The interface between two immiscible electrolyte solutions (ITIES) can act as a scaffold for the assembly of nanometer-sized objects. Here we followed the adsorption of silica nanoparticles of 12 nm diameter at the ITIES by AC voltammetry and their interactions with methylene blue (MB +), selected as a model ion, by cyclic voltammetry and UV-vis absorption spectroscopy. We determined the association constant, , of adsorption of MB + onto silica nanoparticles to be 1.66 10 5 , which indicated a strong affinity between them. This strong affinity shifted the Gibbs free energy of transfer by-8.9 kJ mol-1. This is in contrast with the other two ions investigated (Eosin B and tetraethylammonium), which demonstrated low affinity for the silica nanoparticles. By combining the ability of silica to adsorb onto the ITIES and their affinity for MB + , we were able to accumulate MB + at the ITIES.

A new instrument is presented for investigating interactions between individual colloidal particles, emulsion droplets, foam bubbles, and other particle-particle or particle-surface interactions. Measurement capabilities are demonstrated by measuring interfacial tension, coalescence time for emulsion droplets, adhesion between giant multilamellar vesicles, and adhesion between model food emulsion particles. The magnitude of the interaction force that can be measured or imposed, ranges from 1 nN to 1 mN for particles ranging in size from 10 μm to 1 mm in diameter.

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The interface formed between two immiscible electrolyte solutions (ITIES) is a highly reproducible, defect-free surface that allows the assembly of nanometer-sized objects. Their adsorption at the liquid-liquid interface is governed by their dimensions, zeta potential, wettability and the interfacial tension. The interest for the use of silica nanomaterials at the ITIES is due to their favourable adsorption kinetics and to their rich surface chemistry that can provide selectivity. At first, we followed the adsorption of silica nanoparticles (ø = 12 nm) at the ITIES by AC voltammetry and their interactions with methylene blue (MB+), selected as a model ion by cyclic voltammetry and UV-vis absorption spectroscopy. We determined the adsorption constant of the MB+ onto silica nanoparticles to be 1.66 × 105, which indicated a strong affinity between them. This is in contrast with two other ions tested (Eosin B and tetraethylammonium), which demonstrated low affinity for the silica nanoparticles. In a second step, we synthesized silica nanoparticles with diclofenac molecular imprint with the aim of selective accumulation of diclofenac, a commonly used nonsteroidal anti-inflammatory drug. The presence of imprint cavities greatly improved the affinity for diclofenac for the silica nanoparticles, in contrast with diclofenac analogue such as aceclofenac. Electrochemistry experiments (including cyclic and AC voltammetries) revealed that diclofenac transfer is blocked by the presence of molecularly imprinted nanoparticles at the ITIES. These two experimental examples show that target molecules can be accumulated at the ITIES by combining the ability of silica nanoparticles to adsorb onto the ITIES and their affinity for the targeted molecules. Such an accumulation localized at the interface could be of interest in sensing applications. Figure 1