The development of reconfigurable metamaterials has emerged as a critical frontier in photonics and nanotechnology, enabling dynamic control over electromagnetic wave manipulation. Conventional metamaterials are typically fabricated using top-down lithographic methods and remain static once assembled, limiting their adaptability. To overcome this limitation, researchers have explored external stimuli-driven assembly strategies to achieve on-demand tunability. Among these, electric field-induced self-assembly offers a highly controllable and scalable approach. In this study, we demonstrate the formation of chain-like structures from silica-gold core-shell microparticles under alternating current (AC) electric fields across a wide frequency range. These assemblies exhibit distinct optical responses in the mid-infrared regime, which are characterized via in situ Fourier transform infrared (FTIR) spectroscopy.
Silica-gold core-shell particles were synthesized through a well-controlled chemical process involving surface functionalization with 3-aminopropyltriethoxysilane (APTES), followed by deposition of gold ions and subsequent reduction to form a uniform gold shell. Scanning electron microscopy confirmed the spherical morphology and smooth surface of the resulting particles, with a gold shell thickness estimated at 10–13 nm based on SEM analysis and stoichiometric ratios. The colloidal suspension was introduced into a sealed cell composed of a glass substrate, a 6 μm polymer spacer, and a calcium fluoride (CaF₂) window. CaF₂ was selected due to its high transparency in the mid-infrared region (>90% transmittance from 0.2 to 7 μm), allowing efficient transmission of incident light while minimizing water evaporation during measurements.
Upon application of an AC electric field parallel to the substrate, the particles underwent field-driven self-assembly into one-dimensional chains. The resulting structures were observed under an optical microscope coupled to the FTIR spectrometer. At low frequencies (10 Hz), positive dielectrophoresis (p-DEP) dominated, leading to particle aggregation due to polarization in a non-uniform field. As frequency increased to 300 Hz, induced-charge electro-osmosis (ICEO) began to play a role alongside p-DEP, facilitating chain formation. At 100 kHz, negative dielectrophoresis (n-DEP) became dominant, again promoting alignment into chains. Notably, the system could be reversed to a dispersed state by applying a brief low-frequency (1 Hz) AC pulse, demonstrating full reversibility.
FTIR spectra revealed significant changes upon chain formation. For dispersed particles, spectra showed minimal polarization dependence, consistent with isotropic scattering. In contrast, chain structures exhibited pronounced differences between s-polarized and p-polarized incidence. The reflectivity was enhanced under p-polarization, indicating stronger coupling with plasmonic modes aligned along the chain axis. Four distinct resonant peaks appeared at approximately 2.6 μm, 3.4 μm, 6.1 μm, and 9.1 μm, corresponding to different collective modes.83602-39-5 site Full-wave simulations using COMSOL Multiphysics confirmed these features: the 2.NOX2 Antibody Description 6 μm peak originated from an electric quadrupole mode, the 3.PMID:34338853 4 μm peak from an electric dipole resonance of the SiO₂ core, the 6.1 μm peak from Au-water interface plasmonics, and the 9.1 μm peak from a gap plasmon mode confined between gold and silica.
These findings establish a robust platform for dynamically tunable infrared metamaterials. By adjusting the AC field parameters—frequency, amplitude, and waveform—the optical response can be precisely controlled in real time. This capability opens new avenues for applications in optofluidic devices, liquid-borne microcircuits, and ultrasensitive infrared biosensors. Furthermore, the soft, self-assembled nature of these materials suggests potential use in adaptive drug delivery systems and microactuators within MEMS platforms. The integration of electric-field-responsive colloidal building blocks with advanced simulation tools enables a new paradigm in smart, reconfigurable photonic systems.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
