Nanopipette-Supported ITIES Tips

A nanometer-scale ITIES can be supported by a nanopipette to serve as a versatile SECM tip to probe both electron-transfer and ion-transfer reactions [120]. 

FIGURE 1.21 (a) Setup for nanopipette polishing. SEM images of (b) polished and (c) 

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FIGURE 1.8 (a) Scheme of an SECM line scan with a nanopipette-supported ITIES tip... 

Quasi-steady state conditions were unknowingly used for the study of an IT reaction at the macroscopic DCE/water interface by using nanopipette-supported ITIES tips [111-112], In these studies, a nanopipette was filled with an aqueous K+ solution and immersed in the DCE solution of dibenzo-18-crown-6 (DB18C6) to drive the interfadal complexation reaction at the nanoscale ITIES as given by... 

A number of experimental problems may plague kinetic experiments at the nano-ITIES. A hard question is whether the phase boundary is flat and located exactly at the pipette tip. In early studies at micrometer-sized pipettes, the assumption was that the water/organic interface is convex (i.e., protruding into the external liquid phase). In situ microscopy showed that a micropipette-supported ITIES tends to be flat when no external pressure is applied" however, a nanopipette tip is too small to be visualized by optical microscopy. The SECM approach curves obtained with nanopipette tips suggested that the ITIES is essentially flat and not recessed (see Section 15.3.2 and Chapter 18). 

Similar to solid/liquid electrochemistry, important advantages can be obtained by replacing a macroscopic interface between two immiscible electrolyte solutions (ITIES) with a liquid/liquid nanointerface. In 1986, Taylor and Girault introduced micrometer-sized liquid/liquid interface supported at the tip of a pulled glass pipette. Nanoscale ITIES and their arrays have later been formed by using nanopipettes, nanopores, and porous membranes. Electrochemistry of nanopores and porous membranes is surveyed in Chapter 11 our focus here is on the ITIES supported at the tip of a nanometer-sized pipette. 

To support an ITIES, a nanopipette has to be filled with solution. Using capillaries with filaments makes it easier to bring aqueous solution to the end of the pipette tip otherwise, it is difficult to remove the air and to fill the nanopipette completely. Capillaries without filaments can be used to produce pipettes that will be filled with organic solution. Organic solvents, such as DCE, are relatively easy to inject in a glass or quartz pipettes, and at the same time, the solvent evaporation is slower in the absence of a filament. 

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