Analyzing Benzene and Cyclohexane Emulsion Droplet Collisions on Ultramicroelectrodes

Abstract

We report the collisions of single emulsion oil droplets with extremely low dielectric constants (e.g., benzene, ε of 2.27, or cyclohexane, ε of 2.02) as studied via emulsion droplet reactor (EDR) on an ultramicroelectrode (UME). By applying appropriate potentials to the UME, we observed the electrochemical effects of single-collision signals from the bulk electrolysis of single emulsion droplets. Different hydrophobic redox species (ferrocene, decamethyl-ferrocene, or metalloporphyrin) were trapped in a mixed benzene (or cyclohexane) oil-in-water emulsion using an ionic liquid as the supporting electrolyte and emulsifier. The emulsions were prepared using ultrasonic processing. Spike-like responses were observed in each i-t response due to the complete electrolysis of all of the above-mentioned redox species within the droplet. On the basis of these single-particle collision results, the collision frequency, size distribution, i-t decay behavior of the emulsion droplets, and possible mechanisms are analyzed and discussed. This work demonstrated that bulk electrolysis can be achieved in a few seconds in these attoliter reactors, suggesting many applications, such as analysis and electrosynthesis in low dielectric constant solvents, which have a much broader potential window.

Stochastic Collision Nanoelectrochemistry: A Review of Recent Developments

“…Other methods for size measurements, for example, dynamic light scattering (DLS), could only detect the average properties of the entire sample. By using SCNEC, the size and mass transfer information of individual droplets could be conveniently obtained . Kim et al .…”

“…Metal and metal oxide NPs have been widely used by researchers in SCNEC studies over the past decade . Currently, “soft particles” (SPs) offer a promising new trend in SCNEC research, which has tremendously expanded the application of SCNEC in the area of interface‐transfer analysis, immuno‐detection, and single bio‐particle monitoring …”

Electrocatalytic Reduction of Hydrogen Peroxide by Pd−Ag Nanoparticles Based on the Collisional Approach

“…From molecular level to cell level, this technique can provide abundant information about the dynamic processes at single event level, including frequency detection, charge transfer and catalytic mechanisms. The particles can be classified into hard particles like metal particles (Pt, [6] Ag, [7] Au, [8] Ni, [9] AgÀ Hg alloy [10] ), oxides (IrO 2, [11] TiO 2, [12] CeO 2 [13] ), organic nanoparticles [14] or polymer, [15][16][17] and soft particles such as droplets, [18][19][20][21][22][23][24][25][26] liposomes, viruses, [29][30] vesicles, [31][32] macromolecules [33][34][35] and cells. The particles can be classified into hard particles like metal particles (Pt, [6] Ag, [7] Au, [8] Ni, [9] AgÀ Hg alloy [10] ), oxides (IrO 2, [11] TiO 2, [12] CeO 2 [13] ), organic nanoparticles [14] or polymer, [15][16][17] and soft particles such as droplets, [18][19][20][21][22]…”

“…[2][3][4][5] Nano-collision is a novel electrochemical single entity detection approach proposed by Bard et al in 2007, [6] aiming to investigate the single events between nanoparticles and an ultramicroelectrode (UME). The particles can be classified into hard particles like metal particles (Pt, [6] Ag, [7] Au, [8] Ni, [9] AgÀ Hg alloy [10] ), oxides (IrO 2, [11] TiO 2, [12] CeO 2 [13] ), organic nanoparticles [14] or polymer, [15][16][17] and soft particles such as droplets, [18][19][20][21][22][23][24][25][26] liposomes, viruses, [29][30] vesicles, [31][32] macromolecules [33][34][35] and cells. [36][37] Such approach can study the behavior at single entity level and acquire information about size distribution, concentration, [9,38] degree of cluster, [39] porosity [40][41] electron transfer kinetics [42][43] and catalytic activity which are complementary to their ensemble behaviors.…”

Electropolymerization in a confined nanospace: synthesis of PEDOT nanoparticles in emulsion droplet reactors

“…Detection of stochastic collisions of nano-objects on an electrode has been a research topic of interest in recent years. [1][2][3] Since the first observation of hard nanoparticle collisions by implementation of ultramicroelectrodes (UMEs), 4 detection and statistical analysis of the electrode collisions of many types of nanoobjects were studied, including those of hard nanoparticles, [5][6][7][8] soft nanoparticles, [9][10][11] and biologically relevant entities. [12][13][14][15] More recent adaptations of the electrochemical collision research empowered scientists to utilize these stochastic collisions as a synthetic tool.…”