Stochastic Collision Electrochemistry Of Single Water/Hydrophobic Ionic Liquid Emulsion Droplet

In recent years,single-entity electrochemistry（SEE）has been developing rapidly in the field of analysis and electrochemistry.SEE can study the collision behavior of particles at the single particle level,which yields important information on the individual particle size,size distribution,catalytic activity,collision frequency,and morphological characteristics of the particles at the micro-and nano-scale.SEE methods can be performed via different electrochemical techniques including chronoamperometry（CA）,fast-scan cyclic voltammetry（FSCV）and resistive-pulse.In the past decade,the single-particle collision research has gradually extended from“hard particles”（metal,metal oxide nanoparticles and hard organic nanoparticles）to“soft particles”（vesicles,viruses,emulsion droplets,proteins,etc.）.The aim of this thesis is to construct the water-in-hydrophobic ionic liquid emulsion,and investigate the properties of emulsion droplets at the single-entity level using a combination of SEE and CA（also known as the stochastic collision electrochemistry or nano-impact electrochemistry）to indicate the diffusion coefficient,size distribution,collision frequency,and ion transfer at the liquid/liquid interface of the emulsion droplet at the micro-and nano-scale.The thesis is divided into three chapters with the following work:In chapter one,firstly,the research background of single-entity electrochemistry,electrochemical techniques used in SEE and three common detection principles in the stochastic collision electrochemistry are introduced.Secondly,the applications of single-entity electrochemistry in“hard”and“soft”particle detection are outlined;and the study of non-homogeneous liquid/liquid interface electrochemistry at the micro-and nano-scale is briefly described.Finally,the research content and significance of this thesis are clarified.In chapter two,the collisions behavior of an attoliter water-in-hydrophobic ionic liquid emulsion droplet reactor（EDR）on a carbon fiber ultramicroelectrode（C-UME）was investigated by chronoamperometry.Water droplet emulsions were prepared by the ultrasonication of an hydrophobic ionic liquid(e.g.,1-decyl-3-methylimidazolium bis（trifluoromethanesulfonyl）imide salt,[C₁₀mim][NTf₂])and an potassium hydroxide solution containing guanine as the redox species.Under the appropriate potential,the collision behavior of single emulsion droplet could be observed at the C-UME by chronoamperometry and obtained the i-t curve.From these single-particle collision results,the collision frequency,size distribution,i-t decay behavior of emulsion droplets,and possible mechanisms are discussed.In chapter three,the effect of hydrophobic ionic liquid viscosity in the collision behavior of water/hydrophobic ionic liquid emulsions on gold ultramicroelectrodes（Au UME）was investigated by chronoamperometry.Water droplet emulsions were prepared by the ultrasonication of an hydrophobic imidazole-based ionic liquid and an aqueous solution containing potassium ferrocyanide（K₄Fe（CN）₆）as the redox species.The viscosity of the ionic liquids prepared by two ionic liquids in different proportions was determined by cyclic voltammetry.The collision behavior of the emulsion particles colliding on Au UME with different viscosity of the ionic liquid emulsion system were measured by the chronoamperometry.The“spike”current response in the i-t curves were analyzed,and the results indicated that the collision frequency of the emulsion droplets on the UME could be regulated by changing the viscosity of ionic liquid.