment is not predetermined by particle shape alone but emerges from the synergistic interplay between interfacial forces and confinement effects. Rod-like iron oxide nanoparticles were synthesized through thermal decomposition of urea and stabilized with oleic acid to ensure colloidal dispersion and prevent aggregation. Transmission electron microscopy confirmed a mean length of 240 nm and diameter of 11 nm, with high uniformity across the sample.
The nanoparticles were dispersed in three thermotropic nematic hosts: 6CHBT, 6CB, and their 50:50 volume mixture, at a low volume fraction (~5×10⁻⁵). The colloidal suspensions were prepared by dissolving particles in a volatile solvent, mixing with isotropic LC, and allowing complete evaporation under continuous stirring. These dispersions were then deposited onto freshly cleaved mica substrates and spin-coated to form thin films. Within ~10 minutes, capillary instabilities led to the spontaneous formation of spherical and hemispherical droplets of varying sizes and shapes.
Atomic force microscopy (AFM) in noncontact mode was employed to image the internal structure of individual droplets. In 6CHBT-based systems, the long axes of nanoparticles aligned parallel to the mica surface, indicating planar anchoring at the substrate interface. In contrast, 6CB droplets exhibited a perpendicular orientation of nanoparticles relative to the substrate, consistent with homeotropic anchoring. The 50:50 6CHBT–6CB mixture also displayed a predominantly perpendicular alignment, suggesting dominance of the substrate-induced homeotropic condition over the LC–particle interaction.
Polarizing optical microscopy (POM), combined with birefringence compensation using a tunable LC cell, provided independent confirmation.5-(Pyridin-4-yl)isophthalic acid Purity For 6CHBT droplets, POM images revealed a splay director profile with a central disclination line—characteristic of planar anchoring at the substrate and homeotropic alignment at the air interface.Anthracene-9,10-dicarboxylic acid Biological Activity In 6CB droplets, four bright lobes surrounded a dark center indicated uniform homeotropic alignment at both interfaces.PMID:34836485 The mixture showed similar behavior, especially in larger droplets, reinforcing the trend toward homeotropic anchoring at the substrate.
Further analysis revealed that this anchoring behavior is highly sensitive to molecular structure. While 6CB exhibits homeotropic anchoring on mica, its homologue 5CB shows planar anchoring—a subtle difference attributed to variations in alkyl chain length and intermolecular interactions. Optical simulations based on the Jones matrix method successfully reproduced the observed textures, validating the proposed director configurations.
These findings establish that nanoparticle orientation in confined LC droplets is governed by the competition between substrate-induced anchoring and LC–nanoparticle interfacial forces. By engineering the substrate surface or selecting specific LC materials, it becomes possible to program the final alignment of nanoparticles with high precision. This principle enables the fabrication of functional thin films with tunable optical, magnetic, and mechanical properties. Applications include reconfigurable photonic devices, adaptive coatings, and smart sensors. The results lay the foundation for rational design of next-generation soft matter systems through controlled self-assembly in complex fluid environments.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com