Multimodal microwave analysis of Ag and graphite nanoparticle suspensions: Size, concentration, and temperature effects

초록

This work presents a multimodal microwave characterization of aqueous suspensions of silver and graphite nanoparticles using three complementary methodologies: broadband dielectric retrieval via the Nicholson-Ross-Weir (NRW) technique, resonant analysis with a Hilbert-shaped stripline resonator, and thermoelastic optical indicator microscopy (TEOIM). The complex permittivity of the nanofluids was measured in the X-band (8.2-12.4 GHz), revealing distinct trends associated with particle conductivity, size distribution, and clay content. Resonant measurements in the 2-5 GHz band showed that both nanoparticle concentration and morphological heterogeneity significantly influence resonance frequency, linewidth, and amplitude, enabling sensitive discrimination between metallic and graphitic colloids. Temperature-dependent experiments further demonstrated that the electromagnetic response of these liquids evolves measurably with temperature, with graphite-based samples, particularly the 8H formulation, showing strong thermo-dielectric coupling, while Ag nanofluid exhibited temperature sensitivity primarily associated with nanoparticle-induced water structuring. The combined results establish a unified framework for liquid-phase dielectric diagnostics and highlight the capability of Hilbert resonators and TEOIM imaging to resolve subtle material and environmental effects. These findings support the development of tunable RF sensors and thermally responsive nanofluids for sensing, monitoring, and smart-material applications.

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