Liquid junction confinement

In Section II.C, we described the reactivity of adsorbed dye species at liquid liquid junctions in heterogeneous photoredox reactions. The properties of these systems can be used to catalyze electron-transfer processes. The behavior of dyes at interfaces has been vigorously studied in micelles and microemulsion systems, and many excellent reviews and books are available on this subject [94-97]. In this section, we shall consider some basic aspects of photoprocesses in microheterogeneous systems that are relevant to polarizable ITIES. This is not intended to cover comprehensively the recent developments in the active area of photochemistry at organized assemblies, but to highlight how spatial confinement, hydrophilic hydrophobic forces, and local potentials can affect the course of a photochemical process. We shall also revise some recent developments in photocatalysis and photosynthesis at polarizable liquid liquid interfaces, highlighting advantages and limitations in relation to two-phase catalysis. 

The buried nature of the liquid/liquid junctions introduces tremendous difficulties for in-situ spectroscopic analysis of species confined to the interfacial region. UV-visible absorption, luminescence, and Raman signal associated with species at the interface are overwhelmed by the signal arising from the species in the bulk liquids. In this section, different approaches are highlighted in order to increase the linear optical signals arising from probes located at the interface. 

The subject covered by this heading is a large one, and we shall aim only at describing it in outline by means of some examples. In particular, the discussion will be confined to cells without transference. This is the class of cells in which the electrolyte solution has essenti-allyf the same composition at each electrode. The other class of cells, those with transference contain two or more solutions in contact which differ appreciably in composition. Between these solutions there is an irreversible diffusion process and a corresponding liquid-junction potential. Because of the irreversible diffusion, the e.m.f. s of such cells cannot be discussed in a really exact manner by the methods of classical thermodynamics. ... 

Many of the problems associated with the liquid junction are common to all reference electrodes, while others are confined primarily to the microcapillary electrodes and/or measurements in fluids containing polyelectrolytes and colloidal or suspended components. There are several factors which affect the liquid junction potential of most reference electrodes. One of the most important factors is the mobility and concentration of the bridge electrolyte vis-a-vis the sample electrolyte. Usually the salt bridge solution is chosen to have a high concentration of equi-transferent ions. In this way, conditions are established for the transport of charge at the liquid junction by the salt bridge electrolyte, which, if equitransferent, results in a minimal diffusion potential. 

DSSCs convert sunlight to electricity by a different mechanism than conventional p-n junction solar cell. Light is absorbed directly at the solid/liquid interface by a monolayer of adsorbed dye, and initial charge separation occurs without the need of exciton transport.42,43 Following the initial charge separation, electrons and holes are confined in two different chemical phases electrons in the nanocrystalline... 

---