Ethylammonium nitrate (ionic liquid) based ferrofluids with citrate-coated nanoparticles and Na + counterions were synthesized for a wide range of nanoparticle (NP) volume fractions ( Φ ) of up to 16%. Detailed structural analyses on these fluids were performed using magneto-optical birefringence and small angle X-ray scattering (SAXS) methods. Furthermore, the thermophoretic and thermodiffusive properties (Soret coefficient S T and diffusion coefficient D m ) were explored by forced Rayleigh scattering experiments as a function of T and Φ . They were compared to the thermoelectric potential (Seebeck coefficient, Se) properties induced in these fluids. The results were analyzed using a modified theoretical model on S T and Se adapted from an existing model developed for dispersions in more standard polar media which allows the determination of the Eastman entropy of transfer ( S ^ NP ) and the effective charge ( Z 0 e f f ) of the nanoparticles.

Metal nanoparticles have the ability to strongly enhance the local electromagnetic field in their vicinity. Such enhancement is crucial for biomolecular detection and is used by techniques such as surface plasmon resonance detection or surface-enhanced Raman scattering. For these processes, the sensitivity strongly depends on the electromagnetic field intensity confined around such nanoparticles. In this article, we have numerically studied an array of metallic nanocylinders, which can sustain localized surface plasmons (LSP). However, the excitation wavelengths of the LSP are not tunable due to their limited dispersion. We have demonstrated a plasmonic mode, the hybrid lattice plasmon (HLP), which is excited in such a periodic array by adding a uniform thin metallic film below it. This mode is a result of a harmonic coupling of the propagating surface plasmons present in such a metallic film with the Bragg waves of the array. It shows a strong confinement of the electromagnetic field intensity around the nanocylinders, similar to the LSP, but the dispersion of this HLP mode is, however, similar to that of the propagating plasmons and, thus, can be tuned over a wide range of excitation wavelengths. The structure was fabricated using electron beam lithography and characterized by a surface plasmon resonance setup. These experimental results show that the HLP mode can be excited in a classical Kretschmann configuration with a dispersion similar to the prediction of numerical simulations.