Electroactive surfactants

The first use of the SECM in a study of lateral mass transfer was reported by Unwin and Bard [79]. Several years later, the Unwin group studied the lateral mass transfer of a surfactant at the air-water (A-W) interface by analyzing transient current behavior [81]. The electroactive surfactant, A-octadecylferro-cenecarboxamide (CigFc0) was mixed with 1-octadecanol in a 1 1 ratio and spread onto water surface to form a Langmuir monolayer. A 25-pm diameter submarine tip (i.e., a Pt UME sealed in a U-shaped glass capillary with the conductive surface pointing upward) was placed 1-2 pm away from the A-W... 

A second set of possibilities arises if the electroactive species is adsorbed onto the surface of the micelle under these circumstances the main effects will be a marked decrease (normally) in apparent diffusion coefficient and again the possibility of inhibited electron transfer due to surface aggregate formation. Finally, the micelle itself may be formed from electroactive surfactant species, and their electrochemistry under controlled hydrodynamic conditions used to explore changes in structure with increasing surfactant or background electrolyte concentrations. 

D. J. MiUiron, A. P. AlMsatos, C. Pitois, C. Edder, J. M. J. Frechet, Electroactive Surfactant Designed to Mediate Electron Transfer Between CdSe Nanocrystals and Organic Semiconductors. Adv. Mater. 2003,15,58-61. 

C. Edder and J. M. J. Fr6chet, Synthesis of bridged oligothiophenes toward a new class of thiophene-based electroactive surfactants, Org. Lett, 5, 1879-1882 (2003). 

Studies of electroactive surfactants 1 to 4 (Fig. 7) in dilute or micellar solutions have provided insight into adsorbate structure, interactions, and dynamics at electrodes [14]. Ordered films were formed on glassy carbon electrodes from dilute solutions of 3. Single-molecule residence times on the electrode in micromolar solutions were 4.5 s for Fc-C8,14 s for Fc-C12, and 66 s for Fc-C16. Bilayers of 3 were... 

Tab. 1 Half-wave potential (E1/2) and critical micelle concentration cmc) of electroactive surfactants...

Tab. 3 Results of film formation of pigments using electroactive surfactants...

Electrochemical redox studies of electroactive species solubilized in the water core of reverse microemulsions of water, toluene, cosurfactant, and AOT [28,29] have illustrated a percolation phenomenon in faradaic electron transfer. This phenomenon was observed when the cosurfactant used was acrylamide or other primary amide [28,30]. The oxidation or reduction chemistry appeared to switch on when cosurfactant chemical potential was raised above a certain threshold value. This switching phenomenon was later confirmed to coincide with percolation in electrical conductivity [31], as suggested by earlier work from the group of Francoise Candau [32]. The explanations for this amide-cosurfactant-induced percolation center around increases in interfacial flexibility [32] and increased disorder in surfactant chain packing [33]. These increases in flexibility and disorder appear to lead to increased interdroplet attraction, coalescence, and cluster formation. 

Fig. 5.46 The dependence on time of the instantaneous current / at a dropping mercury electrode in a solution of 0.08 m Co(NH3)6C13 + 0.1 m H2SO4 + 0.5m K2S04 at the electrode potential where -7 -/d (i.e. the influence of diffusion of the electroactive substance is negligible) (1) in the absence of surfactant (2) after addition of 0.08% polyvinyl alcohol. The dashed curve has been calculated according to Eq. (5.7.23). (According to J. Kuta and I.

H. Sun, H.Y. Ma, and N.F. Hu, Electroactive haemoglobin-surfactant-polymer biomembrane-like films. Bioelectrochem. Bioenerg. 49,1-10 (1999). 

Further experiments with the coated electrode suggests that the surfactant bipyridiniums are mobile within the mercaptan monolayer. If the electrode is transferred to a fresh electrolyte, the coverage (measured at 0.1 V/s) greatly diminishes. Likewise rinsing the coated electrode with a stream of pure water between cyclic voltammograms removes most of the electroactive bipyridiniums. 

Smela et al. (2) observed that some conjugated polyelectrolyte dopants caused a layering of polymer chains within a polymer. In other ionic electroactive material additives can be used for crystalline ordering. Such additives may include surfactants and/or liquid crystals. 

The use of surfactant films which resemble lipid bilayers and multilayers represents an important approach to preparing electroactive films of protein molecules. 

Surface-active substances — are electroactive or elec-troinactive substances capable to concentrate at the interfacial region between two phases. Surface-active substances accumulate at the electrode-electrolyte - interface due to -> adsorption on the electrode surface (see -> electrode surface area) or due to other sorts of chemical interactions with the electrode material (see - chemisorption) [i]. Surface-active substances capable to accumulate at the interface between two immiscible electrolyte solutions are frequently termed surfactants. Their surface activity derives from the amphiphilic structure (see amphiphilic compounds) of their molecules possessing hydrophilic and lipophilic moieties [ii]. 

Other related studies concerned with the effects of cyclodextrin complexation on the properties of surfactants of various n-alkyl chain lengths, also incorporating a covalently attached electroactive group, have been reported.Thus, the nature of... 

On the other hand, liquid phase deposition (LPD) has been demonstrated as a flexible wet chemical method for preparing metal oxide nanostructured films on electrode surfaces. By the LPD process, electroactive titanium dioxide (Ti02) films were prepared on graphite, glassy carbon and ITO. The electrochemical properties of such LPD Ti02 films were dependent upon the film thickness controlled by the deposition time. The LPD technique was easily combined with other techniques, e.g., seed-mediated growth, which could provide metal/metal oxide composite nanomaterials. Moreover, hybrid nanostructured films were facilely obtained by doping dyes, surfactants and other... 

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